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SNAME Transactions, Vol. 92, 1984, pp. 125-150 
The High-Speed Displacement Ship Systematic Series Hull 
Forms--Seakeeping Characteristics 
J an J . B lok , 1 V is i to r , and Wim Beuke lman~ 2 V is i to r 
In the operation and design of high-speed ships, a greater emphasis is placed on good seakeeping 
performance because it is found that large motions and high accelerations can significantly degrade 
the operational capabilities. The need for better hull forms and the increased interest in seakeeping 
performance call for more and better data to be available at the design stage to obtain a right bal- 
ance between seakeeping and other, often conflicting, requirements. In this paper the genesis of 
a systematic series of model experiments is given, illustrated with results. Attention is focused on 
the general thoughts underlying the series, the selection of the characteristic section shape, the se- 
lection of the basic hull shape, the choice of the parameters to be varied in the series, and the pa- 
rameters to be fixed from the outset. The choice of the parent hull form and the seakeeping aspects 
associated with this choice are discussed, and the amalgamation of the data in the form of design 
charts is shown. 
1 Senior project manager, Ocean Engineering Division, Maritime 
Research Institute, Wageningen, The Netherlands. 
2 Scientific coordinator, Ship Hydrodynamics Laboratory, Delft 
University of Technology, Delft, The Netherlands. 
Presented at the Annual Meeting, New York, N. Y., November 7-10, 
1984, of THE SOCIETY OF NAVAL ARCHITECTS AND MARINE EN- 
GINEERS. 
125 
Introduction 
RECENT YEARS have seen an increased interest in seakceping 
for naval ships. This has occurred in part because of operators 
having become aware of significant and quantifiable differ- 
ences between ships designed for the same task, and in part 
because researchers have been able to come up with tools to 
predict ship motions, accelerations and extreme effects and 
have put together the framework required to estimate the 
overall performance and its degradation as a result of envi- 
ronmental severity in statistical terms. 
In the naval architectural field an inherent assumption is 
often intuitively made when sufficient data are lacking, that 
is, "small changes have small consecluence~" This may be true 
in many fields of engineering; however, it can prove utterly 
false in fluid dynamics. The first rule the hydrodynamicist has 
to learn is that small changes to flow boundary geometry can 
dramatically alter the flow field [1,2]. a Ship designers live up 
to this rule in the design of the underwater hull form inasmuch 
as they squabble over the lines in a degree unparallelled in any 
other field of the design. 
Seakeeping has long held the stigma of being hard to improve 
upon and subject to statements like "ships do move anyway. 
Yet now that the tools, experimental as well as computational, 
have attained a state of maturity equaling those of other naval 
architectural fields, it is possible to investigate the seakeeping 
aspects of a ship at the design stage. 
The increased interest in seakeeping for naval ships stems 
from the full-scale observations, backed up by research findings, 
that ship's behavior in seakeeping can indeed be improved upon 
if one is willing to look into it, to handle the elusive tradeoff 
between uneven and conflicting requirements, and is ultimately 
willing to pay the price and accept the penalty. 
The importance of seakeeping to a naval ship is of a diver- 
sifted nature. For the ship type we are concerned with in this 
paper- - the fast frigate--seakeeping pervades the operability 
of almost any system and subsystem of the ship, [8-7]. 
Ship motions lead to extreme effects like slamming under the 
bow or green water on deck and attending high loads that can 
cause damage to the hull and the equipment topside. Excessive 
a Numbers in brackets designate References at end of paper. 
motions also lead to substantial weather slowdown or necessitate 
an unsolicited change of course. Likewise, the motions and 
attending high accelerations degrade crew performance 
through restricted movement, increased fatigue and ultimately 
seasickness [8]. 
To take but one example, the operation of a helicopter, a 
feature now to be found on ever smaller frigates and patrol 
vessels. Ship motions roll and pitch can restrict its on-deck 
movement; the ship heading relative to the prevailing wind and 
sea greatly influences its takeoff and landing options in view 
of the turbulence and exhaust fumes, while the vertical and 
lateral motions and accelerations at the heli-pad further de- 
termine whether it can be recovered or not [9,10]. Although 
catch-down devices can serve as an expedient to widen the 
weather window, it is no substitute for a good stable platform. 
Similar stories can be told about towed arrays and replenish- 
ment-at-sea operations, to mention but a few. 
Besides the existing and well-proven concept of the dis- 
placement hull for a high-speed high-performance platform, 
a great number of advanced vehicle concepts are under in- 
vestigation, some of which are more or less actively pursued. 
We may mention here the advanced displacement-type vessels 
under which heading we find the "slender ship" concept-- 
essentially a frigate hull of high length-displacement ratio 
meant to significantly reduce the primary resistance hump. In 
addition, hulls that hide the greater part of their displacement 
at a greater depth underwater such as small-waterplane-area 
single-hull and twin-hull ships (SWASH and SWATH) are 
thought beneficial in reducing the wavemaking resistance and 
the motions in a seaway. Semi-planing or fully planing con- 
cepts are investigated for ships of limited size and a narrow 
speed range to reduce resistance. Hydrofoils of various designs 
have proven their merits and have come into their own as vessels 
with a high transport efficiency, although still restricted to fair 
and mildly unfavorable weather. Finally, we may mention 
air-cushion ships in which high speed and an attractive platform 
size are combined at the expense of ride quality. All these 
concepts, and a good deal more that have never left the drawing 
beards, can operate at high speed and offer an operational ad- 
vantage of some sort [11-16]. 
An intriguing question remains as to what limits the true 
aa ffi acceleration amplitude (single) 
2~a l/a ffi double significant acceleration 
a19 - - acceleration at station 19 
B = ship's breadth 
bt ffi transom stern width 
CA ffi incremental resistance coefficient 
for model-ship correlation 
Ca = block coefficient 
Caa ffi block coefficient aftbody 
CB~ = block coefficient forebody 
C~s = specific frictional resistance coeffi- 
cient of ship according to ITTC- 
57 
CM = midship section coefficient 
CG ffi center of gravity 
Ct, -- horizontal prismatic coefficient 
Ct,A = horizontal prismatic coefficient 
aftbody 
CpF -- horizontal prismatic coefficient 
forebody 
CaM = specific residuary resistance coeffi- 
cient of model 
126 
Nomenclature 
CTS = specific residuary resistance coeffi- 
cient of ship 
Cve = vertical prismatic coefficient 
CveA = vertical prismatic coefficient aft- 
body 
CveF ffi vertical prismatic coefficient fore- 
body 
Cwp = waterplane coefficient 
CWt,A = waterplane coefficient aftbody 
Cwer = waterplane coefficient forebody 
F, = Froude number = V / ~ 
Fnv = Froude number = V / ~ 
g = acceleration due to gravity 
in = waterline entrance angle relative to 
centerplane 
k = wave number = 2r/~ 
L = ship's length 
Let, ffi length between perpendiculars 
LCB = longitudinal center of buoyancy 
LCF = longitudinal center of flotation 
= figure of merit according to Bales 
rms ffi root-mean-square valueof some 
quantity 
Systematic Series Hull Forms 
RAW = wave added resistance 
Rr = residuary resistance 
RT = total resistance, calm water plus 
waves 
RTS = total resistance in calm water 
sa ---- relative motion amplitude (single) 
s17 ffi relative motion at station 17 
T = ship's draft 
T1 = average wave period 
V = speed 
V, = ship speed in knots 
z~ -- heave amplitude (single) 
2~1/8 = double significant heave motion 
A8 = wave added resistance 
~'a = wave amplitude (single) 
(wl/a = significant wave height 
0o = pitch amplitude (single) 
~ l /a = double significant pitch angle 
-- wavelength 
v = displacement volume 
p = water mass density 
r = trim angle 
o~ -- wave circular frequency 
displacement ship can be pushed and how well she can do at 
(very) high speed. 
In the field of seakeeping these novel concepts have one thing 
in common: They all perform well provided the sea does not 
get too rough. The slender ship may exhibit more motions than 
the usual hulls in a high sea state; the semisubmerged SWASH 
and SWATH rely heavily on their control flaps for good per- 
formance; planing hulls just do not perform in waves, while 
hydrofoils whether they cut through the wave crests or contour 
the waves have a limit on sea state above which they simply 
cannot be operated or have to go down to the hull-borne mode. 
Finally, air-cushion ships: Although tlhe ride comfort will be 
dramatically reduced in waves, it is doubtful if the cushion can 
be maintained at all in a severe sea state [11,12]. 
Studies on novel ship types that come into the picture for 
naval applications have shown that the order of importance to 
be attached to the various disciplines is seakeeping first, then 
stability and control both in the vertical plane and in maneu- 
vering, further propulsion hydrodynamics, and finally resis- 
tance. This sequence of importance is quite unlike the order 
usually adhered to in displacement hull design, where perhaps 
the order should also be reversed. 
In the foregoing we have identified the need for seakeeping 
data to be available as early as possible in the design stage of a 
high-speed combatant in order to get the maximum out of it. 
In addition, the oncoming novel hull concepts force us to face 
the question, "How good can displacement hull forms perform 
at high speed?" For both of these reasons a systematic series 
of model experiments has been initiated to produce calm-water 
resistance data and motion, acceleration, and added drag data 
in waves for an extensive series of displacement hull forms. 
The hull forms were to be applicable to 15-m (50 ft) patrol 
craft and up to 150-m (500 ft) cruisers alike, and the speed range 
sufficient to embrace the highest speeds envisaged for the novel 
hull concepts, that is, Froude numbers of well over unity 
(metric, dimensionless). It was further meant to design the hull 
forms in a coherent fashion so that a true family of models 
would emerge~ and to present the data in a form of design charts 
amenable to quick estimation of salient characteristics. Various 
apects of the series are discussed herein, mainly with a view to 
seakeeping. 
The choice of the parameters was an important point, which 
to keep fixed and which to vary, and the resulting parameter 
space is illustrated. Further, a tradeoff was to be made between 
stillwater resistance and seakeeping in the selection of the 
characteristic section shape and the characteristic hull shape. 
Moreover, the reasoning and deliberations that led to the se- 
lection of the parent hull form are given. Experimental setup 
and test program are subjects discussed in some detail and 
typical results are given. 
In addition to the model experiments, a series of computa- 
tions was made with strip theory programs and correlated with 
the measurements to determine to what extent existing ana- 
lytical tools can predict the performance of ships in a speed 
range hitherto not included. Finally, a prediction is shown for 
a typical 85-m (280 ft) frigate on the basis of the series data. 
Setting up the systematic series 
In the design of the series a number of aspects had to be 
considered in detail. Among these were the design criteria for 
the series, its speed range, the appropriate parameters, and the 
parent hull form selection. We will touch upon these in the 
following. 
Design criter ia 
In setting up the Series it was important to adopt design cri- 
teria first. A systematic series hinges on the choice of the 
characteristic hull shape--the parent hull--which can be se- 
lected only in the light of a set of design criteria. Furthermore, 
for the scope of the series and its parameter selection and pa- 
rameter space as .well as the subsequent test program details, 
a set of design criteria would be an imperative departure point. 
The criteria formulated for this hull-form series were: 
• good calm-water resistance properties, and 
• good seakeeping characteristics. 
Concerning the first point, attention focused on resistance; for 
the time being, propulsion was left out of the picture. The 
second point, seakeeping, was elaborated to cover 
• low motion and acceleration levels, 
• low wave added resistance, and 
• small probability of incurring extreme effects like 
slamming under the bow and shipping of water on 
deck. 
These criteria can all be narrowed down to one and the 
same--low motion levels--because usually if the motions de- 
crease, the accelerations and the wave added drag will also go 
down. Extreme effects may not always follow suit, but can be 
remedied easily by ensuring a sufficient draft forward and an 
appreciable freeboard and flare on the forebody. 
For the subject high-speed ships it was further considered that 
the most critical motion and acceleration levels would occur 
in head seas. Wave added resistance is also largest in that case. 
It goes without saying that other wave headings may pose other 
problems on the ship; for instance, rolling in beam seas and in 
stern quartering seas. For the purpose of comparison of hull 
forms, however, it was deemed sufficient to study the hulls only 
in head seas. The restriction following from this design re- 
quirement has to be imposed on the series before the relevant 
parameters are selected. 
Speed range of interest 
The two aims of the study, namely to generate data of use to 
the designer and to investigate what the limits are of the dis- 
placement hull, necessitated a wide speed range for the se- 
ries. 
Patrol craft of small displacement encounter very high 
4 Froude numbers, which may easily get as high as Fn = 1.2, 
while the intermediate range around En = 0.7 is Of interest' for 
frigates of the usual size, L = 120 m (400 ft), when pushed up 
to 45 knots. In addition, however, most navies express a great 
interest in the cruising speed range of 15 to 25 knots for reasons 
of peacetime fuel economy, for all ship types and sizes. 
Consequently it was decided that for the present series tO be 
of any great value and to meet the aims an extremely wide 
speed range had to be adopted ranging from Fn = 0.1 to 1.2. 
For the selection of the parent form a hull would have to be 
selected that would be optimum preferably over the whole 
speed range. If a tradeoff should be encountered, the speed 
range of Fn = 0.7 to 1.0 would have the emphasis. 
Parameters of interest 
In the design of the systematic series a set of parameters had 
to be identified that would have a bearing on stillwater resis- 
tance and seakeeping performance alike. A second and by no 
means less essential requirement was that the parameters be of 
practical significance to the ship designer. A third point lay 
in the fact that we are dealing with ship forms rather than di- 
mensional ships, so that the parametei"s to be selectedhad to be 
nondimensional quantities. Bearing this in mind and keeping 
4 In the text two Froude numbers are used, one based on the ship 
length, the other based on the third root of the displacement. Because 
of the use of the acceleration due to gravity and metric units, both 
exoressions are dimensionless: Fn = V /~ and Fnv = 
v / ~ 
Systematic Series Hull Forms 127 
Table 1 Main parameters 
B/T 
CB 
Cvp 
LCB } 
LCF 
bt[B 
iE 
L/T } -- 
Cwp 
LCB - LCF separation 
(transom width over ship's breadth) 
(waterline entrance angle) 
L/vl/3 
MODEL 1 
MODEL 2 
o 
MODEL 3 20 / / 
~ 8 4 I 
Fig. 1 Body plans of models 
128 
an eye on the design criteria, a number of main parameters 
were selected as listed in Table 1. 
It will be obvious that if all of these are varied over only two 
values, independently from the others, a prohibitively large 
number of models would result, and it is even questionable if 
all of them would be really independent of one another if one 
wants to avoid odd shapes. Therefore, a number of parameters 
have to be"fixed and only a limited number will come in for 
variation. 
Parameters to be fixed and varied 
To reduce the number of models and to adhere to parameters 
of direct interest to the designer, it was decided to take the L/B, 
B/T, and CB coefficients as prime parameter to be varied in 
the series and to fix all others as optimal as could be established 
for the parent hull. 
The choice of these three parameters is certainly justified 
from the stillwater resistance and from the seakeeping point 
of view. Along with the varia{ion of these parameters a. 
number of other parameters vary as well; L/T, L~ V 1/a, Ce, 
CM, Cwv, or Cve; so the choice is not too restrictive. 
The prime parameters L/B and (::8 have a decided influence 
on stillwater resistance as have the secondary variables L/V 1/a, 
Cp, and CM. The prime variable B/T and the Secondary 
variables L/T, Cwe, and Cve have a profound influence on 
seakeeping. 
So, it will be clear that the selection of only these three pa- 
rameters, which will come in useful from the designer's angle, 
is by no means a restriction from the hydrodynamic point of 
view. 
Subseries 1 
It follows as a logical consequence from the foregoing that 
a limited number of parameters will have to be fixed from the 
outset: 
Cp 
Cwe or Cvp 
LCB 
LCF 
bt/B 
iE 
It was felt that sufficient information was available to accurately 
determine the optimum value of LCB and bt/B. See for in- 
stance Bailey [17], who presented results on the effect of sys- 
tematic variation of LCB on calm-water resistance, indicating 
a foremost limit on LCB of 6.2 percent of L abaft the midships. 
As to the choice of LCB, a constant position of 5 percent abaft. 
the midships was chosen as it was shown in the Maritime Re- 
search Institute Netherlands (MARIN) data set to be an opti- 
mum value for the majority of cases. 
The optimum value of Ce could be estimated quite well from 
the extensive data set on existing ships, while the same applied 
to iE. The Ce values adopted for other systematic high-speed 
hull form series were: Series 64 by Yeh [18], Ce = 0.63; 
Lindgrenand Williams series [19], Ce = 0.68; and the National 
Physical Laboratory (NPL) series by Bailey [17], Ce = 0.693. 
For the high-speed hulls in the MARIN data set a clear corre- 
lation existed between CB and CM so that Ce was chosen at a 
fixed value, Ct, = 0.63, for all block coefficients (see Fig. 8). 
Little systematic Work has been done on seakeeping, certainly 
not at Fn = 1, so less certainty existed as to the choice of LCF, 
which was thought to have.a marked influence on seakeeping. 
The decision was taken to devote a short subseries of three 
models to determine the optimum value of LCF within certain 
bounds, that is, between 6 and 9 percent aft of midships. For 
this reason three models were designed having the same curve 
of sectional areas, varying LCF, and of necessity also different 
Systematic Series Hull Forms 
Cwe and Cve. The resulting body plans of these three models, 
Fig. 1, show that for the same displacement and in fact on the 
same curve of sectional areas a gradual transition was-m~de: 
from a narrow-forebody/wide-aftbody shape (Model 1) to a 
wide-forebody/narrow-aftbody shape (Model 3). In order to 
keep to realistic models it was felt that for this great a shift in 
LCF, it was not entirely possible to keep Cwe the same. We 
would have liked to, but the waterplane width forward would 
have been too much and the waterline entrance angle would 
have become too large for Model 3. Therefore, of necessity, 
Cwe was reduced from Model 1 to Model 3 and Cve likewise 
went up for the same CB; see Fig. 2. As a consequence, the 
results to be found from these models, perhaps not so much on 
resistance, but all the more so on seakeeping, cannot be attrib- 
uted to LCF only. Yet the differences in seakeeping between 
the three models, if only attributed to narrow-wide and wide- 
narrow configurations, are unmistaken. 
This was perhaps one of those points in which "scientific 
rigor" (whatever that may be), or the wish to vary only one 
parameter at a time, which is elegant when dealing with sys- 
tematic series, had to give way to the one and only rule that 
pervades this whole series, "the hull forms have to be realistic 
and practical." 
When the results on these three models became available and 
MODEL 1 ~ . 
MODEL 2. ~ . . ~ 
Fig,- 2 Comparison of ! ~ V ~ -----'''~ 
;u;t[oOrnmS by Salient 
were collated with other data, it was found that still more im- 
provements could be made. Therefore the models were cut 
up amidships and the fore and aft bodies combined in a dif- 
ferent way. This resulted in models with a wider waterplane 
area for the same displacement. Three models thus obtained, 
denoted Models 4, 5, and 6, were also tested. Figure 8 gives 
a~ 
o~ m~ 
I.- IJJ 
LL~ 
<: 
o 
122 
rr" 
< 
Z 
"narrow" 
MODEL 1 
"med ium" 
"wide" 
MODEL 4 
=+6 
= 
-6 
-14 
"medium" ~um" 
MODEL 2 
®-0 
= -7 
MODEL 5 
@= +13 
] 
"wide" 
MODEL 6 
:+6 
I 
"wide" 
MODEL 3 
®=-i 
"NARROW" "MEDIUM" FORE BODY 
Fig. "3 Models tested 
"WIDE" 
Systematic Series Hull Forms 129 
0.5 
CB 
0.4 m 
I 
0.35- - 
.4 / 
I 
I 
I 
~4- - - -4 -~- -~ ...... ;~-,5 
s i s . / / / / i / / ~ .t-" J I 
z / / [ / / 
8" 12 / ( J - ;~5 
L/B 
Fig. 4 Parameter space for entire test series 
chine forms. For the characteristic form of the series a rouno 
bilge was adopted as it was felt that hard-chine forms, even 
when optimum for the parent, might not be optimum for the 
transformed shapes. Moreover, hard chines have their benefit 
in the planing or semiplaning mode, which comes about only 
at speeds Fn > 1.2--on the verge of the present series. In ad- 
dition, the series was intended to be for true displacement hulls 
with perhaps some dynamic lift from planing, but not more 
than say 10 percent at the highest speed.. 
The characteristic shape first drawn up is shown as Model 
2 in Fig. 1. The transom stern does not extend over the full 
width of the beam, and the forward sections at least for the 
forward quarter ship length are truly triangular. It should be 
well understood that the characteristic shape--the parent 
hull--emerged as the condensate of a great number of one-off 
designs that were all extensively tested and modified to get the 
maximum out of them and that have actually been built. 
a quick-look impression of how the six models are related to one 
another. 
Parameter space of entire series 
Because the total number of parameters to be. varied in the 
true series amounted eventually to three, the parameter space 
can easily be illustratedas shown in the "magic cube" of Fig. 
4. In this fashion the total number of models would amount 
to 27 and the model in the solid center would play the role of 
parent hull form. The parent hull would feature: 
L/B = 8 
B/T = 4 
CB = 0.4 
The location of the parent hull and the width of the parameter 
space were derived on the basis of the data files of MARIN, in 
which all data of models tested at MARIN are stored. All 
high-speed hulls in the data set were closely investigated and 
plotted in diagrams like those shown in Figs. 5-8. These show 
at a glance that the extent of the variation chosen for the series 
is by no means extraordinary and that the particulars of the 
parent hull are right in the middle of the data set. 
It should be kept in mind that the data pertain to ships ac- 
tually built; thus the variation in parameters would be quite 
wide. L/B ranging from as low as 4 to a high as 12 should in- 
clude anything from a short beamy patrol vessel to a slender 
cruiser. The BIT ranges from 2.5 to 5.5; anything lower than 
2.5 would face serious stability problems while 5.5 is so much 
more than current coefficients that only patrol craft might 
approach it. The range of block coefficients was chosen with 
an eye to determining the limits of applicability of the high- 
speed surface ship, so it is somewhat lower than for current 
surfaee combatants: CB = 0.35 to 0.50. For some time it had 
been the idea to adopt a bottom figure for CB of 0.30, but it was 
found that the characteristic hull shape could not be realistically 
transformed so far down the CB scale without seriously dis- 
torting the section shapes or adopting hollow sections, or sections 
with a hollow deadrise, for the greater part of the length. 
Characteristic shape of parent hull 
For the main particulars selected for the parent hull form a 
characteristic shape had to be selected that would be optimum 
from the aspect of calm-water resistance and seakeeping. The 
body plans and test results of the models related to Figs. 5, 6, 
and 7 were closely investigated and the characteristics of the 
very best models compared. They all showed triangular V- 
shape sections forward and an almost flat ahbody. 
Most of them were round bilge, some of them were hard- 
Exper imenta l program 
For the most part the research program on systematic hulls 
is an experimental program, the experiments being done in 
various basins and in still water and in waves. The general 
approach and some interesting details follow. 
Laboratories 
The experiments were carried out in two basins: the calm- 
water resistance tests in the Deep Water Towing Tank mea- 
suring 250 by 10.5 by 5.5 m (820 by 35 by 18 ft) and the ex- 
periments in head waves in the High Speed Towing Tank 
measuring 220 by 4 by 3.6 m (720 by 13 by 12 ft) in length, 
width, and water depth, respectively. Both basins have a 
manned towing carriage that can attain a speed high enough 
to cover the speed range envisaged: Fn = 0.1 to 1.2. The 
carriage on the Deep Water Towing Tank can do 9 m/s (30 ft/s) 
and the one on the High Speed Basin as much as 15 m/s (50 
ft/s). 
The speeds at which seakeeping experiments were carried 
out were Fn = 0.285, 0.570, 0.855, and 1.140, which for the 5-m 
(16.4 ft) model correspond to 2, 4, 6, and 8 m/s (6.5, 13.1, 19.7, 
26.2 ft/s). For an 85-m (280 ft) frigate this speed range cor- 
responds to 16, 32, 48 and 64 knots. Later on in the program 
an additional speed at 24 knots was added, both because of its 
being a realistic frigate speed and because the heave and pitch 
transfer functions appear to be strongly dependent on speed 
in this range. 
Models and equipment 
Themodel size was typically 5 m (16.4 ft) in length (water- 
line) although eventually the L/B and B/T variations would 
see slight differences in model dimensions in order to keep to 
desired size and displacement measures. A typical displace- 
ment figure was around 0.2 m 3 (7 ft3). 
The attachment system in both basins is virtually the same. 
In the deepwater basin the model was connected to a resistance 
dynamometer and to a fore-and-aft trim apparatus to keep it 
on course while allowing sinkage and trim. In the high-speed 
basin the model was secured to the towing carriage by means 
of a universal joint that restricted the model in sway, yaw, and 
surge motions. The joint itself was mounted to the bottom of 
an air-lubricated cylinder that allowed up and down motion 
of the model without friction. In this way the heave, pitch, and 
roll of the model were not restricted. The attachment point 
of the model to the universal joint was taken at the center of 
gravity (CG). 
Considerable debate goes on whether, for dynamic tests,.to 
tow the model in the CG or in the extended propeller shaft. 
Since neither of the two were known quantities in this series, 
130 Systematic Series Hull Forms 
15 
10 
nnff- 
0 
0 
MODEL DATA 
~ r 
• ..j . " • 
• J~° o uo~oeo e 
Fig. 5 
5 10 
Correlation of BIT to L IV I/3 
1.0 
0.5 
0 
15 0 
Fig. 7 
MODEL DATA 
I o 
.i;,~;;:.."- . _. i-. 
e• • 
5 10 
Correlation of Cs to L IV 113 
15 
15 
10 
...~m 
0 
0 
MODEL DATA 
e 
t 
I 
oe" • 
#. 
. . : . , " 
. c~ . 
Fig. 6 
5 10 
Correlation of UB to L IV 1/3 
15 
MODEL DATA 
0.4 
/ J 
f'# S 
03 0.4 Q5 
CB 
Fig. 8 Correlation of CB to CM 
0.6 
Systematic Series Hull Forms 131 
Table 2 Coefficients of the models 
Nota- 
Designation tion Model 1 
NSMB Model No. 
Model 2 Model 3 Model 4 Model 5 Model 6 
Length/breadth LIB 8 8 8 
Breadth/draft B/T 4 4 4 
Block coefficient: 
total CB 0.396 0.396 0.396 
forebody CBF 0.327 0.327 0.327 
aftbody CBA 0.465 0.465 0.465 
Midship section 
coefficient CM 0.633 0.633 0.633 
Waterplane coefficient: 
total Cwp 0.785 0.768 0.749 
forebody CWPF 0.577 0.588 0.600 
aftbody CWPA 0.992 0.947 0.898 
Horizontal prismatic 
coefficient: 
total Cp 0.626 0.626 0.626 
fore CpF 0.517 0.517 0.517 
aft CpA 0.735 0.735 ' 0.735 
Vertical prismatic 
coefficient: 
total Cvp 0.505 0.516 0.528 
fore CvpF 0.567 0.556 0.545 
aft CVp A 0.469 0.491 0.518 
Longitudinal center of 
buoyancy in % L LCB -4.97 -5.12 -5.16 
Longitudinal center of 
flotation in % L LCF -9.23 -8.11 -6.77 
Angle of waterline 
entrance, deg iE 6.5 9.5 11.0 
Breadth transom/breadth bt/B 0.89 0.74 0.59 
8 8 8 
4 4 4 
0.396 0.396 0.396 
0.327 0.327 0.327 
0.465 0.465 0.465 
0.633 0.633 0.633 
0.790 0.796 0.774 
0.588 0.600 0.600 
0.992 0.992 0.947 
0.626 0.626 0.626 
0.517 0.517 0.517 
0.735 0.735 0.735 
0.501 0.497 0.512 
0.556 0.545 0.545 
0.469 0.469 0.491 
• -5.02 -5.11 -5.22 
-9.01 -8.68 -7.77 
9.5 11.0 11.0 
0.89 0.89 0.74 
a decision was taken to select one point which would be held 
constant for all models. The CG was chosen at 60 percent of 
the depth of the model, which worked out at 0.169 m (0.55 ft) 
above the base for a 5-m-long (16.4 ft) model. 
For the calm-water resistance tests a sand strip was used to 
trip the boundary layer into turbulence. 
The freeboard of the models was kept at 6 percent of the 
length at the fore perpendicular with a gentle slope toward the 
stern. The necessity to have some consistent measure of free- 
board came from the point of view of irregular wave tests and 
relative water motion. Data on freeboard, as for instance given 
in [3] and [20], suggest that this measure is applicable to cor- 
vettes in the 80-m (260 ft) size range, but that longer ships could 
do with less. The continued discussion on deck wetness on 
existing ships, however, may indicate that a number of frigates 
are in want in this respect and would serve better with a little 
more freeboard forward [5,6]. Still, for the purpose of this 
seriesthe 6 percent was a realistic figure. 
For the experiments in head seas the longitudinal weight 
distribution had to be adjusted, for which a gyradius of 25 
percent of the length was selected. Experiments on earlier 
models had indicated that the gyradius is an important pa- 
rameter, while strip-theory-based computations showed it to 
have some influence. Nevertheless the scope of variation that 
current design approaches would allow in longitudinal gyradius 
is extri~mely limited and it is envisaged eventually to devote a 
short subseries of experiments to this parameter by varying the 
gyradius between 0.21 L and 0.27 L, probably on the parent 
hull only. 
As the series was focused on calm-water resistance and on 
motions andresistance in head seas, no appendages of any kind 
were fitted. In due course of this series work it is projected to 
go into detail on trim wedges and on propulsion and pertaining 
appendages such as struts, shaft bossings, rudders, and bilge 
keels. 
Regular-wave and irregular-wave experiments 
The High Speed Towing Tank has a hydraulically operated 
wave generator with a double flap which can be used to gen- 
erate regular sinusoidal waves and irregular seaways con- 
forming to a prescribed spectrum. 
For the present test program a series of 11 regular waves was 
used, spanning the wavelength to ship length range of 0.6 to 2.8. 
Later on the short wave range was slightly extended to improve 
the acceleration prediction on the high-frequency end of the 
scale. The wave height was 2 percent of the ship length. A 
series of waves at different heights was also tried to determine 
the degree of linearity at high speed. For the whole series 
shown in Fig. 4, irregular wave tests were also carried out. For 
the subseries of models, regular waves were thought to suf- 
fice. 
Calm-water experiments 
The resistance tests in calm water in the Deep Water Towing 
Tank were carried out for the whole speed range Fn = 0.1 to 
1.2 with a large number of measurement points to determine 
the humps and hollows of the resistance curve with sufficient 
accuracy• The wetted surface of all models of Subseries 1 was 
very nearly the same. 
Measurements 
Concerning the measurements, he~/ge was measured at the 
CG using a potentiometer fitted on the air-lubricated cylinder; 
pitch was measured with a potentiometer on one of the axes of 
the universal joint in the model; vertical acceleration was 
measured at 5station 19 on the forebody by means of an accel- 
erometer; and the vertical relati~ee motion between water sur- 
face and hull was measured at station 17 using a resistance-type 
5 By European custom the transom stern has been denoted station 
0 and the fore perpendicular station 20. 
132 .Systematic Series Hull Forms 
wave probe. Themodel resistance was recorded in a strain- 
gage cell in the universal joint so that the resistance force 
measured remained horizontal at all times. 
For the correction of the phase angles to the wave crest it was 
necessary to have a measure of the wave; this was taken 3.5 m 
(11.5 ft) ahead of the model. As the very high speed would 
render ordinary wave probes useless because of the wave system 
of the wires themselves, a servo-controlled wave follower device 
was used that could cope with the very high velocities and ac- 
celerations. 
Measurements were all recorded on fiber optics recorder strip 
charts for quick-look inspection and on magnetic tape for 
proper analysis. 
Resu l ts on seakeep ing behav ior 
From the wealth of data obtained from the experiments the 
most salient results are shown in the paper. The results are 
exclusively related to the forerunner series of models shown in 
Fig. 3 that led to the choice of the parent hull in the solid centre 
of the cube in Fig. 4; see also Table 2. 
Inf luence of geometry on heave 
Figures 9-12 serve to illustrate the influence of model ge- 
ometry on characteristic seakeeping transfer functions for one 
.speed, Fn = 0.570. In Fig. 9 for heave the differences between 
the models amount to.some 10 percent in the region of wave- 
length, which is of most interest to this kind of ship at such 
speeds. It is not possible to attribute the differences to one 
single cause, as many influence factors change. 
The wave exciting force for heave is directly proportional 
to the waterplane area, which was different for all six models. 
The one with the largest waterplane area, Model 5 (Cwe = 
0.796), would have the largest wave exciting force. The added 
mass is to leading order proportional to beam squared, then to 
B/T ratio, and finally to section shape. Model 5 would also 
have the largest added mass, which would suppress the motions 
in the high-frequency regime. 
As to the damping, also proportional to beam squared, the 
same can be said, and it may be expected that the model with 
the largest Cwe (No. 5) would have the highest damping and 
the lowest transfer function in the X/L = 1 region. The dif- 
ference in spring rate is proportional to the waterplane area, 
hence the Cwe, and in the long wave range the model with the 
largest Cwe would have the lowest transfer function in heave. 
The differences due to change in heave-pitch coupling can be 
understood only through a direct computation, for instance with 
strip theory. With the foregoing in mind the qualitative trend 
of the data in Figs. 9-12 can be explained to a fair degree. 
Model 5 has the largest Cwe and thus the greatest waterplane 
area for the same displacement, resulting in very low heaving 
for all speeds. Model 3 has the lowest Cwv and thus the 
smallest waterplane area for the same displacement, resulting 
in rather large heave motions for most speeds. Because the 
block coefficient is kept constant, the heave motion exhibits the 
same trend on the basis of (Cve) -1. The differences in heave 
between the six models are largest around X/L = 1.2 for low 
speed and around X/L = 2.4 for the highest speed, which 
demonstrates that the greatest differences are to be' found 
around the peak of the magnification factor Za/~a. The in- 
fluence of Cvv on heave will be noted in Fig. 9; it is even more 
pronounced for higher speeds where it is found that the models 
with the lowest Cve (Models 1, 4, and 5) have the smallest 
heave, whereas the other three with the highest Cve have the 
greatest heave. Because of other effects such as LCB-LCF 
separation, which greatly influences the heave-pitch coupling, 
the heaving may not always be directly in line with the Cvv, 
but a strong dependency certainly exists in this case. When we 
Systematic Series Hull Forms 
relate Cve to hull shape we find that for this family of models 
the great breadth of the transom stern, and as a direct result the 
Width of the whole aftbody, is of direct influence on Cve, so that 
we may qualitatively conclude that a wide aftbody results in 
ahigh Cve, which in turn results in low heaving. This rea- 
soning cannot be detached from the present family of models 
in which the displacement and the block coefficient were kept 
the same, and in which the CweF was not allowed to vary to the 
same extent as Cwva because the waterline entrance angle had 
to remain fine. 
Influence of geometry on pitch 
When we take a look at the pitch functions of all six models, 
shown in Fig. 14, we find a 10 percent difference mainly 
around resonance (where it matters). Since pitching is the most 
dominant motion in head seas, it may be better to take a look 
at Figs. 13 to 16, where the pitch functions are shown for all six 
models and for all four speeds. Where the differences at low 
speed amount to some 10 percent, the differences at high speed 
are by no means marginal, but amount to some 45 percent in 
the )~/L range around 2.2. These figures show a striking trend. 
If the models are again ranked onthe basis of their Cve, it is 
found (Fig. 16) that the model with the lowest Cve exhibits the 
smallest pitch angle. As the Cvv increases, the pitch angle goes 
up, almost proportionally. For the highest speed, Fn = 1.14, 
this comes out beautifully; for the • lower speed, the differences 
are not so large but the same trend still exists. No such clear-cut 
trend can be established on the basis of LCB or LCF or their 
separation, so that the conclusion seems warranted that a low 
Cve brings about a small pitch angle, regardless of the LCB- 
LCF separation. One should, however, be careful about taking 
this conclusion outside the present family of models. 
Influence of geometry on accelerations 
The vertical acceleration at station 19, shown in Fig. 11, is 
for head seas essentially the result of combined heaving and 
pitching, and likewise bears a linear relationship to the wave 
amplitude. In order to adhere to the Froude scaling law and 
to make the acceleration nondimensional in the transfer func- 
tion, the acceleration has been divided by ~a/L, the ratio be- 
tween wave amplitude and model length. Although in the 
present case the accelerations were actually measured, they 
might just as well have been calculated from heave and pitch 
and their relative phase angles. When we compare this Fig. 
11 to the pitch function in Fig. 14, we find the same trend on 
the basis of model geometry. The model with lowest Cve 
produces the lowest acceleration and, as the Cvp goes up, the 
vertical acceleration at synchronous pitching goes up as well. 
It shows, at least for this speed, that a number of models virtu- 
ally coincide as to their acceleration levels, but for other speeds 
this is not the case. 
Relative motions 
The relative motion between hull and water surface was 
recorded only at station 17; this was done with wires flush with 
thehull. Because of the problem of how to define exactly what 
one is measuring in this way--spray; solid water jetted upward 
and a sheet of water creeping upward all have their influence 
on the electronic measurement--this measurement should be 
regarded as indicative, certainly at the highest speed where 
spray was very much in evidence. Much the same, the concept 
of relative motion being the result of combined heaving, 
pitching and incident waves becomes questionable; water 
particles touching the stem at the waterline level will be flying 
past station 17 a little higher up and may wet the deck at station 
10. Concerning the shape of the transfer function there exists 
a close correspondence between the pitch function and the 
acceleration function. 
133 
1.5 
1.0 
0 
0 
0 .5 
Fn = 0 .570 
MODEL 1 
. . . . . . MODEL 2 
. . . . . MODEL 3 
- - - - - - MODEL 4 
. . . . . . . . . MODEL 5 
. . . . . MODEL 6 
/ 
Fig. 9 
1 2 
X/L 
Heave transfer functions 
0 
25 
0 
0 
Fn : 0 .570 
- - MODEL 1 
. . . . . . MODEL 2 
. . . . . MODEL 3 
- - - - - - MODEL 4 
. . . . . . . . MODEL 5 
- - - - MODEL 6 
Fig. 11 
/-,, 
/ / '~, 
2 
~'/L 
Vertical acceleration transfer functions 
ul 
0 
0 
F'n : 0 .570 
- - - MODEL 1 
. . . . . . MODEL 2 
. . . . . MODEL 3 
- - - - - - MODEL 4 
. . . . . . . . MODEL 5 
. . . . . MODEL 6 
Fig. 10 
X/L 
Relative motion transfer functions 
J 
0 
3 0 
Fn = 0 .570 
MODEL 1 
. . . . . . MODEL 2 
. . . . MODEL 3 
- - - - - - MODEL 4 
. . . . . . . . . MODEL 5 
. . . . . MODEL 6 
Fig. 12 
2 
) - /L 
Wave added resistance transfer functions 
134 Systemat ic Ser ies Hull Forms 
1.5 
tO 
C) 
1.0 
0 .5 
0 
0 
Fn= 0 .285 
- - - - MODEL 1 
. . . . . ~ MODEL 2 
. . . . . MODEL 3 
m- - - - MODEL 4 
. . . . . . . . . . MODEL .5 
. . . . . ~ MODEL 6 
2 
X /L 
Fig. 13 Pitch transfer functions 
. . . . - - _ __ . ______ - - _ - - _ . 
1.5 
1.0 
J 
0.5 
0 
Fn = O. 855 
MODEL 1 
. . . . . MODEL 2 " 
. . . . MODEL 3 
- - - - - - MODEL 4 
. . . . . . . . . . . MODEL. 5 
. . . . . MODEL 6 
/,(J 
/ 
/ 
1 2 
X/L 
Fig. 15 Pitch transfer functions 
t~ 
(D 
1.5 
1.0 
0 . , ~ 
0 
0 
Fn :, 0 .570 
- - - - MODEL 1 
. . . . . . MODEL 2 
. . . . . MODE L 3 
. . . . MODEL 4 
. . . . . . . . . MODEL 5 
. . . . . . MODEL 6 
/ 
1, 
(!) 
O. 
2 
) ' / L 
Fig. 14 Pitch transfer functions 
3 0 
Fn = 1.140 
MODEL 1 
. . . . . MODEL 2 
. . . . . MODE L 3 
- - - - - - MODEL 4 
. . . . . . . . . . MODEL 5 
. . . . . MODE L 6 
J 
.///~, 
/ 
/ zZl//" 
/ 
1 2 
X/L 
Fig. 16 Pitch transfer functions 
Systemat ic Ser ies Hull Forms 135 
Relative motion seems to be related to acceleration, judging 
by the shape of the functions. Indeed, both drave on the ab- 
solute vertical bow motion, composed of heave and pitch with 
their proper phasing. Where for accelerations the fre- 
quency-squared term is then introduced, the relative motion 
sees the addition of the undisturbed incident wave with its phase 
angle. So in view of their different composition it is all the 
more interesting to find the shapes so in correspondence. 
Because both accelerations and relative motions draw on the 
absolutevertical bow motion, there exists a tendency for the 
model that comes out best on accelerations to also produce low 
relative motions. Although there is not a one-to-one corre- 
spondence, the figures seem to substantiate this to some degree. 
Although relative motions derive their importance from the 
indication they can give of deck wetness and shipping green 
water on deck, it should be mentioned that for the present 
high-speed hull forms green water can indeed be related to 
them, but deck wetness resulting from spray is not easily related 
to the relative motion. It should also be pointed out that the 
abovewater bow flare forms were really effective in throwing 
the masses of water to the side. The sole exception was Model 
5, which had a wet foredeck, unlike the others. This model was 
eventually to become the parent hull form, but not until the bow 
flare was modified--not much, but just enough--to keep the 
deck dry in high waves. As shown in Fig. 10, Model 5 already 
had a good (low) relative motion transfer function, but because 
• of the curvature of the forebody flare it produced a good deal 
of spray on the deck, which was later rectified. 
Added resistance in waves 
Figure 12 illustrates the resistance increase of the six hull 
shapes. It should be borne in mind that as the speed goes up, 
the stillwater resistance increases with the square of the speed. 
The wave added resistance shows some speed effect but this can 
hardly be expressed as a power function. So, at high speed the 
added resistance becomes comparatively small relative to the 
stillwater resistance so that, first, it is difficult to extract the 
added resistance from the measurement, while second, if it is 
that difficult to extract it, it cannot be important after all. The 
emphasis then falls upon the added resistance in the low and 
intermediate wave range exemplified by Fig. 12. The transfer 
function shown has been made nondimensional in the usual 
way. 
When we compare the shape of these functions to the transfer 
functions of accelerations and relative motions, we observe a 
very close correspondence. This makes sense because most 
mathematical models in this field split up the resistance into a 
motion part, closely related, to pitch and heave and the phase 
angle between these two, and a diffraction part, which is asso- 
ciated with the relative motion. It may be expected that the 
motion part is also related to the accelerations because both 
draw on the same basic ingredients. The influence of hull 
shape is lessobvious. We have found that Models 1, 4, and 5 
stand out as the best because of their low Cve value and their 
low motion level. This clear-cut trend is not so evident when 
we look at Fig. 12. Still, Model 3 with the highest Cve produces 
the highest added resistance and Model 4 with a low Cve pro- 
duces the lowest added resistance at most speeds. 
Only a true mathematical treatment like a strip theory pro- 
gram may shed some light upon this matter, in particular when 
it takes the diffraction part into account through inclusion of 
the relative motion. In general, it could be concluded that at 
comparatively low speed there is little to choose between the 
six models, while as the speed goes up the differences increase. 
This is partly due to the differences in the abovewater hull 
shape. Another factor that must not be overlooked is that at 
the highest speed the wave added resistance constitutes only 
a very small part of the total resistance. Consequently, the 
136 
stillwater resistance figures are more important to reckon with. 
Conversely, the wave added resistance at high speed is more 
difficult to extract from a model test and its measurement ac- 
curacy is lower than for the lower speeds. Nevertheless, Fig. 
12 tells us that there exists a difference of some 20 percent be- 
tween the various underwater hull forms, which would grow 
to 40 percent for the highest speed. 
Effect of speed on pitching 
A series of illustrations, Figs. 13-16, was included to show the 
effect of speed on pitching, which is the most dominant motion 
in head seas. One can see that as the speed goes up the pitch 
transfer function develops a rise around k//L = 2.0, and for even 
higher speeds drops substantially in that wavelength range. 
The Doppler shift of the wave exciting moment relative to the 
pitch response function (viewed as a mass-spring oscillator) has 
much to do with this. The pitch transfer functions shown in 
the Figs. 13-16 have all been made nondimensional on the basis 
of wave slope, as is usual for an angular motion. An even more 
telling way to make it nondimensional is through dividing the 
pitch angle by ~a/L. If one does so, the transfer function as- 
sumes the illustrative peaked form that is better in line with 
observations, because it shows the occurrence of synchronous 
pitching better than on the basis of wave slope; see Fig. 18. This 
figure shows that for an increase in speed the pitch angle goes 
down dramatically, which is indeed what is observed in the 
experiment, and can directly be explained by the Doppler 
shift. 
Effect of speed on other seakeeping quantities 
The effect of speed on the other seakeeping quantities is 
shown in Figs. 17, 19, and 20 for Model 5 only. It is interesting 
to note that for heave at the lowest speed, the peak of the re- 
sponse function (heave as a mass-spring oscillator) very nearly 
coincides with the zero point of the wave exciting force. As the 
.speed increases, heaving increases too for long waves, in par- 
ticular in the range between the two lowest speeds. For this 
reason an extra speed was added between the two in subsequent 
experiments. The same great change between the lower two 
speeds is found in the acceleration, Fig. 19, where the peaks of 
the acceleration curves for the higher speeds are virtually on 
the same level. The wave added resistance in Fig. 20 exhibits 
a speed effect roughly proportional to the radical of the speed, 
and the Doppler shift as much in line with pitch as with the 
accelerations. 
Some typ ica l resu l ts on ca lm-water res i s tance 
Some typical results of the resistance tests are shown in Fig. 
37 for the Hull 5 (which was to become the parent hull). It 
shows the residuary resistance coefficient plotted on a basis of 
Froude number, the latter based on the third root of the dis- 
placement. One can see that the design speed of the series Fn 
= 0.7 to 1.0 (Fnv = 2.0 to 3.0) coincides with the second hollow 
of the residuary resistance curve. 
In the attending sinkage and trim diagram, Fig. 38, it is 
clearly visible that at first in the intermediate speed range the 
CG sinks in, associated with an increase in trim and likewise an 
increase in resistance, which works out to be the first hump 
around Fnv = 1.8. In the design speed range the stern is lifted, 
resulting in a rise in CG and a trim angle around 1.5 deg. The 
resistance in this region benefits from this and exhibits a hollow, 
the second one. 
Ship mot ionca lcu la t ions 
Calculations of the motions and resistance increase in waves 
are based on the well-known strip theory. In this way a two- 
Systematic Series Hull Forms 
1.5 
f0 
N 
1.0 
0 .5 
0 
0 
Fig. 17 
MODEL 5 
- - - - Fn =,0 .285 
. . . . . . . F'n = O. 570 
, Fn = 0 .855 
Fn = 1.1 40 
\ \ \ \ 
0.5 1.0 
Influence of speed on heave transfer functions for 
Model 5 
1.5 0 
Fig. 19 
MODEL 5 
~ F n = 0 .285 
. . . . . . Fn = 0 .570 
. . . . Fn = 0 .855 
- - - - - -Fn = 1 .140 
! 
/ ., ,/'//!,, 
/ 
0.5 1.0 1.5 
Influence of speed on acceleration transfer functions for 
Model 5 
300 
200 
d 
r0 
100 
0 
0 
Fig. 18 
MODEL 5 
- - - -Fn = 0 .285 
. . . . . . Fn = 0 .570 
i 
. . . . . . Fn = 0 .855 
. . . . Fn= 1 .140 
- - . 
/$I -.,, '\ 
/ ' -~ \ \ 
/ \,\\ ',, 
X 
\ 
\ 
5 
0 
0 .5 1.0 1.5 0 
L,/-c-5: 
Influence of speed on pitc.h'transfer functions for Fig. 20 
Model 5 
Systematic Series Hull Forms 
MODEL 5 
Fn = 0 .285 
. . . . . . Fn = 0 .570 
. . . . . Fn = 0 .855 
- - - - - -Fn = 1 .140 
!! A 
/7/ 
Y 
Y 
0.5 1.0 1.5 
Influence of speed on wave added resistance transfer func- 
tions for Model 5 
137 
dimensional multipole approximation of the linear potential 
is used to determine the hydrodynamic mass and damping for 
a ship's section, based on Ursell's analytical solution for an os- 
cillating circular cylinder on the surface of a heavy fluid [21]. 
With the aid of conformal transformation it is possible to 
transfer this solution of a circular cylinder to arbitrary ship 
sections. Such a transformation may be achieved by the gen- 
eral formula 
w= a{~+ n=0 "~" a2n+a~-(2n+ 1)} (1) 
where ~ represents a point on the unit circle and w represents 
the corresponding point on the ship section (w and ~ are com- 
plex coordinates). 
For n = 1 the so-called Lewis transformation is obtained 
which in general provides sufficient accuracy for most ship 
sections. This Lewis transformation determines the ship section 
by the breadth-draft ratio and the sectional area coefficient. 
A procedure of this transformation for shiplike cross-sections 
has been presented by Tasai [22] and Grim [2:3]. A more ac- 
curate description of the ship section may be obtained by the 
"close-fit" transformation, for which case in equation (1), n > 
1. 
After determination of the hydrodynamic coefficients for 
each section the values for the whole ship are found by inte- 
gration over the ship's length according to the method presented 
in [24,25]. 
For different frequencies or wavelengths and the speeds 
considered, the response functions have been calculated for the 
vertical motions, accelerations, and added resistance in waves. 
These response functions have been determined for two versions 
related to the speed influence as mentioned in [24] and [25]: 
• Version 1, sometimes called the ordinary strip method 
(OSM), leads to a set of motion equations which lack some of 
the symmetry relations in the mass coupling coefficients and 
some additional terms in other hydrodynamic coefficients. For 
this version 1 the speed influence is taken into account only for 
the derivative of the sectional added mass with respect to the 
shiplength. In such a way, only terms are introduced with 
din' 
V - - 
dx 
• Version 2 also takes into account the speed influence re- 
lated to the derivative of the damping coefficient with respect 
to the ship length, and so terms are introduced with 
dm' dN' 
V ~ and V d---x- 
In this way the mentioned symmetry relations are present in 
the hydrodynamic coupling coefficients and so the presentation 
of the hydrodynamic coefficients agrees with [26]. 
The added resistance in waves has been calculated according 
to the method of Gerritsma and Beukelman as developed in 
[27}. Their method is based on the relation between the ra- 
diated damping energy as calculated by the strip method and 
the added resistance in waves accounting for the relative motion 
of the ship with respect to the water surface. 
The response functions of the motions, accelerations and 
added "resistance in waves have been calculated for the two 
mentioned versions by the computer program "TRIAL" of the 
Ship Hydromechanics Laboratory of the Delft University of 
Technology. As an example, the calculated values of the ver- 
tical absolute motions, accelerations and added resistance in 
waves are shown in Figs. 21-28 for Model 5 at two speeds: Fn 
= 0.570 and Fn = 1.140. 
These response functions have also been calculated by a Delft 
computer program based on a close-fit transformation with n 
= 9 in equation (1); this means that nine coefficients have been 
Choice of parent hul l fo rm 
In choosing the parent hull form, the work on Subseries 1, 
incorporating LCF variation and Cwv variation, was brought 
to a conclusion and the work on the true series as shown in Fig. 
4 could start in earnest. The most important aspects of this 
choice are related in the following. 
Calm-water resistance aspects 
The resistance measured in calm water was split up into a 
frictional resistance part, calculated according to the ITTC-57 
extrapolation method, and a residuary part. Because all six 
models had virtually the same wetted surface--their dis- 
placement was the same--the comparison of the six models 
could just as well be done on the basis of residuary resistance. 
The values thus obtained were normalized on the basis of the 
residuary resistance of Model 2, which was arbitrarily set at 100 
percent. The percentages are given in Table :3. It is shown 
that Model 5--the parent to be--is not the best model on re- 
sistance. No. 6 would do better at high speed. But model No. 
5 holds an attractive position: 
used for the transformation of the ship section to the unit circle. 
The results are also presented in Figs. 21-28. 
Figures 29 and 30 show the results of computations and form 
the counterpart of Figs. 14 and 16. 
For the same irregular seas as used for the experiments, cal- 
culations have been performed to determine the dimensionless 
values of the significant motions, accelerations and added re- 
sistance. Some of these results are shown in Figs. 33 to :36, again 
for Model 5 but for Fn = 0.570 only, including results based on 
Versions i and 2 and the close-fit transformation. 
It is generally stated that the following assumptions restrict 
application of the strip theory: 
1. The ship form should be slender with gradual change 
of this form in the longitudinal direction. 
2. The frequency of motion should not be too low or too 
high. 
:3. The forward speed of the ship should be low. 
In the past, special experiments have been performed to 
gather more information about the aforementioned limits. 
With respect to the first assumption, reference is made to [24], 
in which investigations are described related to the ship's 
slenderness. The surprising result was that even for L /B = 4 
the calculated responses in head waves show good agreement 
with the measured model experiments. 
In the present work, very high forward ship speeds are con- 
sidered in order to investigate also the limits mentioned in the 
third assumption. It may be concluded that even for the 
highest speed, Fn = 1.140, the agreement between experiment 
and calculation is satisfactory as far as the heaving and pitching 
motions and the vertical accelerations are concerned. 
Up to Fn = 0.570, this agreement is also reasonable for the 
relative motions and added resistance in waves. Above this 
speed, there is a considerable lack of agreement with respect 
to these phenomena. This might be due to the significant in- 
fluence of the ship's own wave profile and dynamic swell-up, 
which is appreciable at these speeds. The influence of these 
phenomena has not been taken into account for the calculations, 
as yet further investigations in this respect are required. 
Another conclusion which may be derived from the com- 
parison between experiments and calculations is that for this 
ship form, hardly any improvement can be achieved with a 
close-fit transformation of the ship section. Moreover, it has 
been shown that the speed influence according to Version 2 
yields less reliable results especially for the highest speeds in 
spite of the presence of the required symmetry relations in the 
hydrodynamic coupling coefficients. 
138 Systematic Series Hull Forms 
1.5 
1.0 
l l} 
W 
0.5 
MODEL 5 
Fn = 0 .570 
- - - - VERSION 1 
. . . . "VERSION 2 
. . . . . CLOSE FIT 
MARIN EXR 
\ 
0 0.5 1.0 1.5 
Fig. 21 Correlation of measurement to computation for heave transfer 
functions 
MODEL. 5 
Fn = 0 .570 
75 
- - VERSION I 
- - - - - - VERS ION 2 
. . . . . CLOSE FIT 
MARIN EXR 
5C 
25 J 
r 
/ 
\ 
\ 
/ 
0 0.5 1,0 15 
Fig. 23 Correlation of measurement to computation for acceleration 
transfer functions 
1.5 
1.0 
Q 
0.5 
0 
MODEL 5 . _ _ - - VERSION 1 
. . . . VERSION 2 
CLOSE FIT 
Fn = 0 .570 o MARIN EXR 
MODEL 5 - - VERSION 1 
- - - - - - VERSION 2 
. . . . . CLOSE FIT 
Fn = 0 .570 o MARIN EXP 
0 
, \ 
1.0 1.5 
1u / 
° / 
oY 
.J/ 
0 0.5 0 0.5 1.0 1.5 
Fig. 22 Correlation of measurement to computation for pitch transfer Fig. 24 Correlation of measurement to computation for wave added " 
functions resistance transfer functions 
Systematic Series Hull Forms 139 
.oo~, ~ v~#s..o~ ~ .oo~. ~ VE#S',o°N 2' 
CLOSE FIT ~-~ CLOSE FIT 
Fn = 1.140 o MARIN EXP Fn = 1,140 /b \ MARIN EXP. 
1.5 
/ - 
o/ . / 
, .o " 5° /1 \ i - 
°°°ii o P/ ~ ~! ~ " 
o o 
0 0.5 1.0 1.5 0 0.5 • 1.0 1.5 
Fig. 25 Correlation of measurement to computation for heave transfer Fig. 27 Correlation of measurement to computation for acceleration 
functions transfer functions 
1.5 
1.0 
~n 
Q5 
0 
0 
Fig. 26 
VERSION 1 MODEL 5 
. . . . VERSION 2 
. . . . . CLOSE FIT 
Fn = 1,140 o MARIN EXP. 
\ 
\ 
\ 
\ 
~-~~--~ ~.o Oo \ 
N~\ i 
0.5 1.0 1.5 
Correlation of measurement to computation for pitch transfer 
functions 
C 
c 
J 
5 
0 
0 
Fig. 28 
MODEL 5 - - VERSION 1 
- - - - - - VERSION 2 
. . . . . CLOSE FIT 
Fn = 1.140 o MARIN EXP. 
f-, 
I\ 
o? / 
io~ 
ool /o 
0 
/ I 
0 
0.5 1.0 1.5 
Correlation of measurement to computation for wave added 
resistance transfer functions 
140 Systematic Series Hull Forms 
1.5 
1.0 
t l 
(D 
0 .5 
C 
0 
Fig; 29 
Fn = 0 .570 
- - MODEL 1 
. . . . . . MODEL 2 
. . . . . MODEL 3 
- - - - - - MODEL 4 
. . . . . . . . MODEL 5 
. . . . MODEL 6 
/ / 
/ 
1 2 3 
) ' /L 
Computed pitch transfer function comparison for six 
models 
300 
200 
._1 
~Q 
IN 
100 
Fn = 0 .570 
/ 
/ 
/ 
/ 
/ 
0 
0 
- - MODEl_ 1 
. . . . . . MODEl_ 2 
. . . . . MODEl_ 3 
- - - - - - MODEl_ 4 
. . . . . . . . . MODE[_ 5 
. . . . . MODE[_ 6 
"h 
\ 
Fig. 312 3 
El{2 
Irregular transfer functions based on regular-wave 
tests 
1.5 
1.0 
tO 
0 
0.5 
0 
0 
Fig. 30 
Fn= 1.140 
- - MODEL 1 
. . . . . . MODEL 2 
. . . . . MODEL 3 
- - - - - - MODEL 4 
. . . . . . . . . . . MODEL 5 
. . . . MODEL 6 
/" /~. 
/ I / ! / .,{/:,y 
/ 
J 
~:~:.~-~ 
300 
200 
_ J 
IO0 
C 
0 
/ 
/ 
/ 
Fn = 1.140 
MODEL. 1 
. . . . . . MODEL. 2 
. . . . . MODEL 3 
- - - - - - MODEL. 4 
. . . . . . . . . MODEL. 5 
. . . . . MODEL. 6 
Y 
1 2 3 
X/L 
Computed pitch transfer function comparison for six Fig. 32 
models 
Systemat ic Ser ies Hull Forms 
2 L/~2 
Irregular transfer functions based on regular-wave 
tests 
141 
~f. 
,r - / 
1.! 
1.0 
i t,..A 
iN 
0.5 
0 
0 
Fig. 33 
J / 
7" 
MODEL 5 
Fn = 0 .570 
- - VERSION 1 
. . . . VERSION 2 
. . . . . CLOSE FIT 
. . . . . . . MARIN EXR 
2 3 0 2 
Correlation of irregular transfer functions measured and Fig. 35 
computed for heave 
MODEL 5 
Fn= 0 .570 
- -VERS ION 1 
. . . . VERSION 2 
. . . . . CLOSE FIT 
. . . . . . . MARIN EXR 
/ 
• ~__ . . _~ 
2 
Correlation of irregular transfer functions measured and 
computed for accelerations 
300 
200 
|~, .n 
- J 
0'1 
=O 
IO0 
0 
0 
Fig. 34 
142 
MODEL 5 ~ VERSION 1 
. . . . VERSION 2 
. . . . . CLOSE FIT 
Fn = 0 .570 . . . . . . . MARIN EXR 
MODEL 5 - - - VERSION 1 
- - - - - - VERSION 2 
. . . . . CLOSE FIT 
Fn = 0 .570 . . . . . . MARIN EXR 
/ 
2 O 
LI{ 
Correlation of irregular transfer functions measured and Flg, 36 
computed for pitch 
ss" 
S''/' / ~ 
1 2 3 
Correlation of irregular transfer functions measured and 
computed for wave added resistance 
Systemat ic Series Hull Forms 
0.08 
0.06 
0.04 
0.02 
0 
0 
Fig. 37 
MODEL 5 
S 
~s 
s 
/ 
/ s 
/ 
i" 
/ 
/ 
s 
/ 
/ 
i 
I 
/ 
/ ' 
/ 
, / 
s 
/ 
I 
i I 
/i 
i 
I 
14 
// 
2 3 4 0 
Vs x 0.514447 FnV= 
Residuary resistance coefficient for Model 5 Fig. 38 
\ 
\ 
L 
MODEL 5 
, 
i i ! 
i / .~s S 
RISE C.G 
t 
/ 
/ 
TRIM ANGLE 
1 2 3 
Vs x 0.514447 
FnV= 
Sinkage and trim in calm water for Model 5 
4 
• It is one of the three best on resistance at high speeds. 
• It is very close to the best model at the design speed around 
Fnv = 2.5. 
So it is shown that a wide forebody combined with a medium- 
to-wide aftbody is good for residuary resistance. 
Seakeeping aspects 
In the foregoing a number of salient aspects in the field of 
seakeeping have been mentioned. For the selection of the 
parent hull it was necessary to obtain statistical data for irregular 
seas. To this end the measured transfer functions were syn- 
thesized with a family of wave spectra of unit significant wave 
height and a range of average periods. The result is a statistical 
measure, like the double significant output quantity presented• 
in Figs. 31 and 32, representing a kind of transfer function for 
irregular seas. Although the diagrams embody the two-pa- 
rameter ISSC wave spectrum and will be subject to change if 
a different spectral form is used, they nevertheless come in very 
handy for the comparison of ships, for design. As both pa- 
rameters of the sea state, height and period, can be introduced 
independently of one another, it provides sufficient latitude to 
be used in practice. 
For the choice of the parent hull, use was made of these kinds 
of diagrams as they are more straightforward than the transfer 
functions, which exhibit crossover points, making an assessment Speed, 
more cumbersome. 
-Seakeeping f igure of mer i t 1.0 
1.5 
In the selection of the parent hull form, use has been made 2.0 
of Bales' regression model for destroyer-type ships [28]. For 2.5 
the purpose of comparing hull forms on their seakeeping merits, 3.0 
he had devised a regression predictor model based on a great 3.5 
Systematic Series Hull Forms 
number of hull shapes. In this model a great number of sea- 
keeping parameters such as heave, pitch and acceleration are 
amalgamated to arrive at one single figure of merit indicative 
of the overall seakeeping performance of a hull. 
The validation of this model is also shown in [28] and stems 
from back-designing a hull shape which has seakeeping char- 
acteristics superior to any ship in the data set. This was ac- 
complished with the predictor model that uses only the ship's 
main particulars and associated quantities. 
At first, the predictor model was tried on our Models 1, 2 and 
3 which, as shown•in Fig. 3, constitute the diag, onal, incorpo- 
rating a shift in LCF. Earlier the work of Bales and Cummins 
[29] had indicated a sizable improvement of heave and pitch 
if the forebody CweF were to be increased. The improvement 
found from the experiments was not as great as had been ex- 
pected, perhaps because CweF had not been increased enough. 
In the series, CWeF was not taken any higher than 0.6 as it was 
felt that this would result in an important calm-water resistance 
increase of more than 10 percent at Froude numbers in excess 
of 0.5. The restriction on Cwev is not made in current frigate 
Table 3 Residuary resistance comparison, normalized on Model 2 
Model No. 
F.v 1 2 3 4 5 6 
95.2 100 100.0 120.8 96.2 120.6 
97.6 100 91.0 96.0 91.6 88.4 
100.3 100 93.8 99.2 89.4 91.1 
101.2 100 93.2 99.5 94.9 90.9 
104.1 100 89.9 100.0 98.0 88.7 
103.5 100 89.8 101.1 98.0 90.4 
143 
/1 
./.-" Table 4 Tradeoff between calm-water resistance and seakeeping characteristics in head waves 
Model 
NO. ' 
Calm-Water Resistance Seakeeping (~haracteristics 
Z 0 817 a19 
CFS + CA CRM CTS RTS (m) (°) (m) (g) RAW 
× 103 × 103 X 103 (tonne) rms rms rms rms (tonne) 
RT 
(tonne) 
1 1.428 1.168 3.046 88.39 0.36 0.66 1.66 0.26 6.77 96.15 
2 1.428 1.651 3.079 88.44 0.39 0.66 1.77 0.27 6.84 95.28 
3 1.428 1.553 2.981 83.87 0.39 0.73 1.94 0.29 7.77 91.64 
4 1.428 1.593 3.021 88.75 0.39 0.61 1.56 0.26 6.77 95.52 
5 1.428 1.511 2.939 86.85 0.36 0.59 1.69 0.25 7.11 93.96 
6 1.428 1.470 2.898 84.44 0.37 0.63 1.63 0.27 7.50 91.94 
1 +0.1 +7.7 +7.6 +6.2 +3.7 +1.0 - i .0 0 
2 0 0 0 0" 0 0 0 0 
3 +5.2 0 -10.6 -9.6 -7.4 -13.6 +4.0 -1 
4 -0.4 +2.6 +7.6 +11.9' +3.7 +1.0 +0 +6 
5 +1.8 +7.7 +10.6 +4.5 +7.4 -3.9 +1.4 +13 
6 +4.5 +5.2 +4.5 +7.9 0 -9.6 +3.6 +6 
design, where figures of 0.7 do occur although for lower 
speeds. 
The seakeeping figures of merit as predicted by Bales' model 
are shown in Fig. 3 as encircled numbers near the appropriate 
body plan, a positive number signifying an improvement. The 
numbers represent a percentage change relative to the central 
model (No. 2) which was set arbitrarily to zero. 
It is shown in the figure that Models 1, 2, and 3 were arranged 
along a diagonal with apparently a weak influence on sea- 
keeping. The predictor further suggested that a significant 
improvement could be made if--for the same displace- 
ment -both the fore and aftbody were given a wider water- 
plane. This appeared a logical step because the draft and 
freeboard remain the same and so do the slamming and green 
water aspects. A wider waterplane overall suppresses heaving 
and pitching. The forebody CwpF was still not allowed to go 
any higher than 0.6. 
The suggestion cast by the figure-of-merit predictor was 
taken up and the three models in the right-hand top corner of 
Fig. 3 off the diagonal were also tested, denoted Models 4, 5 and 
6. The results of the experiments appear to bear out the im- 
provement projected by the prediction model, as the test results 
and the discussion on the seakeeping aspects have shown. 
Tradeoff between calm-water resistanceand 
seakeeping characteristics in head waves 
Eventually the resistance properties of the six models had to 
be traded off against their respective behavior in head waves. 
This tradeoff, or the choice of the parent hull, was made in the 
following way. 
A dimensional numerical design point was selected having 
the followitig particulars: 
Length: 85 m (279 ft) 
Speed: 48 knots 
Fn = 0.855 
Fnv = 2.49 
Sea state 4:~wl/3 = 2.50 m (8.20 ft) 
7~1 = 7.00 s 
For this nominal .point the calm-water resistance, the wave 
added resistance, and the total resistance were determined as 
well as the seakeeping determinants: heave, pitch, relative 
motion at station 17 and vertical acceleration at station 19. 
The values are given in Table 4 for all six models, in the upper 
figures. In order to weigh the different quantities and to select 
the best model, the central model (No. 2) was arbitrarily set to 
100 percent and the change of the numerical values relative to 
Model 2 was given by a percentage. The plus sign indicates 
an improvement. These percentages are shown in the lower 
batch of figures in Table 4. 
On the basis of this table, Model 5 was selected to become the 
parent hull. It had a good calm-water resistance figure (al- 
though Models 8 and 6 were better) and it had a good overall 
resistance figure (still Nos. 3 and 6 were better). The advantage 
Model 8 had over the No. 5 parent hull on the basis of resistance 
is lost when we take a look at the pitching in waves, where 
Model 3 is dramatically worse. The advantage Model 6 holds 
over the parent hull No. 5 on the basis of overall resistance (2.2 
percent) is, in our view, outweighed by the significantly better 
seakeeping characteristics of heave, pitch and accelerations of 
Model 5. The relative motion figure of No. 5 is somewhat in 
want, but could easily be rectified by a small change to the 
abovewater flare forward. 
So, taking everything together, Model 5 is selected because 
it is 6 to 20 percent better on pitching as compared to the next 
models in line (Nos. 3 and 6) at the expense of a 2 percent 
penalty on overall resistance in waves. 
In the last column of Table 4 the seakeeping figure of merit 
@ that Bales [28] computed for these models is given. This 
figure not only led to the extension of this subseries to include 
Models 4, 5 and 6, but it also pointed out the most prospective 
parent hull. In addition to this, other nominal design points 
were tried for a smaller and a bigger ship, in a different sea 
state, but again hull form No. 5 came out as the best balance 
between calm-water resistance and seakeeping aspects. 
Cont inuat ion of the systemat ic ser ies work 
State of affairs 
The experiments related in the paper cover a forerunner 
series of six models that led to the selection of a parent hull. 
With that the parameters-to-be-fixed were established and work 
on the true series as mentioned earlier and elucidated.by its 
parameter space in Fig. 4 could begin in earnest. This work 
is in an advanced stage, with 15 of the 27 models having been 
tested. While all this is in progress, a continuation is in the 
offing in the sense of a subseries devoted to a variation of pris- 
matic coefficients and a series on trim wedges, on longitudinal 
radius of gyration, possibly on spray-rails, and more than likely 
on propulsion, struts, shaft position and related topics. 
Transformation program 
The systematic series of hull forms as shown in Fig. 4 re- 
144 Systematic Series Hull Forms 
quired a transformation procedure to obtain the lines of all the 
models as logical derivatives of the parent hull form. The first 
step was to computerize the parent hull form itself with its local 
details. The second step was the transformation routine itself. 
For LIB and BIT transformations the problem was quite easily 
solved by stretching and widening the hull shape. For the 
block coefficient variation it wasfirst necessary to determine 
how to go about it, either through a change in Cp or CM. 
An additional problem to be solved was the transformation 
of the abovewater hull form. As the underwater hull form 
changes in a consistent fashion, the angle of intercept between 
the sections and the waterplane changes. It was found that 
shaping the abovewater hull in a systematic fashion had to be 
done quite independently from the underwater hull form in 
order to avoid hulls with a very wide forebody overhang or with 
hardly any flare at all. 
Eventually a transformation program resulted that can- - 
within the boundaries set by the series parameters and its 
characteristic hull shape--vary L/B, B/T, CB, Cp, CM, Cwe 
and Cve, so as to interpolate to any set of parameters within the 
cube matrix. " 
Numer ica l data base 
The calm-water resistance data as well as the seakeeping data 
obtained will be put into design charts in as condensed a form 
as possible. 
To make the maximum use of the data in obtairiing an opti- 
mum hull for a given set of design requirements, the data set 
will also be computerized, so that with the use of a search and 
interpolation routine the required hull can be obtained along 
with its resistance and seakeeping characteristics with a mini- 
mum of effort. 
Concluding remarks 
For the twofold purpose of obtaining design data on high- 
speed hull forms in the areas of both calm-water resistance and 
seakeeping and to investigate what the prospects are for dis- 
placement hulls in the extremely high-speed range, a systematic 
series of hull forms has been discussed. It was found that a hull 
can be obtained that incorporates a sizable improvement in 
seakeeping at the expense of just a little extra resistance. 
In the light of the currently growing belief, expressed in 
many a contemporary paper, that seakeeping does matter and 
does have an impact on ship operation, this information may 
be of further assistance in assessing the inevitable tradeoff to 
be .made when more emphasis is to be laid upon seakeeping 
behavior. 
Acknowledgment 
The work reported herein, covering the initial steps toward 
the full series of hull forms, has been funded by the Royal 
Netherlands Navy and by the Maritime Research Institute 
Netherlands (NSMB Wageningen/Ede Laboratories). The 
.considerable assistance of the Royal Netherlands Navy and of 
the David W. Taylor Naval Ship Research and Development 
Center (DTNSRDC), acting on behalf of the Office of Naval 
Research, at this stage, and their both becoming a sponsor of 
the series proper, is gratefully acknowledged. 
In particular, the assistance rendered by the late Nathan K. 
Bales of DTNSRDC during the initial stages of the project and 
the deliberations leading up to the choice of the parent hull is 
most gratefully recalled. 
References 
1 Tritton, D. J., Physical Fluid Dynamics, Van Nostrand Reim 
• hold (U.K.), 1982. 
2 Merk, H. J., "Fysische Stromingsleer," Lecture Notes, Delft 
University of Technology, The Netherlands, 1982. 
3 Comstock, E. N. and Keane, R. G., Jr., "Seakeeping by Design," 
Naval Engineers Journal, April 1980. 
4 Comstock, E. N., Bales, S. L., and Keane, R. G., Jr., "Seakeeping 
in Ship Operations," SNAME Spring Meeting/STAR Symposium, 
1980. 
5 Kehoe, J. W., "Destroyer Seakeeping: Ours and Theirs," 
Proceedings, United States Naval Institute, Nov. 1973. 
6 Kehoe, J. W., Brower, K. S., and Comstock, E. N., "Seakeeping," 
Proceedings, United States Naval Institute, Sept. 1983. 
7 Olson, S. R., "An Evaluation of the Seakeeping Qualities of 
Naval Combatants," Naval Engineers Journal, Feb. 1978. 
8 Mandel, P., "Seaway Performance Assessment for Marine 
Vehicles," Sixth AIAA Conference on Marine Systems, American In- 
stitute of Aeronautics and Astronautics, Sept. 1981. 
• 9 "Helicopter Operations from Small Ships," Combat Craft,July 
1983. 
10 "Certification of Helicopters for Use on Board Ship," Nether- 
lands Aerospace Laboratory, Europort Conference on Naval Con- 
struction and Equipment, Amsterdam, 1978. 
11 Eames, M. C., "Advances in Naval Architecture for Future 
Surface Warships," Trans. RINA, 1980. 
12 Mantle, P. J., "'Cushions and Foils," SNAME Spring Meeting, 
Philadelphia, 1976. 
13 "Status of Hydrodynamic Technology as Related to Model Tests 
of High-speed Marine Vehicles," High Speed Marine Vehicle Panel, 
16th International Towing Tank Conference, 1981. 
14 Rader, H. P., "Wasserfahrzeuge ffir hohe Geschwindigkeiten," 
Schiff und Ha fen, Heft 3, 1981. 
15 Comstock, E. N., Bales, S. L., and Gentile, D. M., "Seakeeping 
Performance Comparison of Air Capable Ships," Naval Engineers 
Journal, April 1982. 
16 Silverleaf, A. and Cook, F. G. R., "A Comparison of Some 
Features of High Speed Marine Craft," Trans. RINA, 1970. 
17 Bailey, D., "The NPL High Speed Round Bilge Displacement 
Hull Series,"Trans. RINA, 1976. 
18 Yeh, H. Y. H., "Series 64 Resistance Experiments on High-speed 
Displacement Forms,." Marine Technology, Vol. 2, No. 3, July 
1965. 
19 Lindgrenl H. and Williams, A., "Systematic Tests with Small, 
Fast Displacement Vessels, including a Study on the Influence of Spray 
Strips," SNAME Diamond Jubilee International Meeting, 1968. 
20 lohnson, "The Changing Design Process," Naval Engineers 
Journal, April 1980. 
21 Ursell, F., "On the Virtual Mass and Damping of Floating 
Bodies at Zero Speed Ahead," Proceedings, Symposium on the Beha- 
viour of Ships in a Seaway, Wageningen, The Netherlands, 1957. 
22 Tasai, F., "'On the Damping Force and Added Mass of Ships 
Heaving and Pitching," Reports of Research Institute for Applied 
Mechanics, Kyushu University, Japan, 1960. 
23 Grim, O., "A Method for a More Precise Computation of 
Heavin~ and Pitching Motions, Both in Smooth Water and in Waves," 
Proceedings, Third Symposium on Naval Hydrodynamics, Scheven- 
ingen, The Netherlands, 1960. 
24 Gerritsma, J., Beukelman, W., and Glansdorp, C. C., "The 
Effect of Beam on the Hydrodynamic Characteristics of Ship Hulls," 
Proceedings, Tenth Symposium on Naval Hydrodynamics, 1974. 
25 Beukelman, W., Huijsmans, R. H. M., and Keuning, P. J., 
"Calculation Methods of Hydrodynamic Coefficients of Ships in 
Shallow Water," Ship Hydromechanics Laboratory, Delft Hydraulics 
Laboratory, Maritime Research Institute, Report No. 571-A, 1983. 
26 Salvesen, N., Tuck, E. O., and Faltinsen, O. M., "Ship Motions 
and Sea Loads," TRANS• SNAME, Vol. 79, 1970. 
27 Gerritsma, J. and Beukelman, W., "Analysis of the Resistance 
Increase in Waves of a Fast Cargo Ship," International Shipbuilding 
Progress, 1972. 
28 Bales, N. K., "Optimizing the Seakeeping Performance of 
Destroyer-type Hulls "Proceedings 13th Symposium on Naval Hy- 
drodynamics, Japan, 1980. 
29 Bales, N. K. and Cummins, W. E., "The Influence of Hull Form 
on Seakeeping;" TnANS. SNAME, Vol. 78, 1970. 
(Discussion follows overleaf) 
Systematic Series Hull Forms 145 
/ 
Discussion 
D. Bailey, 6 Visitor 
Although today there is in the literature model series data 
which cover the resistance qualities of high-speed hulls of the 
type described by the authors, little, if any, systematic sea- 
keeping information exists for these forms and this paper is 
therefore most welcome. The authors should be congratulated 
on their thorough approach in testing a subseries of models in 
search of a parent from which the series as a whole derives. 
The choice of a parent model is very important and not easy, 
and one could of course argue indefinitely over its selection. 
The authors have rightly balanced resistance and seakeeping 
qualities, but in considering the head sea case alone perhaps too 
limiting a view has been taken. Looking at the afterbody 
sections of the chosen parent I am not convinced that its slight 
immersion at rest is to be preferred in beam or following sea 
conditions and it will be interesting to hear the authors' views. 
Also from resistance considerations increased transom im- 
mersion ratio, allowing as it does a gentler slope in the buttock 
lines, can show to advantage and I am not surprised to see Model 
Nos. 3 and 6 superior to the parent. It is also possible that the 
very flat and relatively wide transom will encourage slamming 
at the stern so that a few tests in following seas Would have been 
instructive. 
As to the experiments themselves, although it appears per- 
fectly justifiable to use a towed model in regular waves for the 
purposes of choosing a parent, tests on the complete series 
should preferably be done with p~opelled models. The in- 
clusion of propeller action gives more realistic conditions par- 
ticularly if the model is allowed to surge and also for faster craft 
such as these where running trim influences performance. 
Propeller action modifies running trim from that obtained in 
towed models and this effect should be fully represented in the 
experiments. Evidence as to how model behavior in waves 
differs in propelled or towed tests is given in reference [80] 
(additional references follow some discussions). Here signifi- 
cantly different acceleration levels are shown over a range of 
encounter frequency. There are also differences in pitch and 
heave at resonant frequencies. Although these data relate to 
a planing craft at Fnv = 3.0, I suspect they would be reflected. 
at lower Froude numbers as well. 
High-speed displacement ships of this kind experience severe 
motions which have in extreme cases led to structural damage 
of the hull, and, since this is an important design consideration, 
I am surprised that no plans appear to have been made to obtain 
pressure and slamming measurements at the bow. Also, bridge 
structures are vulnerable wit h respect to loss of visibility from 
flying spray which is generated from the breakup of solid water 
shipped over the bow. A technique for monitoring and mea- 
suring impact and wetness on a bridge front is given by Lloyd 
[81]. 
This paper is of great interest and I hope that the authors will 
be encouraged to publish the results of the whole model series. 
If they can also be persuaded to add seakeeping data for wave 
directions other than head seas, then their findings will be very 
keenly awaited. 
Additional references 
30 17th ITTC, G6teborg, Sept. 1984 (Report of the High-Speed 
Marine Vehicle Committee). 
31 Lloyd, A. R. J. Mi, "Deck Wetness Experiments," 2Oth ATTC, 
198;3. 
Frank Sellars, Member 
This paper considers the influence of seakeeping on the 
6 NMI Ltd., Fehham, Middlesex, England. 
preliminary design of high-speed displacement-type hull forms. 
It provides an important contribution to an aspect of the design 
of ships which has not been covered by experiments. 
The design criteria chosen have a significant influence on the 
results. The design criteria adopted in this paper are good 
calm-water resistance and good seakeeping characteristics. 
The application of the criteria led the authors to limit the 
variation of the forebody waterplane coefficient to be no greater 
than 0.6 to limit expected increases in calm-water resistance 
for higher Froude numbers (in excess of 0.50). Previous studies 
have shown that increase in the waterplane coefficient above 
0.6 can lead to improved seakeeping performance. Table 5 
with this discussion compares other proposed seakeeping design 
procedures. 
Research sponsored by the Society is currently in progress 
to develop a preliminary seakeeping design procedure for 
merchant ships. The design criterion used is minimization of 
freight rate through minimum initial cost and high average 
sustained sea speed. One aspect considered in this work is se- 
lection of proportions and hull form for subcritical tuning.Subcrffical tuning refers to the ratio of ship resonant response 
period to wave encounter periods being less than 0.75. This 
reduces wave excitation and pitch response. Critical tuning 
refers to equal ship and wave encounter periods and is a region 
of maximum motion. Supercritical tuning refers to the ratio 
of ship to encounter periods being greater than 1.2. Reduced 
motions are expected in this region and lower pitch than in the 
subcritical region is possible. These effects of tuning on re- 
sponse are an example of the "Doppler Shift" referred to by the 
authors. 
The results shown in Fig. 18 of the paper can be interpreted 
in terms of tuning. In head seas the encounter period is 
Tw TE = 
, [1 + (kL)I/zFn] 
and the tuning factor for pitch is 
To = To[1 + (kL)I/2F,] 
Te Tw 
where 
To = pitch resonant period 
Tw = wave period 
T£ = period of encounter 
The model heave and pitch periods are not given in the paper 
and it would be useful if the authors could provide these data. 
I have estimated that in model scale the pitch period ranges 
from around 0.95 sec at zero speed to less than 0.80 sec at the 
higher Froude numbers. Applying this result to Fig. 18, the 
following results for tuning were obtained: 
FROUDE NO. TUNING 
0.285 Subcritical, To/T~ < 0.75 for all x/L/)~ 
0.570 Critical, To/TE > 0.75 for v/L/)k > 1.0 
0.855 Critical for 0.70 < v/L/)k < 1.00 
Supercritical v/L/~ > 1.00 
1.140 Supercritical for x/L/k > 0.75 
These results indicate that the reduced pitch response at the 
higher Froude numbers is due to supercritical tuning. Eco- 
nomic constraints prevent design for supercritical tuning for 
merchant ships; however, it is a viable option for advanced 
naval vessels. Constraints on the selection of waterplane 
coefficients were mentioned earlier in this discussion. An in- 
crease in the waterplane coefficient tends toreduce the pitch 
natural period and increases damping. For low-speed opera- 
146 Systematic Series Hull Forms 
Table 5 Comparison of proposed seakeeping design procedures 
Proposed 
Proportions Commercial Seakeeping Frigates Destroyers 
or Form. Design Procedure Schmitke and Murdey (1980) a Bales (1980), [28] 
Length increase to reduce choose on basis of decrease T/L 
wave excitation and arrangement and powering 
thus reduce motion 
Beam increase to increase . . . . . . 
damping 
B/T reduce to reduce choose on basis of ... 
pitch period stability 
T reduce to reduce ... decrease T/L to 
pitch period improve 
seakeeping 
Cwp increase to reduce high (CwP)F for best increase to improve 
pitch period seakeeping seakeeping 
CB has negligible effect keep low for resistance ... 
on seakeeping and seakeeping 
Forebody shape V-sections for reduced periods keep bow sections fine ... 
near keel 
(Cvp) = CB/Cwp . . . . . . decrease (CvP)F 
increase (CvP)a 
a Schmitke, R. T. and Murdey, D. C., "Seakeeping and Resistance Trade Offs in Frigate Hull Design," 13th 
ONR Symposium on Naval Hydrodynamics, Tokyo, Oct. 1980. 
tion this imt)roves seakeeping by shifting responses into the 
suberitical region. For high-speed vessels reduced pitch periods 
may not be beneficial. Higher-pitch periods help to extend 
the region of supercritical tuning and improve seakeeping. 
The authors note that the test results indicate that a low 
verticalprismatic coefficient brings about a small pitch angle. 
• The vertical prismatic coefficient is the ratio of the block to 
waterplane coefficients. The block coefficient: was held con- 
stant; therefore a low vertical prismatic coefficient corresponds 
tO a high waterplane coefficient. 
Comparison of model pitch transfer functions at the highest 
speed, Fig. 16, shows a 45 percent reduction in maximum pitch 
response as the prismatic coefficient is reduced 6 percent. 
Referring to the previous discussion of tuning, this large re- 
duction in pitch occurs in a region of critical tuning. The large 
reductions in pitch are considered to be a result of increased 
damping associated with increased waterplane coefficient. " 
Gabor Karafiath, 7 Visitor 
. [The views expressed herein are the opinions of the discusser and not 
necessarily those of the Department of Defense or the Department of 
the Navy.] 
During recent years seakeeping considerations for naval ships 
have received increased emphasis and have been incorporated 
into the ship design cycle at an early stage. At the same time 
energy considerations in terms of reduced powering require- 
ments have also become increasingly important. It was shown 
in reference [32] that good seakeeping and powering charac- 
teristics can be combined in one design and I am sure that the 
information in this paper and results from the planned fol- 
low-on tests will aid designers to meet both the seakeeping and 
powering goals simultaneously. 
The paper selects a parent hull form for a new series and it 
is important to compare resistance with that of other hull forms 
of its type. Averaged residuary resistance to weight ratios for 
other series of hull forms are presented in reference [88] and 
the following table shows a comparison to the selected parent 
hull No. 5. 
7 David W. Taylor Naval Ship Research and Development Center, 
Bethesda, Md. 
RESISTANCE COMPARISON TO,OTHER SERIES DATA 
RR/A 
Hull model 5 (parent for prol~gsed series) 0.041 
DTNSRDC Series 64 0.088 
NPL Series L/B = 7.5 0.044 
The above comparison is at the sarue nondimensional volume 
Froude number Fnv = 2.49 and thesame length-to-displace- 
ment ratio L/AI/Z = 8.52 for all three hulls. The comparison 
indicates that the smooth-water performance of Hull 5 is 
comparable to that of the designs in the other two series. 
The authors have concentrated on the seakeeping aspects and 
have selected their parent hull form, No. 5, principally on its 
low pitching characteristic and acceptable resistance in waves. 
However, if some of the data in Table 4 are rearranged (see 
Table 6 6f this discussion) in order of increasing resistance, 
relative to that of Model 3, some other trends become evi- 
dent. 
The general trend is that excessive transom width, results in 
poor resistance in calm water and in waves and that a wide 
forebody is beneficial. The selection of Model 5 as parent was 
based principally on the excellent pitching in wave character- 
istics as opposed to any resistance differences. Note that except 
for the insignificant difference in the calm-water resistance of 
Models 2, 4, and 1, the models with higher calm-water resis- 
tance tend to have higher resistance in waves. This similarity 
in the ranking of the resistance in waves and the resistance in 
calm water supports the validity of traditional naval architec- 
tural practice of basing ship resistance comparisons on calm- 
water data. 
The authors state that "Because all six models had virtually 
the same wetted surface--their displacement was the same-- 
the comparison of the six models could just as well be done on 
the basis of residuary resistance." I have shown in Table 6 that 
the wetted surface differs by as much as 5.0 percent for Models 
8 and 5. The wetted surfaces that I have shown were derived 
from the total ship resistance coefficient, CTS, and the total ship 
resistance, RT:s, given in Table 4 of the paper. If one makes 
a resistance comparison on residuary resistance as the authors 
suggest, then one would assume that Model 5 is a significantly 
better performer than Model 8 at a volume Froude number of 
Systematic Series Hull Forms 147 
Table 6 Data of Table 4 normalized on Model 3 and in order of increasing resistance 
Resistance 
Ratio Resistance Wetted 
Model Calm Ratio Surface After Pitching 
No. Water Waves Ratio Forebody Body Ratio 
3 1.000 1.000 1.000 wide narrow 1.0 
6 1..007 1.003 1.035 wide medium• 0.86 
5 1.0361.025 1.050 wide wide 0.81 
2 1.054 1.040. 1.021 medium medium 0.90 
4 1.058 1.040 1.044 medium " wide 0.84 
1 1.054 1.049 1.044 narrow wide 0.90 
1.0 because the residuary resistance is 4 percent lower as shown 
in Table 3 of the paper. In fact a calculation of the total re- 
sistance based on actual wetted surface shows that the resistance 
of Models 3 and 5 is virtually the same. At the 1.0 volume 
Froude number, corresponding to 19.2 knots ship speed, the 
total ship resistance of the Model 5 hull design is an insignificant. 
two tenths of 1 percent greater than that of the Model 3 design. 
The resistance at 19.2 knots, a typical cruise speed, will have 
a great impact on the annual fuel cost and therefore I urge that 
the wetted surface and residuary resistance versus speed curve 
be published in order to facilitate future computation of resis- 
tance with these data. It would also be useful to provide the 
section area curve. 
The design community will certainly welcome the publica- 
tiori of the data on the resistance and seakeeping characteristics 
of the hull forms that are still to be tested. The emphasis has 
been stated to be on seakeeping characteristics; however, I urge 
the authors to place equal emphasis on the resistance aspects 
of l:his series data. 
Additional references 
32 Lin, W. C. et al, "An Advanced Methodology for Preliminary 
Hull Forna Development," presented at the American Society of Naval 
Architects, ASNE Day, 1984. 
33 Van Oossanen, P., "Resistance Prediction of Small High Speed 
Displacement Vessels," International Shipbuilding Progress, Sept. 
1980. 
W. A. Cleary, Jr., Member 
[The views expressed herein are the opinions of the discusser and not 
necessarily those of the Department of Transportation or the U.S. Coast 
Guard.] 
The authors are to be congratulated for offering a paper 
which is relatively easy to follow on such a complex yet im- 
pertant subject. Seakeeping is perhaps the most important and 
least understood subject of ship design today since ships are 
expected to maintain a certain sea speed for operational or 
economic purposes; courts are increasingly critical in respon- 
sibility for heavy weather damage; and the question of sur- 
vivability of the entire ship in a seaway is matter of interest to 
administrations deciding international standards. 
International standards for commercial ships are largely those 
in the International Convention on Load Lines (1966), estab- 
lishing standards for intact reserve buoyancy; sheer; super- 
structure buoyancy in rolling action; bow height; clearance for 
air pipes, ventilators, hatch coamings, etc.; strength of hull, 
hatches, superstructure, etc.--all of which are affected by the 
seakeeping ability of the ship. The International Maritime 
Organization has recently authorized a long-term systematic 
review of the convention with a,view to maintaining its appli- 
cability to present-day ships. Thus it is fortunate that the au- 
thors propose a system to investigate the seakeeping aspects of 
a ship at the design stage. 
My specific questions are submitted with full awareness that 
the authors have used a series of ship.forms which are usually 
found in military ships and much less in commercial ships. 
Referring to Fig. 4, most commercial ships would be a smaller 
cube with CB between 0.5 and 0.9, LIB between 4 and 8, and 
B/T less than 2.5. Yet it would appear that the system espoused 
by the authors could just as easily be used for commercial ships, 
albeit with different responses. Would the authors comment 
on the use of such a'system for commercial ships? 
The statement that freeboard was set at 6 percent length 
taken at the fore perpendicular is also of interest. Has this any 
relation to above-water percentage of intact reserve 
buoyancy? 
The continuation of the systematic series (at the end of the 
paper) does not show any attempt to estimate seakeeping in 
other than head seas. Yet it would seem as important for mil- 
itary ships as it is for commercial ships. 
Finally, referring to the continuation effort, the authors note 
that shaping of the above-water hull form had. to be done in- 
dependently from the underwater hull. In the authors' opinion, 
would slower commercial vessels have the same difficulty, or 
would the fact that only 20 to 30 percent of a commercial hull 
is above the waterline (intact reserve buoyancy) coupled with 
the slower speed reduce the importance of this modifica- 
tion? 
Allan T. Maris, Member 
I congratulate the authors of this paper for their excellent 
presentation of seakeeping data. It provides valuable guidance 
to the naval architect who wishes to consider seakeeping per- 
formance in addition to resistance and propulsion performance 
when selecting hull form characteristics• 
Giannotti. & Associates and the State of Alaska recognized 
this situation in recent ferry design work performed for the 
Southwestern Alaska ferry service where open-water envi- 
ronmental conditions can be severe and ridership is greatly 
affected by ferry seakeeping characteristics. 
To meet these needs we prepared design-oriented sea- 
keeping analyses for a tight range of hull form characteristics 
similar to those presented in this paper and discovered similarly 
that small changes in hull form can significantly affect vessel 
seakeeping performance. We prepared a similar table of fig- 
ures of merit, selected an appropriate hull form and satisfac-' 
torily confirmed the predicted seakeeping performance 
through model tests performed at The Netherlands Maritime 
Research Institute. 
From this background I offer the following observations to 
naval architects wishing to pursue this same design effort in the 
commercial field: 
1. Consider using site specific wave data where possible for 
seakeeping analyses and model testing. 
2. Consider selecting motion sickness indices in evaluating 
hull seakeeping characteristics. Apply the indices at a range 
of locations on the hull and use the results to aid in determining 
the best location of dining and other public spaces. 
3. Even small increases in vessel length can have a signifi- 
148 Systematic Series Hull Forms, 
cant effect on improving vessel seakeeping as well as resistance 
characteristics. 
4. A reasonable amount of pre-model test seakeeping an- 
alytical work can greatly enhance the economics of model 
testing. 
Authors' Closure 
The discussions have brought forth a number of significant 
points which require further amplification. We will respond 
to each discussion separately. 
We appreciate the comment of Mr. Bailey drawing our at- 
tention to the implications that the limited scope of experiments 
may have had. We have limited ourselves to head seas, because 
it was reasoned that this would constitute the most demanding 
case. For the vertical motions and 'accelerations and associated 
extreme effects like slamming on the bow and shipment of 
water over the bow, this is indeed the most: critical wave 
heading for the present ship type. Yet different wave headings 
may pose different problems like rolling in beam seas, steer- 
ing--i[ not broaching--in stern seas. Each of these could give 
rise to an independent investigation and would constitute a 
daunting subject to pursue. One has to restrict oneself. 
As to the slight transom stern immersion at rest, it gave us the 
best tradeoff between resistance and seakeeping although 
viewed from other angles of interest an improvement may still 
be possible. We do not think it will do much to rolling in beam 
seas; the width of the transom stern would, but not the im- 
mersion. However, broaching of a hull with a wide and full 
- stern with little, if any, submerged lateral skeg area i~ likely to 
be more of a problem than on ships having a narrow stern and 
more in theway of skeg. In considering the transom stern we 
have to bear in mind that on a true design one would in most 
,instances apply a stern wedge to improve the calm-water re- 
sistance. No such wedges were tried in the present study al- 
though they are high on the list of priorities for future work. 
We would disagree with the discusser about tile risk of stern 
slamming on such a wide and flat transom stern. It has been 
• observed in other experiments that on a frigate-type ship lying 
hove-to in a rough sea, in particular when lying stern to the seas; 
slamming under the stern does indeed occur. This is a rather 
uncommon thing in the operational profile of a frigate, and it 
has also been observed that just a few knots of forward speed 
reduces dramatically the relative motions at the stern and the 
associated encounter frequency, and slamming ceases to 
occur. 
We would agree with the discusser on the necessity to include 
experiments on propelled models. The province of propulsion 
has a good deal of priority, yet for the selection of the parent 
hull it was reasoned that for the present subseries of models the 
wake field would not be all that much different so as to com- 
pletely contradict the selection of the parent hull. 
Considering the subject of slamming pressures, these did not 
constitute a criterion in the selection of the parent hull form. 
Slamming on a high-speed hull form can be substantial, but it 
was thought that all models of the subseries had a large deadrise 
angle in the forebody and the pressures would for the most part 
be associated with the rate of change of added mass and would 
not vary greatly from model (o model. However, the vertical 
accelerations attendant upon slamming may be dramatic. 
Deck wetness, in addition, was not a selection criterion for 
the parent hull--first, because in general ships of this kind that 
have a low level of vertical absolute motions will also exhibit. 
comparatively small relative motions, and second, because deck 
wetness can easily be rectified through the height of freeboard 
and the form of the bow flare. In actual fact the parent model 
to be--No. 5--turned out to be the wettest of all. Upon scru- 
tinizing the lines it was found that a very small change to the 
bow flare above the waterline, from slightly convex to just a 
little hollow, made a world of difference and made the model 
dry. 
Mr. Sellars draws attention to the most critical point of the 
tradeoff in waterplane coefficient Cwe from the viewpoints 
of resistance and seakeeping. A large Cwe is beneficial to the 
seakeeping aspects while a small Cwe is associated with low 
calm-water resistance. Had it not been for this effect there 
would not have been a tradeof[. It will be clear that anychoice 
on the parent, combining the best properties in both resistance 
and seakeeping, involves some degree of arbitrariness. 
The discusser further raisedthe point of subcritical and su- 
percritical tuning, which from the point of view of system dy- 
namics is an interesting proposition. Yet we believe that the 
variation of Cwe in the present subseries is as large as one is ever 
likely to encounter between design alternatives, and the at- 
tendant change in natural periods of heave and pitch was only 
marginal. The models with a wide waterplane had the edge 
over those with a small waterplane area, in our opinion not 
because of de-tuning of the natui-al periods, but due.to a dra- 
matic change in damping in the vertical plane. 
The discusser's guess of the pitch period was rather accurate. 
The parent hull form had a pitch period of 0.99 sec at zero 
speed. 
Mr. Karafiath rightly stresses the importance of seakeeping 
considerations at an early stage in the design. We are also 
pleased to see his comparison of residuary resistance dal~a to 
other series, which sho.ws that we are on the right track with the 
present series. The table he reproduced in the discussion and 
normalized on Model No. 3 is essentially based on our Table 4. 
It is clear from the original that as the calm-water resistarice 
goes up the wave added resistance (in the selected sea static) goes 
. dov#n. The table shows at a glance that the latter constitutes 
about 8 percent of the former, so the ranking of the models on 
the basis of the total resistance in waves very nearly follows the 
ranking of the models on the basis of calm-water resistance.. 
Here again it may be well to reiterate that Model 5 was not 
the best in any field, but in our judgment the best compromise, 
for the rather high speed range that was projected from the 
outset as being the basis of the tradeoff. 
Mr. Karafiath requests more data on resistance aspects. We 
intend to publish a companion paper on resistance that will 
supplement the present paper. Since the latter deals with 
seakeeping aspects the amount of stillwater data is of necessity 
limited. 
Mr. Cleary underscores the importance of the seakeeping 
aspects from both the damage as well as the survival point of 
view. The approach taken in the present systematic series is 
by no means limited to the ship type. It can, and has been, 
applied to other ships as well. If his interest lies in commercial 
ships with higher block coefficients it may be useful to consult 
the paper by Vossers, Swaan and Rijken entitled: "Experiments 
with Series 60 Models in Waves" that was presented to the 
SNAME Annual Meeting in 1960 (Vol. 68, TRANSACTIONS). 
Although the basic hull form lacks some features of modern, 
ships; like the transom stern, the paper contains a wealth of data 
on the basis of systematic series of experiments along the same 
lines as the present series. As to the choice of the freeboard 
height of 6 percent, this figure was arrived'at on basis of some 
diagrams contained in contemporary literature that relate 
freeboard forward to ship length; see reference [3] of our paper. 
Considering the influence of bow form on deck wetness for 
slower commercial ships, we have observed that larger changes 
are required to substantially reduce the deck-wetness problem 
on a slow ship than on the frigate-type hull under investigation. 
This should be attributed to the lower encountered frequencies 
in pitching. If the bow dips into the water and becomes sub- 
Systematic Series Hull Forms 149 
merged, both types of ships have "green seas" on the foredeck. 
Before that stage is reached, both types suffer from the water 
that is thrown up into the air. Because of the high accelerations 
of the fast running frigate, the water adjacent to the hull gains 
more momentum. Small changes to the bow flare form have 
more effect for a frigate than for a cargo ship. 
Mr. Marls stresses the importance of seakeeping consider- 
ations in the design. This is particularly important in those 
areas of the work where the environment is most hostile to 
seafarers. We can only wholeheartedly agree with him that 
analytical work along with model experiments should be used 
not only to lay out a design but to refine it as well. There is still 
a good deal to be gained in this field. 
Finally, the authors wish to express their thanks to all of the 
discussers. Their comments have provided us the opportunity 
to clarify several points, adding additional information and 
showing us in what area the main interest lies. In addition, they 
have broadly substantiated the conclusions of the paper. 
150 Systematic Series Hull Forms