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NOBLE DENTON MARINE SERVICES 
Disclaimer
The extracted sections below are based on your selections in the wizard. DNV GL do not take on any 
responsibility for your selection related to your project scope and DNV GL expressly disclaims any liability if 
the outcome of the selection does not encompasses the need or does not fit for purpose. 
Where DNV GL Noble Denton marine services is the Marine Warranty Survey provider, it should be read in 
conjunction with DNVGL-SE-0080 Noble Denton marine services – marine warranty survey, which provides a 
description of the process used by DNV GL Noble Denton marine services when providing marine warranty 
survey (MWS) services to evaluate whether a marine operation can be accepted for the purposes of 
insurance-related MWS. It addresses both ‘project’ and MODU/MOU related MWS. 
The use of our standard presupposes and does not replace the application of industry knowledge, 
experience and know-how throughout the marine operation activities. It should solely be used by 
competent and experienced organizations, and does not release the organizations involved from exercising 
sound professional judgment. 
Full version of Standard - DNVGL-ST-N001 & DNVGL-ST-N002
DNVGL-ST-N001
Full version of Standard - DNVGL-ST-N001 & DNVGL-ST-N002
DNVGL-ST-N001 Marine operations and marine warranty (Edition: 2016-06) 
SECTION 0 CHANGES – CURRENT
SECTION 1 Introduction
1.1 General
1.2 Objective
1.3 Scope
1.4 References
1.5 Definitions
1.6 Acronyms, abbreviations and symbols
SECTION 2 Planning and execution
2.1 Introduction
2.2 General project requirements
2.3 Technical documentation
2.4 Risk management
2.5 Planning of marine operations
2.6 Operation and design criteria
2.7 Weather forecast
2.8 Organization of marine operations
2.9 Monitoring
2.10 Inspections and testing
2.11 Vessels
SECTION 3 Environmental conditions and criteria
3.1 Introduction
3.2 Design environmental condition
3.3 Design environmental criteria for weather restricted operations
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3.4 Design criteria for weather unrestricted operations
3.5 Weather/metocean forecast requirements
3.6 Benign weather areas
SECTION 4 Ballast and other systems
4.1 Introduction
4.2 System and equipment design
4.3 Ballasting systems
4.4 Guiding and positioning systems
4.5 ROV systems
SECTION 5 Loading and structural strength
5.1 Introduction
5.2 Design principles
5.3 Specific design considerations
5.4 Testing
5.5 Load categorisation
5.6 Loads and load effects (responses)
5.7 Failure modes
5.8 Analytical models
5.9 Strength assessment
5.10 Materials and fabrication
SECTION 6 Gravity based structure (GBS)
6.1 Introduction
6.2 Floating GBS stability and freeboard
6.3 Structural strength
6.4 Instrumentation
6.5 GBS installation
SECTION 7 Cables, pipelines, risers and umbilicals
7.1 Introduction
7.2 Codes and standards
SECTION 8 Offshore wind farm (OWF) installation operations
8.1 Introduction
8.2 Planning
8.3 OWF installation vessels
8.4 Planning and execution
8.5 Load-outs of OWF components
8.6 Transport of OWF components
8.7 Installation of OWF components
8.8 Lifting operations and lifting tools
8.9 Information required for MWS approval
SECTION 9 Road transport
9.1 Introduction
9.2 Requirements
9.3 Information required
SECTION 10 Load-out
10.1 Introduction
10.2 General
10.3 Loads
10.4 Design calculations
10.5 Systems and equipment
10.6 Vessels
10.7 Operational aspects
10.8 Special cases
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10.9 Information required
SECTION 11 Sea voyages
11.1 Introduction
11.2 Towage or transport design/approval flow chart
11.3 Motion response
11.4 Default motion criteria – General
11.5 Default motion criteria – IMO
11.6 Default motion criteria – Ships
11.7 Default motion criteria – Specific cases
11.8 Directionality and heading control
11.9 Design and strength
11.10 Floating stability
11.11 Transport vessel or barge selection
11.12 Tug selection
11.13 Towing equipment
11.14 Voyage planning
11.15 Bilge & ballast pumping systems
11.16 Anchors (and alternatives) and mooring arrangements
11.17 Manned voyages
11.18 Specific for multiple towages
11.19 Specific for towing in ice
11.20 Specific for towage in the Caspian Sea
11.21 Specific for FSUs (FPSOs, FSOs, FLNG facilities, FRSUs etc.)
11.22 Specific for jacket voyages
11.23 Specific for ship towage
11.24 Specific for voyage to scrapping
11.25 Specific for towing of pipes and submerged objects
11.26 Specific for deep draught towages
11.27 Specific for jack-up voyages
11.28 Approaching a jack-up location
11.29 Rig move procedures (for all MOUs)
11.30 Specific for semi-submersible voyages
11.31 Information required
SECTION 12 Tow out of dry-dock or building basin
12.1 Introduction
12.2 Dry dock/construction basin
12.3 Design and strength
12.4 Mooring and handling lines for tow-out
12.5 Intact & damage stability
12.6 Under-keel clearance for leaving basin
12.7 Side clearances
12.8 Under-keel clearance outside basin
12.9 Towage and marine considerations
12.10 Information required
SECTION 13 Jacket installation operations
13.1 Introduction
13.2 Environmental conditions
13.3 Strength
13.4 Jacket buoyancy, stability and seabed clearance
13.5 Jacket lift
13.6 Jacket launch
13.7 Floating controlled upend and set-down ballasting
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13.8 Jacket position and set-down
13.9 Buoyancy tank
13.10 On-bottom stability and piling
13.11 Information required
SECTION 14 Construction afloat
14.1 Introduction
14.2 Loads and structures
14.3 Stability and damage stability
14.4 Mooring and fendering
14.5 Construction spread
14.6 Operational requirements
14.7 Information required
SECTION 15 Lift-off, mating and float-over operations
15.1 Introduction
15.2 General
15.3 Loads
15.4 Systems and equipment
15.5 Vessels
15.6 Operational aspects
15.7 Specific for lift-off operations
15.8 Specific for mating operations
15.9 Specific for float-over operations
15.10 Specific for docking operations
15.11 Information required
SECTION 16 Lifting operations
16.1 Introduction
16.2 Load factors
16.3 Derivation of hook, lift point and rigging loads
16.4 Sling and grommet design
16.5 Shackle design
16.6 Other lifting equipment design
16.7 Crane and installation vessel
16.8 Structural analysis
16.9 Lift point design
16.10 Fabrication yard lifts
16.11 Fabrication of rigging and lifting equipment
16.12 Certification and inspection of rigging and lifting equipment
16.13 Clearances
16.14 Bumpers and guides
16.15 Heave compensation
16.16 Operations and practical considerations
16.17 Subsea lifting and installation
16.18 Information required
SECTION 17 Mooring and dynamic positioning systems
17.1 Introduction
17.2 Codes and standards
17.3 Design environmental conditions
17.4 Environmental loads and motions
17.5 Mooring analysis
17.6 Design and strength
17.7 Clearances
17.8 Mooring equipment
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17.9 Procedural considerations
17.10 Special considerations for inshore & quayside moorings
17.11 Weather restricted mooring considerations
17.12 Information required
17.13 Dynamic positioning systems
SECTION 18 Decommissioning and removal of offshore installations
18.1 Introduction
18.2 General principles
SECTION 19 References
APPENDIX A Introduction
APPENDIX B Planning and execution
B.1 Documentation and certification for marine vessels
B.2 Documentation requiredfor lifting, towing and mooring gear - Informative
B.3 Iceberg management operations
B.4 Ensemble forecasting - informative
APPENDIX C Environmental conditions and criteria
C.1 General
C.2 Wind conditions
C.3 Wave conditions
APPENDIX D Ballasting and other systems
APPENDIX E Structural strength
E.1 Fillet weld checking
E.2 Bolted connections
APPENDIX F Gravity based structure (GBS)
APPENDIX G Cables, pipelines, risers and umbilicals
APPENDIX H Offshore wind farm installations - Informative
H.1 Introduction
H.2 General
H.3 Cable challenges/cables
H.4 Specific challenges/considerations for array cables
H.5 Exclusions from marine warranty scope
APPENDIX I Land transport
APPENDIX J Load-out
APPENDIX K Towage and sea transport
K.1 Example of main tow bridle with recovery system
K.2 Example of emergency towing gear
K.3 Example of Smit-type clench plate
K.4 Emergency anchor mounting on a billboard
K.5 Alternatives to the provision & use of an emergency anchor
K.6 Alternative arrangements for towing connections for ship towages
K.7 Example of cribbing / seafastening force calculations - Informative
K.8 Good practice recommendations for the tie-down of lifting slings - Informative
K.9 Good practice recommendations for towing - Informative
K.10 Ice Classification - Informative
K.11 Options for MOU voyages in ice - Informative
APPENDIX L Tow out of dry-dock or construction basin
APPENDIX M Jacket Installation
APPENDIX N Construction afloat
APPENDIX O Float-over, mating and float-off operations
APPENDIX P Lifting operations - Informative
P.1 2-Hook lift - load factors and derivation of lift point loads
P.2 Padeye calculations
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DNVGL-ST-N001 Marine operations and 
marine warranty (Edition: 2016-06)
SECTION 0 CHANGES – CURRENT 
This document (DNVGL-ST-N001 - Edition 2016-06) replaces the legacy DNV-OS-H-series and all legacy GL 
Noble Denton Guidelines except 0009/ND, 0016/ND, which are addressed in the DNVGL-ST-N002 standard and 
0021/ND which will be addressed in a service specification. 
The following is a summary provided for guidance on where the contents of the legacy documents can be found 
in this standard. 
Sec.1 Introduction
Sec.2 Planning and execution
This section replaces the following parts of the VMO Standard and the ND Guidelines:
• DNV-OS-H101
• 0001/ND.
Sec.3 Environmental conditions and criteria
This section replaces the applicable sections of the legacy GL Noble Denton Guidelines and legacy DNV-OS-H-
series standards. 
Sec.4 Ballast and other systems
This section replaces the following parts of the VMO Standard and the ND Guidelines:
• DNV, Marine Operations, General, DNV-OS-H101
• DNV, Load Transfer Operations, DNV-OS-H201
• GL Noble Denton, General Guidelines for Marine Projects, 0001/ND
• GL Noble Denton, Guidelines for Load-outs, 0013/ND
• GL Noble Denton, Guidelines for Float-over Installations / Removals, 0031/ND.
Sec.5 Loading and structural strength
This section replaces the applicable sections of the legacy GL Noble Denton Guidelines and legacy DNV-OS-H-
series standards. 
Sec.6 Gravity based structure (GBS)
This section replaces the applicable sections of the following legacy documents:
• GL Noble Denton, Guidelines for concrete gravity structure construction & installation, 0015/ND 
• DNV Offshore Standard, Load transfer operations, DNV-OS-H201.
Sec.7 Cables, pipelines, risers and umbilicals
Sec.8 Offshore wind farm (OWF) installation operations
This section replaces the applicable sections of the following legacy document:
• 0035/ND Guidelines for Offshore Wind Farm Infrastructure Installation.
Sec.9 Road transport
This section is new.
Sec.10 Load-out
This section replaces the applicable sections of the following legacy documents:
• DNV-OS-H201, Load transfer operations
• GL Noble Denton, Guidelines for Load-outs, 0013/ND
Sec.11 Sea voyages
This section replaces the applicable sections of the following legacy documents:
P.3 Calculation of SKL
APPENDIX Q Mooring and dynamic positioning systems
Q.1 Good practice recommendations for quayside mooring - Informative
Q.2 Dynamic positioning systems - Informative
APPENDIX R Decommissioning and removal of offshore installations
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• DNV-OS-H202, Sea transport operations 
• DNV-OS-H203, Transit and Positioning of Offshore Units
• GL Noble Denton, Guidelines For Marine Transportations, 0030/ND.
Sec.12 Tow out of dry-dock or building basin
This section replaces the applicable sections of the following legacy documents:
• GL Noble Denton, General Guidelines for Marine Projects, 0001/ND
• DNV Offshore Standard, Load Transfer Operations, DNV-OS-H201.
Sec.13 Jacket installation operations
This section replaces the applicable sections of the following legacy documents:
• DNV Offshore Standard, Offshore Installation Operations (VMO Standard Part 2-4), DNV-OS-H204
• GL Noble Denton, Guidelines for Steel Jacket Transportation & Installation, 0028/ND.
Sec.14 Construction afloat
This section replaces the applicable sections of the following legacy documents:
• 0015/ND Guidelines for concrete gravity structure construction & installation
• DNV Offshore Standard DNV-OS-H201 Load Transfer Operations.
Sec.15 Lift-off, mating and float-over operations
This section replaces the applicable sections of the following legacy documents:
• GL Noble Denton, Guidelines For Float-Over Installations / Removals, 0031/ND 
• DNV Offshore Standard DNV-OS-H201 Load Transfer Operations.
Sec.16 Lifting operations
This section replaces the applicable sections of the following legacy documents:
• GL Noble Denton, Guidelines For Marine Lifting & Lowering Operations, 0027/ND 
• DNV Offshore Standard DNV-OS-H205 Lifting Operations (VMO Standard – Part 2-5)
• DNV Offshore Standard DNV-OS-H206 Load-out, transport and installation of subsea objects (VMO 
Standard – Part 2-6). 
Sec.17 Mooring and dynamic positioning systems
This section replaces the applicable sections of the following legacy documents:
• GL Noble Denton, Guidelines for Moorings , 0032/ND 
• DNV-OS-H101 Marine Operations, General
• DNV-OS-H102 Marine Operations, Design and Fabrication
• DNV-OS-H203 Transit and Positioning of Offshore Units.
Section [17.13] replaces the applicable Dynamic Positioning related sections of the following legacy documents: 
• GL Noble Denton, General Guidelines for Marine Projects, 0001/ND
• DNV Offshore Standard, Transit and Positioning of Offshore Units, DNV-OS-H203.
Sec.18 Decommissioning and removal of offshore installations
This section replaces Section 14 of 0001/ND “General Guidelines for Marine Projects”.
SECTION 1 Introduction 
1.1 General 
1.1.1
DNV GL Noble Denton marine services is a global provider of Marine Warranty Services and has set the industry 
standard for marine operations and marine assurance activities for the last 50 years. Our collective industry best 
practice and guidance documentation is referenced and used all over the world. This document includes the 
harmonized legacy DNV standards and legacy GL Noble Denton guidelines, with the exception of those for 
MODU/MOU site specific assessment. 
1.1.2
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Where DNV GL Noble Denton marine services is the Marine Warranty Survey provider, it should be read in 
conjunction with DNVGL-SE-0080 Noble Denton marine services – marine warranty survey, /38/, which provides a 
description of the process used by DNV GL Noble Denton marine services when providing marine warranty 
survey (MWS) services to evaluate whether a marine operation can beaccepted for the purposes of insurance-
related MWS. It addresses both ‘project’ and MODU/MOU related MWS. 
1.1.3
This document may be used in its complete form using the relevant sections based on the asset type and/or 
operation. It is recommended that the reader uses the Noble Denton marine services wizard available through 
My DNV GL (https://my.dnvgl.com/ (https://my.dnvgl.com/)) for easier access and to obtain the relevant sections 
based on asset type and/or operation. 
1.1.4
The use of this standard presupposes and does not replace the application of industry knowledge, experience 
and know-how throughout the marine operation activities. It should solely be used by competent and 
experienced organizations, and does not release the organizations involved from exercising sound professional 
judgment. DNV GL has however no obligations or responsibility for any services related to this standard 
delivered by others. DNV GL has a qualification scheme mandatory to approval engineers and surveyors 
providing services related to this standard. This ensures that all approvals and certificates delivered are carried 
out by well qualified personnel who understand the intention behind the standard, the limitations and the correct 
interpretations. The use of this document is at the user's sole risk. DNV GL does not accept any liability or 
responsibility for loss or damages resulting from any use of this document. 
1.1.5
Further provisions and background information are contained in the appendices.
1.1.6
In some cases risk assessments can be used to justify project-specific deviations from the standard criteria 
provided that the results are acceptable. When such risk assessments show that the risk levels are increased 
relative to those inherent in the standard criteria, the operation may be approved subject to disclosure by the 
client to, and agreement by, the insurance underwriters. 
1.1.7
Execution of operations not adequately covered by this Standard shall be specially considered in each case. 
1.1.8
Fulfilment of all requirements in this Standard does not guarantee compliance with international and national 
(statutory) regulations, rules, etc. covering the same subjects/operations. 
1.1.9
This Standard should if required be used together with other recognized codes or standards applicable for 
marine operations. 
1.1.10
In case of conflict between other codes or standards and this document, the latter shall be governing if this 
provides a higher level of safety or serviceability. 
1.1.11
By recognized codes or standards are meant national or international codes or standards applied by the majority 
of professionals and institutions in the marine and offshore industry. 
1.1.12 SWL and WLL: 
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a. Safe Working Load (SWL) has generally been superseded by Working Load Limit (WLL) though both are in 
common use during the change-over period. However confusion can arise due to the very different safety 
factors being assumed by different equipment manufacturers and for different uses (e.g. mooring, lifting 
or towing). Whenever possible this standard uses minimum breaking load (MBL) or ultimate load capacity 
(ULC) to avoid these problems. 
b. If the WLL or SWL of a shackle or other equipment is documented but the MBL or ULC is not, the owner or 
operator should obtain a document from the manufacturer stating the minimum Safety Factor - defined as 
(MBL or ULC) / (WLL or SWL as appropriate). 
c. There is often some confusion about the differences between WLL and SWL. SWL is a derated value of 
WLL, following an assessment by a competent person of the maximum static load the item can sustain 
under the conditions in which the item is being used. SWL may be the same or less than WLL but can never 
be more. 
1.2 Objective 
1.2.1
This standard is intended to ensure marine operations are designed and performed in accordance with 
recognized safety levels and to describe “current industry good practice”. Where applicable, this standard can 
be used in the approval of the marine operation(s) for Marine Warranty Survey purposes. 
1.3 Scope 
1.3.1
This standard addresses the marine operations that can occur during the development of an offshore asset or 
when objects are moved by water from one place to another. It addresses the Marine Warranty Survey 
requirements relevant to load-out, construction afloat, voyages and installation and the load cases that should be 
addressed in the design. 
1.3.2
The integrity of the final structure in the installed condition is the responsibility of the Assured and would 
normally be verified and accepted by the certifying authority. The Marine Warranty Survey company takes no 
responsibility for the installed condition unless the Marine Warranty Survey scope specifically addresses this case 
e.g. for jack-up location approval. 
1.3.3
With the exception of location approval of MOUs (Mobile Offshore Units) which are covered in DNVGL-ST-
N002, /39/, this standard covers most offshore assets and operations that are likely to require MWS approval. 
1.4 References 
1.4.1 Normative (i.e. mandatory) references 
1.4.1.1
The standards and guidelines in Table 1-1 include provisions, through which reference in this text constitute 
provisions of this standard. 
Table 1-1 Normative (i.e. mandatory) standards
Id Name Date Revision
AISC: 360/10 
Specification for Structural Steel Buildings, (included in 
AISC Steel Construction Manual 14 Edition) 
2010 14
DNVGL-OS-C101
Design of offshore steel structures, general – LRFD 
method
2015
th
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DNVGL-ST-N002
Site specific assessment of mobile offshore units [due to 
be issued in 2016, until then GL Noble Denton 0009/ND 
“Guidelines for site specific assessments of jack-ups” 
applies] 
2016
EN 1993 Eurocode 3, Design of steel structures
IMO IMDG International Maritime Dangerous Goods Code 2006
IMO Intact 
Stability Code 
Intact Stability Code
2008 and later 
amendments
IMO International 
Convention on 
Load Lines
IMO International Convention on Load Lines, 
Consolidated Edition 2002
2002
IMO COLREGS
IMO International Regulations for Preventing Collisions 
at Sea, 1972 (amended July 2015) (COLREGS) 
1972 
(amended 
July 2015)
IMO ISM Code
IMO International Safety Management Code - ISM Code 
- and Revised Guidelines on Implementation of the ISM 
Code by Administrations 
2002
IMO ISPS Code
International Ship and Port Facility Security Code 
(amendment to SOLAS convention) 
2002 
(effective 
2004)
IMO Resolution 
A.1024(26)
Guidelines for ships operating in polar waters Jan 2010
ISO 19901-5
Petroleum and Natural Gas Industries “Specific 
requirements for offshore structures – Part 5: Weight 
control during engineering and construction”. 
2016
1.4.2 Informative references 
1.4.2.1
All references appear in Sec.19. 
1.5 Definitions 
1.5.1 Verbal forms 
Table 1-2 Definitions of verbal forms
Term Definition
shall
verbal form used to indicate requirements strictly to be followed in order to conform to the 
document 
should
verbal form used to indicate that among several possibilities one is recommended as particularly 
suitable, without mentioning or excluding others, or that a certain course of action is preferred but 
not necessarily required 
may verbal form used to indicate a course of action permissible within the limits of the document 
Where Guidance Notes have been included they are used for giving additional information, clarifications or 
advice to increase the understanding of preceding text. Therefore Guidance Notes shall not be considered as 
giving binding or defining requirements. Any values in GuidanceNotes are not a requirement and shall be 
considered as an initial recommendation. 
1.5.2 Terms 
1.5.2.1
Underlined definitions are defined elsewhere in Table 1-3. 
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Table 1-3 Definition of terms
Term Definition
1 intercept (angle) 
The first angle of static inclination at which the wind overturning moment is equal to 
the righting moment (see Figure 11-3 and Figure 11-4) 
24-hour Move
A jack-up move taking less than 24 hours between entering the water and reaching 
a safe air gap with at least two very high confidence good weather forecasts for the 
48 hours after entering the water, having due regard to area and season. 
2 intercept (angle) 
The second angle of static inclination at which the wind overturning moment is 
equal to the righting moment (see Figure 11-3 and Figure 11-4) 
9-Part sling
A sling made from a single laid sling braided nine times with the sling rope and 
eyes forming each eye of the 9-part sling. 
A&R Winch
The Abandonment and Retrieval winch on a lay vessel whose primary purpose is to 
lower the pipeline to the seabed and to retrieve it back to the lay vessel with 
sufficient working tension to control the pipe catenary within safe code limits at all 
stages. 
Accidental Limit State
The limit state related to an accidental event. This can apply to either the intact 
structure resisting accidental loads (including operational failure) or the load 
carrying capacity of the structure in a damaged condition. 
Added Mass
Added mass or virtual mass is the inertia added to a system because an 
accelerating or decelerating body shall move some volume of surrounding water as 
it moves through it, since the object and fluid cannot occupy the same physical 
space simultaneously. 
This is normally calculated as Mass of the water displaced by the structure 
multiplied by the added mass coefficient. 
Added Mass 
Coefficient
Non-dimensional coefficient dependant on the overall shape of the structure
Alpha Factor
The maximum ratio of operational criteria/design environmental condition to allow 
for weather forecasting inaccuracies. See [2.6.9]
Angle of Loll The static angle of inclination after flooding, without wind heeling (see Figure 11-4) 
Approval
The act, by the designated the MWS company representative, of issuing a 
Certificate of Approval. 
Array Cable(s) 
Generic term collectively used for Inter Turbine Cables and Collector Cables. See 
also Infield Cables
Asset An structure or object subject to an insurance warranty or at risk from an operation
Assured
The Assured is the person who has been insured by some insurance company, or 
underwriter, against losses or perils mentioned in the policy of insurance. 
Barge A non-propelled vessel commonly used to carry cargo or equipment. 
Base weight
The calculated weight of a structure, excluding all allowances and contingencies. 
Sometimes known as net weight 
Bend Restrictor
A device with several interlocking elements that lock when a design radius is 
achieved.
Bend Strain Reliever 
(BSR)
A tapered plastic sleeve fitted to a flexible pipe, umbilical or cable at the transition 
between a stiff section (typically an end fitting or connector) and the normal body 
of the pipe, umbilical or cable. Also known as Bend Stiffener 
Bending Factor γ
A partial safety factor that accounts for the reduction in strength caused by bending 
round a shackle, trunnion, diverter or crane hook. 
Benign (weather) area An area with benign weather as described in [3.6]
Bifurcated tow
The method of towing 2 (or more) tows, using one tow wire, where the second (or 
subsequent) tow(s) is connected to a point on the tow wire ahead of the preceding 
tow, and with each subsequent towing pennant passing beneath the preceding 
tow. See [11.18.1.4]
st
nd
b
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Bird-caging
A phenomenon whereby armour wires locally rearrange with an increase and/or 
decrease in pitch circle diameter as a result of accumulated axial and radial stresses 
in the armour layer(s). 
Bollard Pull (BP)
Certified continuous static bollard pull of a tug. The mean bollard pull developed in 
a test by a tug at 100% of the Maximum Continuous Rating (MCR) of main engines 
over a period of 10 minutes. This is used for the selection of tugs and sizing of 
towing equipment. 
Maximum bollard pull (at 110% of MCR) should not be used for tug selection.
Buckle “Wet”/“Dry”
A local collapse of pipe cross section in the span of pipe between the lay vessel and 
the seabed. “Dry” means that the pipe wall is not breached and “Wet” means that 
the pipe wall is breached and seawater floods into the pipe. 
Bundle
A configuration of two or more pipelines joined together and either strapped or 
contained within a carrier or sleeve pipe. 
Burial Assessment 
Survey (BAS)
A survey to assess the expected burial depths on a cable route using purpose built 
sledges equipment with bottom penetrating sonar equipment or by towing a 
miniature plough. 
Burial Protection Index 
(BPI)
A process to optimise cable burial depth requirements based on a risk assessment
of threats to the cable and the soil strengths in the location of each risk. 
Cable Burial
A submarine power cable is trenched into the seabed and covered with soil 
providing complete burial of a cable. 
Cable Grips
Cable Grips are used to pull or support cables and pipes. They work on the 
principle of the harder the pull, the tighter the grip. 
Cable Tank A circular storage area where cable is coiled.
Cable-laid grommet
A single length of unit rope laid up 6 times over a core, as shown in IMCA M 
179 /81/, to form an endless loop. Sometimes known as an endless sling 
Cable-laid sling
A sling made up of 6 unit ropes laid up over a core unit rope, as shown in IMCA M 
179, /81/, with a hand spliced eye at each end. 
Cargo
Where the item to be transported is carried on a vessel, it is referred to throughout 
this standard as the cargo. If the item is towed on its own buoyancy, it is referred to 
as the tow. 
Cargo overhang Distance from the side of the vessel to the extreme outer edge of the cargo
Cargo ship safety 
certificates
(Safety Construction) 
(Safety Radio)
(Safety Equipment)
Certificates issued by a certifying authority to attest that the vessel
• complies with the cargo ship construction and survey regulations, 
• has radiotelephone equipment compliant with requirements and 
• carries safety equipment that complies with the rules applicable to that vessel
type. 
Carrier or Sleeve pipe The outer casing of a bundle or pipe-in-pipe. 
Cats-paw
An extreme type of loop thrown into cables where a combination of low tension 
and residual torsion forms a twisted loop. Commonly seen at repair Final Splice
locations where the Final Splice is lowered too quickly. 
Certificate of Approval 
(CoA)
A formal document issued by a MWS company surveyor stating that, in his/her 
judgement and opinion, all reasonable checks, preparations and precautions have 
been taken to keep risks within acceptable limits, and an operation may proceed. 
Certified Having (or proved by) a certificate from an acceptable source
Chinese Fingers
Also known as pulling socks are used to pull or support cables and pipes. They 
work on the principle of the harder the pull, the tighter the grip. 
Classification 
A system of ensuring ships are built and maintained in accordance with the Rules of 
a particular Classification Society. Although not an absolute legal requirement, the 
advantages (especially as regards insurance) mean that almost all vessels are 
maintained in Class. 
Client
The company to which the MWS company is contracted to perform marine warranty 
or consultancyactivities. 
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Cold Stacking
Cold stacking is where the unit is expected to be moored or jacked-up for a 
significant period of time and will have minimum or, in some cases, no services or 
personnel available. 
Column stabilised unit
A MOU which floats on its columns during operation or transit (e.g. semi-
submersible). 
Competent person
A Competent Person carrying out a thorough 
examination/assessment /analysis/certification shall have such appropriate practical 
and theoretical knowledge and experience of the equipment and/or activity. 
Although the competent person may often be employed by another organisation, 
this is not necessary, provided they are sufficiently independent and impartial to 
ensure that in-house examinations are made without fear or favour. However, this 
should not be the same person who undertakes routine maintenance of the 
equipment as they would then be responsible for assessing their own maintenance 
work. 
Note: Where local or national regulations define a Competent Person with more 
onerous requirements, then the definition in these local or national regulations 
shall apply. 
Consequence Factor 
γ
Factor applied in the design of critical components to ensure that these
components have an increased factor of safety in relation to the consequence of 
their failure. 
Controlled Depth Tow 
(CDT)
A special towing operation where the pipe string or bundle is made almost 
buoyant and towed at a controlled depth within the water column, suspended 
between a lead and trail tug. 
Crane vessel
The vessel, ship or barge on which lifting equipment is mounted. For the purposes 
of this document it is considered to include: crane barge, crane ship, derrick barge, 
floating shear-leg, heavy lift vessel, semi-submersible crane vessel (SSCV) and jack-
up crane vessel. 
Cribbing
An arrangement of timber baulks, secured to the deck of a barge or vessel, formally 
designed to support the cargo, generally picking up the strong points in vessel
and/or cargo. 
Cross Linked 
Polyethylene (XLPE)
A type of AC cable conductor insulation commonly used on submarine power 
cables.
Cross Sectional Area 
(CSA)
Normally the CSA of a single conductor in a submarine power cable x 3. For 
example a submarine power cable with 3x600 mm in its designation would be a 
cable with three conductors each of 600 mm . 
Dead Man Anchor 
(DMA)
Anchor or multiple anchors (which may be clump weights, sometimes buried), 
typically used to initiate pipelay. 
Deck mating
The act of installing integrated topsides over a substructure, generally by float-over 
and ballasting. Deck mating may take place inshore or offshore, onto a floating or a 
previously installed substructure. 
Deck Support Unit 
(DSU)
Unit installed on the vessel grillage to support the structure before and during the 
float-over. It can be designed to either provide a rigid vertical support and allow 
horizontal movement or utilise elastomers to absorb vertical and horizontal 
installation motions and forces. 
Deep water
This is determined on a case by case basis but for installation of subsea equipment 
it is generally taken as greater than 500 m. 
Demolition towage Towage of a “dead” vessel for scrapping. 
Design environmental 
condition
The design wave height, wave period, wind speed, current and other relevant 
environmental conditions specified for the design of a particular voyage or 
operation. 
Determinate lift
A lift where the slinging arrangement is such that the sling loads are statically 
determinate, and are not significantly affected by minor differences in sling length 
or elasticity e.g. two and three point lifts 
Double tow
The operation of towing two tows with two separate tow wires by a single tug. See 
[11.18.1.2]
Dry Towage The operation of transporting a cargo on a barge. 
b
2
2
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Dunnage
Typically dunnage is inexpensive material used to protect cargo during transport. 
Dunnage also refers to material used to support loads and prop tools and 
materials. See cribbing. 
Dynamic Amplification 
Factor (DAF)
The factor by which the weight is multiplied, to account for accelerations and 
impacts during the operation 
Dynamic Angle The smallest angle at which the area ratio in [11.10.3.1] is satisfied 
Dynamic hook load Static hook load multiplied by the DAF. 
Engineered lift
A lift which is planned, designed and executed in a detailed manner, with thorough 
supporting documentation. See [16.1.1.4]. 
Export Cable(s)
Submarine power cables connecting the offshore wind farm transformer station to 
a landfall connection. 
Factored weight
The calculated weight of a structure, including all allowances and contingencies. 
Sometimes known as gross weight. 
Fatigue Limit State
The limit state related to the capacity of the structure to resist accumulated effect of 
repeated loading. 
Field Joint Coating 
(FJC)
Refers to single or multiple layers of coating applied to girth welds and associated 
cutback of the line pipe coating. Coating can be applied in factory or field. 
Final Splice
The location where a second joint is inserted into a cable system during a repair 
and includes the excess slack in the cable where the two ends of the final splice
come to the surface. 
Flag state
The state under which a commercial vessel is registered or licenced. It has the 
responsibility to enforce regulations over vessels registered under its flag, 
including inspections, certification and issuance of safety or pollution prevention 
documents. 
Floating off-load The reverse of floating on-load
Floating on-load
The operation of transferring a cargo, which itself is floating, onto a vessel or barge, 
which is submerged for the purpose. 
Floating Production 
System (FPS)
Including FPV, FPU, FPSO, FGSO, spar (buoy) or TLP
Float-Over
The operation of installation/removal of a structure onto or from a fixed host 
structure by manoeuvring and ballasting the transport vessel to effect load transfer 
Forecasted 
Operational Criteria
The metocean limits used when assessing weather forecasts to determine the 
acceptability of proceeding with (each phase of) an operation beyond the next 
Point of No Return. 
For a weather restricted operation/voyage these equal the Operational Limiting 
Criteria multiplied by an Alpha factor. 
Freeboard
Freeboard is defined as the distance from the waterline to the watertight deck 
level. In commercial vessels, it is measured relative to the ship's load line. 
“Effective freeboard” is the minimum vertical distance from the still water surface to 
any opening (e.g. an open manhole) or downflooding point, after accounting for 
vessel trim and heel. 
Global Positioning 
System (GPS)
A satellite based system providing geographic coordinate location.
Grillage
A structure, secured to the deck of a barge or vessel, formally designed to support 
the cargo and distribute the loads between the cargo and barge or vessel. 
Heave Vessel motion in a vertical direction 
Heavy Transport 
Vessel (HTV)
A vessel which is designed to ballast down to submerge its main deck, to allow self-
floating cargo(es) to be on-loaded and off-loaded. 
Host Structure
The host structure (e.g. jacket, GBS, TLP) onto which the structure or structure deck 
will be floated and supported, or from which it will be removed. 
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Hydro-acoustic 
Positioning Reference 
(HPR)
A through water acoustic link between a vessel and a seabed beacon. Used to 
locate and track vehicles in thewater column and can be used as a DP reference. 
Indeterminate lift
Any lift where the sling loads are not statically determinate, typically lifts using four 
or more lift points 
Inshore Mooring A mooring operation in relatively sheltered coastal waters, but not at a quayside. 
Inspection and Test 
Plan (ITP)
A plan in which all test, witness and hold points for all aspects of a cable installation 
are listed. 
Insurance Warranty
A clause in the insurance policy for a particular venture, requiring the Assured to 
seek approval of a marine operation by a specified independent survey house. 
International 
Association of 
Classification Societies 
(IACS)
A listing of IACS members is given on the IACS web site 
http://www.iacs.org.uk/explained/members.aspx
(http://www.iacs.org.uk/explained/members.aspx)
International Cable 
Protection Committee 
(ICPC)
A trade body representing and lobbying on behalf of subsea cable owners. For 
historical reasons membership is predominately comprised of telecom companies. 
International 
Convention for the 
Safety Of Life At Sea 
SOLAS, /92/
An international treaty concerning the safety of merchant and other ships and 
MOUs.
International Maritime 
Organization (IMO)
The United Nations specialized agency with responsibility for the safety and 
security of shipping and the prevention of marine pollution by ships 
International Safety 
Management (ISM) 
The ISM Code provides an International standard for the safe management and 
operation of ships and for pollution prevention. 
Intersection Point
The point at which two straight sections or tangents to a pipeline curve, or two 
slings, meet when extended. 
ISM Code
International Safety Management Code - the International Management Code for 
the Safe Operation of Ships and for Pollution Prevention - SOLAS Chapter IX, /92/
I-tube
A vertical tube fitted to offshore structures to install product between the seabed 
and the structure topsides. 
Jacket
A sub-structure, positioned on the seabed, generally of tubular steel construction 
and secured by piles, designed to support topsides facilities. 
Jack-up
A self-elevating MODU, MOU or similar, equipped with legs and jacking systems 
capable of lifting the hull clear of the water. 
J-Lay
A laying method where the pipe joints are raised to a nearly vertical angle in a 
tower mounted on a pipelay vessel in a tower, assembled and lowered, curved 
through approximately 90° (J shape) to lie horizontally on the sea-bed. 
J-tube
A J shaped tube fitted to offshore structures to install product between the seabed 
and the structure topsides. 
Kilometre Point
The position of on pipeline route at a given distance from an agreed reference 
point, typically at or near one end. 
Lay Back
The horizontal offset from the last pipe support on the lay vessel to the touch down
point on the seabed. 
Leg Mating Unit (LMU)
Unit that is designed and installed between the structure and the host structure in 
order to absorb vertical and horizontal installation motions and forces. The units are 
normally either installed on the host structure legs to receive the structure, or on 
the structure leg stubs, in order to interface with the host structure legs. LMU’s can 
be also installed on the removal vessel. 
Lift point
The connection between the rigging and the structure to be lifted. May include 
padear, padeye or trunnion
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Lifting Beam
A lifting beam is a structure designed to be connected to a lifting appliance at a 
single point, and structure being lifted is connected to the bottom of the beam at 
two or more lift points. The beam shall resist the bending moments. It is not 
designed to carry compression loads. 
Lightship weight The weight of the hull plus permanently installed items.
Limit state
A state beyond which the product or component no longer satisfies the given 
acceptance criteria 
Limit State 1 (LS1)
An ASD/WSD design condition where the loading is gravity dominated; also used 
when the exclusions of [5.9.7.1 3)] apply. 
Limit State 2 (LS2)
An ASD/WSD design condition where the loading is dominated by 
environmental/storm loads, e.g. at the 10 year or 50 year return period level or, for 
weather restricted operations, (where the operational limiting criteria are less than 
the design environmental criteria due to the application of an Alpha Factor, see 
[2.6.9]). 
Line pipe Coated or uncoated steel pipe sections, intended to be assembled into a Pipeline
Linear Cable Engine 
(LCE)
An industry term commonly used to refer collectively to cable lay tensioners. 
Link beam/link span
The connecting beam between the quay and the barge or vessel. It may provide a 
structural connection, or be intended solely to provide a smooth path for skidshoes
or trailers/SPMTs. 
Load Factor (LF)
A factor used on a design load in a limit state analysis and is also used in the design 
of slings and grommets used for lifting operations. 
Load line
The maximum depth to which a ship may be loaded in the prevailing circumstances 
in respect to zones, areas and seasonal periods. A Load line Certificate is subject to 
regular surveys, and remains valid for 5 years unless significant structural changes 
are made. 
Load transfer 
operation
The operation to transfer the load (i.e. an object) from/to vessel(s) without using 
cranes, i.e. by using (de-)ballasting. Typical load transfer operations are load-out, 
lift-off, mating and float-over. 
Load-in
The transfer of an assembly, module, pipes or component from a barge or vessel, 
e.g. by horizontal movement or by lifting. 
Load-out
The transfer of an assembly, module, pipes or component onto a barge or vessel, 
e.g. by horizontal movement or by lifting. 
Load-out Support 
Frame (LSF)
A structural frame that supports the structure during fabrication and load-out and 
may support the structure on a barge/vessel above grillage. 
Load-out, floating A Load-out onto a floating vessel. 
Load-out, grounded A Load-out onto a grounded vessel. 
Load-out, lifted A Load-out performed by crane. 
Load-out, skidded
A Load-out where the structure is skidded, using a combination of skidways, 
skidshoes or runners, propelled by jacks or winches. 
Load-out, trailer A Load-out where the structure is wheeled onto the vessel using trailers or SPMTs. 
Location move
A move of a MODU or similar, which, although not falling within the definition of a 
field 24-hour move, may be expected to be completed with the unit essentially in 
24-hour field move configuration, without overstressing or otherwise endangering 
the unit, having due regard to the length of the move, and to the area (including 
availability of shelter points) and season. 
Magnetic Particle 
Inspection (MPI)
A Non-Destructive Testing (NDT) process for detecting surface and slightly 
subsurface discontinuities in ferroelectric materials such as iron 
Marine operation See Operation
Marine Warranty 
Survey company
MWS Company
The Marine Warranty Survey (MWS) company is one that is specified on an 
insurance warranty and has been contracted to approve specified operations as a 
condition of the insurance. 
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Marine Warranty 
Survey company 
surveyor (MWS 
company surveyor)
An MWS company surveyor is employed to review the proposed procedures and 
equipment and, when satisfied that they and the weather forecasts are suitable, to 
issue a Certificate of Approval for each relevant operation. He /she may also attend 
during such operations to monitor that the procedures are followed or to agree any 
necessary changes. 
Matched pair of slings
A matched pair of slings is fabricated or designedso that the difference in length 
does not exceed 0.5d for cable laid slings or grommets and 1.0d for single laid 
slings or grommets, where d is the nominal diameter of the sling or grommet. See 
Section 2.2 of IMCA M 179 /81/ for cable laid details 
Material Factor γ
A factor used on a material’s yield stress in a limit state analysis and is also a factor 
used in the design of slings and grommets used for lifting operations. Note: For 
slings and grommets, the material factor is a function of the age, certification and 
material type. 
Maximum Continuous 
Rating (MCR)
Manufacturer’s recommended Maximum Continuous Rating of the main engines.
Mechanical 
Termination
A sling eye termination formed by use of a ferrule that is mechanically swaged onto 
the rope. See ISO 2408 and 7531, /104/ and /105/. 
Minimum Bend Radius 
(MBR)
Specified by the manufacturer of a flexible pipe, umbilical or cable. This is the 
minimum radius to which a flexible, umbilical or cable can be bent without 
compromising its integrity. 
Minimum Breaking 
Load (MBL)
The minimum value of breaking load for a particular sling, grommet, wire or chain, 
shackle etc. 
Mobile Mooring
Mooring system, generally retrievable, intended for deployment at a specific 
location for a short-term duration, such as those for mobile offshore units. 
Mobile Offshore Unit 
(MOU)
For the purposes of this document, the term may include Mobile Offshore Drilling 
Units (MODUs), and non-drilling mobile units such as accommodation, 
construction, lifting or production units including those used in the offshore 
renewables sector. 
Monopile Tubular structure used as foundation for offshore wind turbine generator.
Moored Vessel Within the scope of this document refers to any structure which is being moored.
Mooring System
Consists of all the components in the mooring system including shackles 
windlasses and other jewellery and, in addition, rig/vessel and shore attachments 
such as bollards. 
Most Probable 
Maximum Extreme 
(MPME)
The value of the maximum of a variable with the highest probability of occurring 
over a period of 3 hours. 
NOTE The most probable maximum is the value for which the probability density 
function of the maxima of the variable has its peak. It is also called the mode or 
modus of the statistical distribution. It typically occurs with the same frequency as 
the maximum wave associated with the design sea state. 
Multiple towage
The operation of towing more than one tow by a single tug, or more than 1 tug
towing one tow. See [11.18]
Nacelle
The part of the wind turbine on top of the tower, where the hub, gearbox, 
generator and control systems are located. 
Non-Destructive 
Testing (NDT)
Ultrasonic scanning, magnetic particle inspection, eddy current inspection or 
radiographic imaging or similar. Can also include visual inspection. 
Not To Exceed (NTE) 
weight
Sometimes used in projects to define the maximum weight of a structure for an 
operation. See [5.6.2.2]
Off-hire survey
A survey carried out at the time a vessel, barge, tug or other equipment is taken off-
hire, to establish the condition, damages, equipment status and quantities of 
consumables, intended to be compared with the on-hire survey as a basis for 
establishing costs and liabilities. 
Off-load The reverse of load-out
b
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Offshore Converter 
Station
The offshore converter station transforms the collected energy from the offshore 
transformer stations (several wind parks) to Direct Current in order to send it to a 
land based converter station. 
Offshore pull The pulling of a pipeline away from the shore using a lay vessel
Offshore Transformer 
Station
The offshore transformer station is transforming the collected energy from the wind 
turbines to a higher voltage. 
On-hire survey
A survey carried out at the time a vessel, barge, tug or other equipment is taken on-
hire, to establish the condition, any pre-existing damages, equipment status and 
quantities of consumables. It is intended to be compared with the off-hire survey as 
a basis for establishing costs and liabilities. It is not intended to confirm the 
suitability of the equipment to perform a particular operation. 
Operation reference 
period
The Planned Operation Period, plus the contingency period. See [2.6.2] to [2.6.4]
Operation, marine 
operation
Generic term covering, but not limited to, the following activities which are subject 
to the hazards of the marine environment: 
a. Load-out/load-in
b. Voyage
c. Lift/Lowering (offshore/inshore)
d. Tow-out/tow-in
e. Float-over/float-off 
f. Jacket launch/jacket upend 
g. Pipeline installation 
h. Construction afloat
Operational Limiting 
Criteria
The metocean limits used when assessing weather forecasts to determine the 
acceptability of proceeding with (each phase of) an operation beyond the next 
Point of No Return. 
For a weather restricted operation/voyage these equal the design environmental 
condition multiplied by an Alpha factor. 
Padear
A lift point consisting of a central member, which may be of tubular or flat plate 
form, with horizontal trunnions round which a sling or grommet may be passed 
Padeye
A lift point consisting essentially of a plate, reinforced by cheek plates if necessary, 
with a hole through which a shackle may be connected 
Permanent Mooring
Mooring system normally used to moor floating structures deployed for long-term 
operations, such as those for a floating production system. 
Pigging
The practice of passing a device known as a “pig” through a pipeline for 
maintenance (e.g. for cleaning, gauging or inspection) without stopping the flow in 
the pipeline. 
Pipe carrier A vessel specifically designed or fitted out to transport Line pipe
Pipe-in-Pipe A single rigid pipe held within a carrier pipe by spacers and/or solid filler. 
Pipelay
The operation of assembling and laying the pipeline on the seabed, from start-up 
point to lay-down point. 
Pipeline
Any marine pipeline system for the carriage of oil, gas, water or other process 
fluids. It may be of rigid material or flexible layered construction. For the purposes 
of this document the term pipeline includes flowlines as defined in API RP 1111, /3/
Planned Operation 
Period
The planned duration of the operation from the forecast before either the 
operation start or Point of No Return, as appropriate, to a condition when the 
operations/structures can safely withstand a seasonal design storm (also termed 
“safe to safe” duration) this excludes the contingency period 
Platform The completed steel or concrete structure complete with topsides
Point of No Return 
(PNR)
The last point in time, or a geographical point along a route, at which an operation
could be aborted and returned to a safe condition. 
Port (or point) of 
shelter
See Shelter point
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Port of refuge
A location where a towage or a vessel seeks refuge, as decided by the Master, due 
to events which prevent the towage or vessel proceeding towards the planned 
destination. A safe haven where a towage or voyage may seek shelter for survey
and/or repairs, when damage is known or suspected. 
Pre-Loading
The testing of soil foundations or anchors by loading to check that they can take 
subsequent loads. For jack-up foundations it is often done be adding water ballast 
to pre-load tanks or (with units with more than 3 legs) by pre-driving by removing 
load from other legs in turn. 
Procedure A documented method statement for carrying out an operation
Product
A generic term used within this standard to reference pipelines (rigid and flexible), 
risers, jumpers, umbilicalsand submarine cables. 
Pull Back Method
A J-tube pull-in operation where the pull-in winch is mounted on the installation 
vessel and the end of the pull-in wire connected to the cable runs from the vessel to 
the J-tube bottom end up and over a sheave and back to the installation vessel
pull-in winch. 
Quadrant
A structure, usually with rollers, to limit the MBR as the cable travels over or though 
it and changes direction, typically during loading or laying during second end J 
tube pull in operations. 
Quadratic Transfer 
Function (QTF)
Refers to the matrix that defines second order mean wave loads on a vessel in bi-
chromatic waves. When combined with a wave spectrum, the mean wave drift loads 
and low frequency loads can be calculated. 
Quayside Mooring A mooring that locates a vessel alongside a quay (usually at a sheltered location). 
Recognized 
Classification Society 
(RCS)
Member of IACS with recognized and relevant competence and experience in 
specialised vessels or structures, and with established rules and procedures for 
classification/certification of such vessels/structures under consideration. 
Reduction Factor, γ
The Reduction Factor used in the design of slings or grommets representing the 
largest values of γb and γs. 
Redundancy Check
Check of the failure load case associated with the applicable extreme (survival) 
environment, e.g. the one line broken case. 
Reel Lay (for rigid 
pipe)
A laying method where the pipeline is pre-assembled into long strings or stalks and 
wound onto a large reel with the pipe experiencing plastic deformation when 
wound on and off the reel and straightened when reeled off. Typical lay angles of 
20 to 90 degrees are achieved. 
Registry
Registry indicates who may be entitled to the privileges of the national flag, gives 
evidence of title of ownership of the ship as property and is required by the need of 
countries to be able to enforce their laws and exercise jurisdiction over their ships. 
The Certificate of Registry remains valid indefinitely unless name, flag or ownership 
changes. 
Remotely (Controlled) 
Operated Vehicle 
(ROV)
A device deployed subsea on a tether or umbilical, typically equipped with a 
subsurface acoustic navigation system and thrusters, to control its location and 
attitude, and a lighting and video system. Additional devices such as manipulators, 
acoustic scanning for touch down monitoring, etc., may also be provided. 
Response Amplitude 
Operator (RAO)
Defines the vessel’s (first order) response in regular waves and allows calculation of 
vessel wave frequency (first order) motion in a given sea state using spectral 
analysis techniques. 
Rig
General reference term often used to describe a jack-up or semi-submersible
(Mobile Offshore Drilling Unit or MODU)see MOU) e.g. ‘Rig move procedures’ 
Rigging
The slings, shackles and other devices including spreaders used to connect the 
structure to be lifted to the crane 
Rigging weight
The total weight of rigging, including slings, shackles and spreaders, including 
contingency. 
Righting Arm (GZ) Righting Moment divided by the displacement
Risk assessment
A method of hazard identification where all factors relating to a particular operation
are considered. 
r
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Rope
An assembly of strands wrapped around a core. When a rope is used for cable-laid 
sling or cable-laid grommet it is referred to as a unit rope (as per IMCA M 179 /81/). 
Rotor Configuration consisting of the complete set of blades, connected to the hub.
Route Planning List 
(RPL)
A tabularised list of the coordinates defining the route along which a submarine 
cable is to be installed and the planned installation slack. A post installation RPL will 
record the as-built cable route coordinates, installed slack and burial depths. 
Routine lift
“Everyday” lift, without detailed design, planning or documentation, such as 
general cargo lifting operations or lifting portable units on/off a supply vessel. See 
[16.1.1.4]. 
Safe condition
A condition where the object is considered to be exposed to a normal level of risk 
of damage or loss. See guidance note to [2.5.1.2]
Safe Working Load 
(SWL)
SWL is a derated value of WLL, following an assessment by a competent person of 
the maximum static load the item can sustain under the conditions in which the 
item is being used. See [1.1.12]
Safety Management 
System (SMS)
A structured and documented system enabling Company personnel to implement 
the Company safety environmental protection policy. 
Sand Jacks
A compartment filled with sand that is incorporated into the LMU to allow the final 
controlled lowering of the structure onto the host structure
Scour pit
The result of scour around a pile, leg etc. See “Dynamics of scour pits and scour 
protection”, /119/
Sea room
The distance that a disabled vessel or tow in bad weather can drift before 
grounding. See [11.14.1.5]
Seafastenings
The means of restraining movement of the loaded structure on or within the barge
or vessel
Self-Propelled Modular 
Transporter (SPMT)
A trailer system having its own integral propulsion, steering, jacking, control and 
power systems. 
Semi-submersible
A floating structure normally consisting of a deck structure with a number of widely 
spaced, large cross-section, supporting columns connected to submerged 
pontoons. 
Serviceability Limit 
State (SLS)
A design condition where the structure is required to fulfil its primary operational 
function. 
Setback
The space on the derrick floor where stands of drill pipe or tubing are “setback” 
and racked in the derrick. It can also mean the amount of drill pipe etc. in this area. 
Shelter point (or port 
of shelter, or point of 
shelter)
An area or safe haven where a towage or vessel may seek shelter, in the event of 
actual or forecast weather outside the design limits for the voyage concerned. A 
planned holding point for a staged voyage
Shore pull The pulling of a cable or pipeline to the shore from a lay barge/vessel
Simultaneous 
Operations (SIMOPS)
Operations usually involving various parties and vessels requiring co-ordination 
and definitions of responsibilities. 
Single Laid Sling
A sling normally made up of 6 strands laid up over a core, as shown in ISO 2408 
and 7531, (/104/ and /105/), with terminations each end. 
Single tow The operation of towing a single tow with a single tug. 
Site Move
An operation to move a structure or partially assembled structure in the yard from 
one location to another. The site move may precede a load-out if carried out as a 
separate operation or may form part of a load-out. The site move may be subject to 
approval if so desired. 
Skew Load Factor 
(SKL)
A factor to account for additional loading caused by rigging fabrication tolerances, 
fabrication tolerances of the lifted structure and other uncertainties with respect to 
asymmetry and associated force distribution in the rigging arrangement. 
Skidshoe
A bearing pad attached to the structure which engages in the skidway and carries a 
share of the vertical load 
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Skidway
The lower continuous rails, either on the quay or on the vessel, on which the 
Structure is loaded out, via the Skidshoes. 
Slack Management
A generalized term used by the submarine cable installation industry to refer to the 
control of cable pay-out out against a pre-defined installation plan. 
Slamming loads
Transient loads on the structure due to wave impact when lifting through the splash 
zone. 
S–Lay
A laying method where the pipe is assembled horizontally, fed out of the stern or 
bow of the barge or vessel, typically over a stinger 
Can alsobe without stinger at certain depths or at the end of the shore pull before 
the water depth increases to a depth where stinger becomes necessary, and then 
makes a double curve (shallow S shape) to lie horizontally on the sea-bed. 
Sling design Load
The maximum calculated dynamic axial load in a lifting sling, including all relevant 
load factors. 
Sling eye A loop at each end of a sling, either formed by a splice or mechanical termination
Specified Minimum 
Yield Stress (SMYS) 
The minimum yield stress specified in standard or specification used for purchasing 
the material. 
Splice
That length of sling where the rope (or unit rope for cable-laid sling) is connected 
back into itself by tucking the tails of the strands (or unit ropes) back through the 
main body of the rope (or unit ropes), after forming the sling eye
Spreader beam or bar 
(frame)
A spreader bar or frame is a structure designed to resist the compression forces 
induced by angled slings, by altering the line of action of the force on a lift point
into a vertical plane. The structure shall also resist bending moments due to 
geometry and tolerances. 
Spud
A large metal post which penetrates the seabed under its own weight and is used 
to prevent lateral movement of a barge. A dredge barge will typically have two 
spuds in guides near its stern. 
Staged voyage
A weather restricted voyage in which there is a commitment to seek shelter (or jack-
up at a stand-by location) on receipt of a weather forecast in excess of the 
operational criteria. See [11.14.4.1]. 
Static Hook Load (SHL)
The weight plus the rigging weight (see [16.3.2]). This load is suspended by a crane 
hook during lifting operations. 
Strand
An assembly of wires wound together to create a strand. Wire rope consists of 
multiple strands wound together. For example: 6x36 wire rope construction 
indicates that the wire rope consists of 6 strands, each having 36 wires. 
Structure
The object to be transported, lifted or installed, or a sub-assembly, component or 
module. 
Submerged Weight Weight of the Structure minus the weight of displaced water.
Suitability survey
A survey intended to assess the suitability of a tug, barge, vessel or other 
equipment to perform its intended purpose. Different and distinct from an on-hire 
survey. 
Surge
Barge or vessel motion in the longitudinal direction OR 
A change in water level caused by meteorological conditions
Survey
Attendance and inspection by a MWS company surveyor. 
Other surveys which may be required for a marine operation, including suitability, 
dimensional, structural, navigational and Class surveys. 
Surveyor
The MWS company representative carrying out a ‘Survey’ or an employee of a 
contractor or Classification Society performing, for instance, a suitability, 
dimensional, structural, navigational or Class survey. 
Sway Vessel motion in the transverse direction 
System Pressure Test
A pressure test at a pressure normally at a 1.25 to 1.5 times the pipeline design 
pressure (for rigid pipelines), which is made after installation operations are 
substantially or wholly completed, to provide proof of pressure and strength 
integrity of the pipeline and spools. 
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Tandem tow
The operation of towing two or more tows in series with one tow wire from a single 
tug, the second and subsequent tows being connected to the stern of the tow
ahead. 
Tangent Point The point where the bend of a pipeline begins or ends.
Tensioner Equipment to keep and control tension in the product during installation operation.
Termination factor γ
A partial safety factor that accounts for the reduction in strength caused by a splice
or mechanical termination. 
Tether
A tether is a mooring line used for pulling and mooring the installation /removal 
vessel into the required position. It may also be the umbilical to an ROV or part of a 
TLP’s mooring system. 
Tidal range
Where practicable, the tidal range referred to in this document is the predicted 
tidal range corrected by location-specific tide readings obtained for a period of not 
less than one lunar cycle before the operation. 
Tonnage 
A measurement of a vessel in terms of the displacement of the volume of water in 
which it floats, or alternatively, a measurement of the volume of the cargo carrying 
spaces on the vessel. Tonnage measurements are principally used for freight and 
other revenue based calculations. Tonnage Certificates remain valid indefinitely 
unless significant structural changes are made. 
Tonnes
Metric tonnes of 1,000 kg (approximately 2,204.6 lbs) are used throughout this 
document. The necessary conversions shall be made for equipment rated in long 
tons (2,240 lbs, approximately 1,016 kg) or short tons (2,000 lbs, approximately 907 
kg). 
Touch Down (TD)
Seabed location at which a submarine pipeline or cable touches down on the 
seabed during installation, or a mooring line during operation. 
Tow
The item being towed. This can be a barge or vessel (laden or un-laden) or an item 
floating on its own buoyancy. 
Towage
The operation of towing a non-propelled barge or vessel (whether laden or not,) or 
other floating object (wet tow) by tug(s). 
Towed bundle
A pipeline system comprising one or more pipelines, tubes or cables contained 
within a carrier pipe, and fitted with towing and trailing heads. The bundle is usually 
assembled on land and launched. The bundle may be towed off- bottom, on 
surface, or at an intermediate controlled depth. 
Tower (OWF)
The tubular element from the top of the flange on the foundation to the bottom of 
the flange below the nacelle, generally built up of several sections. 
Towing arrangements
The hardware from the towing winch to the towing connections plus the bridle 
recovery and emergency towing equipment. (They do not normally include the 
towing procedures.) 
Towline connection 
strength
Ultimate load capacity of towline connections, including connections to vessel, 
bridle and bridle apex. 
Towline Pull Required 
(TPR)
The towline pull computed to hold the tow, or make a certain speed against a 
defined weather condition. 
Trailer
A system of steerable wheels, connected to a central spine beam by hydraulic 
suspension which can be raised or lowered. Trailer modules can be connected 
together and controlled as a single unit. Trailers generally have no integral 
propulsion system, and are propelled by tractors or winches. See also SPMT. 
Transition Piece A tubular structure on top of a monopile to provide support for the tower. 
Transport The operation of transporting a cargo on a powered vessel. 
Trunnion
A lift point consisting of a horizontal tubular cantilever, round which a sling or 
grommet may be passed. An upending trunnion is used to rotate a structure from 
horizontal to vertical, or vice versa, and the trunnion forms a bearing round which 
the sling, grommet or another structure will rotate. 
s
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Tug
The vessel performing a towage (including tug supply and anchor handling towing 
vessels). Approval by the MWS company of the tug will normally include 
consideration of the general design, classification, condition, towing equipment, 
bunkers and other consumable supplies, emergency communication and salvage 
equipment, and manning. 
Tug efficiency (T or 
T ) 
Effective bollard pull produced in the weather considered divided by the certified 
continuous static bollard pull. 
Tug Management 
Positioning System 
(TMPS)
A system installed on the AHV and the anchoring vessel to allow the accurate 
placing of the tug and anchors. 
Ultimate Limit State 
(ULS)
The limit state related to the maximumload carrying capacity. Also see Limit State 1
and Limit State 2. (ULS) 
Ultimate Load 
Capacity (ULC)
Ultimate load capacity of a wire rope, chain or shackle or similar is the certified 
minimum breaking load. The load factors allow for good quality splices in wire 
rope. 
Ultimate load capacity of a padeye, clench plate, delta plate or similar structure, is 
defined as the load, which will cause general failure of the structure or its 
connection into the barge or other structure. 
Ultrasonic Testing (UT)
Detection of flaws or measurement of thickness by the use of ultrasonic pulse-
waves through steel or some other materials. 
Umbilical
Typically a combination of cables and flexible pipes used to provide energy and/or 
chemicals and remote control for equipment (e.g. subsea), or to provide 
communications and life support for a diver 
Under-Keel Clearance 
(UKC)
The clearance below the keel or base of a vessel or structure, after allowances for 
motions, and the seabed (or the host structure during mating operations) 
Unit Rope
The rope from which a cable-laid sling or cable-laid grommet may be constructed, 
made from either 6 or 8 strands around a steel core, as indicated in ISO 2408 and 
7531, (/104/ and /105/) and IMCA, M 179, /81/
Variable Load
Weight added to the Lightship weight to obtain the total weight for a particular 
towage or operation, including cargo, liquids and temporary equipment. 
Vessel
A marine craft designed for the purpose of transporting by sea or construction 
activities offshore. This can include ships and barges
Voyage
For the purposes of this standard, voyage covers both towages and transport from 
one place to another. 
Watertight
A watertight opening is an opening fitted with a closure designated by Class as 
watertight, and maintained as such, or is fully blanked off so that no leakage can 
occur when fully submerged. 
Wear Factor, γ
A factor used in the design of slings and grommets used for lifting operations to 
account for physical condition of the sling or grommet. 
Weather restricted 
operation
An operation for which (any of) the applied characteristic environmental conditions 
are less than the characteristic environmental conditions calculated based on the 
statistical extremes for the area and season. See also 2.6.7
Weather restricted 
voyage
A voyage for which the strength or stability will not meet the weather unrestricted 
environmental criteria (typically 10 year return). It can either be or staged (see 
[11.14.4.1]) or weather-routed (see [11.14.4.4]) depending on the sea room and 
shelter point availability. 
Weather routed 
voyage
A weather restricted voyage in which a weather forecasting organisation advises 
the relevant captain on the best route to avoid weather exceeding the Operational 
Limiting Criteria. (See [11.14.4.4]). 
Weather routeing may also be used for non-weather restricted voyages to reduce 
fuel costs or voyage time. 
Weather unrestricted 
operation
An operation for which (all of) the applied characteristic environmental conditions 
are calculated based on the statistical extremes for the area and season. See also 
2.6.62.6.5. 
e
eff
w
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Weather unrestricted 
towage
Any towage which does not fall within the definition of a weather restricted towage,
or any towage of a MODU or similar which does not fall within the definition of a 24-
hour move or location move. 
Weather unrestricted 
voyage
Any voyage which does not fall within the definition of a weather restricted voyage 
Weather Window
A period that the forecasted environmental conditions are less than or equal to 
OP (the Forecast Operation Criteria). 
Weathertight
A weathertight opening is an opening closed so that it is able to resist any 
significant leakage from one direction only, when temporarily immersed in green 
water or fully submerged. 
Weighing Contingency 
Factor
A factor applied to the weighed weight of an object to account for uncertainties in 
the weighing equipment. 
Weight Contingency 
Factor
A factor applied to the weight of an object, when an object is not to be weighed, to 
account for uncertainties related to the design and fabrication of the object. 
Wet towage The operation of transporting a floating object by towing it with a tug. 
Wind Heeling Arm 
(WHA)
Wind Heeling Moment divided by the displacement
Working Load Limit 
(WLL)
The maximum static load which a piece of equipment is authorized to sustain in 
general service when the rigging and connection arrangements are in accordance 
with the design. See [1.1.12]. 
1.6 Acronyms, abbreviations and symbols 
1.6.1
Underlined acronyms and abbreviations in Table 1-4 are defined in Table 1-3. 
Table 1-4 Acronyms and abbreviations
Short Form In full
ABS American Bureau of Shipping
ADL Absolute minimum Deployable Length (of towline)
AHC Active Heave Compensation
AHV Anchor Handling Vessel
AISC American Institute of Steel Construction
ALARP As Low As Reasonably Practicable
ALS Accidental Limit State
AMS Anchor Management System
API American Petroleum Institute
ASD Allowable Stress Design (effectively the same as WSD)
ASOG Activity Specific Operations Guidelines (for DP – See [17.13.4.1 11)) 
ASPPR Arctic Shipping Pollution Prevention Regulations
ATA Automatic Thruster Assist
AUT Automatic Ultrasonic Testing
AWTI Above Water Tie-In
BAS Burial Assessment Survey
BBL Bridle Breaking Load
BHP Brake Horse Power
WF
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BP Bollard Pull
BPI Burial Protection Index
BSR Bend Strain Reliever
CAMO Critical Activity Mode of Operation (for DP – See [17.13.4.1 11)) 
CASPRR Canadian Arctic Shipping Pollution Prevention Regulations
CBP Continuous Bollard Pull
CDT Controlled Depth Tow
CGBL Calculated Grommet Breaking Load
CoB Centre of Buoyancy
CoG Centre of Gravity
COMOP Combined Operations
COSHH Control of Substances Hazardous to Health
CR Continuity Resistance
CRBL Calculated Rope Breaking Load
CSA Cross Sectional Area
CSBL Calculated Sling Breaking Load
CSV Construction Support Vessel
DAF Dynamic Amplification Factor
DMA Dead Man Anchor
DP Dynamic Positioning or Dynamically Positioned
DSU Deck Support Unit
DSV Diving Support Vessel
DTL Deployable Towline Length (see [11.13.4.3]) 
D Factor for ratio of mean to specified bolt pretension
ECA Engineering Criticality Assessment
EPC Engineering, Procurement and Construction
EPIRB Emergency Position Indicating Radio Beacon
ESD Emergency Shut Down
FAT Factory Acceptance Tests
FBE Fusion Bonded Epoxy
FEA Finite Element Analysis
FEED Front End Engineering Design
FGSO Floating Gas Storage and Offloading Vessel
FJC Field Joint Coating
FLNG Floating Liquefied Natural Gas
FLS Fatigue Limit State 
FMEA Failure Modes and Effects 
FMECA Failure Modes, Effects and Criticality Analysis
FOI Floating Offshore Installation
FoS Factor of Safety
FPS Floating Production System
u
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FPSO Floating Production, Storage and Offloading Vessel
FPU or FPV Floating Production Unit or Floating Production Vessel
FRSU Floating Storage Re-gasification Unit
F Sling or grommet design load 
FSE Free Surface Effect
FSO Floating Storage and Offloading Vessel
FSU Floating Storage Unit (including FPSO, FSO, FLNG facility, FRSU etc.)
Gamma b, γ Bending Factor
Gamma c, γ Consequence Factor
Gamma f, γ Load Factor
Gamma m, γ Material Factor 
Gamma r, γ Reduction Factor 
Gamma s, γ Termination Factor
Gamma sf, γ Combined factors (Load, Consequence, Reduction, Wear, and Material and Twist)
Gamma w, γ WearFactor
Gamma weight, 
γ
Weight Contingency Factor (unweighed objects only) 
GBS Gravity Base Structure (foundation)
GM Initial metacentric height
GMDSS Global Maritime Distress and Safety System
GN Guidance Note
GPS Global Positioning System
GZ Righting Arm
HAT Highest Astronomical Tide
HAZID Hazard Identification
HAZOP HAZards and OPerability study
HDD Horizontal Directional Drilling
h Factor for fillers in bolted connections
HIRA Hazard Identification and Risk Assessment
HPR Hydro-acoustic Positioning Reference
HSEQ Health, Safety, Environment and Quality
HTV
Heavy Transport Vessel. (not to be confused with HLV (Heavy Lift Vessel) which has heavy 
lifting gear) 
HVAC High Voltage Alternating Current
HVDC High Voltage Direct Current
IACS International Association of Classification Societies
ICPC International Cable Protection Committee
IMCA International Marine Contractors Association
IMDG Code International Maritime Dangerous Goods Code
IMO International Maritime Organization
IOPP Certificate International Oil Pollution Prevention Certificate (see also MARPOL)
SD
b
c
f
m
r
s
sf
w
weight
f
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IR Insulation Resistance
ISM International Safety Management 
ISO International Standards Organisation
ITP Inspection Test Plan
JSA Job Safety Analysis
k Hole clearance factor
LARS Launch And Recovery System
LAT Lowest Astronomical Tide
LBL Long Baseline Array
LCE Linear Cable Engine
LMU Leg Mating Unit
LOA Length Over All
LRFD Load and Resistance Factor Design 
LS1 Limit State 1
LS2 Limit State 2
LSF Load-out Support Frame
MAOP Maximum Allowable Operating Pressure
MARPOL International Convention for the Prevention of Pollution from Ships 1973/78, as amended
MBL Minimum Breaking Load
MBR Minimum Bend Radius
MCR Maximum Continuous Rating
MDR Master Document Register
MLWS Mean Low Water Spring Tides
MoC 
(procedure)
Management of Change (procedure)
MODU Mobile Offshore Drilling Unit
MOU Mobile Offshore Unit
MPI Magnetic Particle Inspection
MPME Most Probable Maximum Extreme
MRU Motion Reference Unit
MSL Mean Sea Level
MWS Marine Warranty Survey
n/a Not Applicable
NDT Non Destructive Testing
NMD Norwegian Maritime Directorate
N Number of slip planes for bolted connections
NTE (weight) Not To Exceed (weight)
OCIMF Oil Companies International Marine Forum
OD Outside Diameter
OP Operational limiting criteria
OP Forecasted operational criteria
s
s
LIM
WF
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OSS Out of Straightness Survey
OTDR Optical Time Domain Reflectometry
OWF Offshore Wind Farm
PHC Passive Heave Compensation
PIC Person In Charge
PLEM Pipeline End Manifold
PLET Pipeline End Termination
PNR Point of No Return
PRT Pipeline Recovery Tooling/Tool
PSA Petroleum Safety Authority Norway
QC Quality Control 
QCFAT Quality Control Factory Acceptance Test
QRA Quantified Risk Analysis
QTF Quadratic Transfer Function
RAO Response Amplitude Operator
RCS Recognized Classification Society
ROV Remotely (Controlled) Operated Vehicle
RPL Route Planning List
RTBL Required Towline Breaking Load
SART Search and Rescue Radar Transponder
SCR Steel Catenary Riser
SE Shore End
SF Safety Factor
SHL Static Hook Load
SIMOPS Simultaneous Operations
SJA Safe Job Analysis
SKL Skew Load Factor
SLS Serviceability Limit State
SMC Safety Management Certificate
SMS Safety Management System
SMYS Specified Minimum Yield Stress
SOLAS International Convention for the Safety Of Life At Sea, /92/, 
SOPEP Shipboard Oil Pollution Emergency Plan
SPMT Self-Propelled Modular Transporter
SSCV Semi-submersible crane vessel
SWL Safe Working Load
TA Thruster Assist
TAM Task Appropriate Mode
T Minimum fastener pretension for bolted connections
TBL Towline Breaking Load
T Contingency period
b
C
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TD Touch Down
TDR Time Domain Reflectometry
T or T Tug efficiency
TLP Tension Leg Platform
TMPS Tug Management Positioning System
TMS Tether Management System
T Peak period
T Planned operational Period (without contingencies, T ) 
TPR Towline Pull Required
T Operation Reference Period (including contingencies, T ) 
T Time to safely cease the operation
T Time between weather forecasts
T Zero-up crossing period for waves
UKC Under-Keel Clearance
UKCS United Kingdom Continental Shelf
ULC Ultimate Load Capacity
ULS Ultimate Limit State
UNCLOS United Nations Law of the Sea
USBL Ultra Short Baseline Array
UT Ultrasonic Testing
UTM Universal Transverse Mercator
UXO Unexploded Ordnance
VIV Vortex Induced Vibration
VLA Vertical Load Anchors
WF Weather Forecast
WHA Wind Heeling Arm
W Lower bound design weight
WLL Working Load Limit
WMO World Meteorological Organisation
WROV Work class Remotely Operated Vehicle
Wrt with respect to
WSD Working Stress Design (effectively the same as ASD)
WTG Wind Turbine Generator
W Upper bound design weight
SECTION 2 Planning and execution 
2.1 Introduction 
2.1.1 Scope 
e eff
p
POP C
R C
safe
WF
z
ld
ud
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2.1.1.1
This Section includes the general requirements for planning, organization, execution and documentation of 
marine operations. 
2.1.2 Revision history 
2.1.2.1
This section replaces the following parts of the VMO Standard and the ND Guidelines:
• DNV-OS-H101
• 0001/ND.
2.2 General project requirements 
2.2.1 Project organisation 
2.2.1.1
An appropriate Project organisation chart shall be set up, illustrating how the marine operations integrate with 
the rest of the project. 
2.2.1.2
All project interfaces between (key) contractors shall be clearly defined. 
2.2.1.3
For organisation during the marine operation see [2.8]. 
2.2.2 Health, safety and environment 
2.2.2.1
Personnel safety shall be duly considered throughout the marine operation(s). This subject shall be managed by 
the client or his nominated contractor in accordance with local jurisdiction, as well as appropriate guidelines and 
specifications regarding health, safety and the environment (HSE). 
Guidance note:
By following the recommendations in this Standard it is assumed that the safety of personnel and an acceptable 
working environment are ensured in general during the operations. However, specific personnel safety issues 
are not covered. 
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2.2.3 Jurisdiction 
2.2.3.1
Marine operations are subject to national and international regulations and standards on personnel safety and 
protection of the environment. It should also be noted that a marine operation can involve more than one 
nation’s area of jurisdiction, and that for barges and vessels the jurisdiction of the flag state will apply. 
Documented relevant regulatory approval is a prerequisite to MWS approval. 
2.2.3.2
If a part of the marine operations is to be carried out near other facilities or their surroundings any safety zone(s) 
defined by the owner shall be duly considered. 
2.2.4 Quality assurance and administrative procedures 
2.2.4.1
A quality management system in accordance with the current version of ISO 9001, /106/, or equivalent should be 
adopted by the designer(s) and installation contractor(s) and be in place. 
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2.2.5 Technical procedures 
2.2.5.1
Technical procedures shall be in place to control engineering related to the marineactivities. 
2.2.5.2
The technical procedures shall consider the planning and design process. For this process it is recommended 
that the following sequence is adopted: 
a. Identify relevant and applicable regulations, rules, company specifications, codes and standards, both 
statutory and self-elected. 
b. Identify physical limitations. This may involve pre-surveys of structures, local conditions and soil 
parameters. 
c. Plan the overall operation i.e. evaluate operational concepts, available equipment, limitations, economic 
consequences, etc. 
d. Describe/define unambiguously with adequate detailing the design basis and main assumptions, see 
[2.2.7]. 
e. Carry out engineering and design analyses.
f. Develop operation procedures.
2.2.5.3
The procedures shall include sufficient information to ensure agreement and uniformity on all relevant matters 
such as: 
a. International and national standards and legislation
b. Certifying authority/regulatory body standards
c. Marine warranty survey company standards and guidelines
d. Project criteria
e. Design basis
f. Metocean criteria
g. Calculation procedures
h. Change management. 
Guidance note:
It will also normally be applicable to include requirements to assure compliance, where relevant, with any 
peer-reviewed best industry practice, e.g. IMCA, MTS, GOMO, NORSOK, etc. 
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2.2.6 New technology 
2.2.6.1
Design and planning of marine operations shall as far as feasible be based on well proven principles, techniques, 
systems and equipment. 
2.2.6.2
If new technology or existing technology in a new environment is used, this technology should be documented 
through an acceptable qualification process, e.g. in DNV-RP-A203, /45/. 
2.2.7 Design basis and design brief 
2.2.7.1
A design basis and/or a design brief shall be developed and provided for early acceptance in order to obtain a 
common basis and understanding for all parties involved during design, engineering and verification. 
2.2.7.2
The Design Basis should describe the basic input parameters, main assumptions, characteristic environmental 
conditions, characteristic loads/load effects, load combinations and load cases, including those for the proposed 
marine operations. 
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2.2.7.3
The Design Brief(s) should describe the planned verification activities, analysis methods, software tools, input 
specifications, acceptance criteria, etc. 
2.3 Technical documentation 
2.3.1 General 
2.3.1.1
Fulfilment of all the requirements in this Standard applicable for the considered marine operation(s) shall be 
properly documented. Guidance on required documentation is given throughout this Standard. However, it shall 
always be thoroughly evaluated if additional documentation is required. 
2.3.1.2
A document plan describing document hierarchy, issuance schedule and scope for each document should be 
provided for major marine operations/projects. 
Guidance note:
Normally this will be in the form of MDR(s) that are distributed for review/mark-up by involved parties including 
the MWS Company. 
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2.3.1.3
A system/procedure ensuring that all required documentation is produced in due time and distributed 
according to plan, should be implemented. 
2.3.1.4
It shall be ensured that all the documentation pertaining to a specific marine operation has been accepted by 
Authorities, Company, other Contractors and MWS, as relevant, before any operation starts. 
2.3.2 Documentation required 
2.3.2.1
The design basis shall be clearly documented, see [2.2.7]. 
2.3.2.2
Environmental conditions for the actual area shall be documented by reliable statistical data, see Sec.3. 
2.3.2.3
The acceptability of the following shall be documented: the object, all equipment, temporary or permanent 
structures, vessels, etc. involved in the operation. Recognized certificates (e.g. classification documents) are 
normally acceptable as documentation if the basis for certification is clearly stated and complies with the 
philosophy and intentions of this Standard. 
Guidance note 1:
By basis for certification it is meant acceptance standard, basic assumptions, design loads, including dynamics, 
limitations, etc. For items without certificates see [2.3.2.4]. 
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Guidance note 2:
Note that all elements of the marine operation should be properly documented. This also includes onshore 
facilities such as quays, bollards and foundations. 
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2.3.2.4
Design calculations/analysis shall be documented by design reports and drawings.
2.3.2.5
The condition of all involved equipment, structures and vessels shall be documented as acceptable by means of 
certificates and test, survey and NDT reports. 
Guidance note:
For vessels, such documentation may be recent inspections to acceptable industry standards, e.g. OVID or 
CMID, provided all relevant non-conformances are closed out. See also [2.11.2]. 
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2.3.2.6
Operational aspects shall be documented in form of operation manuals and records. 
2.3.2.7
Relevant qualifications of key personnel shall be documented.
2.3.2.8
Required 3 Party verification, e.g. to fulfil the warranty clause, shall be properly documented. See also [2.4.4]. 
2.3.3 Documentation quality and schedule 
2.3.3.1
An integrated document numbering system for the entire project is suggested, including documents produced 
by client, contractors, sub-contractors and vendors. 
2.3.3.2
Documents relating to marine operations should be grouped into levels according to their status, for example: 
a. Criteria and design basis documents
b. Procedures and operations manuals 
c. Supporting documents, including engineering calculations, systems operating manuals and equipment 
specifications and certificates. 
2.3.3.3
The documentation shall demonstrate that philosophies, principles and requirements of this Standard are 
complied with. This documentation shall be provided to the MWS Company. 
Guidance note:
The operation and document type dictates the level of review by the MWS company. The following terms have 
been used as an indication of the level of detail: 
• Documented – An in-depth document that is subjected to a detailed review by the MWS company e.g. 
analysis reports, procedures and operation manuals 
• Submitted – A document that is provided to the MWS company in advance where the checking is limited 
e.g. a certificate to confirm that piece of equipment has the required capacity. In some cases this could be 
immediately prior to the operation but this may lead to delays if the documents are incorrect and/or 
insufficient. 
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2.3.3.4
Documentation for marine operations shall be self-contained, or clearly refer to other relevant documents. 
2.3.3.5
The quality and details of the documentation shall be such that it allows for independent reviews of plans, 
procedures and calculations, for all parts of the operation. 
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2.3.3.6
All significant updates shall be clearly identified in revised documents.
2.3.3.7
The document schedule shall allow for the required (agreed) time for independent reviews. 
Guidance note:
The time available for review should be at least 10 working days, and more for complex documents. 
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2.3.4 Input documentation 
2.3.4.1
Applicableinput documentation, such as;
• documents covering the aspects described in [2.2.5], 
• relevant parts of contractual documents,
• concept descriptions,
• basic/FEED engineering results,
• environmental studies including weather window analysis for weather restricted operation. 
should be identified before any detailed design work is performed.
2.3.5 Output documentation 
2.3.5.1
Documentation shall be prepared to prove that all relevant design and operational requirements are fulfilled. 
Typical output documentation is: 
a. Planning documents including design briefs and basis, schedules, concept evaluations, general 
arrangement drawings and specifications. 
b. Design documentation including motion analysis, load analysis, global strength analysis, local design 
strength calculations, stability and ballast calculations and structural drawings. 
c. Operational manuals/procedures, see [2.3.7] and [2.9.5]. 
d. Operational records, see [2.3.8]. 
2.3.6 Availability of technical documentation 
2.3.6.1
All relevant documentation shall be available and accessible on site or on board during execution of the 
operation. In addition to the marine operations manual this should include the documents referenced therein. 
2.3.6.2
The top level procedure document should define the On-Scene Commander in the event of an emergency 
situation and the interfaces between the various parties involved. 
2.3.6.3
Vessel and equipment certificates and NDT reports shall be submitted. See [B.1] and [B.2] for the information 
that is typically required. 
Guidance note:
In order to avoid possible delays due to unacceptable or incomplete documentation, it is recommended that 
such documentation is submitted for review as soon as possible. 
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2.3.6.4
Procedure documents, intended to be used as an active tool during marine operations should include a section 
which clearly shows their references to higher and lower level documents, and should list all inter-related 
documents. 
Guidance note:
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A document organogram is often helpful as shown in Figure 2-1. 
Figure 2-1 Example of document organogram
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2.3.7 Marine operation manuals 
2.3.7.1
An operational procedure shall be developed for the planned operation, and shall reflect characteristic 
environmental conditions, physical limitations, design assumptions and tolerances. 
Guidance note:
For complex operations it is recommended that a high level presentation of the marine operation is made 
available as an animation or picture series. See also 2.8.3. 
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2.3.7.2
The operational procedures shall be described in a marine operation manual covering all aspects of the 
operation and should include the following, as applicable: 
a. reference documents
b. general arrangement
c. permissible load conditions
d. outline execution plan
e. organogram and lines of command
f. job-descriptions for key personnel
g. safety plan, see [2.3.7.5]
h. authorities and permits including notification and approval requirements
i. contractual approvals and hand over, see also [2.3.7.4]
j. environmental criteria, including design and operational criteria
k. weather (forecast) and current/wave reporting 
l. operational bar chart, showing the anticipated duration of each activity, inter-related activities, key 
decision points, hold points 
m. specific step-by-step instructions (procedures/task plans) for each phase of the operation including 
sequence, timing, resources and check lists 
n. reference to related drawings and calculations, e.g. environmental loads, moorings, ballast, stability, 
bollard pull 
o. permissible draughts, trim, and heel and corresponding ballasting plan
p. how to handle any changes in the procedure during the operation, see also 2.2.5.3 h). 
q. contingency and emergency plans
r. emergency preparedness bridging document
s. monitoring during the operation, see [2.9.5]
t. clearances and tolerances
u. systems and equipment including layout
v. systems and equipment operational instructions
w. vessels involved
x. tow routes and ports of refuge
y. navigation
z. safety equipment
aa. recording and reporting routines
ab. sample forms
ac. equipment operation history
ad. check lists for preparation and performance of the operation.
2.3.7.3
Operational limiting criteria for marine operations or parts thereof shall be clearly stated in the Manual. 
2.3.7.4
The Manual shall describe the decision point for issuing the CoA from the MWS company. It may also be found 
relevant to include (other) “gates” at which agreement from representatives of the principal parties involved 
should be obtained before continuing to next stage of operation. 
2.3.7.5
A safety plan shall be included in the operation manual. This plan consists of the safety rules that apply to 
minimise the following risks encountered during each operation: 
a. Risks inherent from the metocean conditions
b. Risks incurred by construction, transport, installation and commissioning activities
c. Risks to the environment
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d. Risks due to simultaneous operations (SIMOPS) – see IMCA M 203, /83/
e. Risks due to working on live assets, etc.
2.3.7.6
Essential documentation in the form of certificates, release notes and classification documents for all equipment 
and vessels involved in the marine operation shall be enclosed and/or listed in the Manual. See also 2.3.6.3. 
2.3.8 Operation records and reporting 
2.3.8.1
The execution of marine operations shall be logged. Recording form templates shall be included in the marine 
operations manual. 
2.3.8.2
The following should as a minimum be recorded during the operation:
a. log of (main) tasks carried out
b. any modifications in the agreed procedure
c. unexpected events and any deviations from or alterations of procedure imposed by such
d. environmental conditions and
e. critical monitoring results. 
2.3.8.3
Any significant modifications in the agreed procedure shall be reported promptly to the MWS Company. 
Guidance note:
It is recommended that all changes to previously agreed/approved procedures are signed off by the principal 
representatives of the parties involved. See also [2.3.7.2 p)], and that this is described in the MOC procedure. 
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2.3.8.4
For larger projects, communications to the client (and MWS company) on site should be confirmed in writing, 
e.g. by daily reports. 
2.3.8.5
Regular, at least daily, reports shall be issued to MWS company from operations (e.g. towage) where the MWS 
company is not attending. 
2.3.8.6
Any incidents, accidents or near-misses relevant to the safety of the structure or future marine operations shall be 
reported to MWS company. 
2.4 Risk management 
2.4.1 General 
2.4.1.1
Risk management shall be applied to the project to reduce the overall risk. The preferred approach is to address 
the following: 
a. Identification of potential hazards
b. Preventative measures to avoid hazards wherever possible
c. Controls to reduce the potential consequences of unavoidable hazards
d. Mitigation of the consequences, should hazards occur.
2.4.1.2
The overall responsibility for risk management shall be clearly defined when planning marine operations. 
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Guidancenote:
It is recommended that risk management is performed according to DNV-RP-H101, /54/, in order to ensure a 
systematic evaluation and handling of risk. It is also a premise for a successful risk management that a project 
team with sufficient competence to understand the marine operation and the potential risk/hazard is mobilized, 
see [2.8]. 
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2.4.1.3
Risk evaluations shall be carried out at an early stage for all marine operations in order to define the extent of risk 
management required, and to identify and mitigate risk as early in the design process as possible. 
Guidance note 1:
The type and amount of risk evaluations should be based on the complexity of each marine operation. DNV-RP-
H101, /54/, Appendix D.5 gives advice on how to carry out initial risk evaluations. The effect of (planned) 
redundancy, back-up, safety barriers, and emergency procedures should be taken into account in the (initial) risk 
estimates. Contingency situations with a documented (joint) probability of occurrence less than 10-4 per 
operation may be disregarded. 
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Guidance note 2:
Ideally, each of the various studies outlined should be managed by a competent independent person familiar 
with the overall concept, but outside the team carrying out the relevant system or structure design or operational 
management. 
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2.4.1.4
Risk assessments shall be documented and the mitigated risks accepted by the MWS company. 
2.4.1.5
Detailed hazard studies should include the personnel and organisations involved in the design of structures and 
systems, as well as those involved in the marine operation and the MWS company. The studies shall be 
performed for: 
a. Each major marine operation. 
b. Each major system essential to the performance and safety of marine operations. For example, the power 
generation and the ballast and compressed air systems. 
Guidance note:
Hazard identification activities (see [2.4.2]) may be used to systematically evaluate risk applicable to any 
operation, to compare levels of risk between alternative proposals or between known and novel methods, 
and to enable rational choices to be made between alternatives. 
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2.4.2 Hazard identification activities 
2.4.2.1
Risk identification techniques and methods shall be used as applicable for the intended operation. Examples of 
applicable techniques and methods are: 
a. Preliminary risk assessment in order to assess concepts and methods
b. Hazard Identification Analysis (HAZID)
c. Early Procedure Hazard and Operability study (EP HAZOP) 
d. Hazard Identification and Risk Assessment (HIRA)
e. Design Review (DR)
f. System HAZOP
g. Failure Mode Effect (and Criticality) Analysis (FMEA/FMECA)
h. Procedure HAZOP
i. Semi-Quantitative Risk Analysis (SQRA)
j. Safe Job Analysis (SJA) / Job Safety Analysis (JSA).
Guidance note:
DNV-RP-H101, /54/, Appendix B defines and describes most of the risk identifying activities listed above in 
detail. The HAZOP is not only focused on possible hazards, but also on issues related to the operability of 
an activity or operation, the plant or system, including possible improvements. 
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2.4.2.2
All identified possible hazards shall be reported and properly managed.
2.4.3 Risk reducing activities 
2.4.3.1
Relevant corrective actions from the risk identifying activities shall be implemented in the planning and execution 
of the operations. 
2.4.3.2
The following risk reducing activities for marine operations shall be used as applicable for the intended 
operation: 
a. Operational feasibility assessments
b. Document verification
c. Familiarisation
d. Personnel safety plans
e. Emergency preparedness
f. Marine readiness verification
g. Inspection and testing
h. Survey of vessels
i. Toolbox talk
j. Safe Job Analysis / Job Safety Analysis
k. Survey of operations. 
Guidance note:
DNV-RP-H101, /54/, Appendix C describes the above listed risk reducing activities in detail. Note that Safe 
Job Analysis is in DNV-RP-H101, /54/, mentioned only in Appendix B - Hazard Identification Activities. 
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2.4.4 3 party verification and MWS 
2.4.4.1
As a part of the risk management the requirements for 3 Party verification of calculations, procedures, vessels, 
equipment, etc. and survey of the operations shall be defined. 
2.4.4.2
If applicable a Marine Warranty Survey company shall be contracted to ensure that the marine warranty clause is 
fulfilled. 
2.4.4.3
It shall be ensured that the MWS (marine warranty survey) Company’s (minimum) scope of work has been 
adequately defined to fulfil the intention of the marine warranty clause. Specific requirements of warranty clause 
to be given to MWS as early as possible. 
2.4.4.4
Thorough knowledge of this Standard shall be documented in order to carry out marine warranty survey with the 
intention of confirming compliance with this Standard. 
2.5 Planning of marine operations 
2.5.1 Philosophy 
2.5.1.1
Marine operations shall be planned according to safe and sound practice, and according to defined codes and 
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standards. 
2.5.1.2
A marine operation shall be designed to bring an object from one defined safe condition to another. 
Guidance note:
“Safe Condition” is defined as a condition where the object is considered to be exposed to a normal level of risk 
of damage or loss (i.e. the risk is similar to that expected for the in-place condition). Normally this will imply a 
(support) condition for which it is documented that the object fulfils the design requirements applying the 
relevant weather unrestricted, see [2.6.6], environmental loads. 
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2.5.1.3
Risk management, see [2.4], should normally be included in the planning. 
2.5.2 Type of operation 
2.5.2.1
To define the (sub-) operations as either weather unrestricted or weather restricted can have a great impact on 
the safety and cost of the operation. Hence, the type of operation should, if possible, be defined early in the 
planning process. See also [2.6.5]. 
2.5.2.2
The planning and design of marine operations should normally be based on the assumption that it can be 
necessary to halt the operation and bring the object to a safe condition e.g. by reversing the operation. 
2.5.2.3
For operations passing a point where the operation cannot be reversed, a point of no return (PNR) shall be 
defined. The first safe condition after passing a PNR shall be defined and considered in the planning. 
2.5.3 Operations in ice areas 
2.5.3.1
The risk of significant ice shall be considered in the operation planning. I.e. operations in ice areas should be 
subject to suitable ice management operations, details of which appear in [B.3]. 
2.5.3.2
Towages in ice are considered in [11.19] and voyages in [K.11]. 
2.5.3.3
The evacuation from rigs/offshore structures in ice shall be properly planned. 
Guidance note:
ISO 19906, /103/ Clause 18 and Annex A.18 provide appropriate normative requirements and informative 
guidance for escape, evacuation and rescue (EER) operations from Arctic offshore structures. 
Additional guidance on the design of an appropriate EER system may be found in DNVGL Barents 2020 
(2012), /21/, Chapter 4. This includes performance standards for emergency response vessels and guidance for 
Arctic evacuation methods. 
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2.5.4 Contingency and emergency planning andprocedures 
2.5.4.1
All possible emergency situations shall be identified, and contingency procedures or actions shall be prepared 
for these situations. 
Guidance note:
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Foreseeable emergencies and contingencies can include:
a. Severe weather
b. Planned precautionary action in the event of forecast severe weather
c. Structural parameters approaching pre-set limits
d. Stability parameters approaching pre-set limits
e. Failure of mechanical, electrical or control systems
f. DP or power failure "black ship"
g. Fire
h. Collision, grounding 
i. Leakage, flooding
j. Pollution
k. Structural failure
l. Equipment failure
m. Mooring failure
n. Icebergs, excessive ice (see also [2.5.3.3]) 
o. Human error
p. Man overboard
q. Personnel accidents or medical emergencies
r. Terrorism and sabotage.
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2.5.4.2
Possible emergency situations to be considered may be defined or excluded based on conclusions from risk 
identifying activities, see [2.4.2]. 
2.5.4.3
Contingency and emergency planning shall consider redundancy, back-up equipment, supporting personnel, 
emergency procedures and other relevant preventive measures and actions. 
2.5.4.4
The contingency procedures should form part of the operational procedures. 
2.6 Operation and design criteria 
2.6.1 Introduction 
2.6.1.1
Marine operations shall be executed ensuring that the assumptions made in the planning and design process are 
fulfilled. 
2.6.1.2
Marine operations shall be classified as weather restricted or as weather unrestricted (see [2.6.5]). 
Guidance note:
The main difference between these operations is how the environmental loads are selected. See Table 5-1. 
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2.6.2 Operation reference period - T
2.6.2.1
The duration of marine operations shall be defined by an operation reference period, T : 
T = T +T
where
T = Operation reference period
T = Planned operation period
T = Estimated maximum contingency time.
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2.6.2.2
The start and completion points for the intended operation or parts of the operation shall be clearly defined. See 
also [2.6.7.3] and [2.6.7.4]. 
2.6.3 Planned operation period – T
2.6.3.1
The planned operation period, T , shall if possible be based on a detailed schedule for the operation. 
Guidance note:
In cases (e.g. in the early planning phase) were a detailed schedule is not available T can be based on 
experience with similar operations. 
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2.6.3.2
The time estimated for each task in the schedule should be based on a reasonably conservative assessment of 
experience with same or similar tasks. 
Guidance note:
Normally a probability of (maximum) 10-20% of exceeding T during the actual operations should be aimed at. 
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2.6.3.3
Time delaying incidents that are experienced frequently should be included in T . 
2.6.4 Estimated contingency time – T
2.6.4.1
Contingency time, T , shall be added to cover: 
a. General uncertainty in the planned operation time, T
b. Unproductive time during the operation, e.g. to solve unforeseen procedural problems
c. Possible contingency situation(s), see [2.5.3], that will require additional time to complete the operation. 
Guidance note:
It is normally not necessary to add the estimated additional time from several (two) rare independent 
contingency situations. However, it can be relevant to consider that more than one of the frequently 
experienced incidents mentioned in [2.6.3.3] (e.g. equipment malfunction) may occur. 
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2.6.4.2
If T uncertainties and the required time for contingency situations is not assessed in detail the operation 
reference period should normally be taken to be at least twice the planned operation period, i.e.T  ≥ 2 × T . 
Guidance note:
A contingency time T of 50% of T can normally be accepted for: 
• Operations with an extensive experience basis from similar operations, e.g. positioning (anchoring) of 
MOUs. 
• Towing operations with redundant tug(s) and properly assessed towing speed, see Sec.11 for more 
information. 
• Repetitive operations where T has been accurately defined based on experience with the actual 
operation and vessel. 
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2.6.4.3
A contingency time T less than 6 hours is normally not acceptable unless thoroughly documented. 
Guidance note:
T < 6 hours is unlikely to be acceptable except for short simple marine operations involving only robust 
equipment. 
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2.6.5 Weather unrestricted and restricted operations 
2.6.5.1
An operation shall be defined as weather unrestricted, see [2.6.6], or weather restricted, see [2.6.7]. See [2.5.2]
and Figure 2-2 for further guidance. 
2.6.5.2
Operations with a duration that is too long to be planned as weather restricted, see [2.6.7.1], may still be defined 
as weather restricted if a continuous surveillance of actual and forecasted weather conditions is implemented, 
and the operation can be halted and the object brought into a safe condition within the maximum allowable 
period for a weather restricted operation. See flowchart in Figure 2-2. 
Guidance note:
The indicated maximum allowable period for a weather restricted operation, as per [2.6.7.1], is a theoretical 
value. For most continuous operations a considerably shorter period should be documented in order to make 
the operation feasible without risking too much delay. 
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Figure 2-2 Flow chart to determine whether an operation is weather restricted or weather unrestricted
2.6.6 Weather unrestricted operations 
2.6.6.1
Marine operations that cannot be defined as weather restricted (see [2.6.5] and [2.6.7]) shall be defined as 
weather unrestricted operations. Environmental criteria for these operations should be based on extreme value 
statistics, see Sec.3. If found beneficial, operations of shorter duration may also be defined as weather 
unrestricted. 
Guidance note:
A reduction in the weather criteria based on extreme value statistics could in some situations be acceptable 
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based on active use of the (long term) weather forecast. Such typical situations are: 
• Operations in areas and seasons where it has been shown and documented that the long term weather 
forecasts can predict any extreme weather conditions within the defined T for the operation. 
• Open (Ocean) voyages where the vessel speed is sufficient to avoid extreme weather conditions. 
Such a reduction in the design criteria may be accepted by the MWS company, but normally an accidental load 
case (ALS) considering extreme value statistics should be included. 
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2.6.6.2
For operations where the design environmental condition is based on extreme value statistics, the forecasted 
operational limiting criteria may theoretically be taken equal to the design environmental condition. However, it 
is normally not recommended that an operation is started if extreme weather conditions are expected, and a 
start criterion may apply. 
Guidance note:
Note that certain operations require a start criterionalthough designed for weather unrestricted conditions. 
Further information is given for the respective operations in this Standard. 
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2.6.7 Weather restricted operations 
2.6.7.1
Marine operations with a reference period (T ) less than 96 hours and a planned operation time (T ) less than 
72 hours may normally be defined as weather restricted. However, in areas and/or seasons where the duration of 
the reliable weather forecast is less than 96 hours, the maximum allowable T is the duration of the reliable 
forecast. 
Guidance note:
The above indicated limits for T and T define the maximum allowable period for a weather restricted 
operation. 
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2.6.7.2
A weather restricted operation shall be planned to be executed within a reliable weather window, see Figure 2-3. 
2.6.7.3
The planned operation period start point for a weather restricted operation shall normally be defined as being at 
the issuance of the last weather forecast. See Figure 2-3. 
Figure 2-3 Operation Periods
2.6.7.4
The operation shall only be considered completed when the object is in a safe condition, see [2.5.1.2]. 
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R POP
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2.6.7.5
Restricted operations may be planned with design environmental conditions selected independent of statistical 
data, i.e. set by owner, operator or contractor. 
Guidance note:
If the weather restricted design environmental condition is too low, severe waiting on weather delays can occur. 
The design environmental condition should be selected based on an overall evaluation of operability i.e. there 
should be an acceptable probability of obtaining the required weather window. See also [3.3]. 
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2.6.7.6
The start of a weather restricted operation is conditional on an acceptable weather forecast, see [2.7.3]. 
2.6.7.7
Operations that could be carried out within the maximum allowed period may be planned with (possible) stops 
in (case of) periods with weather conditions above the OP . The following shall be taken into account: 
a. Increased risk for halting (and re-starting) due to additional operations.
b. Increased risk due to the nature of the “temporary” safe position of the object.
c. Increased weather risk due to an increased total operation period.
2.6.7.8
If the planning indicated in [2.6.7.7] is implemented the Alpha (α) factors shall be adjusted accordingly, e.g.: 
• Depending on the risk evaluations in [2.6.7.7 b)] and [2.6.7.7 c)] it may be applicable to reduce the Alpha 
factor for the final stage of the operation due to an increased total operation period. 
• If no significant increased risk is identified due to [2.6.7.7 a)] and [2.6.7.7 b)] alpha factor(s) according to 
[2.6.9.3] applies. 
2.6.8 Operational limiting criteria 
2.6.8.1
Operational limiting environmental criteria (OP ) shall be established and clearly described in the marine 
operation manual. 
2.6.8.2
The OP shall not be taken greater than the minimum of: 
• The environmental design criteria. See [3.3]. 
• Maximum wind and waves for safe working and object handling (e.g. on vessel deck) or transfer conditions 
for personnel. 
• Weather restrictions for equipment (e.g. ROV and cranes).
Guidance note:
Weather restrictions for equipment should be based on specified limitations if available. They may also be 
assessed and/or refined based on items as criticality, back-up equipment and contingency procedures. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
• Limiting weather conditions of diving system (if any). 
• Limiting conditions for position keeping systems.
• Any limitations identified, e.g. in HAZID/HAZOP, based on operational experience with involved vessel(s), 
equipment, tools, etc. 
• Limiting weather conditions for carrying out identified contingency plans. 
2.6.9 Forecasted and monitored operational limits, alpha factor (α) 
2.6.9.1
Uncertainty in both the monitoring and the forecasting of the environmental conditions shall be considered. This 
should be done by defining a forecasted (and, if applicable, monitored at the operation start) operational criteria 
- OP , defined as OP  = α × OP . 
Guidance note:
LIM
LIM
LIM
WF WF LIM
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To ensemble weather forecasts which identify the expected ‘spread’ of weather conditions and assess the 
probability of particular weather events could be an alternative for applying the tabulated alpha factors. Such 
weather forecasts will anyhow give useful additional information to evaluate uncertain weather situations. Further 
description of ensemble forecasting is in [B.4]. 
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2.6.9.2
The planned operation period (T , see [2.6.3]) from issuance of the weather forecast to the operation is 
completed shall be used as the minimum time for selection of the Alpha Factor. See Figure 2-3. 
2.6.9.3
For operations that can be halted, see [2.6.5.2], the Alpha Factor can normally be selected based on a T
defined as the time between weather forecasts plus the required time to safely cease the operation and bring the 
handled object into a safe condition. If a proper procedure based on continuously reliable (see [2.9.3]) 
monitoring readings, is established the time between weather forecasts can normally be disregarded in the 
estimation of T . However, the maximum expected reaction time from monitoring readings above OP to 
initiation of ceasing of the operation, shall be included in T . A reaction time below 2 hours should normally not 
be considered. 
2.6.9.4
The following should be used as guidelines for selecting the appropriate Alpha Factor for waves: 
a. The expected uncertainty in the weather forecast should be calculated based on statistical data for the 
actual site and the operation schedule, i.e. T . The Alpha Factor should be calibrated to ensure that the 
probability of exceeding the operational environmental limiting criteria (OP ) by more than 50% in LRFD 
(see [2.6.11]) is less than 10 . 
b. Reliable wave and/or vessel response monitoring system(s) and applied weather forecast level, see [2.7.2], 
could be taken into account. 
2.6.9.5
Special considerations should be made regarding uncertainty in the wave periods i.e. if the operation is 
particularly sensitive to some wave periods (e.g. swell), the uncertainty in the forecasted wave periods shall also 
be considered. 
2.6.10 Selection of alpha factors 
2.6.10.1
The (tabulated) Alpha Factor(s) shall be selected based on:
• The applicable table, see [2.6.10.4] and Table 2-1
• Operational limiting criteria, OP , see [2.6.8]
• The planned operational period, T , see [2.6.9.2]
2.6.10.2
The Alpha Factor could be assumed to vary in time for one operation, e.g. for an operation with T = 36 hours, 
H = 4.0 m, the Alpha Factor is 0.79 for the first 12 hours, 0.76 for the next 12 hours and 0.73 for the last 12 hours 
of the operation. 
2.6.10.3
Design wave heights less than one (1) meter are normally not applicable for offshore operations. If a smaller 
design wave height nevertheless has been applied the Alpha Factor should be duly considered in each case. 
2.6.10.4
In the North Sea and the Norwegian Sea the Alpha Factor table to be used shall be selected using Table 2-1
considering the applied weather forecast (WF) level, see [2.7.2], applicable environmental monitoring, see 
[2.9.3], and design method (LRFD or ASD/WSD). 
2.6.10.5
POP
POP
POP WF
POP
POP
LIM
-4
LIM
POP
POP
s
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mentioned in 2.6.10.4. If reliable data is not available to establish alpha factors, see 2.6.9.4, the approach in 
2.6.10.4 should also be used for other areas. 
Guidance note:
The tabulated Alpha Factors are based on the work performed in a Joint Industry Project during the years 2005-
2007 with the aim to establish a revised set of α-factors for European waters. For details of the JIP see DNV 
Report 2006_1756 Rev. 03, “DNV Marine Operation Rules, Revised Alpha Factor JIP Project”. 
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Table 2-1 Selection of Alpha Factor table(s) 
WF level A1 A2 & B C 
Environmental monitoring? Yes No Yes No Yes No
Wave Alpha Factor – LRFD Table 2-7 Table 2-6 Table 2-5 Table 2-4 Table 2-3 Table 2-2
Wave Alpha Factor – 
ASD/WSD
Table 
2-14
Table 
2-13
Table 
2-12
Table 
2-11
Table 
2-10
Table 2-9
Wind Alpha Factor – LRFD Table 2-8
Wind Alpha Factor – 
ASD/WSD
Table 2-15
2.6.11 Tabulated alpha factor – LRFD method 
2.6.11.1
The Alpha Factor for waves applying LRFD, see [5.9.8], shall be selected according to Table 2-1 and are given in 
Table 2-2 through Table 2-7. Values for wind are in Table 2-8. 
Table 2-2 LRFD Alpha Factor for waves, Level C – No Environmental Monitoring
Planned 
Operation 
Period [h]
Operational limiting (OP ) significant wave height [m]
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 12 0.65
Linear 
Interpolation
0.76
Linear 
Interpolation
0.79
Linear 
Interpolation
0.80
T ≤ 24 0.63 0.73 0.76 0.78
T ≤ 36 0.62 0.71 0.73 0.76
T ≤ 48 0.60 0.68 0.71 0.74
T ≤ 72 0.55 0.63 0.68 0.72
Table 2-3 LRFD Alpha Factor for waves, Level C – With Environmental Monitoring
Planned 
Operation 
Period [h]
Operational limiting (OP ) significant wave height [m]
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 4 0.90
Linear 
Interpolation
0.95
Linear 
Interpolation
1.00
Linear 
Interpolation
1.00
T ≤ 12 0.72 0.84 0.87 0.88
T ≤ 24 0.66 0.77 0.80 0.82
T ≤ 36 0.62 0.71 0.73 0.76
T ≤ 48 0.60 0.68 0.71 0.74
T ≤ 72 0.55 0.63 0.68 0.72
Table 2-4 LRFD Alpha Factor for waves, Level A2 or B – No Environmental Monitoring
Planned 
Operation 
Period [h]
Operational limiting (OP ) significant wave height [m] 
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 12 0.68 Linear 0.80 Linear 0.83 Linear 0.84
LIM
s s s s s s s
POP
POP
POP
POP
POP
LIM
s s s s s s s
POP
POP
POP
POP
POP
POP
LIM
s s s s s s s
POP
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T ≤ 24 0.66
Interpolation
0.77
Interpolation
0.80
Interpolation
0.82
T ≤ 36 0.65 0.75 0.77 0.80
T ≤ 48 0.63 0.71 0.75 0.78
T ≤ 72 0.58 0.66 0.71 0.76
Table 2-5 LRFD Alpha Factor for waves, Level A2 or B – With Environmental Monitoring
Planned 
Operation 
Period [h]
Operational limiting (OP ) significant wave height [m] 
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 4 0.90
Linear 
Interpolation
0.95
Linear 
Interpolation
1.00
Linear 
Interpolation
1.00
T ≤ 12 0.72 0.84 0.87 0.88
T ≤ 24 0.66 0.77 0.80 0.82
T ≤ 36 0.65 0.75 0.77 0.80
T ≤ 48 0.63 0.71 0.75 0.78
T ≤ 72 0.58 0.66 0.71 0.76
Table 2-6 LRFD Alpha Factor for waves, Level A1 – No Environmental Monitoring
Planned 
Operation 
Period [h]
Operational limiting (OP ) significant wave height [m] 
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 12 0.72
Linear 
Interpolation
0.84
Linear 
Interpolation
0.87
Linear 
Interpolation
0.88
T ≤ 24 0.69 0.80 0.84 0.86
T ≤ 36 0.68 0.78 0.80 0.84
T ≤ 48 0.66 0.75 0.78 0.81
T ≤ 72 0.61 0.69 0.75 0.79
Table 2-7 LRFD Alpha Factor for waves, Level A1 – With Environmental Monitoring
Planned 
Operation 
Period [h]
Operational limiting (OP ) significant wave height [m] 
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 4 0.90
Linear 
Interpolation
0.95
Linear 
Interpolation
1.00
Linear 
Interpolation
1.00
T ≤ 12 0.78 0.91 0.95 0.96
T ≤ 24 0.72 0.84 0.87 0.90
T ≤ 36 0.68 0.78 0.80 0.84
T ≤ 48 0.66 0.75 0.78 0.81
T ≤ 72 0.61 0.69 0.75 0.79
2.6.11.2
The appropriate Alpha Factor for wind should be selected (estimated) considering the following: 
• Statistical data and local experience for the actual site.
• Planned operation period from issuance of weather forecast, T . 
• Applied wind speed compared with the maximum possible wind speed, i.e. 10 year return wind speed. 
• Criticality of exceeding the design wind speed, e.g. by considering the contribution from wind on the total 
design load. 
2.6.11.3
If no reliable data is available the Alpha Factors indicated in Table 2-8 shall be considered as the maximum 
allowable. 
POP
POP
POP
POP
LIM
s s s s s s s
POP
POP
POP
POP
POP
POP
LIM
s s s s s s s
POP
POP
POP
POP
POP
LIM
s s s s s s s
POP 
POP
POP
POP
POP
POP
POP
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Table 2-8 LRFD Recommended Alpha Factor for wind
Planned Operation Period
Operational limiting (OP ) wind speed – V
V < 0.5 x V10 year return V > 0.5 x V10 year return 
T ≤ 24 0.80 0.85
T ≤ 48 0.75 0.80
T ≤ 72 0.70 0.75
2.6.11.4
The possibility for unpredictable strong wind, e.g. squalls and polar lows, should be duly considered in the 
selected Alpha Factor for wind (and if relevant also for waves). Alternatively, if possible, operational contingency 
actions that sufficiently reduce the criticality of such wind, could be planned. 
2.6.12 Tabulated alpha factor - ASD/WSD method 
2.6.12.1
The Alpha factors for waves and wind applicable to the ASD/WSD, see [5.9.7] design approach shall be selected 
based on Table 2-1 and are shown in Table 2-2 through Table 2-8. These factors are calibrated for the ASD/WSD 
format, with the objective of ensuring that a given structure will be treated equally under ASD/WSD and LRFD. 
The Alpha factors for ASD/WSD are therefore lower than the values given in [2.6.11] because the inherent safety 
margin in ASD/WSD checks is less than that in LRFD checks, so higher design values are needed to achieve this 
equivalence. 
Table 2-9 ASD/WSD Alpha Factor for waves, Level C – No Environmental Monitoring
Planned 
Operation 
Period [h]
Operational Limiting (OP ) significant wave height [m]
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 12 0.58
Linear 
Interpolation
0.68
Linear 
Interpolation
0.70
Linear 
Interpolation
0.71
T ≤ 24 0.56 0.65 0.68 0.69
T ≤ 36 0.55 0.63 0.65 0.68
T ≤ 48 0.53 0.61 0.63 0.66
T ≤ 72 0.49 0.56 0.61 0.64
Table 2-10 ASD/WSD Alpha Factor for waves, Level C – With Environmental Monitoring
Planned 
Operation 
Period [h]
Operational Limiting (OP ) significant wave height [m]
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 4 0.80
Linear 
Interpolation
0.85
Linear 
Interpolation
0.89
Linear 
Interpolation
0.89
T ≤ 12 0.64 0.75 0.77 0.78
T ≤ 24 0.59 0.69 0.71 0.73
T ≤ 36 0.55 0.63 0.65 0.68
T ≤ 48 0.53 0.61 0.63 0.66
T ≤ 72 0.49 0.56 0.61 0.64
Table 2-11 ASD/WSD Alpha factors (waves) - Level A2 or B – No Environmental Monitoring
Planned 
Operation 
Period [h]
Operational Limiting (OP ) significant wave height [m]
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 12 0.61 Linear 
Interpolation
0.71 Linear 
Interpolation
0.74 Linear 
Interpolation
0.75
T ≤ 24 0.59 0.69 0.71 0.73
T ≤ 36 0.58 0.67 0.69 0.71
LIM d
d d
POP
POP
POP
LIM
s s s s s s s
POP
POP
POP
POP
POP
LIM
s s s s s s s
POP
POP
POP
POP
POP
POP
LIM
s s s s s s s
POP
POP
POP
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T ≤ 48 0.56 0.63 0.67 0.69
T≤ 72 0.52 0.59 0.63 0.68
Table 2-12 ASD/WSD Alpha Factor for waves, Level A2 or B – With Environmental Monitoring
Planned 
Operation 
Period [h]
Operational Limiting (OP ) significant wave height [m]
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 4 0.80
Linear 
Interpolation
0.85
Linear 
Interpolation
0.89
Linear 
Interpolation
0.89
T ≤ 12 0.64 0.75 0.77 0.78
T ≤ 24 0.59 0.69 0.71 0.73
T ≤ 36 0.58 0.67 0.69 0.71
T ≤ 48 0.56 0.63 0.67 0.69
T ≤ 72 0.52 0.59 0.63 0.68
Table 2-13 ASD/WSD Alpha factors (waves) - Level A1 – No Environmental Monitoring
Planned 
Operation 
Period [h]
Operational Limiting (OP ) significant wave height [m]
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 12 0.64
Linear 
Interpolation
0.75
Linear 
Interpolation
0.77
Linear 
Interpolation
0.78
T ≤ 24 0.61 0.71 0.75 0.77
T ≤ 36 0.61 0.69 0.71 0.75
T ≤ 48 0.59 0.67 0.69 0.72
T ≤ 72 0.54 0.61 0.67 0.70
Table 2-14 ASD/WSD Alpha factors (waves) - Level A1 – With Environmental Monitoring
Planned 
Operation 
Period [h]
Operational Limiting (OP ) significant wave height [m]
H = 1 1 < H < 2 H = 2 2 < H < 4 H = 4 4 < H < 6 H ≥6 
T ≤ 4 0.80
Linear 
Interpolation
0.85
Linear 
Interpolation
0.89
Linear 
Interpolation
0.89
T ≤ 12 0.69 0.81 0.85 0.85
T ≤ 24 0.64 0.75 0.77 0.80
T ≤ 36 0.61 0.69 0.71 0.75
T ≤ 48 0.59 0.67 0.69 0.72
T ≤ 72 0.54 0.61 0.67 0.70
2.6.12.2
If no reliable data is available the Alpha Factors indicated in Table 2-15 shall be considered as the maximum 
allowable in ASD/WSD. See also [2.6.11.2] and [2.6.11.4]. 
Table 2-15 ASD/WSD Alpha factors (wind - all forecast requirements)
Planned Operation Period
Operational Limiting Wind Speed (V )
V < 0.5 x V10 year return V > 0.5 x V10 year return 
T ≤ 24 0.71 0.76
T ≤ 48 0.67 0.71
T ≤ 72 0.62 0.67
POP
POP
LIM
s s s s s s s
POP
POP
POP
POP
POP
POP
LIM
s s s s s s s
POP
POP
POP
POP
POP
LIM
s s s s s s s
POP
POP
POP
POP
POP
POP
d
d d
POP
POP
POP
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2.7 Weather forecast 
2.7.1 General 
2.7.1.1
Arrangements shall be made for receiving weather forecasts at regular intervals before, and during, the marine 
operations. Such weather forecasts shall be from recognized sources and be project specific. 
Guidance note:
Public domain weather forecast(s) may be found acceptable as Level C forecasting, but the inherent increased 
uncertainty should be considered. Applicable Alpha Factors are found by multiplying the factors in Table 2-2
(Table 2-9) and Table 2-15 (Table 2-16) with 0.75. 
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2.7.1.2
Independent weather forecasts shall be taken from different weather providers. The providers shall be different 
organizational bodies. Each body shall document which different atmospheric and oceanographic models have 
been evaluated and taken into account in the generation of the forecasts. 
2.7.1.3
The weather forecasts (WF) shall be area/route specific. For non-stationary marine operations (e.g. sea voyages 
or subsea laying operations) it shall be ensured that weather forecasts comprise the position (at the time of the 
WF) of the transport vessel/barge and all alternative routes that could be chosen in the period covered by the 
weather forecast. 
2.7.1.4
Weather forecast procedures should consider the nature and duration of the planned operation, see [2.7.2.1]. 
2.7.1.5
The weather forecasts shall be in writing and the confidence level(s) should be stated. 
2.7.1.6
In addition to a general description of the weather situation and its predicted development, the weather forecast 
shall, as relevant, include: 
• wind speed and direction
• waves and swell, significant and maximum height, mean or peak period and direction
• rain, snow, lightning, ice etc.
• tide variations and/or storm surge
• visibility
• temperature
• barometric pressure
• possibility for unpredictable strong wind, see [2.6.11.4]. 
for each 12 hours for a minimum of the T plus 24 hours. In addition an outlook for at least the next 24 hours 
should normally be included. 
2.7.1.7
The forecast shall clearly define forecasted parameters, e.g. average time and height for wind, characteristic 
wave periods (T or T ). The content and format of the weather forecast should be agreed with the meteorologist 
in due time before the operation starts. 
2.7.2 Weather forecast levels 
2.7.2.1
The required weather forecast level shall be selected based on the operational sensitivity to weather conditions 
and the operation reference period (T ). The following weather forecast levels are defined in this standard: 
• Level A that applies to major marine operations sensitive to environmental conditions. 
• Level B that applies to environmental sensitive operations of significant importance with regard to value 
R
z p
R
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and consequences 
• Level C that applies to conventional marine operations less sensitive to weather conditions, and carried 
out on a regular basis. 
2.7.2.2
For operations that require a Level A weather forecast it shall be thoroughly considered to have the dedicated 
meteorologist present on site. See Table 2-16 for further advice regarding selection of the forecast level and for 
requirements to the weather forecast procedure. 
Table 2-16 Weather forecast levels
Weather Forecast 
Level
A1 A2 B C
Operation 
Sensitivity
High Moderate Low
Examples
• mating operations
• offshore float over
• multi barge towing
• major (e.g. GBS) tow out 
operations
• offshore installation 
operations
• jack-up rig moves.
• sensitive laying 
operations
• tow-out 
operations
• weather routed 
sea transports
• offshore lifting
• subsea 
installation
• semi-
submersible rig 
moves
• standard laying 
operations.
• onshore/inshore 
lifting
• load-out operations
• short tows in 
sheltered 
waters/harbour 
tows
• standard sea 
transports without 
any specified wave 
restrictions.
Meteorologist on 
site
Yes No No
Dedicated 
Meteorologist
Yes Yes No No
Minimum 
independent WF 
sources
2 2 1
Maximum WF 
interval
12 hours 12 hours 12 hours
Notes:
1. See 2.7.1.1 GN. 
2. Meteorologist shall be consulted if the weather situation is unstable and/or close to the defined limit. 
3. See [2.7.1.2] for definition of independent WF sources. 
4. It is assumed that the dedicated meteorologist (and other involved key personnel) will consider weather 
information/forecasts from several (all available) sources. 
5. The most severe weather forecast shall be used.
6. Based on sensitivity with regards to weather conditions smaller intervals may be required. However, see 
[2.7.3.5]. 
2.7.3 Acceptance criteria 
2.7.3.1
The acceptance criteria for the weather forecast(s) shall clearly define the applicable limitations, see [2.6.9] and 
the minimum required weather window, see [2.6.2] and Figure 2-3. The acceptance criteria shall be included in 
the marine operation manual. 
2.7.3.2
If the weather forecasts received from the two sources do not agree the most severe weather forecast should be 
considered governing, unless otherwise justified. If the discrepancy between the forecasts is significant the 
weather situation should be carefully evaluated to determine whether it is too uncertain to safely start an 
operation. 
1)
2)
2)
4) 5)
6)
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2.7.3.3
Based on the available weather forecasts the weather situation shall be assessed according to a worst case 
scenario development. This is particularly important for unstable weather situationsand for forecasts which are 
stated (considered) to be of low confidence. 
2.7.3.4
Uncertainties in forecasted weather window duration shall be duly considered i.e. the forecasted weather 
window duration should be conservatively assessed. 
2.7.3.5
Weather forecasts are based on extensive computer analyses. In cases where forecast updates are made at 
intervals of less than 12 hours it shall be documented that the updates are based on sufficient data to be as 
accurate as ordinary forecasts. 
2.8 Organization of marine operations 
2.8.1 General 
2.8.1.1
The organisation and responsibility of key personnel involved in marine operations shall be established and 
described before execution of marine operations. The responsibilities and duties of each function shall be clearly 
defined to minimise uncertainties and overlapping responsibilities. 
2.8.1.2
Organisation charts, including names and functional titles of key personnel, shall be included in the marine 
operations manual. Authority during the operation shall be clearly defined. 
2.8.1.3
Operations shall be carried out in accordance with the conditions for design, the approved documentation, and 
sound practice, such that unnecessary risks are avoided. This is the responsibility of the operation 
superintendent or manager. 
2.8.1.4
Responsibilities in possible emergency situations shall be described.
2.8.1.5
Access to the area for the operation should be restricted. Only authorised personnel should be allowed into the 
operation area. 
Guidance note:
Where necessary, a suitable security and tracking system should be in use to record personnel on the structure 
or vessels, to track their whereabouts. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
2.8.2 Qualification and training 
2.8.2.1
Operation supervisors shall possess thorough knowledge and have experience from similar operations. Other 
key personnel shall have knowledge and experience within their area of responsibility. 
2.8.2.2
CVs for supervisors and key personnel involved in major marine operations shall be submitted. 
2.8.2.3
Vessel manning and personnel qualifications shall as a minimum fulfil statutory requirements. Additional 
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manning shall be considered for complex operations or to satisfy specific project requirements. 
2.8.2.4
Adequate training appropriate to each individual’s function and situation should be given, including job training, 
site safety training and briefings, marine safety and survival training. 
2.8.2.5
A qualification matrix is recommended for correct tracking and control of personal qualifications. 
2.8.2.6
Computer simulation and training, and/or model tests can give valuable information for the personnel carrying 
out the operation. Where relevant, a full-mission simulation should be undertaken. 
2.8.3 Familiarisation and briefing 
2.8.3.1
Operation supervisors shall familiarise themselves with all aspects of the planned operations and possess a 
thorough knowledge with respect to limitations and assumptions for the design. 
2.8.3.2
Key personnel shall familiarise themselves with the operations. A thorough briefing by the supervisors regarding 
responsibilities, communication, work procedures, safety and other items of importance shall be performed. 
2.8.3.3
Other personnel participating in the operations shall be briefed about the operation with emphasis on their 
assigned tasks/responsibilities and safety. 
Guidance note:
The use of visual aids for presenting complex marine operations is highly recommended, either through picture 
series and/or animations. 
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2.8.3.4
For complex marine operations a separate and detailed familiarisation program shall be prepared and 
thouroughly implemented involving all personnel. 
Guidance note:
Familiarisation should for offshore operations normally be initiated prior to vessel mobilisation. The 
familiarisation should cover all involved personnel, including marine crew, project personnel and third party, and 
should address all aspects of the operation. 
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2.8.4 Communication and reporting 
2.8.4.1
Communication lines and primary and secondary means of communication shall be defined, preferably in a 
communication chart, including as appropriate: 
• Client’s representative and 3 Party/MWS representative (if relevant) 
• Overall project management
• Operation management
• Involved vessels
• Mooring systems and marine spread
• Ballast system operation
• Monitoring 
• Weather forecasting
• Support services
• Field engineers providing expertise as required
• Safety
• Statutory, regulatory and approving bodies
rd
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• Emergency response.
2.8.4.2
Communication systems, including radio channels, telephone numbers, e-mail addresses and out-of-hours 
numbers shall be identified and checked for accuracy. 
2.8.4.3
The primary operational communication system should be used only for information needed for managing and 
controlling the operation. Important information should be given dedicated lines/channels. 
2.8.4.4
The planned flow of information during the operation shall be described. 
2.8.4.5
A common language understood by all personnel involved should be used for VHF/UHF communication. Radio 
channels should be allocated early to avoid possible interference. 
Guidance note:
If a common language could lead to misunderstandings, it can be acceptable to use two or more languages. 
Such communication needs to be duly planned and rehearsed. 
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2.8.4.6
Communication of important information that may be misunderstood, e.g. monitoring results, should be 
confirmed in writing. 
2.8.4.7
All communication and reporting should be made available for continuous monitoring by the MWS during the 
operation. (See also [2.3.8]). 
2.8.5 Shifts 
2.8.5.1
For operations with a planned duration exceeding 12 hours, a shift plan shall be established.
2.8.5.2
Where personnel changes occur during the course of an operation because of shift changes, these shall be 
identified. Every effort should be made to avoid changes of key personnel during critical stages of the operation. 
2.8.5.3
Where transfer of responsibility is involved, times of and procedures for hand-over from one organisation to 
another (e.g. from fabrication to marine operations, from on-shore to offshore) shall be identified. 
2.8.5.4
When continuous operations using more than 1 shift are not standard practice then special provision to prevent 
fatigue shall be made for operations that could continue beyond normal working hours. This includes provision 
of suitably experienced and briefed alternate personnel with good hand-overs at each shift change. 
2.9 Monitoring 
2.9.1 General 
2.9.1.1
Actual parameters should be monitored and compared against those used in design to as great an extent as 
practicable during and also if applicable before marine operations. 
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2.9.1.2
The monitoring methods should duly reflect the required accuracy (i.e. acceptable monitoring tolerances). 
2.9.1.3
Target values and maximum deviations from target values, i.e. tolerances, for monitoring should be clearly 
defined. 
Guidance note:
Maximum allowable measured deviations should normally be within 75% of ‘deviations considered in the design’ 
less the ‘monitoring tolerance’. 
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2.9.1.4
General and back-up requirements to monitoring instrumentationsystems are given in [4.2]. 
2.9.2 Environmental conditions 
2.9.2.1
Environmental conditions can be monitored by both direct monitoring of environmental conditions and by 
monitoring responses caused by environmental effects, see [2.9.3]. 
2.9.2.2
For marine operations particularly sensitive to environmental conditions such as waves, swell, current, tide etc., 
systematic monitoring of these conditions before and during the operation shall be arranged. 
Guidance note:
In some areas, tide behaviour can vary considerably locally. In such cases a local tide variation curve should be 
established based on extensive tide monitoring including at least one period with the same lunar phase as for 
the planned operation. Tidal variations should be plotted against established astronomical tide curves. Any 
discrepancies should be evaluated, considering barometric pressure and other weather effects. 
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2.9.2.3
Expected values, for the remaining time of the operation, of significant environmental conditions should be 
continuously predicted during execution of a marine operation. Such predictions should, as relevant, be based 
on the monitored variations, tabulated values and weather forecasts. 
2.9.3 Loads and/or responses 
2.9.3.1
Full scale monitoring can be used for the determination of responses (e.g. accelerations on a vessel) or loading 
effects (e.g. strain-gauge measurements). All full scale load and/or response monitoring should be carried out 
according to agreed procedures, see e.g. [2.9.5]. 
Guidance note:
Full scale monitoring is normally carried out to meet one or both of the following objectives: 
• To obtain valuable design information for future projects.
• To control that design criteria (ULS or FLS) are not exceeded during an operation.
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2.9.3.2
During full scale monitoring it can be difficult to accurately measure the load which causes the measured 
response. The information obtained may therefore be of a statistical nature, and the use of statistical methods 
can be necessary in order to draw conclusions. 
Guidance note:
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Full scale monitoring has limitations, e.g. as indicated above, that need to be duly considered if such monitoring 
is used as an (assisting) operational means of control. 
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2.9.4 Alpha factor related monitoring 
2.9.4.1
It shall be documented that monitoring systems and procedures used as a means to increase the Alpha Factor 
for waves have adequate accuracy and reliability. Normally this implies fulfilment of all the following: 
• Continuous monitoring.
• The monitoring device should be adequately located (e.g. no shielding effects) to give correct readings 
and not in any case more than 3 (three) nautical miles from the location of the operation. 
• Documented monitoring accuracy better than ±5% of the measured maximum values.
• Statistical treatment of the results which continuously indicate the expected maximum value within a 
defined time period (normally 3 hours). 
• It should be possible to relate the response monitoring results to the wave conditions. See also [2.9.3]. 
• A secondary system and/or procedure that will detect any significant erroneous results produced by the 
primary system. 
2.9.4.2
A procedure shall be made that describes how the interface between monitoring results and weather forecasts is 
to be handled. 
Guidance note:
The procedure should, as a minimum, cover the following:
• Discrepancies between weather forecast for the present time and monitoring results.
• How to calibrate the weather forecast for the coming hours based on the monitoring results. 
• Feed-back to meteorologist(s)
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2.9.5 Monitoring procedure 
2.9.5.1
A monitoring procedure describing at least monitoring methods and intervals, responsibilities, reporting and 
recording shall be prepared. 
2.9.5.2
Any unforeseen monitoring results shall be reported without delay.
2.9.6 Back-up and contingency 
2.9.6.1
The requirements of [4.2.1.10] apply. 
2.9.6.2
If the monitoring back-up system does not have the same accuracy as the original system this should be 
considered in the contingency planning. 
2.10 Inspections and testing 
2.10.1 General 
2.10.1.1
Testing and inspection of equipment, structures, systems and vessels shall be carried out according to relevant 
and recognized codes/standards and/or relevant specifications, functional requirements and assumptions for the 
design. 
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2.10.1.2
Inspection during the operation shall include a systematic review and evaluation of monitoring results, see [2.9]. 
2.10.1.3
The MWS company shall identify any inspections and tests to be witnessed by its own representatives. 
2.10.2 Test program 
2.10.2.1
The required inspections and tests both in the preparation phase and during the operation shall be described in 
a test and inspection program. 
2.10.2.2
The test and inspection results shall be documented. 
Guidance note:
The inspections and testing can be documented by reports and completed checklists.
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2.10.2.3
For larger operations it is recommended that a test/commissioning program is developed specifying the 
planned inspections and tests. The test program should indicate expected characteristics, and state acceptance 
criteria based on the design assumptions. 
Guidance note:
Acceptance criteria for tests may also be functional requirements.
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2.10.3 Systems 
2.10.3.1
All systems and their back-up shall be tested before the start of an operation. Such tests shall demonstrate that 
they function as intended. If critical, the capacity of the system shall be adequately checked. 
2.10.3.2
Change over from a primary to a secondary system shall be tested.
2.10.3.3
Instrumentation systems shall be calibrated and tested before the operation. The calibration procedure may be 
subject to review. 
2.10.3.4
Essential systems shall be function and capacity tested in their final configuration and connected to the same 
power supply/HPU as intended to be used during operation. If several consumers are connected to the same 
power supply/HPU, the test should be performed realistically with all consumers running in order to test capacity. 
2.10.3.5
Emergency systems/functions and fail safe configurations should, as far as practically possible, be tested in a 
realistic scenario with adequate loading. 
2.10.4 Communication 
2.10.4.1
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Primary and secondary means of communication shall be tested before operation.
2.10.4.2
For operations with complex communication and reporting procedures, or where proper information flow is vital, 
a run-through of communication routines shall be carried out. 
Guidance note:
This rehearsal should be performed with the nominated personnel and under conditions similar to those 
expected during the actual operation. See also [2.8.4.5]. 
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2.10.5 Inclining tests 
2.10.5.1
The requirement to perform inclining and/or displacement tests shall be agreed with the MWS Company. 
Guidance note:
Vessels with a valid Trim and Stability booklet, including all modifications since the last inclining test, do NOT 
normally require an inclining test when conservative estimates of cargo weight and centre of gravity show 
adequate reserves of intact and damagestability. 
Where ideally an inclining test would be performed but may not give sufficiently accurate results the calculations 
may be based on outputs from the weight control programme checked against a displacement test. This would 
only apply if there is a sufficient reserve of stability to cover possible inaccuracies. 
Where a number of very similar units are constructed at the same place, the requirement for inclining tests on the 
later units may be reduced after a study of weight variations (from displacement tests) and Centre of Gravity 
variations (from inclining tests) of the previous units, and agreement with the MWS company. 
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2.10.5.2
Where inclining and/or displacement tests are required:
a. They should be performed before any marine operation where the displacement, centre of gravity or 
stability may be critical. 
b. They should be performed according to guidelines in IMO Intact Stability Code 2008, /89/, Part B Annex 1. 
c. if applicable an allowance shall be made for the presence and compressibility of any air cushion 
d. if the vessel is not axisymmetric then inclining tests may be required about two axes, as agreed with the 
MWS company. (This normally applies to bodies with an irregular shaped plan view, not vessels with a list). 
e. Upon completion of the inclining test, a report containing measurements/readings and corresponding 
calculations of displacement (and light displacement if relevant), metacentric height (GM), and the position 
of the centre of gravity of the structure, should be prepared. 
f. The output from the inclining test should be used to check and calibrate the output from the weight 
control programme. A rigorous weight control system should be enforced from the inclining test until the 
relevant marine operation is completed. 
g. A sensitivity analysis of the parameters affecting the test results should be performed.
2.11 Vessels 
2.11.1 General 
2.11.1.1
This section includes general requirements for vessels involved in marine operations. Where applicable, further 
requirements are given for each type of operation vessel in Sec.6 through Sec.18. 
2.11.1.2
Vessels shall satisfy the relevant hydrostatic stability requirements given in [11.10]. 
2.11.1.3
A general description of the vessel systems to be used shall be documented. Ballast and towing 
equipment/systems shall be described in detail if used. 
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2.11.1.4
Vessels should be suitable for their planned tasks during the operation.
Guidance note:
If there is any doubt about the vessel suitability for a specific operation it is recommended to carry out an 
independent suitability survey of the vessel. 
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2.11.1.5
See [17.13] for further requirements to Dynamic Positioned vessels. 
2.11.2 Condition and inspections 
2.11.2.1
All vessels shall be in acceptable condition and with valid certificates, see [B.1]. 
2.11.2.2
All vessels involved in the operations should be inspected before the operation to confirm compliance with the 
design assumptions, validity of certificates, suitability (see [2.11.1.4]) and acceptable condition. 
2.11.2.3
The global and local condition of the vessels with respect to corrosion shall be confirmed and considered in 
strength verifications. 
2.11.3 Structural strength 
2.11.3.1
Adequate global and local structural strength shall be documented for all vessels.
Guidance note:
The strength may be documented by either ensuring that the vessel is operated within the Class requirements, 
see [2.11.4], or by calculating the strength according to the relevant requirements in Sec.5. 
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2.11.3.2
If the allowable deck load is based on load charts, the limitations and conditions for these with respect to 
number of loads and simultaneousness of loads shall be clearly stated. The applied design factors shall be 
specified. 
2.11.4 Class requirements 
2.11.4.1
Where a vessel is classed by a Classification Society it shall be operated in accordance with requirements from 
the Society. The limitations for Class as given in “Appendix to Class Certificate” or similar shall be submitted. 
2.11.4.2
For Mobile Offshore Units the following annexes (or similar) to the maritime certificates shall be submitted; 
• Annex I - Operational limitations,
• Annex II - Resolutions according to which the unit has been surveyed, and possible deviations from these. 
2.11.4.3
Valid recommendations (conditions) given by the Classification Society shall be submitted.
Guidance note:
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Modifications to vessel structure or equipment can require approval from the Classification Society. 
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2.11.4.4
If it is planned to use a vessel or its equipment (e.g. crane) outside the limitations stated by Class, a statement of 
acceptance from Class shall be submitted. 
2.11.5 Certificates 
2.11.5.1
All required certificates shall be valid, or relevant exemptions shall be submitted. 
Guidance note:
The documents (certificates) to be carried on board different types of vessels can be found in IMO FAL.2/Circ.87-
MEPC/Circ.426-MSC/Circ.1151. 
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2.11.6 Navigation lights and shapes 
2.11.6.1
All vessels and towed objects (unless submerged) shall carry the lights and shapes, towed objects required by 
the International Regulations for Preventing Collisions at Sea, 1972 amended 1996 (COLREGS, /91/) and any 
local regulations. 
2.11.6.2
Navigation lights shall be independently powered (e.g. from an independent electric power sources or from gas 
containers). Fuel or power sources shall be adequate for the maximum duration of the towage, plus a reserve. 
Spare mantles or bulbs should be carried, even if the tow is un-manned. 
Guidance note:
Solar powered navigation lights should be compliant with UL 1104 (USCG) and/or EN14744 (EU Marine 
Equipment Directive). Additional power provided by solar panels may be considered if an adequate track record 
is documented. 
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2.11.6.3
Where possible, a duplicate system of lights should be provided.
2.11.6.4
Towed objects which may offer a small response to radar, such as barges or concrete caissons with low 
freeboard, should be fitted with a radar reflector. The reflector should be mounted as high as practical. 
Octahedral reflectors should be mounted in the “catch-rain” orientation. 
2.11.7 Contingency situations 
2.11.7.1
All vessels shall be selected with due consideration to possible contingency situations.
Guidance note:
This could e.g. result in the selection of redundant (twin screw) tugs for towing operations in narrow waters. See 
also the operation-specific requirements in Sec.10 to Sec.18 of this Standard for further guidance. 
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2.11.7.2
Where several tugs (vessels) are involved, a stand-by tug to assist or remove vessels in case of black-out, engine 
failure, etc. should be considered. 
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SECTION 3 Environmental conditions and criteria 
3.1 Introduction 
3.1.1 General 
3.1.1.1
This Section refers to the environmental design criteria applicable for marine operations. The focus is on the 
criteria applicable to weather unrestricted marine operations however, design environmental criteria for weather 
restricted marine operations are addressed in [3.3]. 
3.1.1.2
Metocean criteria are generally used for analysis to a recognisedstandard (including relevant safety factors). In 
this standard, the environmental criteria to be used for the ASD/WSD approach are different to those to be used 
for the LRFD approach. 
3.1.1.3
Each marine operation shall be designed to withstand the loads caused by the most adverse environmental 
conditions expected. In the case of a voyage this shall account for the areas and seasons through which it will 
pass. Any agreed mitigating measures may be taken into account. 
3.1.1.4
For each phase of a voyage or marine operation, the design criteria should be defined, consisting of the design 
wave or sea state, design wind and, if relevant, design current. It should be noted that the maximum wave and 
maximum wind may not occur in the same geographical area, in which case it may be necessary to check the 
extremes in each area, to establish governing load cases. 
3.1.2 Scope 
3.1.2.1
The environmental design criteria should be established dependent on the duration of each discreet phase of a 
marine operation, which may be a weather restricted or a weather unrestricted operation as defined in [2.6.5]. 
3.1.2.2
This section defines the default return periods that can be used to determine applicable environmental criteria. 
App.C gives more detailed approaches for the determination of design winds and waves as a function of the 
exposure duration and location-specific metocean parameters. 
3.1.3 Revision history 
3.1.3.1
This section replaces the applicable sections of the legacy GL Noble Denton Guidelines and legacy DNV-OS-H-
series standards. 
3.2 Design environmental condition 
3.2.1
The design environmental condition consists of the wave height, wind speed, current and other relevant 
environmental conditions specified for the design of a particular marine operation. 
3.2.2
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A weather unrestricted operation is not limited by practical aspects, and therefore the operational criteria are the 
design environmental condition. In this case the design environmental condition is based on extreme statistical 
data and is addressed in [3.4]. 
3.2.3
The environmental design data should be representative of the geographical area or site and operation in 
question. 
3.2.4
Where it is impractical and/or uneconomical to design marine operations based on extreme statistical data, the 
design environmental condition can be set independent of extreme statistical data for weather restricted 
operations - see [2.6.7] and [3.3]. 
3.3 Design environmental criteria for weather restricted operations 
3.3.1
For weather restricted operations the design wind could be selected independent of statistical data. 
Guidance note:
Characteristic wind velocities less than 10 m/s are generally not recommended. See also [3.3.4] for general 
considerations. 
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3.3.2
The ratio between forecasted wind and design wind should be determined in accordance with Table 2-8 or 
Table 2-15 as applicable. 
3.3.3
Wave conditions for weather restricted operations, i.e. operations with wave heights (and/or periods) selected 
independent of statistical data, should be as described by [C.3.4]. 
3.3.4
The significant wave height(s) and associated period(s) should be selected considering: 
• Feasibility and safety of the planned operation.
• Typical weather conditions at the site.
• Operation period.
• Uncertainties in weather forecasts.
Guidance note:
Other factors such as the length of delay that can be accepted due to waiting on weather, and possible 
contractual obligations should be considered as found relevant. 
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3.3.5
Maximum wave height for weather restricted operations should be calculated according to the following 
equation: 
H = STF × H
where
STF = 2.0 for all reference periods. 
Guidance note:
For short reference periods STF < 2.0 may be acceptable. See DNV-RP-H102, /55/, Table 2.2 for guidelines. 
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An appropriate range of wave periods associated with H should be considered. In the absence of other data, 
the range of T can be taken as: 
max s
max
ass
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3.3.6
Where relevant, applicable information from [3.4] may be used e.g. [3.4.12]. 
3.4 Design criteria for weather unrestricted operations 
3.4.1 General 
3.4.1.1
Whilst an operation may be defined as weather unrestricted, specific portions can be dependent on suitable 
weather forecasts, e.g. the departure of a tow from safe haven as described in [11.14.1.4]. Such restrictions shall 
be agreed before the start of an operation and are normally included on the Certificate of Approval. 
3.4.2 Environmental statistics 
3.4.2.1
Environmental phenomena are usually described by physical variables of statistical nature. Statistical data should 
as far as possible be used to establish characteristic environmental conditions. The statistical description should 
reveal the extreme conditions as well as the long and short-term variations. 
3.4.2.2
Statistical data used as basis for establishing characteristic environmental criteria shall cover a sufficiently long 
time period. 
Guidance note:
For meteorological and oceanographic data a minimum of three to four years of data collection is 
recommended. When using seasonal data longer periods are required. See DNV-RP-C205 /46/ for more info. 
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3.4.2.3
The validity of older (typically more than 20 years) statistical data should be carefully considered with respect to 
both monitoring methods/accuracy and possible long term climate changes. 
3.4.2.4
If statistical environmental data are assumed to follow a two-parameter Weibull distribution, the regression 
analysis should be performed with emphasis on a correct representation of the extreme values. 
Guidance note:
Regression analysis of two-parameter Weibull distributions are recommended based on the 30% highest data 
points, i.e. P(x > X) = 0.3. 
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3.4.3 Return periods for determining environmental criteria (apart from moorings) 
3.4.3.1
The return periods that shall be used for determining environmental criteria for weather unrestricted marine 
operations (apart from moorings and the elevated operation of jack-ups), should be related to its operation 
reference period, as defined in [2.6.2]. For design criteria for moorings see [3.4.4], and for the elevated 
operation of jack-ups see DNVGL-ST-N002, /39/. 
3.4.3.2
As general guidance, the criteria in Table 3-1 may be applied provided that the independent extremes are 
considered concurrently. 
3.4.3.3
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The intention of the return periods and load, safety and material factors used in the LRFD approach is to ensure a 
probability for structural failure less than 1/10000 per operation (10-4 probability). Note that this probability level 
defines a structural capacity reference. When the probability of operational errors is included, the total 
probability of failure is increased. 
Guidance note:
When including operational errors, the level of probability of total loss per operation cannot be accurately 
defined. However, the recommendations and guidance given in this Standard are introduced in order to obtain a 
probability of total loss As Low As Reasonable Practicable (ALARP principle). 
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3.4.3.4
The return periods for the ASD/WSD approach have been calibrated with the objective of ensuring that a given 
structurewill be treated equally under ASD/WSD and LRFD. The inherent safety margin in ASD/WSD checks is 
less than that in LRFD checks, so that higher design values are needed to achieve this equivalence. 
3.4.3.5
Seasonal and/or directional variations may be used. Data for the month(s) of the operation and the following 
month shall be used. If the operation is to be carried out in the first 10 days of the month, the data used shall 
include the preceding month. 
3.4.3.6
When seasonal variations are taken into account, this shall not imply a shorter return period, as would occur if the 
monthly return period values are derived from only the data in that month without adjustment of the target 
probability level. There are differing approaches to obtaining the monthly or seasonal data at required return 
period (e.g. the “one year return”). One approach is to perform an extreme value analysis by month/season, and 
consider a conditional probability corresponding to that month/season. For example, to determine the N-year 
return period extremes for say March, perform extreme value analysis on the subset of data for March, consisting 
of 3 hr sea-states, 240 per month in the data, and fit a Weibull curve to the cumulative distribution function. 
Select the required probability level for the N-yr extreme calculated as: 1/(365.25*8*N*C) where C = conditional 
probability for month = 1/12. Another approach is to obtain relative weightings of the severity of each month in a 
year, and scale the monthly or seasonal values such that the worst month in the year has the same extremes as 
the all-year value at the required return period. 
3.4.3.7
Similarly, when directional variations are taken into account, this shall not imply a shorter return period. 
Table 3-1 Metocean minimum design return periods, T – unrestricted operations 
Operation 
reference 
period
ASD / WSD LRFD 
Wind 
Wave and 
Current 
Wind 
Wave and 
Current 
Up to 3 days T ≥5 year T ≥3 month T ≥10 year T ≥1 month 
3 to 7 days T ≥10 year T ≥1 year T ≥10 year T ≥3 month 
7 days to 1 
month
T ≥25 year, (or obtain 
from 10 yr and 50 yr 
environmental criteria 
values using: 10yr + 
0.7*(50 yr-10 yr) ) 
T ≥10 year T ≥10 year T ≥1 year 
1 month to 1 
year
T ≥75 year (or obtain 
from 50 yr and 100 yr 
environmental criteria 
values using: 50yr 
+0.7*(100 yr-50 yr) ) 
T ≥50 year T ≥100 year T ≥10 year 
More than 1 
year
100 year return T ≥100 year T ≥100 year T ≥100 year 
d
3) 3)
1)
2)
1)
2)
4)
d d d d
d d d d
d
d d d
d
d d d
d d d
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Notes: 
1. More accurate design wind speeds may be determined as a function of the operation reference period 
and site-specific metocean parameters using the method shown in [C.1]. 
2. More accurate design waves may be determined as a function of the operation reference period and 
site-specific metocean parameters using the method shown in [C.3]. 
3. See [3.4.3.6]. 
4. Operations up to 3 days may also be defined as weather restricted operations. See Section [2.6.7]. 
5. 1 year return period for a 3 month seasonal period will normally be acceptable.
3.4.3.8
If conditions are determined using the joint probability of different parameters, then the return period should be 
increased by a factor of 4 i.e. 10 years to say 50 years and 50 years to 200 years, unless the loadings are 
dependent on a single parameter in which case the value of that parameter shall be taken from a joint probability 
combination in which it is maximised. 
3.4.3.9
For voyages that are governed for ULS and ALS by a single sea area, the operation reference period may be 
taken as 7 days to 1 month. For FLS the whole voyage shall be considered, see [11.9.12]. 
3.4.3.10
For voyages, the design extremes may be reduced below the 10 year seasonal return, to give the same 
probability of encounter as a 30 day exposure to a 10 year seasonal storm. In this case the “adjusted” design 
extremes are defined in terms of the 10% risk level, see [3.4.17.3]. The design extremes for weather unrestricted 
voyages shall not be reduced below the 1 year seasonal return. 
3.4.4 Return periods for determining environmental criteria for moorings 
3.4.4.1
Table 3-2 identifies minimum return periods applicable to a various of mooring types for weather unrestricted 
operations. The return periods specified in this document are based on ISO 19901-7 /100/, however the 
selection of return period will depend on the choice of the design code (See 17.2 for acceptable mooring codes) 
and the associated factor of safety. For weather restricted operations, see [3.3]. More onerous, local 
requirements can override the requirements stated in Table 3-2, for example ISO 19901-7, Annex B. 
Table 3-2 Return periods for determining environmental criteria for moorings 
MOORING TYPE RETURN PERIOD
Quayside/Inshore 100 year 
Offshore - Mobile near another asset 10 year
Offshore - Mobile in Open Location 5 year
Notes:
1. Where the exposure is limited to less than 30 days, or unit capable of leaving the quay on receipt of 
poor weather forecast, 10 year return period extremes can be used in the assessment. 
3.4.4.2
For mobile moorings deployed for a duration extending beyond the inspection cycle of the components of the 
mooring system, the system and its components should be assessed against the requirements for designing a 
permanent mooring sytem. 
3.4.4.3
Joint probability data should only be used when permitted by the referenced standard. 
3.4.4.4
1)
1)
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Mobile moorings should generally be designed with reference to a 10 year return period when in the vicinity of 
any other infrastructure. Where a mobile mooring is in an open location, with reduced consequence from 
mooring failure, a five year return period may be acceptable. Where applicable seasonal/monthly and/or 
directional metocean data as in [3.4.5] can be used with the specified return period. 
3.4.4.5
When evaluating the consequence of failure, consideration should be given to whether risers will be connected, 
proximity to other installations and the type of operation being undertaken. For pipe laying operations, the 
expected duration of the operation, plus a suitable contingency value, should be addressed. 
3.4.5 Use of seasonal/directional metocean data for moorings 
3.4.5.1
Metocean data specific to the month(s) or season(s) during which the mooring will be utilised may be used 
where appropriate. 
3.4.5.2
Directional metocean data may also be used with suitable spreading functions to reflect directional divergence 
in the design environment. 
3.4.6 Wind 
3.4.6.1
The averaged wind velocity over a defined time is referred to as the mean wind.
Guidance note:
Forecasted wind velocity is normally given as the 10 minute mean wind (t = 10 min) at a reference height of 
10 m (z = 10 m). 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
3.4.6.2
The design wind speed shall generally be the 1 minute mean velocity at a reference height of 10 m above sea 
level. A longer or shorter averaging time should be used for design depending upon the nature of the operation, 
the size of the structure involved and the response characteristics of the structure to wind. 
Guidance note 1:
The following averaging times are given as examples;
- Fixed structures L < 50 m 3 [s]
- Fixed structures L > 50 m 15 [s]
- For any structure if wave load dominating 1 [minute]
- Quay mooring, small vessels/objects 15 [s]
- Quay mooring, large (Wind area > 2000 m ) vessels/objects 1 [minute]
- Stability calculations, normally 1 [minute]
- Catenary mooring of vessels/objects 10 [minutes]
- Catenary mooring of GBS 60 [minutes]
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---Guidance note 2:
OCIMF (2007) gives further guidance with respect to mean wind periods to be used for quay mooring of vessels. 
For static wind calculations on lifted objects the recommendations for fixed structures above normally apply. See 
also DNV2.22, /16/, Appendix A. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
3.4.6.3
For dynamic wind analysis the mean wind period recommended for the applied wind spectrum should be used. 
mean 
2
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See [3.4.6.7]. 
3.4.6.4
The mean wind velocity varies with the averaging time and height above the sea surface or height above ground 
(yard lift). For these reasons, the averaging time for wind speeds and the reference height shall always be 
specified. 
3.4.6.5
The wind velocity profile in open sea can be related to a reference height (z ) and mean time period (t ) 
according to the equation below, see also Table 3-3 and ISO 19901-1 “Metocean design and operational 
considerations”, /98/. 
Where:
z = Height above sea surface.
z = Reference height 10 [m].
t = Averaging time for design.
t = Reference averaging time 10 [minutes].
U(z, t )= Average wind velocity.
U(z , t
) = Reference wind speed.
Table 3-3 Wind profile, U(z, t )/ U(z , t ) 
z (m)
Averaging time
3 s 15 s 1 min. 10 min. 1 hour
1 0.93 0.86 0.79 0.69 0.60
5 1.15 1.08 1.01 0.91 0.82
10 1.25 1.17 1.11 1.00 0.92
20 1.34 1.27 1.20 1.10 1.01
50 1.47 1.39 1.33 1.22 1.14
100 1.56 1.49 1.42 1.32 1.23
Guidance note:
The wind profile given in Table 3-3 is for open sea and should not be considered applicable to (partly) sheltered 
inshore locations. Wind profiles for such locations should be selected based on local data. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
3.4.6.6
Gust wind: For elements or systems sensitive to wind oscillations (e.g. where dynamics or fatigue governs the 
design) the short and long term wind variations should be considered. 
3.4.6.7
The wind variations may be described by a wind spectrum. See e.g. DNV-RP-C205, /46/; NORSOK N-003, /111/
or ISO 19901-1, /98/. 
3.4.6.8
Squalls: If squalls are possible during a marine operation maximum realistic (in the actual area) characteristic 
wind speeds during squalls shall be considered in the planning and execution of the operation. 
Guidance note:
Squalls are strong winds (22 knots or more) characterised by a sudden onset, duration of minimum 1 minute, and 
then a rather sudden decrease in speed. Squalls are caused by advancing cold air and are associated with active 
weather such as thunderstorms. Their formation is related to atmospheric instability and is subject to seasonality. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
r r, mean
r
mean
r, mean
mean
r r, 
mean
mean r r, mean
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3.4.7 Wind for moorings 
3.4.7.1
In addition to the requirements in [3.4.6], for permanent moorings the more onerous of the following should be 
considered: 
• Steady one minute mean velocity; or
• One hour mean plus a suitable gust spectrum. Generally the ISO 19901-1 gust spectrum, /98/, would be 
applicable unless an alternative can be clearly justified. 
3.4.7.2
For mobile moorings either a steady state wind speed or a suitable gust spectrum may be used depending upon 
the stiffness of the mooring system. 
3.4.7.3
For inshore or quayside moorings care shall be taken to ensure that all natural periods of response of the system 
have been considered. Some of the mooring system response periods may be shorter than one minute but on 
the other hand the use of shorter gust periods may not represent a sustained design wind that will act at the 
same time across the whole of the structure. The representative design wind sampling period, therefore, has to 
be carefully established on a case by case basis for inshore and quayside moorings, but the averaging time shall 
not be longer than 1 minute if applying static wind load. 
3.4.7.4
For locations prone to squall events, system design should include assessment for squall events. Guidance on 
squall assessment is provided in DNVGL-OS-E301, /27/. 
3.4.8 Waves - design methods 
3.4.8.1
Wave conditions are defined by characteristic wave height, H , or the significant wave height, H , and 
corresponding periods. 
3.4.8.2
Wave conditions for design may be described either by a deterministic design wave method, or by a stochastic 
method. 
3.4.8.3
In the deterministic method the design sea states are represented by regular periodic waves characterised by 
wave length (or period), wave height and possible shape parameters. 
3.4.8.4
In the stochastic method the design sea states are represented by wave energy spectra characterised by main 
parameters H and T or T . 
3.4.9 Waves - weather unrestricted operations, general 
3.4.9.1
Characteristic wave conditions for weather unrestricted operations shall be based on long term statistical data. 
3.4.9.2
Long term variations of waves may be described by a set of sea states characterised by the wave spectrum 
parameters. 
3.4.10 Wind seas and swell 
3.4.10.1
c s
s z p
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All possible combinations of wind seas and swell should be considered.
Guidance note:
The wave conditions in a sea state can be divided into two classes, i.e. wind seas and swell. Wind seas are 
generated by local wind, while swell have no relationship to the local wind. Swells are waves that have travelled 
out of the areas where they were generated. Note that several swell components may be present at a given 
location. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
3.4.11 Characteristic waves for weather unrestricted operations 
3.4.11.1
Characteristic values shall be based on the defined operation reference period. Periods less than 3 days shall not 
be used. These can be based on the return periods given in Table 3-1 or Table 3-2 as applicable. Alternatively, 
the Characteristic significant wave height, H may be taken according to [C.3.2.1] and the corresponding 
maximum wave height, H , may be taken according to [C.3.2.2]. 
Guidance note 1:
The significant wave height where m is the sea surface variance. In sea states with only a narrow 
band of wave frequencies, H is approximately equal to (the mean height of the largest third of the zero 
up-crossing waves). 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
Guidance note 2:
The H corresponds to an approximate 10% probability of exceeding this individual wave height during the 
anticipated operation reference period. If an alternative method is applied it should be documented that this 
corresponds to an equal or less probability. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
3.4.11.2
When a regular wave analysis is applicable, the design maximum wave shall be the most probable highest 
individual wave in the design sea state, assuming an exposure of 3 hours. The determination of the height, crest 
elevation and kinematics of the maximum wave should be determined from an appropriate higher-order wave 
theory and account for shallow water effects. For most practical purposes the kinematics of regular deterministic 
waves can be described by the following theories: 
h/λ ≤ 0.1
Solitary wave theory for particularly shallow water
0.1 < h/λ ≤ 0.3
Stokes 5 order wave theory or Stream Function wave theory. 
h/λ > 0.3
Linear wave theory (or Stokes 5 order) 
where
h = water depth.
λ = wave length.
A range of wave height-period combinations shall be investigated, including those that can cause resonance, see 
[C.3.3]. 
For more information on the kinematics of regular waves, see DNV-RP-C205,/46/. 
3.4.11.3
Sea states shall include all relevant spectra up to and including the design storm sea state for the construction 
site or voyage route. Long-crested seas shall be considered unless there is a justifiable basis for using short-
crested seas or these are more critical, see [3.4.12]. Consideration should be given to the choice of spectrum. 
3.4.11.4
Wave spectra defined by the Jonswap or the Pierson-Moskowitz spectra are most frequently used. Wave 
conditions with combined wind sea and swell may be described by a double peak wave spectrum. See DNV-RP-
C205, /46/, for further guidance. 
3.4.11.5
s, c 
max, c
0
s
max, c
th
th
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In the simplest method the peak period (T ) for all sea states considered, should be varied. In areas where swell 
is insignificant, the range of T can be taken as: 
in areas where swell is significant, the range of T can be taken as: 
 for H ≤ 5.7 m
 for H > 5.7 m
where:
H = significant wave height in metres
T = wave peak period in seconds
Guidance note:
The equations for areas where swell could be significant are based on the equations for T given in [C.3.4.3], 
assuming that T = 1.24T for steep waves (gamma = 5) and T = 1.4T for long waves (gamma = 1.0). The relation 
between zero-crossing period T and the spectral peak period T can be found in Table 3-4. See also DNV-RP-
H103, /56/, Sec.2.2.6 or DNV-RP-C205, /46/, Sec.3.5.5. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
Alternatively, see [C.3.4.3]. 
3.4.11.6
The effects of swell, see [3.4.14], should also be considered if not already covered in this peak period range. A 
reduced range of T may be used if the route or site-specific data and natural periods allow. 
3.4.11.7
However, [3.4.11.5] incorrectly assumes that all periods are equally probable. As a result this method should 
generally produce higher design responses than would be the case when using the more robust H -T method 
described in [3.4.11.8], which may be used when desired. 
3.4.11.8
In the alternative method, a contour (IFORM) is constructed within the H -T plane that identifies equally 
probable combinations of H and T for the design return period. This contour should also cover swell. The 
contour should be checked for accuracy e.g. against the theoretical constraints on wave breaking. H -T
combinations from around the contour should be tested in motion response calculations to identify the worst 
case response (there is no need to consider a range of T with each H ). 
3.4.11.9
The relationship between the peak period T and the zero-up crossing period T is dependent on the spectrum. 
For a mean JONSWAP spectrum (γ=3.3) T /T = 1.286; for a Pierson-Moskowitz spectrum (γ=1) T /T = 1.41. 
3.4.11.10
Table 3-4 indicates how the characteristics of the JONSWAP wave energy spectrum vary over the range of 
recommended sea states. The constant, K, varies from 13 to 30 as shown in the equation in [3.4.11.4]. T is the 
mean period (also known as T ). 
Table 3-4 Value of JONSWAP γ, ratio of T :T and T : T for each integer value of K
Constant K γ T / T T / T Constant K γ T / T T / T
13 5.0 1.24 1.17 22 1.4 1.37 1.27
14 4.3 1.26 1.18 23 1.3 1.39 1.28
15 3.7 1.27 1.19 24 1.1 1.40 1.29
16 3.2 1.29 1.20 25 1.0 1.40 1.29
17 2.7 1.31 1.21 26 1.0 1.40 1.29
18 2.4 1.32 1.23 27 1.0 1.40 1.29
19 2.1 1.34 1.24 28 1.0 1.40 1.29
p
p
p
s
s
s
p
z
p z p z
z p
p
s p
s p
s p
s p
p s
p z
p z p z
1
m
p z p 1
p z p 1 p z p 1
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20 1.8 1.35 1.25 29 1.0 1.40 1.29
21 1.6 1.36 1.26 30 1.0 1.40 1.29
3.4.11.11
For operations involving phases sensitive to extreme sea states, such as temporary on-bottom stability or green 
water assessment, the maximum wave height and associated period should be used. 
3.4.11.12
For precise operations sensitive to small fluctuations of the sea level even under calm sea state conditions, the 
occurrence of long period, small amplitude swell on the site should be checked and its effects on the operations 
evaluated. 
3.4.11.13
Attention should also be paid to areas prone to strong currents acting against the waves which would amplify the 
steepness of the sea state (i.e. reduce the wave encounter period that drives dynamic response). 
3.4.12 Short crested seas 
3.4.12.1
A directional short crested wave spectrum, see the equation below, may be applied based on non-directional 
spectra. 
where
= Wave spectrum, see [3.4.11.4].
θ = Angle between direction of elementary wave trains and the main direction of the short crested 
wave system.
= Directional short crested wave power density spectrum.
= Directional function.
3.4.12.2
Energy conservation requires that the directional function fulfils;
In absence of more reliable data the following directional function may be applied for wind sea, 
where 
Γ( ) = gamma function. Due consideration should be taken to reflect an accurate correlation 
between the actual sea-state and the constant n. Typical values for wind seas are n = 2 to n = 10. Swell 
should normally be taken as long crested, n > 10. 
Guidance note:
For cases where long crested seas are conservative, it is recommended that long crested seas are used for the 
original design work. If short crested seas are introduced in connection with estimating extremes, the exponent, 
n, should not be taking lower than 10 without more detailed documentation. Swell seas should be taken as long 
crested. For fatigue assessment, where low and moderate sea states are governing the fatigue accumulation, n
could be taken as the most unfavourable value between 2 and 6. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
3.4.12.3
Short crested seas should not be considered for significant wave heights exceeding 10 m, unless they cause 
more onerous response(s). 
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3.4.13 Waves for moorings 
3.4.13.1
In addition to the requirements in [3.4.8], for mobile moorings it is generally acceptable to consider a single 
extreme significant wave height and a range of associated peak periods corresponding to the relevant return 
period for a location. 
3.4.13.2
For permanent moorings a number of H -T combinations along the 100 year return period contour line shall be 
considered in the analysis. If a contour plot is not available, a sensitivity study by varying peak period for the 100 
year return period sea state is required. This is to ensure that extreme line tensions due to low frequency motion 
at lower periods are captured in the analysis, especially for ship shaped floaters. 
3.4.13.3
Long crested waves shall be assumed for analysis unless otherwise documented.
3.4.14 Swell 
3.4.14.1
Swell type waves should be considered for operations sensitive to long period motion or loads. 
3.4.14.2
Swell type waves may be assumed regular in period and height, and may normally also be assumed 
independent of wind generated waves. 
3.4.14.3
Critical swell periods should be identified and considered in the design verification.
3.4.14.4
Characteristic height(s) and period(s) for swell type waves for weather restricted operations may be selected 
independently of statistical data. 
3.4.14.5
Characteristic height(s) and period(s) for swell type waves for weather unrestricted operations should be based 
on statistical data and the applicable return periods. 
3.4.15 Current 
3.4.15.1
The design current shall be the rate at mean spring tides, taking account of variations with depth and increases 
caused by the design environmental condition, storm surge, fluvial (river) and wind-driven components.3.4.15.2
Currents can be divided into two different categories:
• Tidal currents
• Residual currents that remain when the tidal component is removed, including river outflows, surge, wind 
drift, loop and eddy currents. 
3.4.15.3
Tidal currents can be predicted reliably, subject to long term measurement (at least one complete lunar cycle at 
the same season of the year as the actual planned operation). Residual currents can only be reliably predicted or 
forecast using sophisticated mathematical models. 
s p
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3.4.16 Other parameters 
3.4.16.1
Other factors including the following may be critical to the design, operations or voyages and should be 
addressed: 
• Water level including tide and surge
• Sea icing, icing on superstructure 
• Exceptionally low temperature 
• Large temperature differences
• Water density and salinity 
• Bad visibility. 
3.4.17 Calculation of “adjusted” design extremes, weather unrestricted voyages 
3.4.17.1
The risk of encounter of extreme conditions on a particular voyage is dependent on the length of time that it 
spends in those route sectors where extreme conditions are possible. If the length of time is reduced, then the 
probability of encountering extreme conditions is similarly reduced. 
3.4.17.2
It is generally accepted that for a prolonged weather unrestricted voyage the wind and wave design criteria 
should be those with a probability of exceedance per voyage of 0.1 or less. For a voyage of 30 days (or more), 
through meteorologically and oceanographically consistent areas, this corresponds to the 10 year monthly 
extreme. 
3.4.17.3
Many voyages last less than 30 days, or are potentially exposed to the most severe conditions for less than 30 
days. Consequently, for shorter exposures, the 10 year monthly extreme may be adjusted for reduced exposure. 
This value is equivalent to the 10 voyage extreme and is also referred to as the 10% risk level extreme. This shall 
not be confused with the 10% exceedance value for the voyage, as discussed in [3.4.19.6]. 
3.4.17.4
When the 10% risk level extremes are less than the 1 year return monthly extremes, the 1 year monthly extremes 
are the minimum that shall be used for design. 
3.4.17.5
If the 10 year extremes are due to a tropical cyclone it may not be appropriate to design to adjusted extremes. 
This is likely to be the case for barge or MODU towages that are not able to respond effectively to weather 
routeing. 
3.4.18 Calculation of exposure 
3.4.18.1
For the purpose of the calculation of “adjusted” extremes the exposure time to potentially extreme or near 
extreme conditions is calculated taking consideration of the following points: 
• The initial 48 hours of the voyage is assumed to be covered by a reliable departure weather forecast and is 
excluded 
• The speed of the voyage is reduced by taking the monthly mean wave heights along the route into 
consideration as described in [3.4.18.3]. 
• The speed of the voyage is adjusted to take into consideration the mean currents as described in 
[3.4.18.4]. 
• A contingency time of 25 per cent of the time is added. This allowance is to account for severe adverse 
weather, for tug breakdowns or other operational difficulties 
• A minimum exposure time of 3 days is considered.
3.4.18.2
The voyage duration in each route sector shall be calculated using the speed in the monthly mean sea state for 
each route sector and shall allow for adverse currents and adverse prevailing winds as described in [3.4.18.3]. 
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3.4.18.3
The effect of the mean sea state on the voyage speed in each route sector shall be calculated as a function of the 
wave height in which the voyage is assumed to come to a dead stop, b (metres). This can typically be taken 5 m 
for barge towages, and 8 m for ships. The speed in the each route sector can be taken as the calm weather 
speed is multiplied by the factor, F, for that route sector defined by: 
where H is the monthly mean wave height in that route sector. 
3.4.18.4
The effect of the mean current on the voyage speed in each route sector shall be calculated by adding the 
current vector (resolved with respect to the voyage heading). 
3.4.18.5
For the calculation of exposure to the extreme conditions only prevailing winds or currents which act to delay the 
voyage shall be taken into account. 
3.4.19 Calculation of “adjusted” extremes 
3.4.19.1
The probability of non-exceedance of a value of wind speed or significant wave height in a particular route sector 
is expressed as a cumulative frequency distribution (e.g. a Weibull distribution). 
3.4.19.2
The probability that during some 3 hour period for waves (or 1 hour for wind) the voyage will experience a 
significant wave height (or wind speed) less than some value x is given by F (X). 
3.4.19.3
If it takes M hours to pass through the route sector and making the assumption that consecutive wave height and 
wind speed events are independent then the probability of not exceeding the value x is given by 
where N = M/T where T = 1 hour is applied for winds and T = 3 hours for waves, which are a more persistent 
form of energy. 
3.4.19.4
If it is reasonable to expect that extremes of wind speed or wave height could occur in more than one route 
sector then the probability of not exceeding the value x is given by the product 
3.4.19.5
The probability of encountering an extreme value of wind speed or significant wave height, during a particular 
voyage, that is reached or exceeded once on average for every 10 voyages, is 0.1. The value of x is varied until 
to give the 10 voyage extreme for the voyage or towage.
3.4.19.6
This value is also referred to as the “adjusted” extreme for the voyage, or as having a risk level of 10%. The 
method can be adjusted to give other risk levels (e.g. 1% or 5%). This should not be confused with the 
percentage exceedance (see Guidance Note to [3.4.19.7]). 
m
x
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3.4.19.7
The extremes used for design shall not be less than the 1 year return monthly extremes.
Guidance note:
The percentage exceedance is obtained as follows:
• Given a series of values of wind speed or significant wave height, as may be observed during a complete 
voyage, some value y will be exceeded at some times but not others and the percentage exceedance of 
value y is equal to:
• If each observed value of wind speed or significant wave height is assumed to last for some duration 
(typically 1 hour for winds and 3 hours for waves) then for example, during a voyage lasting 10 days there 
will be 240 wind events and 80 wave events. On the voyage, if a wind speed greater than 30 knots is 
observed during 24 separate, hourly occasions then the percentage exceedance of 30 knots is 10%. 
• The 10% risk level (as defined in [3.4.17.3]) for a voyage along a specific route, departing on a specific date 
is expected to occur only once, on average, in every 10 voyages. However a value with a 10% exceedance 
level for the same route and departure date is likely to occur on average for 10% of the time on every 
voyage. 
• Thus a 10% exceedance value is far more likely to occur than a 10% risk level value, or an adjusted, 10 year 
extreme value. 
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3.4.20 Criteria from voyage simulations 
3.4.20.1
If continuous time series of winds and waves are available along the entire voyage route (e.g. from hindcast data 
or satellite observations), an alternative way to develop criteria with a specified risk of exceedancein a single 
voyage is to perform tow simulations. A large number of simulations can be performed, with uniformly spaced (in 
time) departure times during the specified month of departure over the number of years in the database. For 
each simulated voyage, the maximum wind speed and the maximum wave height experienced somewhere 
along the tow route are retained. Then the probability distribution of these voyage-maxima can be used to 
determine the design value with a specified risk of exceedance. For example, the value exceeded once in every 
20 voyages, on average, can be determined by reading off the value of wave height from the distribution of 
voyage-maximum wave heights at the 95 percentile level. 
3.4.20.2
If fatigue during tow is an issue, the complete distributions of winds and waves experienced during the simulated 
voyages (not just the voyage-maximum values) can be retained. These can be used to give scatter diagrams of 
wave height against period and/or direction, and wind speed against direction. 
3.4.20.3
The voyage simulation method can be made to be very realistic and account for variation of speed due to 
inclement weather or ocean currents, weather avoidance en-route through forecasting/routeing services, or the 
use of safe havens, etc. If the voyage simulator cannot accommodate all these features, a reasonably 
conservative estimate of criteria can be derived by using a conservative (slow) estimate of the average speed. 
Care should be taken when choosing the average speed estimate - a slow speed may not be conservative if it 
results in the vessel apparently arriving in a route sector late enough to miss severe weather, which might have 
been encountered if arrival had been earlier. 
3.4.21 Metocean database bias 
3.4.21.1
Regardless of whether the method described in [3.4.19] or the method described in [3.4.20] is used, it is 
important to know the accuracy of the metocean database being used. Specifically, if there is a known bias in the 
wind or wave statistics for any segment of a tow, it is essential to adjust the criteria accordingly. 
3.4.22 Metocean data for bollard pull requirements 
3.4.22.1
The design extremes are not normally used for calculation of bollard pull requirements (except when there is 
limited sea room), which is covered in [11.12.2]
th
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3.5 Weather/metocean forecast requirements 
3.5.1
The requirements for weather forecasting are given in [2.7] and the requirements for environmental monitoring 
in [2.9]. 
3.6 Benign weather areas 
3.6.1
Areas considered benign are shown in Table 3-5 and Figure 3-1 for different months. In general they have the 
following characteristics: 
• virtually free of monsoons, Tropical Revolving Storms or Tropical Cyclones
• exceeding Beaufort Force 5 for <20% of any month (in a “typical” year)
• However these areas may experience sudden vicious squalls and very rare tropical storms or cyclones. 
Table 3-5 Northern and Southern boundaries of benign weather areas by month
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Figure 3-1 Map showing benign weather areas
SECTION 4 Ballast and other systems 
4.1 Introduction 
4.1.1 Scope 
4.1.1.1
This section includes general requirements to system and equipment design. It covers all (temporary) systems, 
see [4.2.1.7], used during marine operations, with emphasis on ballast systems. 
4.1.2 Revision history 
4.1.2.1
This section replaces the following parts of the VMO Standard and the ND Guidelines:
• DNV, Marine Operations, General, DNV-OS-H101
• DNV, Load Transfer Operations, DNV-OS-H201
• GL Noble Denton, General Guidelines for Marine Projects, 0001/ND
• GL Noble Denton, Guidelines for Load-outs, 0013/ND
• GL Noble Denton, Guidelines for Float-over Installations / Removals, 0031/ND
4.2 System and equipment design 
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4.2.1 General 
4.2.1.1
Systems and equipment shall be designed, fabricated, installed, and tested in accordance with relevant codes 
and standards. 
4.2.1.2
Systems and equipment shall, as far as possible, be designed to be fail safe and arranged such that a single 
failure in one system or unit cannot spread to another unit. The most probable failures, e.g. loss of power or 
electrical failures, shall result in the least critical of any possible new conditions. 
4.2.1.3
Alarm system(s) should be incorporated for essential functions and be audible/visible at operators’ station. 
4.2.1.4
Work stations shall be arranged to provide the user with good visibility and easy access to controls required for 
the operations. 
4.2.1.5
Systems and equipment shall be selected based on a thorough consideration of functional and operational 
requirements for the complete operation. Emphasis shall be placed on reliability and the expected behaviour in 
possible contingency situations. 
4.2.1.6
Depending on the complexity and duration of the operation, and the structure itself, risk evaluations may be 
required to determine the systems and equipment required for a safe operation, see [2.4.2]. Such studies shall 
include normal operations as well as emergency situations. 
4.2.1.7
The following systems shall be considered where applicable:
1. power supply
2. fuel supply
3. electrical distribution systems
4. machinery control systems
5. alarm systems
6. valve control systems
7. bilge and ballast systems
8. compressed air systems
9. firefighting systems
10. Cooling systems
11. ROV systems
12. lifting systems
13. positioning systems, see Guidance Note
14. communications systems and
15. instrumentation systems for monitoring of;
◦ loads and/or deformations
◦ environmental conditions, such as tide
◦ ballast and stability conditions
◦ heel, trim, and draught
◦ position (navigation)
◦ tide
◦ under-keel clearance and
◦ penetration/settlements.
Guidance note:
Object guiding and positioning systems, including structural and functional requirements are covered in 
[4.4]. If applicable, the requirements in this section should be considered regarding mechanical parts and 
operation of such systems. Vessel position systems are described in Sec.17. 
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4.2.1.8
Computerised control or data acquisition systems should be equipped with uninterruptible power supply system 
(UPS). 
4.2.1.9
All systems shall be inspected and tested according to [2.10]. 
4.2.1.10
Where a permanent system is complimented by a temporary system, the integration of the two systems shall be 
inspected and tested according to [2.10]. 
4.2.2 Back-up 
4.2.2.1
All essential systems, parts of systems or equipment shall have back-up or back-up alternatives. Necessary time 
for a change over to the back-up system or equipment shall be assessed. 
Guidance note:
It is recommended that the marine operation manual includes an inventory of main spare parts available on site. 
It is also recommended to assess the necessity of having repair or service personnel available on site during 
operations. 
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4.2.2.2
All back-up systems should be designed and fabricated to the same standard as the primary systems. 
4.2.2.3
Back-up systems should be adequately separated from the main system such that failure of any component does 
not adversely affect the safe conduct of the operation. 
4.2.2.4
For systems consisting of multiple independent units, back-up may be provided by havinga sufficient number of 
available spare units available on site. 
4.2.2.5
If umbilicals are necessary to provide power and/or hydraulic services during any marine operation, adequate 
back-up capability shall be provided, and fail-safe systems shall be incorporated into critical controls. 
4.2.2.6
Automatic control systems shall be provided with a possibility for manual overriding.
4.3 Ballasting systems 
4.3.1 General 
4.3.1.1
This sub-section is mainly applicable for ballasting and de-ballasting of vessel(s) involved in load transfer 
operations. 
Guidance note:
See [11.15] regarding pumping capacity requirements during voyages. For jacket installations additional 
requirements apply, see [13.7.2]. For ballasting of (crane) vessels during lifting see Sec.16. 
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4.3.1.2
Regardless of any requirement to change draught during construction, towage or installation operations, floating 
structures should normally be fitted with a means of pumping out water from all compartments. 
4.3.1.3
The (de)ballasting system design shall properly consider the operation class (see [4.3.2]) as well as functional 
requirements related to: 
• lay-out and reliability of the system
• tank capacities including contingency situations
• ballasting capacity including contingency situations
• strength limitations
• easily controllable ballasting
• tide
4.3.1.4
General requirements to (de)ballasting systems are given in [4.2.1]. 
4.3.1.5
Adequate testing of the ballast system considering the actual operation shall be carried out, see [2.10]. 
4.3.2 Ballast system power supply 
4.3.2.1
Adequate power supply considering the actual operation shall be provided for the ballast system. 
4.3.2.2
The need for emergency power supply due to the following situations shall be considered:
a. Breakdown of any one power unit
b. Breakdown of the common energy supply
c. Unexpected increase in the consumption of energy above the expected value.
Guidance note:
The back-up capacity for accidental conditions represented by a) and b) may be spare units in stand-by 
position. The back-up capacity for conditions represented by c) may be spare capacity in the main unit or a 
back-up unit installed to assist the main unit. 
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4.3.2.3
Sufficient main and back-up power supply capacity should be documented by calculations.
Guidance note:
Necessary power supply for ballasting should be based in the required ballasting capacity given in Table 4-2 for 
the relevant load-out class. For evaluations of back-up requirements, an independent power supply source 
should be regarded as a “pump system”, see note 3) in Table 4-2. 
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4.3.3 Operation classes 
4.3.3.1
An operation class should be defined for load transfer operations see Table 10-1 for load-outs and Table 15-1 for 
lift-off, mating and float-over operations. 
4.3.4 Ballast system lay-out and reliability 
4.3.4.1
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The ballast pumps may be the vessel’s internal pumps, pumps purposely installed for the operation/project, or a 
combination of these. Internal vessel pumps that are not frequently in use, as the primary pumping means, 
should be carefully considered and demonstrated fit for purpose. 
Guidance note:
Internal vessel pumps can have unreliable service records. Also, permanent piping systems are inherently 
inflexible. 
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4.3.4.2
Where accurate control of the ballast amount is crucial, ballasting by flooding (i.e. opening of bottom valves) 
and/or de-ballasting by air pressurisation (or ballasting by vacum – low pressure) of ballast tanks shall be avoided 
during load transfer phases. 
Guidance note:
Ballasting by flooding during load transfer phases where accurate control of ballast amount is crucial may be 
allowed if the system has sufficient redundancy (e.g. double valves to compensate a failure to close a valve) 
and/or back-up ballast plans are available where mechanical failures can be compensated by an alternative 
ballast procedure. 
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4.3.4.3
Umbilicals used for air pressurisation of submerged vessel compartments should be connected to valves at the 
vessel tanks. 
4.3.4.4
Where a compressed air system is used, the time lag needed to pressurise or de-pressurise a tank should be 
taken into account, as should any limitations on differential pressure across a bulkhead. It should be 
remembered that compressed air systems cannot always fill a tank beyond the external waterline. Air pressurised 
vessel tanks shall be fitted with safety (pressure relief) valves. 
4.3.4.5
Hoses, umbilicals and power cables shall be placed with due consideration to other ongoing activities during the 
load transfer. 
4.3.4.6
Required access throughout the load transfer for (possibly) needed equipment, e.g. fork lifts for replacing 
pumps, should be demonstrated. 
4.3.4.7
All internal compartments shall be cleaned of debris before ballasting starts.
4.3.4.8
When inlets are near the seabed, care shall be taken to avoid sucking in mud or sand that can block the pumping 
systems or filters. 
4.3.4.9
Where inlets or outlets are near the seabed, care shall be taken to avoid scour that could have adverse effects on 
foundations of any structure or grounded vessel, or reduce under-keel clearances. 
4.3.4.10
Except when in use for inlet or discharge, all openings to sea shall be protected by a double barrier. 
4.3.4.11
Any external valves and pipework shall be protected against collision and fouling by towlines, mooring lines or 
handling wires. 
4.3.4.12
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All essential pipework in temporary systems should be of permanent-type construction and shall be 
hydrostatically tested to a minimum of 1.3 times the design pressure. Temporary flexible hoses shall only be 
used when a risk assessment, in accordance with [2.4], demonstrates the acceptability of the system. 
Guidance note:
For offshore operations temporary flexible hoses are not generally permitted unless their use cannot be avoided, 
for instance for supply of back-up compressed air from a compressor barge alongside. 
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4.3.4.13
Permanent-type ballast sytems used in marine operations should fulfil the Class requirements for construction 
and testing. 
Guidance note:
For permanent ballast systems not subject to Class approval the requirement in [4.3.4.12] apply. 
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4.3.5 Ballast tank capacity 
4.3.5.1
The ballast tanks shall meet the capacity requirements in Table 4-1 for the required floating position(s) 
throughout the operation for both planned and contingency situations. 
4.3.5.2
A reasonable amount of residual water in the tanks should be taken into account.
Guidance note:
The amount to be considered will depend on details and location of the pumping intake(s), heel/trim of the 
vessel and structural elements at the tank bottom. For tanks in use during the load transfer without any special 
arrangements allowing easy tank stripping, the minimum water head should be taken equal to the height of the 
tank bottom stiffeners plus 0.05 metres. 
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4.3.5.3
The required tank capacities should include relevant spare capacity to compensate for the following: 
a. Tide levels below or above the predicted values. 
b. Total vessel weight, including vessellightship, consumables and temporaries (e.g. project equipment, 
grillages, etc.), being higher or lower than expected 
c. Possible object weight and CoG variations
d. Operational delays. 
Table 4-1 Tank capacity requirements
Operation 
Class
The tank capacity shall be adequate for the following scenarios (see Table 10-1 for load-out 
classes and Table 15-1 for float-ons and float-offs). 
All
• Normal (planned) operations
• Spare tank capacity to cover items [4.3.5.2] and [4.3.5.3] shall be ensured in all 
situations. 
• Any necessary pumping capacity contingency involving modifications in ballasting 
procedures. See Table 4-2. 
1
• See All
• Reversing of the operation. Tide compensation if stop of load transfer, considering 
maximum possible (defined) duration of the load transfer. 
2
• See All
• Ballasting through a complete tide cycle at any stage of the load transfer. Maximum tide 
variations within the operation period (T ) shall be considered. Reversing of the 
operation, if applicable. 
R
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3
• See All
• Ballasting through a complete tide cycle at any stage of the load transfer. Maximum tide 
variations for at least the coming 3-5 days shall be considered. 
4
• See All
• Reversing of the operation, if applicable.
5 • See All
4.3.6 Ballast pumping capacity 
4.3.6.1
The ballast pumping capacity shall meet the capacity requirements in Table 4-1 for the required floating position
(s) throughout the operation for both planned and contingency situations. Pump capacity shall be based on the 
published pump performance curves, taking account of the maximum head for the operation and pipeline 
losses. 
4.3.6.2
Adequate capacity shall be documented considering the requirements to nominal, spare and back-up capacity 
given in this sub-section. 
4.3.6.3
The nominal ballasting capacity shall be determined by the worst combination of expected tide rise/fall and 
planned load transfer velocity. 
4.3.6.4
For operation classes 2 and 3, it shall be documented that the ballast systems have capacity to compensate for 
the tide rise/fall through one complete tide cycle with the object in any position. 
Guidance note:
If the tidal range increases in the days following the planned operation start, this should be considered when 
evaluating the consequences of a delayed start or delays during the operation. 
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4.3.6.5
Pumps which require to be moved around the barge in order to be considered as part of the back-up capacity, 
shall be easily transportable, and may only be so considered if free access is provided at all stages of load-out 
between the stations at which they may be required. Adequate resources shall be available to perform this 
operation. 
4.3.6.6
Spare pumps should normally be installed and tested in the position they are planned to be used as back-up. 
However, for pumps that may be replaced during the operation, spare pumps in stand-by position that require 
minimum replacement time may be used. Required number of spare pumps should be conservatively assessed. 
The replacement time shall be documented. See [4.3.4.6]. 
4.3.6.7
Requirements for minimum total ballasting capacity, including back-up, are given in Table 4-2, including the 
notes. 
Table 4-2 Ballast pumping capacity requirements
Operation Class
Normal Operation
Load transfer as planned
Tide Compensation
Load transfer unexpectedly stopped
1
Minimum 200% capacity with intact 
system and minimum 120% capacity in all 
tanks with any one pump system failed. 
Minimum 150% capacity with intact system 
and minimum 100% capacity in all tanks 
with any one pump system failed. 
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2
Minimum 130% capacity with intact 
system and minimum 100% capacity in all 
tanks with any one pump system failed. 
As for Class 1
3
Minimum 130% capacity with intact 
system and a contingency plan covering 
pump system failure. 
As for Class 1
4 As for Class 2 No requirements
5 As for Class 3 No requirements
Notes:
1. 100% pump capacity during normal operation is the capacity required to carry out the operation at the 
planned speed. The required pump capacity for a reduced speed could be acceptable as “100%”, if 
ballast calculations are documented for this case, and the impact of the increased activity duration is 
properly taken into account. 
2. 100% pump capacity during tide compensation is the capacity required to compensate for the 
maximum expected tidal rate of change. 
3. A pump system includes the pump(s) which will cease to operate due to a single failure in any 
component. 
4. The back-up requirement X% capacity in all tanks could be covered by a modified ballast procedure 
giving X% capacity in all tanks involved in this modified procedure. 
4.3.7 Vessel strength considerations 
4.3.7.1
All ballast conditions shall be checked against longitudinal strength requirements. Any hull beam strength 
limitations shall be considered in the ballast procedure. 
4.3.7.2
The effect of hull beam deflections on the object support load distribution shall be considered, see [5.6.11]. 
4.3.7.3
Differential pressures across bulkheads shall be demonstrated to be within allowable values. 
4.3.7.4
Any restrictions, e.g. any requirement to mimic the vessel voyage condition, on ballast condition(s) during 
welding of seafastening shall be considered. 
4.3.7.5
Possible significant strength reduction due to cut outs (e.g. for ballast hoses, pumps or other equipment) in 
structural elements shall be considered. 
4.3.8 Ballasting control 
4.3.8.1
A straightforward ballasting control system and procedure shall be used. 
Guidance note:
It is recommended that it is possible to operate the ballast pumps from one control centre during operation. For 
multi barge operations, a control centre on each barge may be applicable. However, the control centre at one of 
the barges should be defined as the master ballast control centre. The arrangement should be such that 
simultaneous de-ballasting can be effected for all the relevant tanks at each stage. 
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4.3.8.2
It shall be thoroughly documented how the ballasting will be done (controlled) for all possible combinations of 
tide level and load transferred. 
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4.3.8.3
Each tank should preferably be used to compensate one effect (see Guidance Note) only. To use a system/tank 
for compensation of more than two effects shall be avoided. 
Guidance note:
In order to maintain maximum control with the ballasting it could be advisable to use separate systems/tanks for 
compensation of the effects of tide variation, weight transferred, and CoG position in both directions (trim and 
heel). 
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4.3.8.4
A ballasting control monitoring system including back-up shall be established. A communication system shall be 
established when pumps are operated manually away from the control centre. 
4.3.9 Ballast calculations 
4.3.9.1
Ballast calculations shall be carried out in order to establish required nominal capacity (i.e. the 100% capacity, 
see note 1 in Table 4-2) pumping capacities. 
4.3.9.2
For ballast calculations the expected CoG and weight without any contingencies should normally be used as the 
base case. However, the effect of possible weight and CoG variations shall be considered, see [5.6.2]. 
4.3.9.3
The ballast calculations shall include sufficient steps to accurately define the required ballasting throughout the 
(load transfer)operation. 
4.3.9.4
All considered contingency situations shall also be covered with an adequate number of ballast calculation steps. 
4.3.9.5
The results of the ballast calculations, i.e. required pumping in all steps, shall be clearly outlined in ballast 
procedure(s). 
4.3.10 Contingency and back-up 
4.3.10.1
Means for adequate handling of all ballast system contingencies identified in the risk management process shall 
be provided. 
4.3.10.2
The contingencies indicated in Table 4-3 shall be considered. Minimum requirements to back-up have also been 
indicated. 
Table 4-3 Contingency requirements
No Contingency situation Minimum requirement
1
Tidal velocities above (or below) the predicted 
values.
Spare pump(s) or spare capacity in the main pump
(s). See Table 4-2 for specific requirements. 
2
Unplanned stops in load transfer (e.g. object 
movement stopped due to repair work, etc.) 
Adequate tank and pump capacities to handle the 
situation. See Table 4-1 and Table 4-2 for specific 
requirements. 
3 Reversal of operation, if required.
Ballast procedures/calculations with 
corresponding pump lay-out and tank capacities 
for this case shall be documented. 
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4 Reduced pump capacity.
Spare pump capacity. See Table 4-2 for specific 
requirements in %. 
5 Breakdown of ballast pump(s).
Spare pump(s) or spare capacity in the main pump
(s). See Table 4-2 for specific requirements. 
6 Breakdown of power supply, including cables.
Back-up required, see [4.3.2.2], or adequate 
pump capacity, see Table 4-2, considering any 
power supply unit failed shall be documented. 
7 Failure of any control panel/switchboard.
Sufficient back-up to fulfil the requirements in 
Table 4-2 for one pump system failure. Alternative 
pump/valve control methods (locations and 
procedures) could also be accepted as back-up. 
See Notes. 
8 Failure of any ballast valve or hose/pipe.
Notes:
1. All remotely controlled valves shall be capable of operation by a secondary, preferably manual system. 
Any automatic or radio controlled system shall have a manual override system. 
2. The secondary valve operation system may be by ROV, provided that ROV access and a suitable ROV 
are available at all stages of the operation. The time for the ROV to get to and operate the valve shall 
ensure that the valve can be operated before the flow through it is critical. 
4.4 Guiding and positioning systems 
4.4.1 General 
4.4.1.1
This sub section applies for design and verification of (object) guiding and positioning systems to be used for 
marine operations. 
Guidance note 1:
Guiding systems are often designed with a primary and secondary system. The primary system is normally 
designed to absorb possible impact energy, and provide guiding onto the secondary system. The secondary 
system is normally designed to ensure accurate and controlled positioning of the object. 
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Guidance note 2:
Additional operational specific guidance and requirements to guiding and positioning systems for lifting may be 
found in [16.14]. Requirements to positioning systems for vessels are given in Sec.17. 
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4.4.1.2
Guides and bumpers shall have sufficient strength and ductility to resist impact and guiding loads during 
positioning without causing operational problems (e.g. excessive positioning tolerances), and without 
overloading members of the supporting structure. Plastic deformation of guides and bumpers due to impact 
loads may be allowed. The possibility and consequences of multiple impacts shall be considered. 
4.4.1.3
After the design impact(s), guides and bumpers shall be able to resist loads due to the environmental conditions 
during operation, and operational loads from tugger lines, mooring lines etc. 
4.4.1.4
After the design impact(s), guides and bumpers shall also provide a positive clearance towards neighbouring 
and supporting structure, and maintain their functionality. 
4.4.1.5
DNV-RP-H102, /55/, Sec. 3.3.5 contains more recommendations and guidelines especially related to guiding 
systems used during removal of offshore platforms. 
4.4.1.6
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The stiffness of bumper and guide members should be as low as possible, in order that they may deflect 
appreciably without yielding. 
4.4.1.7
Design of bumpers and guides should cater for easy sliding motion of the guide in contact with a bumper. 
Sloping members should be at an acute angle to the vertical. Ledges and sharp corners should be avoided in 
areas of possible contact, and weld beads should be ground flush. 
4.4.1.8
As-built bumper and guide dimensions shall be documented. 
4.4.2 Characteristic loads 
4.4.2.1
Characteristic impact loads for bumpers should be based on impact and deformation energy considerations. 
Alternatively for lifts in air only, the characteristic guide loads may be calculated according to the simplified 
method in [16.14.4]. 
4.4.2.2
Realistic impact velocities, impact positions and deformation patterns shall be assumed.
4.4.2.3
Characteristic loads for the guiding and positioning phase shall be based on environmental conditions during 
operation, in addition to operational loads from tugger lines, mooring lines etc. 
4.4.2.4
Combination of horizontal and vertical loads during guiding shall be considered in the design load cases. 
Realistic friction coefficients shall be used. 
4.4.2.5
Characteristic loads for positioning lines (tugger lines, mooring lines, etc.) and attachments (padeyes, brackets 
etc.) shall be the expected maximum line tension. Possible dynamic effects shall be considered. 
4.4.2.6
The characteristic loads shall be used as the basis for determining the maximum entry speed of the lifted object 
into the guiding system. 
4.4.3 Design verification 
4.4.3.1
Structural strength of guiding and positioning systems should be verified according to Sec.5. 
4.4.3.2
The connection into the object and the members framing the bumper or guide location should be at least as 
strong as the bumper or guide. 
4.4.3.3
The bumpers and guides shall be designed as either 
• To the ASD/WSD approach LS2 or,
• To the LRFD approach ULS.
4.4.3.4
To avoid overloading the supporting structure it shall be designed either 
• To the ASD/WSD approach LS1 or,
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• To the LRFD approach ULS with an additional load factor of 1.3.
4.4.3.5
Positioning padeyes should be designed to behave in a ductile manner in case of overloading.
4.4.3.6
Submerged brackets or padeyes shall be arranged such that failure will not breach any tank or compartment. 
4.4.4 ALS conditions 
4.4.4.1
If greater impact loads (velocities) than used in the ULS verification are considered possible, the guide system 
should be verified for ALS. 
4.4.4.2
If the ALS (impact) load considered can cause failure (extensive damage) in the guiding system, it should be 
documented that installation of the object still will be feasible. Alternatively it should be possible to reverse the 
operation and return the object to a safe condition. 
4.4.5 Position monitoring systems 
4.4.5.1
The positioning equipment system accuracy and redundancy shall be specified. System accuracy shall be 
suitable for congested areas or where dimensional tolerances become tighter, e.g. for tie-ins, capture of docking 
piles. 
4.4.5.2
System redundancy shall be in accordance with [4.2.1.10] appropriate to safety criticality and operational 
criticality requirements. 
4.4.5.3
Sub-surfacepositioning of ROV’s or other targets shall interface with the surface positioning system and should 
display on the same equipment. Subsea acoustic transceivers/beacons shall be separately identifiable and on 
coordinated channels. Survey systems using line-of-sight shall recognise and cater for crossing surface vessels 
possibly occluding the system. Survey systems should be commissioned and calibrated before start of 
installation operations. 
4.4.5.4
Normally, two independent on board positioning monitoring systems (PMSs) shall be utilized for operational 
monitoring and control purposes. Both systems shall be in operation at any time, each serving as the back-up for 
the other. Each should be fed by an independent power source. 
4.4.5.5
Where underwater accuracy is important, at least one PMS shall be an underwater, hydro-acoustic reference 
system. 
4.5 ROV systems 
4.5.1 Planning 
4.5.1.1
ROV systems and tooling shall be selected based on the environmental conditions that are to be expected at the 
worksite during the planned and contingency intervention/observation tasks. 
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4.5.1.2
When planning for a subsea operation, the following ROV limitations and recommendations should be noted: 
a. Minimum practical operational depth in the expected wave conditions, also considering possible wake 
from vessel thrusters. 
b. ROV working range, i.e. maximum horizontal offset vs. available tether length, considering the worst 
expected current conditions. 
c. Planning and design of the ROV operation shall as far as possible minimise the operational influence of the 
ROV operator's skill and experience. 
d. Poor visibility due to e.g. disturbed soil conditions, stirred up by contact or thruster or tool use close to 
seabed. 
e. Access to working site.
4.5.1.3
Planned ROV downtime and statistical uptime of ROV shall be taken into consideration when establishing T , 
see [2.6.3]. If statistical data for ROV uptime is not available a conservative estimate shall be made. 
4.5.1.4
For subsea operations where the operation reference period (T , see [2.6.2])is based on using ROVs (i.e. ROV 
activities are on critical path), ROV contingencies shall be documented and available. This can include a back-up 
ROV spread on an independent system, i.e. there shall be no possible single failure identified that may cause an 
unacceptable long downtime for both ROV spreads. 
4.5.1.5
The need for backup of essential ROV tools shall be assessed, and if applicable, the time needed to switch ROV 
tools/skids between ROVs shall be considered in the planning. 
4.5.1.6
ROV tooling shall be provided with sufficient spares and back-up tooling to allow the work to proceed with 
minimum delay. 
4.5.1.7
For operations requiring assistance of both ROV(s) and diver(s), any restrictions on simultaneous working shall be 
considered and be clarified in advance. 
4.5.2 Stationkeeping and positioning 
4.5.2.1
The stationkeeping capability and manoeuvrability of the ROV during operation shall be considered. If the ROV 
is carrying equipment or is equipped with tooling packages/skids, this needs to be accounted for. 
Guidance note:
Any ROV manipulator or tooling operation that requires the pilot to actively control the position of the ROV, e.g. 
if the target is moving, during performance of the task should be avoided. See also 4.5.2.3. 
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4.5.2.2
The required ROV thrust capacity shall be documented by verified capability plots (if available) and/or detailed 
calculations considering: 
• maximum current speeds at applicable depth(s), see 3.4.3. 
• approprate drag areas and -factors for ROV, cable and any tools
• all relevant relative ROV and current directions
• need for spare capacity, to be at least 30% for crucial ROV operations. 
Guidance note:
If detailed calculations are not made the horizontal current force on the ROV and the submerged cable may be 
taken as: 
[kN] 
where
POP
R
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d = diameter of submerged cable [m]
l = projected length of submerged cable [m]
A = projected cross sectional area of ROV including any tools [m ]
v = maximum current velocity [m/s]
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4.5.2.3
Grab bars to aid ROV positioning for manipulative or observation tasks should be provided where critical path 
ROV operations are planned. 
4.5.3 Testing 
4.5.3.1
For complex and critical stages of the installation that are dependent on ROV operations, Client/Contractor shall 
demonstrate ROV capability of executing the planned intervention. This can be demonstrated by used of 3D 
models, mock-up tests, previous experience, etc. 
Guidance note:
This may involve the manufacture of mock-ups. If mock-ups are used, great care shall be taken to ensure that the 
mock-ups replicate the actual item. 
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4.5.3.2
System Integration Testing should be carried out onshore to prove that the integration of all components and 
tooling can be achieved. 
4.5.3.3
Dry tests and FAT should be carried out for critical and complex systems, the failure of which would result in 
significant and unacceptable schedule delay. 
4.5.3.4
Before acceptance of ROV operations, maintenance records and dive logs for each ROV should be submitted. 
Sufficient spares should be available. 
4.5.4 Launch and recovery system 
4.5.4.1
Once installed, the launch and recovery system (LARS) shall be load tested according to the applied 
design/certification standard. 
4.5.4.2
ROV launching and recovery restrictions shall be defined based on the capacity of the launch and recovery 
system, including capacity of the umbilical. In addition any restrictions related to operational aspects need to be 
considered. 
Guidance note:
The following should be considered as rough guidance when establishing the ROV restrictions:
• The launch and recovery system should incorporate a (guide/cursor) system that ensures adequate 
clearance with vessel side during lowering through the splash zone in the limiting wave conditions. 
• Overboard launching and retrieval of large ROV's is not generally recommended to take place in sea 
states exceeding 2.5-3.0 m (H ) if the ability to operate in a safe manner under more severe conditions has 
not been documented. Higher waves may be applicable if the launch and recovery always may take place 
on leeward, for Moon-pool ROV operations and if heavy weather side rail systems are used. 
• High wind speeds, and operational aspects (e.g. risk of entanglement) may also be critical. 
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4.5.4.3
cab
cab
ROV
2
cur
s
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The over-boarding system shall be safely operated within its intended design limit and due consideration of ROV 
recovery needs to accounted for in the definition of the weather criteria. 
4.5.4.4
Launch and recovery shall as much as practically possible take place at safe distance from sensitive subsea 
infrastructure. See [5.6.6.6]. 
4.5.4.5
A tether management system (TMS) should be used in deep water sites to ease the deployment of the ROV to 
the worksite. The tether shall be of sufficient length to allow the ROV to get from the TMS to the worksite. 
4.5.5 Monitoring 
4.5.5.1
Video monitoring of all subsea operations should in general be provided, e.g. ROV, diver-operated, etc. Any 
critical part of the operation should be performed with such monitoring. 
4.5.5.2
All diving and complex Work-ROV operations should be monitored by independentROV with monitoring as its 
only task in the period it is carrying out such critical monitoring. 
4.5.5.3
The ROV used for monitoring subsea operations should, as far as practically possible, be operated from the 
installation vessel. 
4.5.5.4
If the ROV operation has to be performed by a vessel other than the installation vessel, the stability and reliability 
of the video-link system between the vessels shall be proven under the given conditions. 
Guidance note:
Some operations can require a large horizontal distance between the installation vessel and the observation 
ROV, thus necessitating a separate ROV vessel. The video-link should be tested before start of operation. 
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4.5.5.5
Means for locating and tracking of the ROV from the surface are required for navigational purposes and 
emergency recovery. 
4.5.6 Human factors 
4.5.6.1
The feasibility of subsea operations often relies on the correct completion of tasks by ROV - it should therefore 
be ensured that ROV operators have the necessary experience and skills. 
4.5.6.2
If complex operations reliant on the skill of the ROV operator alone cannot be avoided, ROV operator experience 
shall be evaluated. Training sessions specially adapted for the proposed operation can be appropriate. 
4.5.7 Deepwater ROV operations 
4.5.7.1
ROV equipment capacities shall be chosen to suit the relevant depth and consider the following: 
• Both the ROV and any ROV tooling should be “depth rated”, and their stated depth limitation should not 
be exceeded. 
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• General wear on the complete ROV spread during deep water operations is more extensive than during 
moderate depth operations, it is important therefore that all required maintenance is done before 
operation. 
• During deep water operations special attention shall be given to lubrication systems which can be affected 
by the external water pressure. 
4.5.7.2
Current forces acting on the umbilical and ROV shall be defined, see guidance note in [4.5.2.2]. 
4.5.7.3
Potential effects due to resonance in wires, cables, umbilicals, etc. shall be investigated and accounted for in the 
design. 
SECTION 5 Loading and structural strength 
5.1 Introduction 
5.1.1 General 
5.1.1.1
This section addresses loading categorisation, load effects, load cases and load combinations. 
5.1.1.2
The requirements for structural strength are given, mainly related to steel structures. For structures of other 
materials, adequate safety levels shall be achieved by use of recognized standards. 
5.1.2 Scope 
5.1.2.1
This section presents the requirements for strength checking of steel structures using both Allowable Stress 
Design (ASD) / Working Stress Design (WSD) and Load and Resistance Factor Design (LRFD). Alternatively, 
probabilistic methods can be used. 
5.1.2.2
The ASD/WSD and LRFD checks have differing inherent levels of safety. To compensate, this Standard has 
differing requirements for the design loading. It is therefore important that the applied environmental loading is 
determined using the return period applicable to the checking method selected. 
5.1.3 Revision history 
5.1.3.1
This section replaces the applicable sections of the legacy GL Noble Denton Guidelines and legacy DNV-OS-H-
series standards. 
5.2 Design principles 
5.2.1 Introduction 
5.2.1.1
The object subject to marine warranty survey, together with the associated equipment shall be shown to possess 
adequate strength to resist the loads imposed during the marine operation. 
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5.2.1.2
The overall design shall be performed with due consideration to the execution of marine operations. 
5.2.1.3
Structures shall be robustly designed such that an incident does not lead to consequences disproportional to the 
original cause. 
5.2.1.4
Simple load and stress patterns shall be aimed for in the design. 
5.2.1.5
Structural elements should be fabricated according to the requirements given in DNVGL-OS-C401, /26/, or 
another recognized standard. 
5.2.1.6
Structural components and details should be designed so that the structure behaves, as far as possible, in a 
ductile manner. 
Guidance note:
A structure or a structural element, can exhibit brittle behaviour even if it is made of ductile materials e.g. when 
there are sudden changes in section properties, when exposed to low temperatures. 
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5.3 Specific design considerations 
5.3.1 Connections 
5.3.1.1
Connections should be designed with smooth transitions and proper alignment of elements. Stress 
concentrations should be avoided as far as possible. 
5.3.1.2
The transmission of tensile stresses through the thickness of rolled steel elements (plates, beams etc.) should be 
avoided unless materials with proven (tested) z-quality are applied. Alternatively, the material can be subject to 
non-destructive testing (NDT) using UT to demonstrate that it is free of laminations, see [5.10.2.3 5)]. 
5.3.1.3
Structural details above the still water level shall be so arranged that water will not be trapped in the structure if 
this can cause damage such as e.g. rupture due to freezing of the water, when the operation is in an area and 
season when this can occur. 
5.3.2 Penetrations 
5.3.2.1
The object shall be reinforced as necessary in the area adjacent to any penetrations (e.g. for risers or J-tubes) 
below the water line against hydrostatic pressures and against accidental impact from dropped objects and 
vessel impact if likely at any draught. 
5.3.2.2
Penetrations shall be positively sealed to prevent the ingress of water whilst the structure is afloat. 
5.3.3 Doubler plates 
5.3.3.1
Doubler plates are generally recommended for use:
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• When attaching seafastenings or sacrificial anodes to permanent steel work subject to fatigue or if the 
permanent structure could be damaged when the attachments are burnt off after use. 
• To avoid welding onto other welds.
5.3.3.2
Doubler plates are generally NOT recommended for use when tension can cause overstress in the doubler plate 
or the structure to which it is attached. 
5.3.4 Tension connections 
5.3.4.1
Where tension connections to a vessel deck are required, attention shall be given to the connection between the 
deck plate and underdeck members. In cases of any doubt about the condition, an initial visual inspection should 
be undertaken, to establish that fully welded connections exist, and that the general condition is fit for purpose. 
Further inspection may be required, depending on the stress levels imposed and the condition found. See also 
[5.10.2.3 5)] regarding through-thickness properties of the deck plate. 
Guidance note:
The welds between vessel deck plates and under deck stiffeners/bulkheads (including cut out infills) are normally 
small and can limit the capacity. 
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5.3.5 Bolted connections for seafastening 
5.3.5.1
Appendix [E.2] gives the requirements for bolted connections for seafastenings which involving cyclic loading 
due to the dangers of progressive collapse. 
5.3.6 Light-weight metallic and composite structures 
5.3.6.1
The designers or manufacturers shall specify any handling/connection requirements which shall appear in the 
relevant procedures and towing/transport manuals. 
Guidance note:
Tugger line systems are especially important when handling light-weight alloy, composite and other items in 
order to avoid any impact with seafastening,grillage or offshore structures which could cause plastic 
deformations. 
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5.3.6.2
The structural strength of objects of innovative design and/or material shall be documented.
Guidance note:
Particular attention should be given to local strength in way of supports, seafastening etc. 
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5.3.7 Compressed air 
5.3.7.1
Compressed air may be used to resist hydrostatic head on internal or external walls during ballasting, for 
reducing draught, or for reducing overall bending moments by air cushions in skirt cells under well controlled 
conditions. However its absence should not, in general, result in structural collapse i.e. it should be used only to 
increase structural safety factors. 
5.3.7.2
Where the requirements of [5.3.7.1] cannot be met, then a risk assessment shall be carried out to determine 
possible causes and probabilities of loss of compressed air. Mitigating measures to reduce the risks to an 
acceptable level shall be agreed with the MWS company. 
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5.3.7.3
Some practical considerations on the use of compressed air are given in [12.6.2]. 
5.3.8 Inspection 
5.3.8.1
Sufficient access for inspection, maintenance, and repair shall be provided during planning of the operation. 
5.3.8.2
Instrumentation (monitoring) can be used as a supplement to other inspection, see [2.9]. 
5.3.9 Existing structures 
5.3.9.1
Strength calculations for marine operations often include the verification of existing steel structures of e.g. 
barges, other vessels and objects for dismantling. The calculations shall account for any reductions in the design 
capacity. Examples of possible causes include: 
• corrosion
• damage
• modifications not shown on drawings.
5.3.9.2
Existing structures should normally be inspected in order to assess possible reductions in the design capacity, 
see [5.3.9.4], [5.9.8.4], [5.10.2.2], and [5.10.2.3 5)]. See DNV-RP-H102, /55/ for further guidance on existing 
structures and their inspection. 
5.3.9.3
Project related strength verifications of vessels should normally be carried out conservatively with either the as-
built thickness reduced to account for possible corrosion or based on detailed inspections including thickness 
measurements. Where the thickness is reduced to account for corrosion the thickness used in calculations should 
be the thickness indicated on the as-built drawings less the vessel’s class corrosion allowance, or reduced by 0.2 
mm per year from each side. For new vessels with a proper corrosion protection system, e.g. painting or coating, 
no thickness reduction need to be considered for the first five years of the vessel’s life. 
Guidance note:
Typical corrosion allowance requirements can be found in the DNV GL Rules for classification: Ships, /35/, Jan 
2015, Pt.3 Ch.3 Sec.3. Normally a total thickness allowance of 3 mm is applicable for the top 1.5 m of ballast 
tanks. 
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5.3.9.4
Weld capacity should be calculated according to [5.9.7.1] for ASD/WSD or [5.9.8.4] for LRFD, as applicable. 
Guidance note:
When checking vessel welds the following should be noted:
a. Class acceptance for these welds can be required, especially for new/reinforced welds.
b. All loads (force components) normal to the deck plate should generally be considered transferred to the 
under deck welds. However, when the force is only compressive, i.e. there is no tension force in any load 
combination, this force component may be assumed to be transferred through direct contact between the 
deck plate and the web frames/bulkheads, and the weld may be checked for shear stress only, see item f). 
If the force varies between compression and tension, the weld should be able to transfer also the 
compression force in order to ensure intact welds, unless the capacity of the seafastening system is 
documented in ALS assuming that the connection under consideration is broken. 
c. All loads (force components) parallel to the deck plate can be disregarded, see however item f). 
d. The dispersion angle through the deck plate should be taken as maximum 45° unless a greater dispersion 
can be justified. 
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e. Size reduction due to possible corrosion should be considered. If not otherwise documented the size 
should be as shown on the drawing less the Class corrosion allowance. 
f. Note that shear stress in stiffener/girder welds due to local bending/shear in these should be included in 
the equivalent stress (the effects due to global vessel behaviour can be ignored). 
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5.3.10 Protection against accidental damage 
5.3.10.1
The structure shall be protected against accidental damage by application of the following two principles: 
• reduction of damage probability
• reduction of damage consequences.
5.3.10.2
If damage to piping, equipment, structures, etc. could lead to severe consequences (e.g. accidental flooding, 
explosion, fire or pollution) such items shall be protected to minimise the risk of accidental damage. 
Guidance note:
Protection may be established by methods such as providing a sheltered location, by local strengthening of the 
structure, or by appropriate fender systems. 
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5.4 Testing 
5.4.1 General 
5.4.1.1
Testing can be used in order to establish or verify design parameters. Material and weld testing should be 
carried out according to a relevant recognized standard, e.g. DNVGL-OS-C401, /26/, see also [5.10] which 
summarises key requirements. 
5.4.1.2
Adequate and reliable test data should be used to verify/correlate values that are considered unreliable based 
on theoretically calculations only. This is particularly relevant for geometrically complex structures and for new 
design or operational concepts. 
5.4.1.3
For marine operations, such (project) specific testing is normally most relevant to determine or verify: 
• response, e.g. motions by model testing,
• loads, e.g. by direct measuring of loads in model tests and
• resistance, e.g. by load testing or testing of friction.
5.4.2 Model testing 
5.4.2.1
Model testing is most frequently used for the determination of response and loading effects but can also be used 
for determination of structural resistance. 
5.4.2.2
Model tests should be carried out according to a verified test program/procedure using: 
• models representing the object(s), vessel(s) and real conditions as accurately as required, 
• qualified test personnel, 
• adequate testing facilities, and
• calibrated monitoring equipment with sufficient accuracy.
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5.4.2.3
Normally the testing should be combined with theoretical calculations. 
5.4.2.4
The laws of similarity shall be considered in order to ensure that the quantities measured in the model test can 
be correctly transformed. 
5.4.2.5
Effects that can influence the measured quantities and that are not represented in the model test shall be 
identified and the consequences of these effects should be evaluated. 
Guidance note:
For example, the correct relative stiffness (of vessels/structures) will normally not be obtainable in model tests 
and effects of this on the results should be evaluated. 
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5.4.3 Full scale load testing 
5.4.3.1
Full scale load testing should be carried out according to agreed procedures.
5.4.3.2
Requirements for standardised load testing, e.g. of lifting appliances,are not described in this standard. Such 
testing should be carried out as described in the relevant standard, e.g. DNV 2.22, /16/, and DNV 2.7-3, /17/. 
5.4.3.3
Full scale load testing may be carried out by loading test pieces to destruction. The characteristic strength 
should normally be defined based on the 5 or the 95 percentile of the test results, whichever is the most 
conservative. 
5.4.3.4
If sufficient design documentation is not available to verify the strength (capacity) of an item, it can be acceptable 
to document the strength of the item by means of a load test. 
Guidance note:
Typical items for which this type of testing could be applicable include:
• Anchors for which no holding power calculations have been carried out.
• Shore bollards without relevant certificates or where the underground design and workmanship is not 
documentation. 
• Holding power of clamps or other types of connections.
• Local soil capacity (deflection), e.g. of load-out tracks.
• Existing (steel) structures with no/limited inspection access. 
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5.4.3.5
For such tests the load should normally be at least 0.9 times the maximum design load (i.e. including load factor) 
for the item. All relevant load directions should be tested. 
5.4.3.6
A thorough inspection shall be carried out of items that have been subject to testing. Defects that could reduce 
the strength (capacity) shall not be allowed. 
5.4.4 Testing of friction 
5.4.4.1
Testing may be carried out in order to establish applicable friction coefficients. The testing conditions should 
represent the expected friction surface and load intensity as close as possible. 
th th
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5.4.4.2
In marine operations the dynamic friction coefficient will normally be the most relevant and testing of this should 
hence be included unless it is not needed for the particular application. 
5.4.4.3
Where testing is carried out, a detailed test procedure shall be documented. 
Guidance note:
The test procedure should consider the following:
a. Possible variations in applicable conditions (e.g. wet and dry surfaces). See [5.4.4.1] and [5.4.4.2]. 
b. Dynamic friction, if applicable, should be tested and measured by a recognised method. 
c. The characteristic friction coefficient should be defined based on the 5 or the 95 percentile confidence 
level of the test results, whichever is the most conservative. 
d. At least 5 test pieces should be made, and each tested at least twice for each actual condition. 
e. The design friction coefficient is calculated using the characteristic friction coefficient and an appropriate 
material factor. See [5.9.8.6], [5.9.5.3] and [5.9.6.2]. 
f. Where fewer tests are performed e.g. because of the scale, more conservative material factors should be 
used. 
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5.5 Load categorisation 
5.5.1 Introduction 
5.5.1.1
This section defines load categories and describes loads of general interest for marine operations. 
5.5.1.2
The appropriate characteristic value should be defined (calculated) for all relevant loads. 
5.5.1.3
More detailed descriptions of the loads to be considered are given for each type of marine operation/object 
type in Sec.6 to Sec.18. 
5.5.1.4
See [5.6] for load combinations, [5.7] for the failure modes to be considered, [5.8] for guidance on analytical 
models and [5.9] for strength assessment. 
5.5.2 Load categories 
5.5.2.1
Loads and load effects shall be categorised as follows:
• Permanent Loads - G
• Variable Functional Loads - Q
• Deformation Loads - D
• Environmental Loads - E
• Accidental Loads - A.
5.5.2.2
The characteristic values of loads shall be selected as indicated in Table 5-1 for all applicable loads. 
Table 5-1 Characteristic load selection
Load category 
Limit states – Temporary design conditions 
ULS FLS
ALS
SLSIntact 
structure
Damaged 
structure
th th
1)
2)
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Variable (Q)
Specified
value 
Specified
load history 
Specified value(s) 
Environmental (E) – 
Weather restricted
Specified 
value
Specified 
load history
NA
Specified value(s)
Environmental (E) – 
Weather unrestricted 
Operations 
Based on 
statistical 
data 
Expected 
load history
Based on statistical data & 
Accidental (A) NA NA
Specified 
value
NA NA
Deformation (D)
Expected 
extreme 
value
Expected 
load history
Specified value(s)
Notes:
1. See [5.5.3] to [5.5.7] for definitions of load categories 
2. See [5.9.1.3] for definitions of limit states. 
3. The specified value (load history) shall, if relevant be justified by calculations. See also [5.6.6]. 
4. See [2.6.6]
5. See Sec.3. 
6. Joint probability of accident and environmental condition could be considered.
5.5.3 Permanent loads (G) 
5.5.3.1
Permanent loads are loads which will not be moved or removed during the phase of the marine operation being 
considered. Such loads can be due to: 
• weight of stationary structures
• weight of permanent ballast and equipment that cannot be removed
• external/internal hydrostatic pressure of permanent nature
• pretension.
5.5.3.2
Characteristic permanent loads shall be based on reliable data. For weight see [5.6.2]. 
5.5.4 Variable functional loads (Q) 
5.5.4.1
Variable functional loads are loads that can be moved, removed or added. Such loads can be due to: 
• operation of winches
• pull/push forces
• weight of moving structures
• loads from adjacent vessels
• ballasting
• operational impact loads
• stored materials, equipment or liquids.
5.5.4.2
Characteristic variable functional loads shall be specified with maximum and minimum values, which shall be 
considered as necessary to determine the worst case(s). 
5.5.5 Deformation loads (D) 
5.5.5.1
Deformation loads are associated with inflicted deformations. Such loads can be caused by: 
• installation or set down tolerances
• barge hull beam global deformations caused by moving ballast water (or temperature)
2) 2)
2)
4) 5)
5) 6)
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• structural restraints between structures
• differential settlements
• temperature deformations.
5.5.5.2
Characteristic deformation loads shall be maximum or minimum specified values, which shall be considered as 
necessary to determine the worst case(s). The specified values shall, if applicable, be based on results from 
analysis considering extreme conditions. 
5.5.6 Environmental loads (E) 
5.5.6.1
All loads caused by environmental phenomena shall be categorised as environmental loads. Such loads can be 
due to phenomena including: 
• wind
• waves
• current
• storm surge
• tide
• ice.
5.5.6.2
Where applicable, see [5.6.11], seafastening (and grillage/cribbing) reactions due to barge hull beam global 
deformations caused by waves should be considered as environmental loads. See also [5.6.17]. 
5.5.6.3
Gravity load components caused by the roll and pitch angles of a floating object due to wind and waves, shall be 
categorised as environmental loads. 
5.5.6.4
The environmental design loads shall be calculated based on a process involving, as applicable: 
• definition of characteristic conditions - see [2.2.7]
• calculation of characteristic loads – see [5.5] and [5.6]
• load analysis - see [5.6.2] to [5.6.11]
• motion analysis - see [5.6.12]
• selection of load cases - see [5.6.13]
• load factors - see [5.9]. 
5.5.7 Accidental loads (A) 
5.5.7.1
Accidental loads are loads associated with exceptional or unexpected events or conditions. Such loads can be 
due to:• collisions from vessels
• dropped objects
• loss of hydrostatic stability
• flooding
• loss of internal pressure.
5.5.7.2
Characteristic accidental loads shall be based on realistic accidental scenarios. See also [5.6.6]. 
5.6 Loads and load effects (responses) 
5.6.1 General 
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5.6.1.1
This section describes the loads and load effects that should be considered. 
5.6.2 Weight and centre of gravity (CoG) 
5.6.2.1 Introduction 
1. For calculation purposes, conservative values of weight and CoG should be used.
2. Weight control shall be performed by means of a well-defined and documented system, complying with 
ISO 19901-5 – Weight control during engineering and construction, /99/. 
3. ISO 19901-5 states (inter alia) that:
◦ “Class A (weight control) will apply if the project is weight or CoG-sensitive for lifting and marine 
operations or during operation (with the addition of temporaries), or has many contractors with 
which to interface. Projects may also require this high definition if risk gives cause for concern”. 
◦ “Class B (weight control) shall apply to projects where the focus on weight and CoG is less critical for 
lifting and marine operations than for projects where Class A is applicable”. 
◦ “Class C (weight control) shall apply to projects where the requirements for weight and CoG data 
are not critical”. 
4. Class A weight control shall apply unless it can be shown and agreed with the MWS company that a 
particular structure and all its marine operations are not weight or CoG sensitive. 
5. Weight reports should be issued in accordance with Section 6 of /99/. Contents and format of weight 
reports that are not in accordance shall be agreed with MWS company at an early stage of the project. 
5.6.2.2 Weight considerations 
1. An upper bound design weight (W ) shall be defined for all operations. Where the minimum weight could 
be critical in an operation e.g. voyage motions, a lower bound design weight (W ) shall be defined. 
Guidance note 1:
The upper/lower bound design weights are normally defined to cover the expected range of weights in 
the weight report with additional margins to account for uncertainties during the design process and the 
factors in [2)] or [5.6.2.2 3)] for unweighed and weighed objects respectively. 
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Guidance note 2:
Where a Not To Exceed (NTE) weight has been defined and used as the upper bound design weight the 
actual maximum permissible value is less than the NTE weight. 
In addition to any in-place considerations, the following can control the NTE weight:
◦ Draught and stability for tow-out, towages, mating operations and installation;
◦ Allowable stresses in the structure for marine operations;
◦ Limitations due to crane, load-out trailers, other equipment or ground-bearing capacity.
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2. Where an object (excluding piles) is not to be weighed, the following shall be true for the as-built weight 
report: 
W ≤ W /γ
W ≥ W γ (where applicable)
Where:
W
= Factored weight in weight report
W
= Base weight in weight report
W = Upper bound design weight
W = Lower bound design weight
γ = Unweighed object weight margin factor as per Table 5-2
3. Where an object (excluding piles) is to be weighed, the following shall be true for the final weighed 
condition corrected for any post weighing modifications: 
W ≤W /γ
W ≥ W γ (where applicable) 
Where:
W = Net weight in weight report
W = Upper bound design weight
W = Lower bound design weight
γ = Factor to account for weighing equipment inaccuracy i.e. ( )
ud
ld
Report, Factored ud Weight
Report, Base ld Weight 
Report, 
Factored
Report, 
Base
ud
ld
Weight
Weighed ud Weighing
Weighed ld Weighing
Weighed
ud
ld
Weighing
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4. The weight contingency factors for piles shall be agreed with the MWS company and shall consider the 
following as a minimum: 
◦ plate thickness tolerance
◦ fabrication tolerances.
Table 5-2 Unweighed object weight margin factors
Weight Class
(as defined by ISO 19901-5, /99/)
γ
A 1.05
B and C 1.10
5.6.2.3 Centre of gravity factors 
a. For weight Class A and B structures, see [5.6.2.1 3)], a CoG envelope shall be applied to allow for CoG 
inaccuracies. For Class C structures a CoG envelope is recommended. 
b. The size of the CoG envelope should reflect the operational and structural sensitivity to CoG variations and 
the most conservative centre of gravity position within the envelope should be taken. 
Guidance note 1:
For early design stages, too small an envelope should be avoided and envelope sizes should generally be 
no less than 0.05L x 0.05B x 0.05H, where L, B and H are the Length, Breadth and Height of the structure. 
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Guidance note 2:
For operations with a linear relation between shift in CoG and resulting load effects, or operations less 
sensitive to CoG shifts, the inaccuracy in estimated CoG may alternatively be accounted for by an 
inaccuracy factor applied to the weight. This factor should normally not be taken less than 1.05. 
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c. For Class C, if a CoG envelope is not used then a CoG inaccuracy factor of 1.10 shall be applied to the 
weight. Where it can be documented that a lower CoG inaccuracy factor is applicable, this should be 
agreed with the MWS company. 
d. The CoG contingency factors for piles shall be determined considering the pile length and the plate 
manufacturer’s plate thickness tolerance specification. 
e. Normal weighing operations can be used only to identify the CoG position in a horizontal plane. 
Consequently, inaccuracies in the vertical CoG position should be specially considered for operations that 
are sensitive to the vertical CoG position. If applicable the vertical CoG can be verified by means of an 
inclining test (see [2.10.5]). 
5.6.2.4 Weight control 
a. The actual weight and CoG position shall be determined by weighing unless agreed otherwise with MWS 
company. 
Guidance note:
Gravity based structures and launched jackets are generally excluded from being weighed.
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b. A weighing procedure for the structure shall be produced and include the specification, including 
accuracy, for all equipment. The accuracy of the weighing equipment shall be certified by a Competent 
Body. The weighing should preferably be carried out a minimum of 3 times with the load cells 
interchanged between each of the weighing operations. 
c. Before any structure is weighed, a predicted weight and CoG report shall be issued, so that the weighed 
weight and CoG can immediately be compared with the predicted results. The cause(s) of significant 
deviations between the weighed and predicted results (both weight and CoG) shall be investigated and 
reported. 
d. Where weight is added to/removed from the structure after weighing, a weight control system shall be 
adopted to ensure that the weight and CoG details based on the weighing are updated with any changes. 
The weight changes due to items that are added and removed shall include their weighing contingency 
factors. 
e. The final calculated or weighed weight and CoG values shall be documented. Where the calculated or 
weighed weight, including weighing and contingency factors, or the CoG is outside the design values 
considered, the effects of the deviations shall be quantified and the operational procedures and 
documents modified as required. 
f. When the installation of a large number of nominally identical items is to be approved, the weight control 
programme should bedocumented to show the effects of all potential variations on the final weights and 
the results documented by a competent person. 
Weight 
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g. See [18.2.1.2] for weight control for decommissioning/removal. 
5.6.2.5 Buoyancy 
a. Buoyancy (hydrostatic external load) normally counteracts another load and shall be categorised 
accordingly. 
b. Where the buoyancy or distribution of buoyancy is critical to the marine operation, the dimensional and 
buoyancy control and monitoring shall be maintained to an appropriate degree of accuracy. 
c. The buoyancy of the object and the position of the centre of buoyancy should be determined on the basis 
of an accurate geometric model. 
d. Characteristic buoyancy loads should be based on maximum and/or minimum expected values.
e. Buoyant cargoes, particularly where the buoyancy contributes to stability requirements, shall be 
adequately secured against lift-off unless it can be shown that lift-off will not occur. 
5.6.3 Wind loads 
5.6.3.1
Wind loads shall be calculated based on the characteristic wind speed, see Sec.3, and recognised calculation 
methods. 
5.6.3.2
Wind induced loads shall be based on projected area. The total wind load shall consider both lateral and parallel 
load components. 
5.6.3.3
The possibility of lift effects and their magnitude shall be considered.
5.6.3.4
The gravity components due to wind induced heeling shall be considered.
Guidance note:
DNV-RP-C205, /46/, gives further information with respect to shape coefficients as well as to effects of wind 
direction relative to member, solidification and shielding. 
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5.6.4 Current loads 
5.6.4.1
Current loads shall be calculated based on the characteristic current velocity, see Sec.3, and recognised 
methods. 
5.6.4.2
The increase in current velocities/loads due to shallow waters or narrow channels shall be considered. 
Guidance note:
DNV-RP-C205, /46/, gives further information with respect to shape coefficients as well as to effects of flow 
direction relative to member, solidification and shielding. 
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5.6.5 Wave-current loads 
5.6.5.1
Combined wave-current induced drag loads shall be calculated considering the vector sum of the current and 
wave particle velocities. 
5.6.5.2 First order wave loads 
a. Wave loads should be estimated according to a deterministic or stochastic design method. A wave period 
range according to [3.4.11.5] and [3.4.11.2] should be investigated. 
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Guidance note:
If any responses are found governing for the response should be checked in these 
areas with 
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b. Wave loads shall be determined using methods applicable for the location and operation, taking into 
account the type of structure, its size and shape and its response characteristics. 
c. The effects of wave elevation shall be evaluated, and if necessary included in the design. 
d. Wave slamming, see [5.6.5.4], hydrodynamic and hydrostatic loads on members protruding over the 
vessel side shall be considered. The effect of such loads on the motion characteristics and on the 
seafastenings and grillage/cribbing shall be taken into account. 
5.6.5.3 Second order wave loads 
a. Second order wave drift forces can be important in the design of some marine operations. The effects of 
second order drift forces shall be considered in these cases, which include large volume structures, 
mooring and positioning systems, towing resistance estimates, etc. Second order wave loads consist of 
mean wave drift forces and slow varying wave drift forces. 
b. Long period responses excited by slow drift forces shall be investigated.
5.6.5.4 Slamming loads and breaking waves 
a. Cargo overhangs and elements in the splash zone or overhanging the periphery of the floating body shall 
be investigated with regards to possible slamming loads and/or immersion. 
b. The effect of shock pressures on surfaces in the splash zone, caused by breaking waves, shall be 
investigated for conditions up to the design sea state for all headings. 
c. Loads due to slamming and breaking waves should normally be calculated according to DNV-RP-
C205, /46/. 
Guidance note:
Further information regarding slamming loads and breaking waves can be found in DNV GL Rules for 
classification: Ships /37/ Pt.3 Ch.10 and NORSOK N-003, /111/. 
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5.6.5.5 Green water 
a. The possible effects of green water (extensive amounts of water on deck due to waves), shall be 
considered. The effects on both the structure and stability (weight and free surface) shall be investigated. 
Guidance note:
See e.g. NORSOK N-003, /111/, for further information regarding green water effects. Design forces for 
sea pressure from green water can be based on requirements for deck houses, see DNV GL Rules for 
classification: Ships, /36/, Pt.3 Ch.4 Sec. 5.3. 
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b. Deck cargoes vulnerable to damage from green water on deck should be protected by breakwaters or 
increasing freeboard. 
5.6.5.6 Swell 
a. The effects of loads and motions due to swell shall be considered. See [3.4.14] and [5.6.18]. Swell can be 
governing for operations designed for small irregular waves (e.g. weather restricted tows). In such cases 
swell operational limits and forecasting shall be established. 
5.6.6 Accidental loads 
5.6.6.1
Accidental loads should be defined based on relevant accidental scenarios. In many cases the probability of 
accidental scenarios can be reduced to a level such that there is no need to consider them further. 
5.6.6.2
The accidental load design principles indicated in DNV-OS-A101, /40/, should be considered as applicable for 
the planned marine operation. DNVGL-RP-C204, /31/, gives further guidance related to design philosophy and 
calculation of relevant accidental loads due to e.g. collisions and dropped objects. 
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5.6.6.3
Load effects due to all possible accidental scenarios/conditions shall be considered. Accidental cases and 
contingency situations may be defined or excluded based on results from HAZOP’s or risk 
evaluations/assessments. 
5.6.6.4
DNV-OS-A101, /40/, is, in general, based on annual probabilities, whilst this Standard is based on probability per 
operation. This can be considered when the (magnitude of) applicable accidental loads are defined. However, 
unless a justification for lower loads is documented the loads indicated in DNV-OS-A101, /40/, should be 
considered. 
5.6.6.5 Vessel collision 
a. Characteristic collision loads shall be estimated from energy considerations. Estimates of the collision 
energy should be based on reasonable assumptions of possible collision scenarios, velocities, directions, 
ship or object type, size, mass and added mass. Estimates of deformation energy should be based on the 
most likely impact points and probable deformation patterns. 
b. The behaviour of the vessels or structures during the impact, and thus the distribution of impact energy 
between kinetic rotation and translation and deformation energy, should be considered by dynamic 
equilibrium or energy considerations. 
c. Local effects (deformation, damage, etc.) and global load effects (acceleration, global stress, etc.) shall be 
considered. 
Guidance note:
In some cases collisions will have been covered under the design and classification of the vessel. 
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---5.6.6.6 Dropped objects 
a. Loads caused by dropped objects can be relevant for some ALS load cases. The characteristic load due to 
a dropped object should be based on the weight of objects that could fall and their potential fall height. 
b. For objects falling through water maximum possible impact velocity should be considered. The maximum 
velocity is normally the terminal (free fall in water) velocity. See DNV-RP-H103, /56/, [4.7.3.5] and DNV-RP-
F107, /52/, [5.3] for guidance. 
c. Loads on subsea items due to dropped objects may be ignored if operations that could cause dropped 
objects are carried out at a safe distance. The safe distance should be calculated considering the 
maximum possible dispersion angle for each type of object falling through the water. The effect of current 
should be considered. Risk analysis may be used in order to eliminate physical possible high dispersion 
angles by showing that the risk of hitting specified critical locations is acceptably low for such high angles. 
See DNV-RP-F107, /52/, for further risk assessment guidance. If detailed assessments are not made, the 
safe distance can normally be taken as the larger of 50 meters or that determined from a dispersion angle 
of 20° to the vertical. 
5.6.6.7 Other causes 
a. Other relevant accidental loadings shall be considered. These can include, but are not limited to, cases 
such as: “one line broken”; “one compartment damaged”; malfunction of critical systems e.g. heave 
compensation, leaking valves; erroneous operation e.g. the use of the wrong valve; unexpected values of 
parameters e.g. deformations, friction, vessel GM, tidal variation, weights & CoG’s, etc. 
b. The static loads resulting from any one compartment damage, as described in [11.10.4] to [11.10.7], shall 
be considered and, if significant, designed for as a LS2 or ULS case. 
5.6.7 Dynamics 
5.6.7.1
The potential for dynamic response shall be investigated, and the effects shall be included in the design analysis 
when they are of significance. Dynamic response is typically caused by wave forces, wind loads (gusts), vortex 
shedding in air or water, slamming loads, etc. 
5.6.7.2
Dynamics shall be investigated by recognised methods using realistic assumptions for the natural period, 
damping, material properties etc. 
5.6.7.3
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The response to dynamic effects e.g. structural stress and deflections can be relevant for all Limit States. 
5.6.7.4
Means of determining whether vortex shedding could be critical for any particular member are contained in 
Section 9 of “DNV-RP-C205 Environmental Conditions and Environmental Loads”, /46/ and Section 7.2 of 
“Dynamics of Fixed Marine Structures” - Barltrop and Adams, /122/. 
5.6.8 Non-linearities 
5.6.8.1
Non-linear effects shall be considered in cases where these significantly influence the estimated responses. Non-
linear effects are typically caused by: 
• non-linear materials
• non-linear geometry (large-displacement effects)
• non-linear damping
• non-linear combination of load components or response components
• wave elevation e.g. due to wave-in-deck, non-linear effects of drag-loading (especially with current), etc.. 
5.6.8.2
Non-linear load effects due to combinations of environmental loads should be taken into account e.g. wave-
current drag forces are a function of the square of the sum of the wave and current particle velocities. 
5.6.9 Friction 
5.6.9.1
Possible unfavourable effects of friction shall be considered. Well documented favourable effects of friction may 
be included in the design. 
5.6.9.2
A friction coefficient range, i.e. both a maximum and a minimum friction coefficient, should be considered in the 
design calculations or it should be proven that a conservative minimum (or maximum) coefficient suffices. 
5.6.9.3
The characteristic friction coefficient range shall be defined according to recognised industry standards or tests, 
see [5.4]. Indicative operation-specific values are given Table 10-2, [11.9.2], Table 11-8, Table 11-20, Table 13-5
and in DNV-RP-H102, /55/, Table 2-4. For soil-material interfaces, guidance is provided in DNV-RP-F109, /53/, 
Section 3.4.6 and DNV-RP-F105, /51/, Section 7. Pipe-Soil Interaction. 
5.6.9.4
The lower bound design friction coefficient (μ ) shall be the lower bound characteristic value (μ ) divided by a 
material factor. 
5.6.9.5
The upper bound design friction coefficient (μ ) shall be the upper bound characteristic value (μ ) multiplied by 
a material factor. 
5.6.9.6
The appropriate material (safety) factor for friction shall be selected dependent upon the limit state considered 
and the risk involved in exceeding (or going below) the design friction. See [5.9.7] or [5.9.8.6], [5.9.5] and [5.9.6]. 
These are also applicable to both ASD/WSD. 
5.6.9.7
The minimum design friction force shall be taken as the minimum design load (i.e. including relevant load 
factors) perpendicular to the friction surface multiplied by μ . 
ld lc
ud uc
ld
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5.6.9.8
The maximum design friction force shall be taken as the maximum design load (i.e. including relevant load 
factors) perpendicular to the friction surface multiplied by μ . 
5.6.9.9
If the friction coefficient range is based on uncertain data the consequences of the maximum possible variation in 
friction coefficients shall be evaluated. See [5.6.14]. 
5.6.9.10
Vibrations, varying or uncertain surface conditions etc. affecting the friction shall be considered. 
5.6.9.11
Restraint effects caused by combination of friction and global deflections shall be considered. 
5.6.10 Tolerances 
5.6.10.1
Loads caused by operational or fabrication tolerances exceeding the tolerances stated in the design 
standards/codes shall be considered. Typical examples include: 
• set-down tolerances (load-out, positioning)
• shimming tolerances
• uncertain deformation (in load distributing material)
• fabrication tolerances, see [5.10.1.4]. 
5.6.10.2
Loads caused by effects described in [5.5.5]. 
5.6.11 Relative deflections 
5.6.11.1
The effects of relative deflections between structures shall be considered and included in the design whenever 
applicable. These can be of particular significance when they induce loads in connections and supports such as 
grillages and seafastenings. The causes of relative deflections include: 
• vessel deflection (longitudinal bending) in waves,
• ballasting, de-ballasting or re-distribution of ballast,
• temperature differences,
• relative deflections that need to be considered during the operation.
5.6.11.2
For sea voyages the potential effects of longitudinal wave bending effects should always be considered when: 
a. The towed hull is not a classed, seagoing vessel or barge, or
b. The cargo is longer than about 1/3 of the transport barge or vessel length, or 
c. The cargo is supported longitudinally on more than 2 groups of supports, or
d. The relative stiffness of the hull and cargo could cause unacceptable stresses to be induced in either, or 
e. The seafastening design allows little or no flexibility between cargo and vessel.
5.6.11.3
Some cargoes, such as large steel jackets, can be inherently much stiffer than the barge, and will reduce vessel 
deflections, at the expense of increased cargo stresses. 
5.6.11.4
See also [11.9.3.2] for friction, [11.9.5] for seafastening design and [11.27.4.3] for jack-ups. 
5.6.11.5
The restraint loads should be defined in the same category as the load that causes the relative deflections, i.e. 
ud
rd
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5.6.12 Motion analysis 
5.6.12.1 General 
1. Motions of floating objects shall be determined for the relevant environmental conditions and loads. These 
may be from simplified conservative estimates, however it is normally recommended that the analysis (and 
tests) described in this sub-section are carried out. 
Guidance note:
Detailed analyses and model tests are not normally needed for the transportation of smaller cargoes on 
standard vessels. 
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2. Inertia loads due to motion should be calculated for all six degrees of freedom.
Guidance note:
This includes also an evaluation of mass (rotational) inertia effects from roll and pitch. These effects should 
as a minimum be quantified, and the effect evaluated. This is particularly relevant for barge voyages with 
large roll motions. 
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3. Testing of models, see [5.4.2], or full scale structures, see [5.4.3], may be carried out where the accuracy of 
theoretical approaches is uncertain, or where the design is particularly sensitive for motions. 
Guidance note:
Estimation of motions from model testing or by theoretical calculation has associated advantages and 
disadvantages. The two approaches are generally to be considered as complimentary rather than as 
alternatives. 
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4. It is recommended that theoretical calculations are correlated against relevant model test data (if available) 
in cases where strongly non-linear behaviour is expected. Such cases can occur when, for example: 
◦ overhanging cargo is occasionally submerged, or
◦ there are large changes in the waterplane area with draught.
5. The analytical models should be checked with respect to sensitivity to input parameters, see [5.6.14]. 
6. Recognised and well proven six-degree of freedom linear or linearized computer programs, utilising the 
strip theory or 3D sink source techniques are generally recommended. Special consideration shall be 
given to non-linear damping effects. The effect of forward speed shall be evaluated, where this is more 
onerous. 
7. Computer programs shall be validated against a suitable range of model test or full scale results in 
irregular seas. When using new software or for new or unconventional applications or new problems, this 
validation shall be documented. Similarly justification of drag coefficients, added mass and damping shall 
be documented. 
Guidance note:
Guidance on drag and added mass coefficients for a range of standard shapes can be found in DNV-RP-
C205 /46/. 
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8. First-order motion response analysis program generally report heave in a global fixed axis system. In these 
cases heave shall be assumed to be parallel to the global vertical axis and therefore the component of 
heave parallel to the deck at the computed roll or pitch angle (theta) is additive to the forces caused by the 
static gravity component and by the roll or pitch acceleration. 
9. In general, motion response calculations should be based upon a 3D panel model of the vessel. If a 2D 
strip theory model is used, the computer program needs to include the proper treatment of head/stern 
sea wave excitation loads. Simplified calculations should only be applied for non-critical routine operations 
or screening purposes. 
5.6.12.2 Wave headings 
a. The full range of wave headings shall be analysed. Spacing between the analysed wave headings should 
not exceed 45°. 
Guidance note:
For the cases where reduced design wave heights are acceptable from some headings, see [11.8], this 
applies to all headings. However, symmetry can be considered when relevant provided appropriate 
means of accounting for cargo CoG offset are included. 
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b. Short crested sea shall be considered for wave analysis where all headings are not carried out with equal 
wave heights i.e. typically motion analysis in order to find limiting installation wave heights for different 
vessel headings. 
Guidance note:
If short crested waves are considered the spacing between analysed wave headings should normally not 
exceed 22.5°. See also [3.4.12]. 
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c. Short crested sea may be considered for wave analysis where all headings are included with equal wave 
height i.e. typically motion analysis for sea voyages without any heading restrictions. 
5.6.12.3 Wave periods 
a. A wave period range with corresponding wave heights, see [3.4], shall be considered when evaluating 
characteristic motions and accelerations. 
5.6.12.4 Response amplitude operators (RAO’s) 
a. RAO’s for the basic six degrees of freedom can be utilised to calculate displacements, velocities, 
accelerations, and reaction forces for points in a body fixed co-ordinate system, or to establish RAO’s for 
these points. These RAO’s may be used for calculation of significant and maximum responses. 
b. When combining different responses, the phase angle between the different components may be 
considered. 
c. The gravity component shall be considered when determining the RAO’s for inertia loads (e.g. transverse 
accelerations). 
5.6.13 Load cases and load combinations 
5.6.13.1
Loads and load effects shall be combined to form load cases that are applicable to and physically feasible for the 
actual object(s) and type of operation under consideration. 
5.6.13.2
All possible load cases which can influence the feasibility of the marine operation shall be considered in the 
design. 
5.6.13.3
Characteristic loads may be combined taking into account their probability of simultaneous occurrence. 
5.6.13.4
Characteristic static (mean) load components and characteristic dynamic (varying) load components which are 
statistically independent may be combined according to the formulae below. 
where
F = Characteristic static load components
F = Amplitude of dynamic load components
Guidance note:
Dynamic load components in the above formulae are normally restricted to loads with periods less than 
10 minutes. The maximum values of dynamic loads with periods greater than 10 minutes are normally added as 
static loads (i.e. F equal to the maximum load, and F =0). 
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5.6.13.5
Correlated dynamic load components shall be added as vectors, unless statistical data of simultaneous 
occurrence are available. Load components due to first order motions should be considered to be correlated. 
The combination of these components is described in [5.6.15.2] and [5.6.15.4]. 
i,mean
i,amp
i,mean i,amp
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5.6.14 Sensitivity analysis 
5.6.14.1
The load cases shall include a parametric sensitivity analyses whenever a single load or parameter significantly 
affects the design or selection of the method or equipment to determine whether small changes significantly 
affect the design. 
5.6.14.2
Where the operational safety is critically dependent on a sensitive input, conservative characteristic values shall 
be used. 
5.6.15 Loads due to motions and wind 
5.6.15.1
Load cases for each heading shall be derived by the addition of fluctuating loads resulting from wind and wave 
action to static loads resulting from gravity and still water initial conditions. 
5.6.15.2
In lieu of a refined analysis the worst possible combination of the individual responses for the same heading, 
including components from the self-weight and wind, shall be combined, i.e.: 
where
S = Design load or load effect.S( ) = Response/load effect function.
F , F , F = Inertia forces (vectors), in x, y and z directions including relevant load factors and gravity 
components.
F , F = Wind forces (vectors), in x and y directions including relevant load factors. The horizontal load 
components due to wind induced heel or trim shall be included.
W = Load due to self-weight (vectors).
5.6.15.3
Alternatively, the fluctuating components shall be the worst possible combination of the loads resulting from 
calculations or model tests carried out in accordance with [11.3.7.1] through [11.3.7.3], with due account to be 
taken of the effects of phase. All influential loadings shall be considered: however the following static and 
environmental loadings are the most likely to be of importance: 
S = Loadings caused by gravity including the effects of the most onerous ballast condition on the 
voyage.
F = Loadings caused by the wind heel and trim angle.
F = Loadings caused by surge and sway acceleration
F = Loadings caused by pitch and roll acceleration
F = Loadings caused by the gravity component of pitch and roll motion
F = Loadings caused by direct wind
F = Loadings caused by heave acceleration, including heave.sin(theta) terms
F = Loadings caused by wave induced bending
F = Loadings caused by slam and the effects of immersion.
5.6.15.4
One of the following four methods in this paragraph shall be used to determine the design loadings: 
a. Except as noted in [11.7.2.1], the effects of phase differences between the various motions can be 
considered, if resulting from model test measurements, or if the method of calculation has been suitably 
validated. 
b. In cases where it is not convenient or possible to determine the relative phasing of extreme wind loadings 
and heave accelerations with roll/sway or pitch/surge maxima, a reduction of 10 percent may be applied 
to fluctuating load cases F through F which combine maximum wind and wave effects. However, if wind 
induced or wave induced loads individually exceed the reduced load, then the greatest single effect shall 
be considered. 
c. The total loads may be calculated by combination of loads as follows:
d
x y z
wx wy
1
1
2
3
4
5
6
7
8
1 8
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where:
F = Maximum load due to wind and wave motions 
F = Loads based on 1 hour mean wind speed
F = Loads based on 1 minute mean wind speed
F = F through F as applicable
d. For deck cargo units carried on ships assessed using DNV GL Rules for the Classification of Ships, /36/, 
Part 3, Chapter 4, Section 3, see [11.6]. 
Guidance note:
If the deck cargo is carried on a vessel classed an earlier edition of the DNV Rules for the Classification of 
Ships, the earlier version can be used. 
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5.6.15.5
Where transfer functions for motions are available these may be combined to a transfer function for the actual 
response or load effect. The phasing between the different components may be considered. 
Guidance note:
This method requires careful evaluation of the responses to be analysed. All responses which will be governing 
for the design should be considered. 
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5.6.16 Default motion criteria 
5.6.16.1
For loads computed in accordance with [11.4], the loads applied to the cargo shall be: 
S +F +F +F +F
where: S , F , F , F and F are as defined in [5.6.15.3]. 
The effects of buoyancy and wave slam loading shall also be considered if appropriate.
As stated in [11.7.2.1] roll and pitch cases are to be considered separately. Combined roll and pitch are not 
required. 
Guidance note:
Quartering seas should also be included if deemed critical for any structural element. (See also IMO Res. A.714
(17), Annex 13 regarding allowable angles of securing devices.) Quartering seas can be included by combining 
80% of the horizontal transverse and 60% of the longitudinal acceleration with both the minimum and maximum 
vertical acceleration. 
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5.6.17 Loads due to restraint deflections, vessel motions and wind 
5.6.17.1
Restraint loads due to vessel deflections in waves, see [5.6.11], loads due to vessel motions and wind may be 
combined as shown below. 
where
F = Total design load
F = Maximum loads due to deflections
F = Maximum load due to wave motions and wind. 
5.6.18 Loads due to irregular waves and swell 
5.6.18.1
Loads and load effects from irregular waves and swell shall be combined. These loads and load effects may 
normally be combined assuming that they are statistically independent. See [5.6.13.4]. 
mot
#(1 hour)
#(1 min)
# 1 8
1 1 3 4 6
1 1 3 4 6
tot
def
mot
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5.7 Failure modes 
5.7.1
All relevant failure modes shall be investigated. A failure mode is relevant if it is considered possible and the 
anticipated consequence(s) of the failure cannot be disregarded. 
5.7.2
The relevant failure modes can be grouped as either as global (total system) or local (individual members) as 
indicated in the following sections. 
5.7.3
Global modes of failure include: 
• structural collapse
• overturning
• sliding
• lift-off
• loss of hydrostatic or hydrodynamic stability
• sinking
• settlement
• free drift.
5.7.4
Local modes of failure include: 
• plastic deformation (yield)
• buckling
• fracture
• large deflections
• excessive vibration.
5.8 Analytical models 
5.8.1
The analytical models used for evaluation of loads, responses, structural behaviour and resistance shall be 
relevant considering: the design philosophy, the type of operation and the possible failure modes. The models 
should satisfactorily simulate the behaviour of the object’s structures, its supports and the environment. 
5.8.2
Design analyses shall be carried out considering all relevant loads and failure modes, see [5.7]. 
5.8.3
The design analysis shall be thoroughly documented that the results shown to satisfy the relevant requirements 
and criteria. 
5.9 Strength assessment 
5.9.1 General 
5.9.1.1
Structural strength can be assessed using either ASD/WSD methodology or LRFD methodology. These are 
discussed below. 
5.9.1.2
Whichever methodology is applied, the loading conditions/limit states shown in Table 5-1 shall be considered 
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when verifying structural strength. 
5.9.1.3
A limit state is commonly defined as a state in which the structure ceases to fulfil the function, or to satisfy the 
conditions, for which it was designed. See also DNVGL-OS-C101, /24/, Ch.2 Sec.3. 
5.9.1.4
Limit states shall be defined for all possible failure modes, see [5.7]. 
5.9.1.5
The FLS and SLS load cases requirements are the same for ASD/WSD and for LRFD. It is however important that 
the load cases for assessed for the ALS and LS / ULS are developed using the applicable environmental inputs 
for ASD/WSD or LRFD. 
Table 5-3 Description of loading conditions/limit states
Loading condition / limit state ASD / WSD name LRFD name
Maximum capacity, usually for maximum environmental and 
functional loads (permanent, variable, deformation) 
LS1
LS2
ULS-a
ULS-b
Loading history – important for structures exposed to 
significant cyclic/repetitive loading 
FLS FLS
Intact structure subjected to loads from an accidental event ALS-I ALS-I
Damaged structure subjected to post-damage loading ALS-D ALS-D
Serviceability checks (alignment, clearances, deflection, 
vibration, etc.)
SLS SLS
5.9.2 Design approach 
5.9.2.1
The format of the ASD/WSD method implies that strength/capacityverification of structures or systems involves 
the following steps: 
• Identify all relevant limit states, see [5.9.1]. 
• Identify all relevant loading conditions, see [5.6.13]. 
• For each loading condition define the relevant characteristic loads, see [5.5.2], and design conditions, see 
Table 5-1. 
• For each loading condition and failure mode, see [5.6] and [5.7], find the design loads 
• For each loading condition determine the design load effect, see [5.6]
• Ensure adequate safety by proving that the design load effect does not exceed the allowable, as 
described in [5.9.4], [5.9.5], [5.9.6] and [5.9.7], 
LS2 is applicable only when the loading is dominated by environmental/storm loads, e.g. for weather 
unrestricted operations the extreme loads due to the applicable design return period environmental criteria, see 
Table 3-1; for weather restricted operations, where an Alpha Factor according to [2.6.9] is to be applied. Any LS2 
load case may be treated as a gravity-load dominated limit state (LS1). 
5.9.2.2
The format of the LRFD method implies that strength/capacity verification of structures or systems involves the 
following steps: 
• Identify all relevant limit states, see [5.9.1]. 
• For each limit state define the relevant characteristic loads, see [5.5.2], and design conditions, see Table 
5-1. 
• For each limit state find the design loads by applying the relevant load/design factors, see [5.9.4.2], 
[5.9.5.2], [5.9.6.2] and [5.9.8.3]. 
• For each limit state determine the design load effect, see [5.6] and [5.9.3.2 b)]. 
• For each limit state determine the characteristic resistance, see [5.9.3.3]. 
• For each limit state determine the design resistance, see [5.9.3.2 d)]. 
• Ensure adequate safety by proving that the design load effect does not exceed the design resistance, See 
[5.9.3.2 a)]. 
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5.9.3 LRFD checks 
5.9.3.1 General 
a. Where the LRFD (load and resistance factor design) method is used for design verification the load and 
material factors specified in this section shall be used according to the principles of the method. 
Guidance note:
The safety factor format applied for lifting slings in Sec.16 could be regarded as an ASD/WSD (permissible 
stress) method, but the safety level is correlated according to the applicable LRFD factors. 
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5.9.3.2 Acceptance criteria 
a. The level of safety is considered to be satisfactory if the design load effect, S , does not exceed the design 
resistance, R , i.e.: 
S ≤ R for all limit states 
The equation S = R defines the respective limit state. 
b. A design load effect is an effect (e.g. stress, mooring line load, sling load, deformation, overturning 
moment, cumulative damage) due to the most unfavourable combination of design load(s) i.e.: 
where
S = design load effect
F = design load(s)
S = load effect function.
c. A design load (F ) is obtained by multiplying the characteristic load (F ) by the appropriate load factor, see 
[5.9.8.3], [5.9.4.2], [5.9.5.2] and [5.9.6.2]. 
d. A design resistance (R ) is obtained by dividing the characteristic resistance (R ), see [5.9.3.3], by a material 
or design factor, see [5.9.8.3], [5.9.4.1 g)], [5.9.5.2] and [5.9.6.2]. 
5.9.3.3 Characteristic resistance 
a. R shall be calculated based on the characteristic values of the relevant parameters or determined by 
testing. Characteristic values should be based on the 5 or the 95 percentile of the test results, whichever 
is the most conservative. See also [5.4]. 
Guidance note 1:
The resistance for a particular load effect is, in general, a function of parameters such as structural 
geometry, material properties, environment and load effects (interaction effects). 
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Guidance note 2:
The characteristic static resistance of steel, f , is to be taken as the smaller of: 
◦ the guaranteed minimum yield stress, f , or 
◦ 0.85 times minimum tensile strength of the material.
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Guidance note 3:
R for materials not mentioned e.g. concrete, concrete reinforcement, wood, synthetic materials, soil, etc. 
could normally be based on recommendations/requirements in the applied design code or standard. For 
soil see DNVGL-OS-C101 /24/ Section 10 1.3. 
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b. R for (wire & fibre) ropes and chains should be taken as the certified MBL. 
5.9.4 Fatigue limit states – FLS 
5.9.4.1 General 
a. For all structures exposed to significant cyclic loads during a marine operation the possibilities and effects 
of fatigue should be considered. 
b. The FLS design conditions should be based on the defined operation period and the anticipated or 
expected load history during the marine operation. See Table 5-3. 
c. Possible dynamic load effects due to e.g. slamming and vortex shedding should be investigated. See 
[5.6.7]. 
d. Restraint loads, see [5.6.17.1], could be important and shall hence be thoroughly evaluated and included 
in the FLS calculations. 
e. The FLS shall be evaluated according to procedures given in a recognised code or standard. See e.g. 
d
d
d d
d d
d
d
d c
d c
c
th th
c
y
c
c
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DNVGL-OS-C101, /24/, Ch.2 Sec.5 for general requirements for checking of fatigue limit states. 
Guidance note 1:
Reference can be made to DNVGL-RP-C203, /29/, and DNV CN 30.7, /20/, for practical details with respect 
to fatigue design. 
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Guidance note 2:
For new structures that are susceptible to fatigue, it is advisable to check for adequate fatigue life by 
analysis for voyages over about 50 days, including possible waiting time at sea, where the nominal peak-
stress range is less than 350 N/mm and the SCF does not exceed 2.5. If the peak-stress range is increased 
to 550 N/mm then a fatigue analysis is advisable for voyages over about 10 days. 
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Guidance note 3:
New-build MOU's are normally verified for fatigue for the initial delivery voyage in the classification 
process and a separate analysis is not normally required for this voyage. For subsequent voyages, it is 
desirable to undertake a fatigue analysis, however in many cases there is insufficient time and/or data 
regarding prior use. In such cases it is good practice to undertake a thorough NDT inspection of fatigue-
critical areas before the voyage and to repair any cracks, see [11.27.4.4]. 
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f. For mooring systems, the FLS is mainly of concern for steel components where fatigue endurance limits 
the design. For fibre-rope segments, the time-dependent strength can limit the design; consequently 
stress rupture or creep failure should be incorporated in the checks for ULS and ALS as appropriate. See 
also DNVGL-OS-E301, /27/. 
g. Where structural items e.g. grillages and seafastenings, are to be re-used they should be demonstrated to 
have sufficient fatigue life for the sequence of planned operations, including all previous operations. An 
appropriate inspection regime shall be proposed including NDT at appropriate intervals e.g. close visual 
examination after every use and NDT after every 10 uses; if there are highly utilised areas, more frequent 
NDT could be appropriate. For bolts, see [E.2]. 
5.9.4.2 Design factors - FLS 
a. All load factors shall be:
γ =1.0
b. Design fatigue factors (DFF) shall be applied to increase the probability of avoiding fatigue failures 
c. The calculated cumulative damage ratios for the defined design conditions times the applicable DFF 
according to Table 5-4 shallbe less or equal to 1.0. 
d. Lower values for the Miner’s sums than 1.0 can be relevant if the structure has been or will be subjected to 
fatigue loading before or after the considered marine operation. In such cases the maximum allowable 
Miner’s sum for the actual marine operations shall be determined by considering the total load history the 
structure will be exposed to. 
Table 5-4 Design fatigue factors (DFF) 
Inspection during operation (and 
repair) planned
Elements in inspection category I
Elements in inspection categories 
II & III
Yes 2.0 1.0
No 3.0 2.0
Notes:
1. The elements shall be categorised according to the definitions in Table 5-9. 
2. Higher DFF than indicated may be applicable based on other (project) governing codes.
3. The indicated DFF are applicable only for the fatigue utilization during the considered marine operation. 
Hence, if the fatigue utilization is combined with the utilization from other phases, see [d)], a different 
DFF may be applicable. 
5.9.5 Accidental limit states – ALS 
5.9.5.1 General 
1. Accidental limit states for marine operations include verification of:
◦ ALS-I: The intact structure or system for the defined accidental load effect(s) combined with other 
relevant load effects, see Table 5-5 (i.e. loads of type E may be ignored). 
◦ ALS-D: The damaged structure or system, see [5.9.5.1 2)], for relevant design load effects, see Table 
2
2
f
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5-5. 
Guidance note:
See also Table 5-3 for definition of ALS-I and ALS-D. 
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2. The damage to the structure or system in ALS-D is normally defined by either:
◦ the damage caused by the defined accidental load effect(s) or,
◦ a defined damaged or an accidental condition/scenario, see [5.6.6]. 
5.9.5.2 Design approach and load and resistance factors 
a. Accidental loads are defined in [5.6.6]. 
b. Design against accidental loads shall primarily consider global failure modes, see [5.7.3]. E.g. increasing of 
local strength which may reduce the safety against overall failure of the structure should be avoided. 
c. Load factors should in ALS normally, see [d)], be taken according to Table 5-5 or Table 5-6. 
d. Load factors greater than 1.0 shall be considered if an LRFD method ALS load or condition is not 
considered to have a sufficient low, i.e. ≤10-4 per operation, probability. If working to the ASD/WSD 
approach, the factors should be similarly increased. 
e. The characteristic environmental load (E) in the ALS-D load condition should/may be defined considering 
the probability of the analysed accident/damage and the anticipated maximum period (i.e.T , see [2.6.2]) 
the damaged situation will remain. 
Table 5-5 ASD/WSD Load factors for ALS
Type AISC 14 WSD option strength checking allowables
ALS-I 0.6
ALS-D 0.6
Notes:
1. The load factor of 0.6 for the ASD/WSD case arises because the basic allowable stress in 
AISC WSD 14  edition is 0.6*yield. In order to effectively work to yield, the load is multiplied by 0.6 and 
used with the standard allowable of 0.6*yield. 
Table 5-6 LRFD Load factors for ALS
Load
Condition
Load Categories
G Q D E A
ALS-I 1.0 1.0 1.0 NA 1.0
ALS-D 1.0 1.0 1.0 1.0 NA
Notes: 
1. Load categories G, Q, D, E and A are described in [5.5.2]
5.9.5.3 Material factor - ALS 
The material factor may in ALS generally be taken equal to:
γ =γ /1.15
where γ = the applicable material factor in ULS, see [5.9.8.3]. 
Guidance note:
E.g. the ALS material factor for steel wire ropes may be taken as γ  = 1.5/1.15 = 1.3. 
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5.9.6 Serviceability limit states – SLS 
5.9.6.1 General 
a. For some marine operations it is relevant to check SLS related to the feasibility of the operation. Such 
serviceability limit states could be associated with required clearances, push/pull capacities and vessel 
(barge) level (compared e.g. with quay height). 
b. See DNVGL-OS-C101, /24/, Ch.2 Sec.7 for typical SLS requirements for offshore steel structures. 
R
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5.9.6.2 Safety factors 
a. For SLS related to feasibility the load factors are normally equal to 1.0. Relevant safety factors/margins 
should be defined considering the actual operation. See Sec.6 to Sec.18 for guidance. 
b. SLS for structural elements shall normally be checked applying load and material factors equal to 1.0. 
Guidance note:
In SLS the object (or equipment/vessel) owner is free to define higher load- and material factors if this is 
found applicable. 
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5.9.7 ASD/WSD strength checks for structural steel subject to LS1 or LS2 loading 
5.9.7.1 Design approach 
1. The ASD/WSD design approach is described in 5.9.2.1. 
2. The primary structure and any critical temporary works like lifting attachments, spreader bars and 
seafastenings shall be of high quality structural steelwork with full material certification and NDT inspection 
certificates showing appropriate levels of inspection. 
3. The infrequent load cases, generally limited to survival and damaged cases, including design cases for 
weather restricted operations where an Alpha factor according to [2.6.12] is to be applied, may be treated 
as an LS2 case (environmental load dominated). This does not apply to: 
a. Steelwork subject to deterioration and/or limited initial NDT unless the condition of the entire load 
path has been verified, for example the underdeck members of a barge or vessel. 
b. Steelwork subject to NDT before elapse of the recommended cooling and waiting time as defined 
by the Welding Procedure Specification (WPS) and NDT procedures. In cases where this cannot be 
avoided by means of a suitable WPS, it may be necessary to increase the strength or impose a 
reduction on the design/permissible sea state. 
c. Steelwork supporting sacrificial bumpers and guides.
d. Spreader bars, lift points and primary steelwork of lifted items.
e. Structures during a load-out.
4. Traditionally AISC has also been considered a reference code, e.g. by API RP2A. If the ANSI/AISC 360-10 
American National Standard “Specification for Structural Steel Buildings” of June 2010 (in the AISC 14
edition) is used, the allowables shall be compared against member stresses determined using a load 
factor on all loads (dead, live, environmental, etc.) of no less than the applicable of those detailed in Table 
5-7. 
Guidance note:
The API RP2A 22 edition references the 9 Edition of AISC, which includes the traditional “1/3 increase”
for infrequent environmentally dominated load cases. The 14 Edition does not reference the 1/3 increase, 
instead it allows the referencing code to specify load factors. The LS2 load factors herein effectively allow 
the 1/3 increase. 
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5. Stresses in welds shall be assessed according to either:
a. The method given in DNVGL-OS-C102 Ch.2 Sec.9.2.5, /25/, or equivalent, or 
b. The method illustrated by the example given for the assessment of fillet welds for brackets given in 
[E.1]. 
c. The permissible usage factors for a) and b) are as follows: 
◾ Where the loads are due to accelerations determined according to Class Rules, see [11.6]: 
◾ 0.60 for welds made at fabrication site
◾ 0.52 for welds made on board the vessel.
◾ Where the loads are determined using other approaches given in this standard: 
◾ LS1 (cases where the loading is gravity dominated – see Table 5-3): 
0.58 for welds made at fabrication site
0.51 for welds made on board the vessel.
◾ LS2 (cases where the loading is dominated by environmental/storm loads – see Table 
5-3): 
0.78 for welds made at fabricationsite
0.67 for welds made on board the vessel.
d. Below deck welds in vessels classed to DNV ship rules may be checked against 90f in shear on the 
weld throat and 160f for normal stress perpendicular to the weld throat, where f is the material 
factor for the applicable strength group as given in /15/. 
Guidance note:
If good welding conditions, see [5.10.2.2], and weld fit-up (e.g. control of correct/no gaps to deck 
plate) on board the vessel are ensured by procedures and well planned inspection it could be 
acceptable to increase the permitted utilisations to those applicable for welds made at a fabrication 
site. 
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6. The allowable strength of slip critical bolted connections shall be assessed according to the method given 
in [E.2]. The permissible usage factors for slip critical bolted connections, assuming all loads are assessed 
using the LS1 condition as shown in Table 5-7, are as follows: 
a. Where the loads are due to accelerations determined according to Class Rules, see [11.6]:: 
◾ η = 0.48 for joints made with standard hole clearances. 
◾ η = 0.42 for joints made with oversize or slotted holes. 
b. Where the loads are determined using other approaches given in this standard: 
◾ η = 0.62 for joints made with standard hole clearances. 
◾ η = 0.55 for joints made with for oversize or slotted holes. 
The design of non-tubular connections shall be in accordance with an appropriate standard such as AISC /2/, 
using a consistent safety format and factors. 
Table 5-7 Load factors for use the ASD/WSD method and AISC 14 edition 
Type AISC 14 WSD option strength checking allowables
Limit State 1 (LS1) 1.00 
Limit State 2 (LS2) 0.75 
Notes:
1. The load factor of 0.75 for ASD/WSD in the LS2 case arises because the basic allowable stress in 
AISC WSD 14  edition is 0.6*yield and the traditional 1/3 increase to 0.8*yield (i.e. to 0.6*yield*4/3) for 
environmental load cases is not included. As an alternative, the load is multiplied by 3/4 and used with 
the standard allowable of 0.6*yield in order to achieve the safety levels that have been used and 
accepted over many years. 
2. Any load case may be treated as a gravity-load dominated limit state (LS1). 
3. Where the loads are due to accelerations determined according to DNV and DNV GL Class Rules, see 
[11.6], LS2 shall be used with a load factor of 1.2. 
5.9.8 LRFD strength checks for structural steel subject to ULS loading 
5.9.8.1 General 
DNVGL-OS-C101, /24/, Ch.2 Sec.4 gives provisions for checking of ultimate limit states for typical structural 
elements used in offshore steel structures. 
5.9.8.2 Load factors - ULS 
For the ultimate limit states (ULS) the two load conditions “ULS-a” and “ULS-b” as given in the Table 5-8 shall be 
considered. 
Table 5-8 Load factors for ULS
Load
Condition
Load Categories
G Q D E A
ULS-a 1.3 1.3 1.0 0.7 NA
ULS-b 1.0 1.0 1.0 1.3 NA
Notes:
1. Load categories G, Q, D, E and A are described in [5.5]. 
a. For loads and load effects that are well controlled a reduced load factor γ = 1.2 may be used for the G and 
Q loads instead of 1.3 in load condition ULS-a. 
Guidance note:
Examples where γ = 1.2 may be applicable are: 
◦ External hydrostatic pressure caused by an accurately defined water level.
◦ Loads due to an accurately distributed (i.e. static determinate) well defined self-weight.
◦ Functional loads accurately defined (limited) by the maximum (possible) capacity of equipment. 
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b. Where a permanent load G (e.g. self-weight or hydrostatic pressure) causes favourable load effects, a load 
factor γ = 1.0 shall be used for this load in load condition a. See also [5.6.2.2] and [5.6.2.3]. 
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c. In cases where the load is the result of counteracting and independent large hydrostatic pressures the 
appropriate load factor shall be applied to the pressure difference. However, the pressure difference 
should not be taken less than 0.1 times the hydrostatic pressure. 
d. In dynamic problems the application of load factors should be given special consideration. In lieu of a 
probabilistic analysis, the load effects may be found by application of load factors after having found the 
responses, e.g. after having solved the equations of motion for vessel motion response analysis. 
5.9.8.3 ULS material factors 
a. Applicable material factors in ULS are given in [5.9.8.4] to [5.9.8.6]. Material factors for materials not 
mentioned in [5.9.8.4] to [5.9.8.6] e.g. concrete, concrete reinforcement, wood, synthetic materials, soil, 
etc. shall be in accordance with a recognised code or standard. See also [5.9.3.3]. 
b. If a material factor γ = 1.0 is found more unfavourable than the indicated values, γ = 1.0 shall be used. 
5.9.8.4 Material factors for structural steel: 
1. In ULS the material factors for steel structures should be taken as minimum: γ =1.15. 
2. For members in compression a higher material factor may be applicable. The material factor should 
normally be chosen according to the applied design code, but never smaller than 1.15. 
3. If EN 1993 (Eurocode 3) /61/ is used for calculation of structural resistance, the material factors listed in 
DNVGL-OS-C101, /24/, Ch.2 Sec.4 for steel structures and DNVGL-OS-C101, /24/, Ch.2 Sec.8 for welded 
connections shall be applied. 
Guidance note:
See also Table 6-1 in NORSOK N-004, /112/, for applicable material factors. 
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4. In ULS the material factor for static strength of tubular joints should be chosen according to the applied 
design code, but never smaller than 1.15. 
5. An increased (i.e. larger than 1.15) material factor shall be considered if the production is carried out in an 
environment where reduced control of dimensions, materials and fabrication could be expected, e.g. 
welding on board vessels. The following minimum material factors, γ , apply when the weld capacity is 
calculated according to DNVGL-OS-C101 Ch.2 Sec.8, /24/, EN 1993-1-8 or [E.1]: 
◦ For welds made at fabrication site: γ = 1.3 
◦ For welds made on board the vessel: γ = 1.5 
Guidance note:
If good welding conditions, see [5.10.2.2], and weld fit-up (e.g. control of correct/no gaps to deck plate) 
on board the vessel are ensured by procedures and well planned inspection γ = 1.3 could be found 
adequate. 
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5.9.8.5 Material factors for ropes, chain and bolts 
1. The design load in any chain, wire or webbing strap used for seafastening should not exceed the certified 
(lifting) Working Load Limit (WLL) of the seafastening. 
2. In ULS the material factor for certified steel wire ropes and chains should normally be taken as: 
γ = 1.5
Guidance note:
γ = 1.15/0.85/0.9 = 1.5 
where
1.15 is the general steel material factor,
0.85 is a factor to account for that the characteristic strength, see [5.9.3.3] Guidance Note 2, of ropes and 
chains is based on the tensile strength (MBL), and 
0.9 is a general factor because wire ropes are considered more vulnerable to “undetectable” wear and 
material irregularities than regular steel structures. For new ropes with a 3.2 certificate it may be 
acceptable to use 1.0, see [15.10]. (Note also that an additional wear factor could be applicable). 
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3. For fibre ropes the material factor depends on the material and relevant failure mode. The following 
minimum factors apply: 
◦ Polyester: 1.65
◦ HMPE and Aramid: 2.0
◦ Other fibre materials: 2.5. 
Guidance note:
For fibre slingssubject to a robust certification process, other material factors may be considered 
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acceptable; however, γ should not be less than 1.65 
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4. When using DNVGL-OS-C101 /24/, Ch 2 Sec 4.8, Eurocode 3 /61/ or [E.2], the material factor for slip 
resistant bolt connections shall be taken as minimum: 
◦ γ = 1.25 for standard clearances in the direction of the force. 
◦ γ = 1.4 for oversize holes or long slotted holes in the direction of the force. 
Guidance note:
[E.2] provides for further information regarding slip resistant bolt connections and an alternative 
methodology. 
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5.9.8.6 Material factors for friction 
a. A material factor of minimum γ = 1.4 should normally be used to calculate the lower bound design 
friction coefficient for load bearing friction effects. 
b. A material factor of maximum γ = 0.8 should normally be used to calculate the upper bound design 
friction coefficient. See [5.4]. 
Guidance note:
In each case, the design friction coefficient should obtained by dividing the characteristic friction 
coefficient by the material factor. 
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5.10 Materials and fabrication 
5.10.1 Design considerations 
5.10.1.1 Applicable codes 
a. In general material selection, fabrication method, and non-destructive testing should be carried out 
according to a recognised offshore code, e.g. DNVGL-OS-C101, /24/, or DNVGL-OS-C401, /26/. 
Guidance note:
Recognised codes or standards are meant to be national or international codes or standards applied by 
the majority of professional people and institutions in the marine and offshore industry. 
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b. Independent of the applied code, it shall be documented that the requirements in this section [5.10] are 
fulfilled. 
5.10.1.2 Structural categories 
1. Structural elements and connections shall be grouped in categories determined according to: 
◦ type of stress
◦ presence of cyclic loading
◦ presence of stress concentrations
◦ presence of restraint
◦ loading rate
◦ consequences of failure
◦ redundancy.
2. Guidelines for selection of applicable materials for offshore steel structures can be found in DNVGL-OS-
C101, /24/, Ch.2 Sec.3. 
Guidance note:
For steel with yield stress below 500 MPa, the test temperature need not be taken lower than -40° C 
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3. For materials in temporary structures used for marine operations, the following apply:
◦ The design temperature, see DNVGL-OS-C101, /24/, Ch.2 Sec.3.2, should be defined based on the 
season and location(s) of the marine operation. Note that a design temperature above 0ºC may be 
applicable. 
◦ See Table 6-1 for guidelines regarding selection of structural category. See also DNVGL-OS-
C101, /24/, Ch.2 Sec.3.3. 
◦ For materials that could be welded under adverse conditions the yield strength (SMYS) should not 
exceed 355 MPa. 
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5.10.1.3 Material quality 
a. Selection of steel types shall be determined based on the structural application and the required category 
Table 5-9. 
b. All steel materials shall be suitable for the intended service conditions and shall have adequate properties 
of strength, ductility, toughness, weldability and corrosion resistance. 
c. Material types and qualities should comply with requirements in DNV-OS-B101, /23/. 
d. Non-structural steels shall have mechanical properties and weldability suitable for the intended 
application. 
Table 5-9 Structural categories
Selection criteria for structural 
category Examples for typical 
structures involved in 
marine operations
Recommended 
structural 
category
NORSOK N-004 
Equivalent /112/ 
Insp. 
Cat.,
DNV 
GLFailure 
consequence
Structural 
part
DNVGL-OS-C101
Substantial, the 
structure 
possesses 
limited 
residual
strength 
Complex
joints 
• Padeyes and 
other lifting 
points
• Seafastening 
elements 
without 
redundancy
• Spreader bars 
Special DC1 – SQL1 I
Simple joints 
and 
members 
Primary (Special) DC2 – SQL2 
(SQL1)
I or 
II
Not substantial, 
the structure 
possesses 
residual
strength 
Complex
joints 
Structures for 
connection of:
• Mooring and 
towing lines
• Grillages
• Redundant
seafastening 
elements 
Primary (Special) DC3 – SQL2 
(SQL1)
II
Simple joints 
and 
members
Primary (Special) DC4 – SQL3 
(SQL1)
II
Un-substantial, 
as local failure 
will be without 
substantial 
consequences 
Any 
structural 
part 
• Bumpers and 
guides
• Fender 
structures
• Redundant
(parts of) 
grillages 
Secondary DC5 – SQL4 III
Notes:
1. Complex joints are joints where the geometry of connected elements and weld type leads to high 
restraint and to tri-axial stress pattern. 
2. Residual strength (redundant) means that the structure meets requirements corresponding to the 
damaged condition in the check for ALS, with failure in the actual joint or component as the defined 
damage. 
3. Selection where the joint strength is based on transference of tensile stresses in the through thickness 
direction of the plate. 
4. The design classes and material selection according to NORSOK M-120, /110/ should be considered as 
guidance only. 
5. Extent of NDT to be according to DNV GL category I in Table 5-10, but category II may be used as 
“input” in Table 5-10 regarding waiting time for these welds. Regarding extent of inspection according 
to NORSOK M-101, /109/ inspection category B is normally acceptable. 
5.10.1.4 Tolerances 
a. As-built deviations shall not exceed fabrication tolerances assumed in the applied structural codes and 
standards, or in the design analysis, unless specially considered on a case-by-case basis. 
b. Acceptance of any as-built deviations exceeding specified tolerances shall be confirmed in writing by, as 
applicable, the owner, designer, installation contractor, etc. 
c. DNVGL-OS-C401, /26/, Ch.2 Sec.2.5 indicates fabrication tolerances that are normally acceptable. 
4)
2)
1)
3) 3) 5)
2)
1)
2)
3) 3)
3) 3)
2)
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d. Some marine operations procedures can be difficult (or impossible) to execute when standard tolerances 
are applied. In these cases consideration can be given to defining and documenting the consequences of 
using tolerances that are less onerous than those indicated in DNVGL-OS-C401, /26/
5.10.2 Fabrication 
5.10.2.1 Workmanship 
a. Workmanship during fabrication shall be of good standard and according to accepted practice. See also 
DNVGL-OS-C401, /26/, Ch.2, Sec.1 and Sec.2.1 through 2.5. 
b. Guidelines regarding assembly and welding can be found in DNVGL-OS-C401, /26/, Ch.2 Sec.2.6. 
5.10.2.2
Marine work Environmental conditions during marine construction work can be unfavourable and the time 
available is often limited. Also accurate fit-up can be difficult to obtain e.g. due to a dented barge deck. Such 
issues regarding marine work shall be duly considered in the planning of the work. See also [5.9.8.4]. 
Guidance note:
Due to the special conditions during marine construction work, the following precautions are recommended: 
a. Welding procedure specifications should be qualified by welding procedure tests carried out under 
conditions representative of the actual working environment; see DNVGL-OS-C401, /26/, Ch.2 Sec.1.2.5. 
b. Thorough inspections of fit-up and welding should be planned for. 
c. Weather conditionsand forecast to indicate acceptable conditions for welding considering the welding 
method and available shelter at the welding locations. 
d. Use of increased weld size in order to compensate for inaccurate fit-up (i.e. over-sized gaps) to be 
considered. 
e. Robust and well proven welding methods and procedures to be applied.
f. Use of material with improved weldability; see DNVGL-OS-C101, /24/, Ch.2 Sec.3.4.2, to be considered. 
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5.10.2.3 Weld inspection 
1. All NDT (non-destructive testing) of structures and structural components shall be carried out by qualified 
personnel and covered by written specifications and procedures. 
2. Personnel evaluating results from NDT shall possess thorough knowledge and experience with NDT. 
3. The NDT method selected shall be suitable for detection of the type of defects considered detrimental to 
the safety and integrity of the structures. 
4. The extent of NDT shall be based upon the importance of the connection in question. Aspects which shall 
be considered in specifying the extent of NDT are: 
◦ stress level and stress direction
◦ cyclic loading
◦ material toughness
◦ redundancy of the member
◦ overall integrity of the structure
◦ accessibility for examination.
5. Where through thickness properties of the steel are used, the material should be certified accordingly 
(Z-quality). Where this is not feasible, the material under through-thickness tension should be checked for 
laminations after the recommended cooling and waiting time as defined by the Welding Procedure 
Specification (WPS) and NDT procedures. The reason for waiting is that laminations can also be subject to 
hydrogen embrittlement, the same as welds, see SSC-290, /118/, for more details of lamellar tearing. If 
access is not possible after welding, pre-welding checks could be acceptable. 
Guidance note 1:
For non-critical seafastenings and their supports, through-thickness testing should be carried out when the 
tensile stress normal to any plate exceeds 100 MPa. 
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Guidance note 2:
The tensile stress should be calculated in a section between the deck plate and the weld (i.e. not in the 
critical weld section). If the under deck weld is smaller, this weld should be used as a reference, see also 
Guidance note to [11.9.5.27]. Stresses greater than 100 MPa, caused by e.g. a local moment on 
seafastening brackets can generally be accepted in limited areas without lamination testing. 
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6. Requirements to non-destructive testing (NDT) of welds can be found in DNVGL-OS-C401, /26/, Ch.2 
Sec.3. Equivalent standards may be used e.g. EEMUA 158 “Construction specification for fixed offshore 
structures in the North Sea” /59/ and AWS D1.1/D1.1M-2015 “Structural welding code – steel” /8/. 
7. Minimum extent of inspection should be as shown in DNVGL-OS-C401, /26/, Ch.2 Sec.3 Table 1 with 
“Inspection Category” as defined in Table 5-9. See also Table 5-10 for a summary and especially note 4) to 
the table. 
8. Normally final inspection and NDT of welds shall not be carried out before 48 hours after completion. 
However, for materials with yield strength of 355 MPa or less this could be reduced to 24 hours. See 
NORSOK M-101, /109/, Sec.9.1 and DNVGL-OS-C401, /26/, Ch.2 Sec.3. 2 for further details. 
9. For marine operations with weld inspection on the critical path, the minimum waiting time should be 
selected according to Table 5-10 however, the decreased waiting may only be used if the precautions 
listed in [5.10.2.2] are fulfilled. 
Guidance note:
Weld inspection can be completed after a voyage has commenced provided that procedures are in place 
to remediate or mitigate any defects that are found. 
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Table 5-10 Minimum extent of NDT and waiting time
Inspection 
Category
Minimum extent of NDT Minimum waiting time before NDT
Visual Other
SMYS ≤355 
MPa
SMYS ) > 355 
MPa
I 100% 100% 24 hours 48 hours
II 100% 20% Cold weld 24 hours
III 100% 5% Cold weld 24 hours ) 
Notes:
1. Test method to be selected according to the type of connection, see DNVGL-OS-C401, /26/, Ch.2 
Sec.3, Table C1. 
2. SMYS to be defined according to the specification for the actual material used and not according 
to the minimum required design value. 
3. For thickness less than 40 mm the limiting SMYS is 420 MPa.
4. The use of PWHT (post weld heat treatment) can reduce the required waiting time.
5. An increased % extent shall be evaluated if defects are found and/or the weld conditions and 
precautions, see [5.10.2.2], are not fully satisfactory. 
6. The NDT can start when the weld is cold, but it is recommended to wait as long as practicable. 
SECTION 6 Gravity based structure (GBS) 
6.1 Introduction 
6.1.1 General and scope 
6.1.1.1
This Section is mainly applicable to “Condeep”-type gravity based structures (with one or more columns above a 
submerged base). However the principles will apply to most types of steel and concrete gravity based platforms. 
6.1.1.2
The areas shown in Table 6-1 are covered. Depending on the type of structure and method of construction, 
some or all of the following sections will give the relevant requirements. 
Table 6-1 Requirements for different GBS phases
General requirements See Sec.2 to Sec.4
Stability and freeboard (all phases) See [6.2]
Structural strength See [6.3] and Sec.5
Temporary ballasting and compressed air systems See [4.3]
1)
2)
3)
2
3)
4) 4)
5) 6) 4)
5) 6) 4
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Construction basin and tow-out See Sec.12
Construction and/or solid ballasting afloat See Sec.14
Deck-mating (inshore or offshore) See Sec.15
Towage(s) See Sec.11
Instrumentation See [6.4]
Installation at location See [6.5]
Ensuring on-bottom stability See [13.10]
6.1.2 Revision history 
6.1.2.1
This section replaces the applicable sections of the following legacy documents:
• GL Noble Denton, Guidelines for concrete gravity structure construction & installation, 0015/ND 
• DNV Offshore Standard, Load transfer operations, DNV-OS-H201
6.2 Floating GBS stability and freeboard 
6.2.1 General 
6.2.1.1
Sufficient positive stability and reserve buoyancy shall be ensured during all stages of the marine operations. 
Both intact and damage stability shall be evaluated, on the basis of an accurate geometric model. This shall 
include inclining tests of the GBS in accordance with [2.10.5] at stages agreed with the MWS company. 
6.2.1.2
In calculations of stability and reserve buoyancy/freeboard, due allowance shall be included for uncertainty in 
mass, buoyancy, volume, location of centre of gravity, density of liquid and solid ballast, and density of seawater. 
6.2.1.3
The output of the weight control programme as described in [5.6.2] shall be taken into account. 
6.2.1.4
Stability calculations should include corrections and allowances for:
a. Free surface
b. Air cushion
c. Icing
d. Influence of moorings, including a check on the consequences of failure.
e. Temporary Loads and Structures (including any cantilevered structures)
6.2.1.5
The number of openings in buoyant elements adjacent to the sea shall be kept to a minimum. Where 
penetrations are necessary for access, piping, ventilation, electrical connections, etc. arrangements shall be 
made to maintain watertight integrity. During construction phases, particular attention should be paid to 
openings near the waterline, which will vary as construction proceeds. 
6.2.1.6
Damage stability requirements shall be evaluated considering the operation procedure, environmental loadsand responses, the duration of the operation and the consequences of possible damage. Compartments that 
may be subject to flooding or partial flooding include: 
a. Compartments adjacent to the sea
b. Compartments inside the structure, crossed by seawater filled pipes
c. Skirt compartments containing compressed air.
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6.2.1.7
Special attention should be paid to flooding which may be caused by:
a. Impact loads from vessels
b. Damage to structure or pipework from dropped objects
c. Mechanical system failure
d. Human error.
6.2.1.8
The consequences of water ballast escaping from any compartments above the waterline, or the escape of air 
from any air cushion shall be evaluated where applicable. 
6.2.1.9
Flooding as a result of vessel impact is assumed to occur in a zone bounded by two horizontal planes normally 
positioned 5 m above and 8 m below the waterline. These levels should be reviewed if deep draught vessels are 
likely to be operating nearby. 
6.2.1.10
For operations where the structure cannot meet damage stability criteria, measures shall be taken to minimise 
the risk, by: 
a. Limiting the exposure period
b. Providing additional local structural strength
c. Providing additional protection, such as fendering
d. Minimising vessel movements near the structure
e. Dedicated procedures and experienced personnel.
6.2.1.11
For operations where at any stage stability or reserve buoyancy is critical or where damage stability cannot be 
obtained, a risk assessment in accordance with [2.4] shall be carried out. The duration of the critical condition 
should be minimised. Requirements for back-up or protection systems, or special procedures should be 
assessed. 
6.2.2 Intact stability 
6.2.2.1
The initial GM shall not be less than 0.5 m (after allowing for all possible inaccuracies in measuring it) unless 
agreed with MWS Company. 
6.2.2.2
The maximum inclination of the floating GBS or platform should not exceed 5° in the design environmental 
condition as defined in [3.1] apart from possible exceptions during installation as described in the guidance note 
to [6.5.4.4]. Calculation of maximum inclination should take into account: 
a. Maximum amplitude of pitch or roll motion in the design sea state, plus
b. Inclination due to design wind, plus
c. Inclination due to mooring line tensions or required towline pull.
Guidance note:
The maximum inclination of 5° is due to the large height of GBS structures and the corresponding motion 
experienced at this height. 
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6.2.2.3
During towing, the static inclination in still water when subjected to 50% of required towline pull should not 
normally exceed 2°. Differential ballasting may be used to reduce the static inclination resulting from towline pull 
only by not more than 1°. 
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6.2.2.4
The area under the righting moment curve shall be not less than 140% of the area under the overturning 
moment curve as shown in Figure 11-2. Both curves shall be bounded by the least of: 
a. The second intercept of the righting and overturning moment curves
b. The angle of downflooding
c. The angle which would cause any part of the GBS to touch bottom in the minimum water depth at the 
construction site or along the towage route. This requirement may be deleted for installation at the 
offshore site. 
d. The angle at which allowable stresses are reached in any part of the structure, construction equipment, 
topsides or topsides attachments, if applicable. 
6.2.2.5
The wind used for overturning moment calculations should be the design wind for the operation, as defined in 
[3.3]. Short duration operations during construction or towage may be considered as weather restricted 
operations, provided the structure can achieve or be returned to a safe condition, within the operation reference 
period 
6.2.3 Effective freeboard 
6.2.3.1
For inshore towages and construction afloat, the effective freeboard, as defined in Table 1-3, shall not be less 
than the greater of: 
a. 1 m above the design wave crest height, with allowance for run-up, all around the structure, under the 
design storm loading from the most critical direction, 
b. 6 m in the intact condition, if the unit does not have one-compartment damage stability.
6.2.3.2
For offshore towages, after damage, an effective freeboard of not less than 5 m shall remain above the design 
wave crest height, with allowance for run-up, all around the structure, from the most critical direction. Calculation 
of the freeboard shall account for motions experienced as a result of the design environmental conditions and 
mooring line tensions or required towline pull. 
6.2.4 Damage stability for tow-out and inshore tows 
6.2.4.1
For tow-out from dry-dock, one-compartment damage stability is not required as it is a controlled operation and 
the under-keel clearance is limited. 
6.2.4.2
For other inshore tows the structure should have one-compartment damage stability, as defined in [6.2.1.6]
through [6.2.1.9]. 
6.2.4.3
If one-compartment damage stability requirements cannot be fulfilled, the requirements for construction afloat in 
[6.2.5.2] shall apply. 
6.2.5 Damage stability during construction afloat 
6.2.5.1
During the period of construction afloat, the platform shall possess one-compartment damage stability, for as 
much of the construction period as is practical. 
6.2.5.2
When the platform does not possess one-compartment damage stability, then in addition to [6.2.1.10]: 
a. A means should be available to compensate for inclination due to flooding of any compartment, and 
b. There shall be sufficient structural strength in the outer walls to withstand impact loads from the 
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construction spread and vessels, which may be in close proximity to the platform, and 
c. Fendering may be used to reduce impact loads in critical areas, and
d. Lifting of heavy objects shall be carefully controlled. Protection shall be provided against dropped objects. 
Any lifts which, if dropped, could endanger the platform shall be identified and additional precautions 
taken, and 
e. Any objects or equipment on barges alongside, which if dropped, could endanger the platform shall be 
similarly identified and additional precautions taken, and 
f. Rigorous procedures shall be developed to minimise the risk of flooding. These shall include 
consideration of collision, leakage through the ballast or other systems, reliability and redundancy of 
pumping arrangements and power supplies, and 
g. At all times there shall be adequately trained personnel on board the platform, and
h. As per [6.2.1.11], a risk assessment of flooding shall be carried out in accordance with [2.4]. 
6.2.6 Damage stability for offshore tows and installation 
6.2.6.1
When towing on the caisson or columns the platform should possess one-compartment damage stability. 
6.2.6.2
It is acknowledged that for an offshore tow, the requirement in [6.2.6.1] might be impractical, in which case: 
a. The structure shall be locally reinforced within the zone defined in [6.2.1.9], to withstand impact from the 
largest towing or attending vessel, and/or 
b. Rigorous procedures shall be developed to minimise the risk of flooding, and
c. A risk assessment of flooding shall be carried out in accordance with [2.4]. 
6.2.6.3
It is acknowledged that during installation, it might be impractical to provide reinforcement against collision over 
the full range of waterlines. Planning and risk assessmentshall include a procedure to return the structure to the 
reinforced waterline should the installation operation be aborted. 
6.3 Structural strength 
6.3.1 Concrete gravity structures - load cases 
6.3.1.1
The requirements of Sec.5 apply. 
6.3.1.2
Load cases shall be derived by the addition of fluctuating loads resulting from wind, wind heel, wave action and 
the effect of towline pull or mooring loads to the static forces resulting from gravity and hydrostatic loads for the 
following temporary phases before it is safely installed: 
1. tow-out from construction basin or dry-dock (with and without any air cushion)
2. the most critical construction afloat stages
3. any towages, with or without a deck
4. deep submergence for deck mating
5. installation on the seabed, including:
◦ any impact with the seabed including any rocks or debris during installation 
◦ penetration and grouting phases 
◦ any impact with scour protection during its placement.
◦ Any other critical phase as agreed with the MWS company
6.3.1.3
Accidental loadings shall also be considered for all of the phases in [6.3.1.2]. 
6.3.1.4
The specific load cases considered shall be documented. For all load cases it shall be documented that the 
design (global and local) is acceptable. 
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6.3.1.5
The unit shall be able to safely withstand a static heel angle of 10°, or any greater angle required during 
construction, towage or installation. If it has damage stability, the unit shall also be able to withstand the static 
and dynamic loads caused by the flooding of any one compartment in the lesser of the 10-year return period 
environmental conditions or a 25 m/s wind and associated waves. These should be assessed as LS1 or ULS 
conditions, unless it is demonstrated that alternative criteria apply. 
6.3.1.6
Hydrostatic loads on the substructure at the deepest draught during deck-mating can be the governing load 
case. It shall be demonstrated that a thorough independent check of the calculations covering this load case has 
been carried out, and that the design and reinforcement details assumed in the calculations concur with the as-
built condition. 
6.3.1.7
Any limitations on the maximum allowable duration of deep immersion due to concrete creep, in relation to the 
structural stability of the unit, should be established and the procedures planned accordingly. 
6.3.2 Structural concrete 
6.3.2.1
The strength of concrete and its reinforcement including any pre- or post-tensioning shall comply with a 
recognised and appropriate concrete design code, such as those listed in ISO 19903, /101/. Any time-
dependent properties of the materials shall be taken into account. Adequate global and local strength shall be 
documented. 
6.3.2.2
The strength of the structure in the installed condition should be covered by the relevant certifying authority or 
classification society who will normally refer to a suitable offshore structural code or rules such as DNV-OS-C502 
– Offshore Concrete Structures, /41/, or the GL Rules, /68/. 
6.3.2.3
Testing of concrete for permanent works should be covered by the certifying authority and testing for temporary 
works should follow the same requirements. 
6.4 Instrumentation 
6.4.1
Instrumentation shall be in accordance with [4.2] and adequate instrumentation shall be installed to monitor the 
following, as applicable, during the operation to ensure loads, etc., remain within analysis and/or operational 
limits and assumptions: 
a. The water level in all compartments, quantity and percentage
b. Status of all valves
c. Pump status and flow rates 
d. Main and emergency power supply status 
e. Platform draught, heel and trim 
f. Compartment air pressure
g. Compressor status 
h. Air cushion pressure 
i. Water seal level in skirt compartments
j. Status of access doors and manholes.
6.5 GBS installation 
6.5.1 General 
6.5.1.1
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This section describes the general requirements for the installation of a concrete gravity platform at its final 
offshore location. The installation procedures will vary, depending on parameters including: 
a. The size and design of the platform
b. Water depth
c. The positioning tolerances required in all 6 degrees of freedom
d. The positioning/stationkeeping system proposed
e. Whether cranes, winches or external buoyancy is required for lowering and/or positioning
f. Whether the operation involves docking over a template, docking piles or other structures
g. Stability at all stages of immersion
h. Whether a vertical or inclined installation is required
i. Tolerances on differential ballast levels
j. The skirt design, and penetration method
k. Whether under-base grouting is required
l. Whether solid ballast or scour protection is required.
6.5.2 Survey 
6.5.2.1
The position of the site location shall be given in both geographical and grid coordinates.
6.5.2.2
The water depth and bathymetric tolerances shall be determined.
6.5.2.3
When determining the extent of the survey area, the following shall be accounted for:
a. Tolerances on site survey position
b. Inaccuracy of position monitoring systems during installation
c. Operational tolerances
d. The approach corridor
e. Whether a holding location is required close to the site
f. Whether an inclined installation, with previous off-site touch-down is required
g. The proximity of any other platforms or subsea assets at or near the location.
6.5.2.4
The bottom topography shall be established by swathe bathymetry, high resolution echo sounder techniques, 
side scan sonar, and checked by magnetometer and ROV video for obstructions and possible unexploded 
ordnance. The extent of any required levelling or other seabed preparation should be decided at the design 
stage. 
Guidance note:
Swathe bathymetry is now available in portable units and is installed on most survey vessels so should be used as 
standard on all survey projects. Due to constraints imposed by calibration and processing requirements (single 
point obstructions may be removed in processing), conventional high-resolution bathymetry and side scan sonar 
should be run in conjunction. 
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6.5.2.5
The seabed and sub-seabed conditions shall be established by coring, magnetometer, in-situ testing, lab testing 
and sub-bottom profiling. 
6.5.2.6
Sufficient current surveys shall be completed to determine the current profile with depth. 
6.5.2.7
The area should be checked to ensure that there are no travelling sand-waves or other seabed erosion/accretion 
that could affect the structure during installation. 
6.5.2.8
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A site survey of the installation area covering the full area of any anchor pattern, carried out not more than 4 
weeks before the start of installation, shall be provided to verify the location of all subsea infrastructure, debris 
and obstructions. 
6.5.3 Seabed preparation 
6.5.3.1
The required tolerances for level and compaction shall be documented at an early stage. 
6.5.3.2
Where surveys shows the seabed is out of tolerance it shall be prepared to correct for uneven levels or 
consistency. Description of the preparation works, including details of how tolerances shall be achieved, shall be 
documented. 
Guidance note:
Typical seabed preparation methods include:
a. Controlled dumping and compacting of gravel before final levelling
b. Placing sand-bags 
c. Excavating of unsuitable soils before replacing as in a) or b).
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6.5.4.1
In general it is desirable for all installation phases to be reversible though this may not always be possible, 
especially if there are temporary unstable phases. 
6.5.4.2
The approval criteria shall be agreed with the MWS Company. The agreed criteria shall depend on the 
installation methods and consider the following: 
a. The required external assistance (e.g. temporary buoyancy, winches, cranes, etc.) 
b. Range of positive stability at all stages of installation. Also see [6.5.4.4]. 
c. Length of weather windows required and sensitivity to bad weather or strong currents
d. Possible requirement of scour protection immediately after emplacement (see [6.5.7]). 
6.5.4.3
For structures towed on their side, an agreed Up–End procedure shall be documented. 
6.5.4.4
Ideally platforms should be shown to be stable at all phases of the installation. 
Guidance note:
Shallow draught platforms frequently undergo a phase of instability during submergence of the base, and an 
inclined installation procedure may then be used in which case the requirements of [6.5.4.5] will apply. 
Sometimes it may be necessary to touch down on one edge to achieve stability or to use temporary buoyancy or 
crane /winch assistance. 
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6.5.4.5
In the event of an inclined installation the following shall be considered:
a. All machinery, systems and personnel, if aboard, shall be able to work efficiently in the inclined condition 
b. Monitoring of ballast levels, and allowable differential levels 
c. Structural capacity of the skirt at touch down, and possible impact loads imposed
d. Skirt touch down, if on the final site, may disturb the seabed, and prejudice the final skirt penetration or 
base slab bearing 
e. If the skirt touch down is on the final site, accurate position control may be difficult in the inclined condition 
f. If skirt touch down is remote from the final site, the deballast capability required by [4.3.5] will be used. 
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6.5.5 Positioning and position monitoring systems 
6.5.5.1
The positioning system shall be designed to meet the required installation tolerances. This will normally be by 
means of tugs, often the tow fleet is rearranged into a star configuration. 
6.5.5.2
Where more precise positioning is required, the tugs may be connected at the bow to pre-laid anchors though 
other mooring systems are possible. Mooring systems shall comply with Sec.17. 
6.5.5.3
Where the position and orientation tolerances are not critical, the tugs may be in free floating configuration. 
6.5.5.4
Where docking piles are to be used the requirements in [13.8.4] apply 
6.5.5.5
A position monitoring system in accordance with [4.4.5] shall be provided. The system shall allowing monitoring 
of capturing docking piles if being used. 
6.5.6 Ensuring on-bottom stability/skirt penetration 
6.5.6.1
The requirements in [13.10.1] apply including specifying the depth(s) of any required penetration(s). 
6.5.6.2
Calculations shall be documented to demonstrate that the base or skirts will penetrate to the required depths. 
The calculations shall specify if negative pressure is required in addition to gravity/buoyancy loads. Additionally 
the calculations should consider the following: 
a. expected (and maximum and minimum) soil friction
b. expected (and maximum) suction versus penetration depth
c. soil sealing differential pressure versus penetration depth
d. capacity of suction pumps
6.5.6.3
A venting system sufficient to ensure foundation integrity shall be provided to allow water in the skirt 
compartments to escape and where required to allow negative pressure to be applied. 
Guidance note:
Design of the pipework should take into account the requirements for removal on decommissioning.
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6.5.6.4
Skirts shall be shown to meet the requirements of [4.4.5.1] for all expected loads during the installation process. 
6.5.6.5
If differential pressure or suction is applied, then it shall be demonstrated that an adequate seal can be obtained 
at the skirt tip, with minimal risk of “piping” between outside and inside each skirt compartment. 
6.5.6.6
Requirements to minimum pumping pressure and flow rate should be established
6.5.6.7
All relevant parameters shall be controlled, monitored and recorded during the installation. This shall include: 
a. differential pressure (suction)
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b. penetration
c. flow rate
6.5.7 Anti-scour precautions 
6.5.7.1
All locations, especially with high current speeds, should be investigated to see if scour could cause problems 
during the installation and subsequent temporary stages. 
6.5.7.2
Details of anti-scour precautions where required shall be documented. Possible solutions to scour include: 
• Controlled rock dumping or placing sand-bags immediately after the unit is installed. Care shall be taken 
to avoid any damage to the unit especially near penetrations, pipelines, cables or other sub-sea assets. 
Scour may start immediately after installation, especially in bad weather. 
• Artificial seaweed or other seabed stabilisation methods. This solution needs to be demonstrated to be 
successful under these conditions. 
• Increased skirt lengths, though this should have been determined at an early design stage. 
SECTION 7 Cables, pipelines, risers and umbilicals 
7.1 Introduction 
7.1.1
This section is currently under development and therefore for work related to cables, pipelines, risers or 
umbilicals the following legacy documents apply: 
• 0029/ND, GL Noble Denton, Guidelines for Submarine Pipeline Installation 
• 0035/ND, Section 10 (for cables), of GL Noble Denton, Guidelines for Offshore Wind Farm Infrastructure 
Installation, and 
• DNV-OS-H206 ,DNV Offshore Standard, Load-out, transport and installation of subsea objects (VMO 
Standard Part 2-6). 
7.1.2
The legacy documents shall be used in their entirety including any referenced documents and NOT the 
equivalent sections of this Standard. 
Guidance note:
For example if DNV-OS-H206 is applied then DNV-OS-H101, and DNV-OS-H102 and DNV-OS-H205 also apply 
along with any other referenced documents. 
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7.1.3
For the installation by lifting of other subsea equipment the requirements of this document should apply unless 
agreed otherwise. 
Guidance note:
Generally, where subsea equipment is installed by lifting as part of a project using the documents referenced in 
[7.1.1] then the legacy documents would apply. 
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7.2 Codes and standards 
7.2.1
A number of recognised standards and design codes covering pipelines, risers and umbilicals are already in 
existence and should be considered. 
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Guidance note 1:
The following are examples of relevant industry standard codes:
• Pipelines in general: API RP 1111, /3/and BS EN 14161, /10/, 
• Risers in general: API RP 2RD, /4/
• Submarine pipelines: DNV-OS-F101, /42/, 
• Dynamic risers: DNV-OS-F201, /43/, 
• Flexible pipe systems: ISO 13628-2, /95/, or ISO 13628-11, /97/, 
• Umbilicals: ISO 13628-5, /96/, 
• Subsea power cables: see Guidance note 4.
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Guidance note 2:
Generally the default for rigid pipeline system design and approval is DNV-OS-F101 Submarine Pipeline 
Systems. DNV-OS-F101 Sec.10 gives requirements for installation/offshore construction of submarine pipeline 
systems.Parts of DNV-OS-F101 Sec.10 are also generally applicable for flexible pipes and risers. 
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Guidance note 3:
Detailed guidance regarding installation of cables may be found in DNV-RP-J301 Sec. 6. 
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SECTION 8 Offshore wind farm (OWF) installation 
operations 
8.1 Introduction 
8.1.1 General 
8.1.1.1
This section gives the MWS requirements for installing offshore wind farm infrastructure (apart from cables which 
are covered in Sec.7). Operators should also consider national and local regulations, which can be more 
stringent. Background information is in App.H. 
8.1.2 Scope 
8.1.2.1
This standard provides requirements and guidance for installation of offshore wind farms, in particular: 
• Foundations including monopiles, steel jackets, gravity bases, suction bases, floating bases including 
spars, TLPs and semisubmersibles. 
• Towers, turbines and blades to be installed on foundations.
• Offshore substations, offshore converter platforms, offshore transformer station, control and other 
platforms, including those on jack-up platforms. 
8.1.3 Revision history 
8.1.3.1
This section replaces the applicable sections of the following legacy document:
• 0035/ND Guidelines for Offshore Wind Farm Infrastructure Installation.
8.2 Planning 
8.2.1 General 
8.2.1.1
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See Sec.2 for general planning requirements and Sec.3 for environmental conditions and criteria. 
8.2.2 Tolerances and criteria 
8.2.2.1
Tolerances and criteria should be agreed with the MWS company at an early stage of the project. 
Guidance note 1:
The selection of many installation tolerances and criteria will be a trade-off between reducing the cost of 
manufacture and reducing the costs of delays waiting for good weather in consequence. Manufacturers often 
prefer tighter installation tolerances which require better weather criteria for installation. It is generally beneficial 
to select the transport/installation contractors before such tolerances and criteria are fixed as they may 
significantly affect the installation methods, risks and costs. 
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Guidance note 2:
The MWS company normally has input to the selection to ensure that the tolerances and criteria are not so 
severe that there is a possibility that the equipment may never be able to be installed without taking 
unacceptable risks. 
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8.2.2.2
Such tolerances may include:
a. Position and orientation of monopiles, pile templates, jackets and other structures.
b. Pile or structure verticality.
c. Clearances between piles inside pile sleeves, including allowances for weld beads and grout keys. 
8.2.2.3
Such criteria may include:
a. Wind speeds (at specified heights and gust durations) for critical lifts.
b. Any restrictions on current speeds or wave heights (and how they will be measured) for specific 
operations. These could include stabbing piles or jackets into templates. 
c. Degree of acceptable damage to grout keys during piling.
d. Any restrictions on helicopter or vessel movements within the field in bad visibility or other adverse 
conditions. 
e. Any restrictions on transfer of people and equipment onto fixed or floating installations by various means. 
f. Requirements for disposal of any dredged materials, drilling cuttings or soil plugs removed from piles (to 
comply with national or international laws or conventions, and to avoid problems with other contractors). 
g. Piling operations – sound effects on sea life.
8.2.3 Vulnerable items or areas 
8.2.3.1
Due to the many parties and vessels working in close proximity, it is necessary that each party understands what 
items are particularly vulnerable to actions by others. These items need to be identified at an early stage so that 
they can be considered in the relevant risk assessments. The list of vulnerable items needs to be updated and 
promulgated as required during the life of the wind farm. 
8.2.3.2
Typical vulnerable items or areas may include:
a. J-tube entry holes being covered with soil or debris.
b. Changes in seabed level (from scour, dredging, jack-up footprints, drill cuttings, etc.) varying the natural 
frequency of foundations. 
c. Scour can also affect jack-up foundations, cables, anchors etc. Scour model tests may be required in areas 
with high current speeds and soft or sandy seabeds. 
d. Damage to grout seals and back-up seals.
e. External fittings (including anodes, J-tubes, etc.) being damaged by dropped objects, vessel collision or 
mooring lines. 
f. Operations of divers (vulnerable to propellers and propeller wash, noise and blast, bubble curtains, cables 
and dropped or lowered objects). 
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8.2.4 Planned moorings 
8.2.4.1
Geotechnical and bathymetric surveys should determine at an early design stage if the seabed will provide good 
anchor holding and may determine the type of anchors that will be needed. If anchor holding is poor (leading to 
a high probability of dragging anchors damaging cables) then prelaid or piled anchors may be desirable. 
Allowable anchor locations should be agreed at the same time as the cable routes. 
8.3 OWF installation vessels 
8.3.1 Jack-ups – general 
8.3.1.1
Jack-up legs can be a major threat to cables. The as-laid cable routes should be updated as required and 
properly distributed through the project in order to prevent cable damages. A suitable safe distance shall be 
maintained between the as-laid cable route and the intended positions of the jack-up legs. This is of particular 
importance in OWF developments where cable laying/installation is progressing near turbine installation 
activities in a similar time frame. 
8.3.2 Jack-ups in weather unrestricted operations 
8.3.2.1
Jack-ups that are designed and classed for elevated operations in conditions in excess of those at the installation 
site (either all year or for particular months) shall comply with the requirements of DNVGL-ST-N002, /39/
8.3.2.2
The jack-up can operate at a lower air gap than required for survival in a design storm as long as it is able to jack-
up to a safe air gap for a design storm before bad weather. 
Guidance note:
If a breakdown prevents jacking up, then the crew may need to be evacuated.
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8.3.3 Jack-ups in weather restricted operations 
8.3.3.1
Jack-ups that cannot comply with [8.3.2] for a specific location and season shall comply with the requirements for 
weather restricted operations in [2.6.5]. 
Guidance note:
Useful practical guidance on weather restricted jack-up operations is given in Section 5.3 of RenewableUK 
Guidelines for Jack-ups, /115/, but note that [2.6.7] allows a greater operational window. This is summarised as: 
a. Agree procedure documents which include limiting criteria, allowing for uncertainty due to monitoring 
and the forecasting of the environmental conditions (see [2.6.9]), for relevant decision points and identify 
suitable alternative jack-up locations between the site and safe ports. 
b. The jack-up is only to leave a safe location to go to the installation site on receipt of a favourable weather 
forecast with high confidence to cover the time (including a contingency for delays) from departure to 
return to a safe location. 
c. The jack-up is to leave the installation site unless there is a confident good weather forecast to cover the 
remaining time on site and to return to a safe port or to elevate to a safe air gap at a suitable stand-by 
location, including a contingency for delays. 
d. If the jack-up cannotreach a safe port or location before meeting bad weather (above the laden jacking 
limits of the jack-up, typically about 1 m to 1.5 m significant wave height), then it should jack-up to survival 
air gap at a suitable shallow water location and evacuate the crew if necessary. 
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8.3.3.2
The procedures and criteria described in [8.3.3.1] shall be the subject of a risk assessment in accordance with 
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[2.4]. 
8.3.3.3
Jack-ups can also operate on DP or when moored afloat to save time jacking up and down and pre-loading. 
These operations require favourable weather and shall follow the weather restricted operations requirements in 
[2.6.7]. The use of the crane in floating mode shall be specified in the vessel’s operation manual with the 
associated allowable environmental limits and approved by the classification society. 
8.3.3.4
Jack-ups can operate in semi-jacked-up condition (vessel stabilised in water by a low leg pre-loading and a 
reduced draught) under good weather conditions. This condition can make it feasible to operate the jack-up at 
critical locations where the risk of punch through is high. It will require approval by the vessel’s classification 
society as it is not typically a normal operating condition. 
8.3.4 Crane vessels (seagoing) 
8.3.4.1
Any crane vessel or sheerlegs shall be classed for operating in the relevant area. The design and operating 
criteria shall be defined according to Sec.2. 
8.3.4.2
Carrying a suspended load on a crane hook in transit offshore is not generally considered good practice, unless 
it is for very short distances in calm weather. In bad weather the load can be very difficult to control, stability is 
reduced and the crane can be overloaded. Approval of such operations will require agreement from the vessel’s 
Classification Society and a risk assessment in accordance with [2.4]. 
8.3.5 Inshore crane vessels and barges 
8.3.5.1
Inshore crane vessels and barges shall only be used if allowed by their class notation and: 
a. The MWS company has agreed procedure documents which include limiting environmental criteria for 
relevant decision points and identifies safe ports or locations. These criteria shall take into consideration 
the Alpha Factors described in [2.6.9]
b. The vessel is only to leave a safe port or location to go to the installation site on receipt of a confident 
good weather forecast to cover the period from departure to safe return, including a contingency for 
delays. 
c. The vessel to leave the installation site unless there is a confident good weather forecast to cover the 
remaining time on site and to reach a safe port or location, including a contingency for delays. 
8.3.6 Grounded OWF installation vessels and barges 
8.3.6.1
Some vessels working in shallow water may need to be grounded at low water or over one or more tidal cycles. 
This can only be approved provided that: 
a. The vessel’s classification society allows such operations.
b. The seabed is such that the vessel will not be damaged and it will not hold the vessel down when 
attempting to refloat. 
c. There is a method (e.g. moorings or “spuds”) for holding the vessel on location when grounding and 
floating off in the design conditions agreed with the MWS company at the design stage without damaging 
any cables or other structures or equipment. 
d. A confident good weather forecast is obtained before grounding to cover the period (including a suitable 
allowance for delays) until float-off without exceeding the operational criteria. 
8.3.7 Other OWF installation vessels 
8.3.7.1
The following vessels usually do not require the approval of the MWS company unless their operations represent 
a risk for other structures or operations. 
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a. Crew transfer or accommodation vessels with proprietary crew access arrangements.
b. Escort and stand-by vessels can be needed in some areas to warn off other vessels, especially during 
sensitive operations or transports. 
c. Bubble curtain deployment and energising vessels which can be needed if regulations on piling noise 
pollution apply (see [13.10.2]). 
8.3.7.2
In some cases, it may be unclear whether the approval of the MWS company is required or not for smaller vessels 
approaching existing structures. Planned operations should be discussed between the OWF owner, the 
Underwriter and the MWS company in order to identify the major risks for the existing structure and decide case 
by case the scope of the MWS company. 
8.4 Planning and execution 
8.4.1 Procedures and manuals 
8.4.1.1
Technical documentation shall be completed for all operations. See [2.3] for details. In general, this should 
include: 
a. The anticipated timing and duration of each operation, including contingencies.
b. The limiting wave states, wind speeds and currents, and where applicable any visibility/day-light, 
temperature and precipitation limits, as well as the site-specific equipment or methodology prescribed for 
measuring each limit-state. 
c. The transport route including shelter points.
d. The arrangements for control, manoeuvring and mooring of barges and/or other craft alongside 
installation vessels. 
e. Effects on and from any other simultaneous operations (SIMOPs – see IMCA M 203, /83/). 
f. Contingency and emergency plans.
g. Requirements from the relevant MWS company standards for each individual phase.
8.4.2 Weight control 
8.4.2.1
The requirements in [5.6.2] apply. 
8.4.2.2
The manufacturer shall supply a weight statement with tolerance and CoG envelope for all weight-sensitive 
items. 
8.4.2.3
When a large number of virtually identical items are built with very good quality control, reduced weight 
contingency factors can be agreed with the MWS company based on the standard deviation from weighing of 
initial items, with random subsequent weighing used to confirm consistency of manufacture. 
8.4.2.4
Where rigorous quality control is in place, and predictions of final weights in initial weighings are demonstrated 
to be accurate, a reduced requirement for weighing can be agreed with the MWS company. 
8.4.3 Weather restricted operations and weather forecasts 
8.4.3.1
For requirements see [2.6.7] for requirements for weather restricted operations and [2.7] for weather forecasts. 
8.4.3.2
For areas with high tidal currents there can be additional restrictions on operations due to the need to wait for 
slack (or slacker) tides for current-sensitive operations such as: 
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• Moving jack-ups on or off location
• Stabbing piles or installing jackets, substructures or equipment on the seabed
• Bringing cargo vessels alongside installation vessels.
• Diving operations.
8.4.3.3
When high currents are combined with shallow water then additional current forces will be caused by “blockage” 
effects. These shallower conditions also lead to increased seabed turbulence due to wave action, and additional 
contingency measures can be necessary to make allowances for accelerated scouring around jack-legs and 
spudcans. However suitable moorings, stabbing guides and other aids can help to reduce the sensitivity to 
currents and decrease downtime waiting for slack tide. 
8.4.3.4
Weather forecasts shall follow the requirements in [2.7]. Forecasts for wind speed shall specify the height (to be 
agreed in advance) and wind speeds measured on site should be corrected to that height for direct comparison. 
The swell height, direction, and period should alsobe included, as well as the probability of precipitation, fog 
and lightning within the next 24 hours. The time of sunrise and sunset, and the phase of the moon can be 
advantageous though these will normally be found in nautical almanacs. 
8.4.3.5
For subsea lifts in areas where it is known that high currents exist in the water column, in-field monitoring of 
currents (speed and direction) should be considered to enhance the regular forecasts. The monitoring of sub-sea 
currents with acoustic Doppler or similar systems should be considered when the operational limits of ROVs, and 
drag on piles during stabbing can lead to operational delays. 
8.4.4 Site and route survey requirements 
8.4.4.1
As well as ensuring that all positional, bathymetric, soil and current surveys are performed using the same datum 
and coordinate systems, various requirements to ensure sufficient accuracy like the frequency of survey 
equipment calibration (for salinity, temperature etc.) shall be agreed. There shall be an agreed procedure for 
ensuring that all survey results are disseminated to all relevant parties as required. 
8.4.4.2
The “as built” locations of structures, cables and subsea equipment shall be recorded accurately on charts using 
a common survey datum used by all parties. These charts shall be kept updated, including all jack-up footprints 
as soon as they are made and issued to all vessels operating in the field. “No anchoring” zones shall be well 
marked. 
8.4.4.3
In advance of the final detailed design being carried out for the foundations, the seabed material, geophysical, 
and geotechnical surveys of the sub-bottom profile should have been carried out, as well as magnetometer 
surveys for ferrous objects, including UXO. The Cone Penetrometer Test results and other appropriate survey 
details for each foundation location should be documented, to jack-up vessel operators. This will allow them to 
carry out site-specific assessments in accordance with ISO 19905-1, /102/, and to assess the possibility of 
scouring around jack-legs and spudcans. 
8.4.4.4
Unexploded ordnance (UXO) disposal, although important, is not generally subject to a Marine Warranty and is 
normally excluded. However it is recommended that it will be managed in accordance with the requirements of 
‘Risk Management Framework’ provided in CIRIA C754, Assessment and management of unexploded ordnance 
(UXO) risk in the marine environment, /13/ or similar. 
8.4.4.5
Additional requirements for the cable route surveys are given in Sec.7. 
8.4.5 Scour protection 
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8.4.5.1
If scour is a possible problem, procedures or contingency procedures shall be prepared and anti-scour materials 
stockpiled and deployment equipment prepared for mobilisation. See [8.4.3.3] and [8.4.4.3] for information that 
will help in prediction of scour. 
Guidance note 1:
“Dynamics of scour pits and scour protection”, /119/ gives the results of research into scour on early UK offshore 
wind farms. 
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Guidance note 2:
Cables are generally be trenched or otherwise protected in scour-prone areas. However additional precautions 
can be required close to J-tubes or I-tubes at monopiles or platforms, especially immediately after laying. 
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Guidance note 3:
Scour around jack-up legs can make them more vulnerable to punch-through and around cables can make them 
more vulnerable to damage. 
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8.4.5.2
Care shall be taken when laying scour protection to ensure that bad weather and/or high currents during the 
installation phase do not cause damage to the lower layers. 
8.4.6 Wet storage of jackets or OWF foundations 
8.4.6.1
Any unpiled jackets or foundations should be able to comply with the requirements in [13.10] for the return 
period applicable to the operation reference period given in [3.4]. This can require any chosen location to be 
sheltered from high waves and currents. 
8.4.6.2
A constant exclusion zone for marine traffic shall be enforced.
8.5 Load-outs of OWF components 
8.5.1 Structure load-out 
8.5.1.1
Load-outs shall be in accordance with Sec.6. However the following special cases apply, as applicable. 
a. Special consideration should be given to purpose-built lifting appliances for blades. The lifting tool 
Certificate shall specify the maximum load and any limits regarding the overall dimensions of the lifted 
item and any environmental limitations (e.g. maximum wind speed). 
b. In the event of structural modifications to an item of lifting equipment, it shall be re-approved by a 
Recognized Classification Society before further use. 
c. Bolts used for removable lifting lugs shall generally be used one time only. In special cases, re-use can be 
accepted as described in [E.2] but only if initial pretensioning does not exceed 60% of the bolt yield 
strength and the loads during lifting have not exceeded the maximum design values. For re-use of bolts, a 
detailed inspection plan with regular NDT including rejection criteria and exchange intervals should be 
documented. As a minimum, bolts should be visually inspected after each lift and with MPI (Magnetic 
Particle Inspection) after every 3 lifts unless fatigue calculations accepted by the MWS company show that 
less frequent inspections are acceptable. 
d. Re-useable lifting lugs shall be tested in accordance with [16.9.7]. 
8.6 Transport of OWF components 
8.6.1 General 
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8.6.1.1
Sea voyages are covered in Sec.11 and road transport in Sec.9. The rest of [8.6] describes items specific to OWF 
components. 
8.6.1.2
Seafastening of blades and other fragile components require special care to avoid damage from welding or 
locating guides. Where friction is required to resist some or all of the seafastening forces, the coefficients of 
friction shall be shown to be adequate in both the wet and dry states. See [11.9.2]. 
8.6.1.3
The requirements of [E.2] will apply for bolted connections used for seafastening. The strength of bolted 
connections may be assessed to DNVGL-OS-C101 /24/, Ch 2 Sec 4.8, Eurocode 3 /61/ or [E.2]
8.6.1.4
Minimum clearance between cargo items to be lifted is given in [16.13.2] and [16.13.3]. 
8.6.2 Transport of complete rotor 
8.6.2.1
Rotors with diameters of well over 100 m may be transported horizontally (rotor axis vertical) on vessels or 
barges of only about 30 to 40 m beam. The voyage and installation planning shall account for the large 
overhangs in particular avoiding wave slam on the blades. 
Guidance note 1:
The blades will generally be very vulnerable to wave slam, especially when the vessel rolls and/or pitches into a 
wave. 
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Guidance note 2:
Normally the voyage and installation planning considers some or all of the following:
a. The rotor being designed to safely withstand the accelerations (from [11.3]). 
b. Reducing to negligible the probability of wave slam on the blades by securing them well above the still 
water level. 
c. Selecting vessels that can be ballasted to reduce the motions in likely wind and wave combinations. 
d. Doing motion response calculations to optimise the loading and ballasting arrangements so as to 
minimise the probability of wave slam on the blades in likely wind and wave combinations. 
e. Weather routing the transport to avoid any weather that could cause wave slam on the blades. (This cannot 
always be practicable for some seasons and longer routes between suitable shelter points). 
f. Developing procedures to avoid blade collision damage when coming alongside