The MARIN Systematic Series Fast Displacement Hulls

Date 2012

Author Kapsenberg, Geert

T U D e l f t

Ship Hydromechanics and Structures Laboratory Mekelweg 2, 2628 CD Delft

Delft University ofTechnology

T h e M A R I N S y s t e m a t i c S e r i e s Fast D i s p l a c e m e n t H u l l s

b y

Geert Kapsenberg

R e p o r t N o . i S ^ Q - P 2 0 1 2 Published in Proceedings of t h e 22"" I n t e r n a t i o n a l HISWA

Symposium on Y a c h t Design and Y a c h t C o n s t r u c t i o n , A m s t e r d a m , 12 & 13 November 2 0 1 2 , I S B N : 9 7 8 - 9 4 - 6 1 8 6 ¬ 0 7 9 - 8

IROyAL H U I S M A N)

EADSHIP

ROYAL DUTCH SHIPYARDS

22"d International

HISWA Symposium

on Yacht Design and Yacht Construction

Amsterdam, 12 & 13 November 2012

PROCEEDINGS

Organized by

HISWA - National Association of Watersport Industries in The Netherlands

The International Trade Show of Marine Equipment METS 2012

Delft Unh/ersity of Technology

The Royal Institution

o f Naval Architects

IBI

lOTERNATONAL BOAT INDUSniV

HISWA

M E T S

<

22"° International HISWA Symposium on

"Yacfit Design and Yacht Construction"

A m s t e r d a m , 12 & 13 N o v e m b e r 2012

PROCEEDINGS

Edited by PietW. de Heer

Organizing Committee

J a n Alexander Keuning Delft University of Technology

Michael Steenhoff HISWA Vereniging the National Association

of Watersport Industries

Irene Dros Amsterdam RAI Convention Centre

Scientific Committee Prof. Jelie Gerritsma T h y s Nikkels

Prof. Richard Birmingham IVIichael Steenhoff Bram Jongepier Hans Hopman Pepijn de Jong Geert Kapsenberg TU Delft

Dijkstra Naval Architects University of Newcastle HISWA Vereniging Feadship TU Delft TU Delft MARIN November 2012

Organized by HISWA - National Association of Watersport industries in The Netherlands, The International Trade Show of Marine Equipment METS 2012

Delft University of Technology

Photo cover: Ed Holt

Delft University ofTechnology Ship Hydromechanics Laboratory

Printed by: Service Point Flemingweg 20 : Postbus 164

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KONINKLIJKE BIBLIOTHEEK, DEN HAAG Depot van Nederlandse Publicaties Postbus 74

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2 1 " International Symposium on "Yacht Design and Yacht Construction": Proceedings of the 2 1 " International Symposium on ;'Yacht Design and Yacht Construction", Amsterdam, 15 & 16 November 2010 - Delft University of Technology, Ship Hydromechanics laboratory, The Nethedands.

ISBN: 978-94-6186-079-8

Subject headings: Yacht Design, Yacht Construction

T A B L E OF CONTENTS

Program Monday

Program Tuesday

Introduction

Session 1 - J.A. Keuning

Session 2 - F. Verbaas

Session 3 - U. Kleinitz

Session 4 - A. Claughton

Session 5 - G.K. Kapsenberg

Session 6 - F. Fossati

Session 7 - B. Pryszo, D. Sparreboom, M. Leslie-Miller

Session 8 - J.A. Keuning (No Paper)

Session 9 - A . Meredith-Hardy

Session 10 - D. Motta

Session 11 - A. Winistoerfer

Session 12 - A. Shimell and H. Ten Have

Session 13 - R. Stelzer

a a " " * International HISWA Symposium

on Yacht Design and Yacht Construction

12 and 13 Novembei- 2012, Amsterdam, The Netherlands, Amsterdam RAI

Location: E m e r a l d R o o m , A m s t e r d a m RAI

P r o g r a m Monday N o v e m b e r 12, 2012

Moderator: C a r l C r a m e r

0 8 . 3 0 - 10.00 Registration

10.00-10.15 Opening

10.15 -11.00 The development of the next generation lifeboats for the KNRM

Speaker: J.A. Keuning

1 1 . 0 0 - 1 1 . 1 5 Coffee Break

1 1 . 1 5 - 1 2 . 0 0 Use of g l a s s in yachtbuiiding and the regulations

Speaker: F. Verbaas

12.00 - 12.45 IMO regulations on NOx and S O x and its effects for yachtdesign

Speaker. U. Kleinitz

1 2 . 4 5 - 13.30 Lunch Break

13.45 - 14.30 Hull sailplan balance 'lead' for the 21th Century

Speaker: A. Claugiiton

14.30 -15.15 Early design estimation of resistance and seakeeping properties

based on systematic model experiments

Speaker: G.K. Kapsenberg

1 5 . 1 5 - 1 5 . 3 0 Coffee Break

1 5 . 3 0 - 1 6 . 1 5 Motions of a sailing yacht in large waves: an opening simple

instationary modelling approach

^ Speaker: F. Fossati

16.15 -17.00 Weather routing for motorsailors

Speakers: B. Pryszo, D. Sparreboom, M. Leslie-Miller

I

17.00 - 17.45 Delft Systematic Yacht Hull Series

Speaker: J.A. Keuning

1 7 . 4 5 - 18.45 Reception

19.00 Dinner

on Yacht Design and Yacht Construction

12 and 13 November 2012, Amsterdam, The Netherlands, Amsterdam RAI

Location: E m e r a l d R o o m , A m s t e r d a m R A I

P r o g r a m T u e s d a y N o v e m b e r 13, 2012

Moderator: C a r l C r a m e r

09.00 - 09.45 The new generation off passenger siiperyachts- S O L A S or P a s s e n g e r

Yacht C o d e ?

Speaker: A. Meredith-Hardy

09.45 - 10.30 Investigation of the effects of rig tension on sailing yacht performance

using real time pressure and sail shape measurements at full s c a l e

Speaker: D. Motta

1 0 . 3 0 - 10.45 Coffee Break

10.45 - 11.30 Carbon fiber rigging, yesterday, today and the l e s s o n s learned along

the way

Speaker: A. Winistoerfer

1 1 . 3 0 - 1 2 . 1 5 Structural design of S / Y Dream Symphony: the largest wooden s h i p

ever built

Speakers: A. Shimeli and H. Ten Idave

12.15 - 1 3 . 0 0 The robotic sailingboat, A S V Roboat a s a maritime research platform

Speaker: R. Stelzer

INTRODUCTION.

Once again you will find here the Proceedings o f t h e International HISWA Symposium on Yacht Design and Construction.

As usual for a considerable time by now the Symposium is to be held in the RAI Congress Centre in Amsterdam on 12'" and 1 s"" of November 2012.

This year it is the 22"" time that the symposium is being organized and in that respect it is the oldest symposium in the area of yacht design and research!

The Organizing Committee again is very content with the work carried out by the Scientific Committee, which put together a very interesting program with a variety of topics. Between the more usual topics, such as issues involved with high performance yachts and new'developments, a particular emphasis has been put this time on the construction: such as very large yachts entirely in build in wood and the application of glass as a more structural member. A few papers also deal with the aspects o f t h e rules and regulations and their possible impacts on the design. W e are still successful in attracting a large group of students from all kind of educational programs to the symposium. This is an important aspect because the future of our yachting industry is with them and we hope to be able to stimulate their interest through this symposium. Also the symposium offers a nice opportunity for both the new and the elder generation to meet each other and exchange ideas and share common interest. I hope you will all make ample use of the opportunities we arrange in the time schedule to meet other people.

I would also like to place ample emphasis on the drinks organized at the end of today's papers and the dinner cruise through the Amsterdam canals later this evening.

Finally I would like to express my gratitude to our sponsors, DAMEN Shipyards, Maritime Research Institute the Netherlands, Royal Huisman Shipyards and Feadship, without whom the aims of the symposium, i.e. offering a worthwhile and motivating gathering of interested people from the various branches, research institutes and schools, would not be possible at an affordable price.

I am sure we will meet again in the future during next editions of this HISWA Symposium, although for me it will be the last time as member of the Scientific Committee, because after so many years of active participation I decided that the time has come to hand it over to a newer generation.

Jan Alexander Keuning

Chairman Organizing Committee Scientific Committee

HISWA Yacht Symposium 1

THE M A R I N S Y S T E M A T I C SERIES FAST D I S P L A C E M E N T HULLS

Geert Kapsenberg - MARIN

Summary

The paper describes the development of a systematic series of high speed displacement hull forms. The series is built around a parent model by varying the length t o beam ratio, the beam to daft ratio and the block coefficient. Eventually thirty-three hull forms were built and tested in calm water up to a maximum speed of Froude number 1.14. Twenty-four of these hull forms were also tested in head waves. Regression analysis has been done on the experimental results t o allow interpolation for intermediate speeds or intermediate hull forms.

All results of the experiments are now made available in the form of a computer program; the program also contains the regression equations to allow interpolation. The use of the program is illustrated by way of a case study.

Introduction

A Joint Industry Project (JIP) on high speed displacement ships was carried out in the period 1979 - 1989 by the Royal Netherlands, US and Australian Navies, Delft University of Technology and MARIN. Western navies were very interested in high speed vessels in the seventies and they studied all sorts of advanced concepts ranging from hydrofoil to air cushion supported vessels and even wing-ln-ground effect vehicles. Performance and endurance at high speed in waves was an issue for most of the studied types, so some people believed that also the monohuli concept could be a viable alternative. This belief was the starting point of the JIP and It was decided to develop a systematic series around a parent hull form. The main parameters to vary in the series were length over beam ratio, beam over draft ratio and block coefficient and the

FDS - The MARIN Systematic Series 2

speed range to be considered should reach Fn = 1. Contrary to most existing systematic series, not only resistance characteristics in calm water was t o be measured, but also performance in waves. Head seas was considered the most severe wave direction and therefore experiments were restricted to this condition. Most of the models were tested both in calm water and in head seas, the latter at fixed Froude numbers of Fn = 0.285, 0.430, 0.570, 0.855 and 1.140. Now, 25 years after closing the project, the results were de-classified by all the partners. It was considered that the results of the project are still valuable today, not only for the naval market, but also for the market of the (mega) yachts. Because of this and with the help of a subsidy of the Dutch Ministry of Economic Affairs (Maritime Innovation Platform) a project was started to make all results available. The format chosen was to make a PC program for numerical results and to write a book on the why, how and what o f t h e project. The PC program contains all the hull forms, the experimental data and the small programs to interpolate In the existing hull forms (geometry) and t o predict the hydrodynamic performance for this newly generated hull form. The book will explain in detail the background of the project, how all the work was done and analysed and how the Interpolation methods were developed. Some additional topics were also investigated; some of these are mentioned in this paper, all of them are described in the book.

This paper gives an overview of the early phase of the project were the parent hull form was selected, an overview of all the work done and finishes with a case study showing how the results might be used in a design office.

Selection of the parent hull form

The selection o f t h e parent hull form of this systematic series was considered very important and was treated as a separate project. A selection was carried out on the database of hull forms available at Marin; the selection was based on frigate type hull forms tested at high speeds. An average value of the geometrical parameters of the available models was selected at L/B - 8; B/T = 4.0 and CB = 0.40. Sufficient knowledge was considered to be available for the choice of the prismatic coefficient and the longitudinal position o f t h e centre of buoyancy; these coefficients were fixed at Cp = 0.63 and LcB/Lpp = -0.052; the latter with reference t o amidships and positive in a forward direction. Such knowledge was not present for the optimum position of the water plane coefficient Cwp and the optimum position of the centre of floatation LcF. Therefore a subseries was designed with a narrow, medium and wide fore body and similar three different aft bodies; the hull forms are shown in the diagram of Figure 1. The fore and aft bodies could be connected at will and finally six of them were tested in calm water and in head waves. The results o f t h e tests in calm water are shown in Figure 2 and the pitch motion in head seas at a speed of Fn = 0.855 in Figure 3. The results show that the models with a low resistance, models 3 and 6, have a "narrow" or "medium" width of the aft body and a "wide" fore body. These same models have however the largest pitch motion as shown in Figure 3. The final selection was based on the calm water resistance at a speed of Fn = 0.855 anda number of seakeeping aspects like heave and pitch motion, relative motion at St 17, vertical acceleration at St 19 and added resistance in waves. Taking the central model, model 2, as a reference, the relative changes t o this model were listed in Table 1. The participants o f t h e project all agreed that the wide/wide hull form constituted the best compromise between low resistance in calm water and low

HISWA Yacht Symposium 3

motions in waves. This hull form was therefore selected as the parent of the systematic series. The selection procedure is described in more detail by Blok and Beukelman [1984].

Table 1 Relative difference (to model 2) of calm water resistance and various seakeeping aspects ofthe six models at a speed ofFn = 0.855

Calm Rel Vert

water Heave Pitch motion accel St Realm + model resistance motion motion St 17 19 Raw Raw

1 +0.1 +7.7 +7.6 +6.2 +3.7 +1.0 -1.0 2 0 0 0 0 0 0 0 3 +5.2 0 -10.6 -9.6 -7.4 -13.6 +4.0 4 -0.4 +2.6 +7.6 +11.9 +3.7 +1.0 0 5 +1.8 +7.7 +10.6 +4.5 +7.4 -3.9 +1.4 6 +4.5 +5.2 +4.5 +7.9 0 -9.6 +3.6 M3DEL 1 ® * 0

®

®.

FDS - The MARIN Systematic Series 4 0 . 0 8 0 1 2 3 4 F r o u d e d i s p l a c e m e n t n u m b e r [-] 0 . 0 8 o £ 0 . 0 4 4 0 . 0 2 0 . 0 0 •model 4 •model 5 •model 6 0 1 2 3 F r o u d e d i s p l a c e m e n t n u m b e r [-]

Figure 2 Results ofthe experiments in calm water

I

I

1.

—

/ '

—

model 4 model 5 model 6

^"^^^

tJ

IJ

'y__S

1/

U

wave frequency [rad/s]

Figure 3 Pitch motion of the models in head waves at a speed of Fn - 0.855.

The systematic series

Once the parent hull form was defined, the systematic series could be developed. The transformation t o different values of L/B and B/T were quite straightforward since it constituted only a linear factor on the offsets. There was no suitable method for the variation of the block coefficient C B , S O a new method was developed together with Delft University of Technology, [Koops 1985]. The objective was to change the block coefficient while keeping the "character" of the sections. The method transforms the offsets of a particular section by keeping the transverse y-coordlnates the same and adopting a specific rotation for the vertical z-coordinates:

y^Ew •

Z N E W • V O L D

Z Q L D + Z O + yoLD*tan a

In principle a value zO = 0 was used and a non-zero value of a was determined to create the required submerged sectional area. This method worked well for sections in the fore body, but could result in a negative deadrise for the flat sections in the aft body. This problem was solved by lowering the contour line (the point y=0, Z N E W ) of the section which results in a negative value

HISWA Yacht Symposium 5

of Z Q . This last aspect involved some manual intervention of the transformation procedure to arrive at a fair hull form. Figure 4 shows an example of a normal transformation of a section in the fore body and of a section in the aft body where the contour line had t o be changed. Figure 4 also shows that the width at the design waterline, especially in the fore body, changes as a function of the block coefficient; this effect was accepted as an unavoidable consequence of the transformation. The main hull form coefficients of 3 models differing in block coefficient are shown in Table 2; the table shows the magnitude of the changes In the parameters for the water line.

Figure 4 Example ofthe geometry transformation method for a section in the fore body (left) and a section in the aft body (right) where the contour line was lowered.

Table 2 Main hull form coefficients of models with different block coefficients.

Low block Parent Higti block L/B 8 8 8 B/T 4 4 4 C B 0.35 0.40 0.50 Cp 0.63 0.63 0.63 C W P 0.77 0.80 0.82 LcB -0.052 -0.052 -0.052 LcF -0.092 -0.087 -0.070

Using this method a systematic series of 27 models was built. In order t o identify the models, use was made o f t h e fact that just three parameters completely define the shape: L/B, B/T and C B . The hull forms were represented in the so-called "magic cube". Figure 5, in which each dot indicates a hull form.

FDS - The MARIN Systematic Series 6

I 1 1 1 1 2.5

4 6 8 10 12 UB

Figure 5 Ttie "magic cube" stiowing the hull forms of the systematic series in black dots.

Because the project ran for a period of 10 years, inevitably the Ideas about interesting "design areas" changed. The initial plan involved three "levels" of C B , but later on a fourth level at C B = 0.55 was added to extend the applicability also to larger destroyer type of hull forms. In a very late stage it was realized that the step from L/B = 4 to L/B = 8 was a very large one, especially concerning the resistance characteristics. A fourth L/B plane at L/B = 6 was added and a series of models was designed, built and tested in calm water; not in waves.

Experiments

Experiments in calm water have been carried out on an unappended hull. Turbulence stimulation at the bow has been applied as customary by way of pins. The models were towed at the longitudinal position of the CoG and at a height corresponding t o the supposed propulsion drive train. Calm water resistance, trim and sinkage were measured for speeds up to Fn = 1.14 unless excessive trim and spray prohibited such high speeds. Propulsion tests were not carried out.

Motions and added resistance in regular head waves were measured using a semi-captive set-up: the model was connected at the CoG to the carriage by way of a gimballed heave post. Measurements were done at a series of fixed values of the wave length - ship length ratio for a fixed series of speeds: Fn = 0.285, 0.430, 0.570, 0.855 and 1.140. Again the tests In waves could not all be done at the highest speeds due to excessive trim and spray; this was especially the case for the low L/B hull forms.

HISWA Yacht Symposium 7

Interpolation methods

In the final stages of the project the data was further analysed. The idea was t o determine the trends on resistance in calm water and on motions in waves based on the 3 hull form parameters and, for the results in waves, also based on the fixed values o f t h e Froude number. This would then allow the prediction of the performance of intermediate hull forms based on the actually measured values.

For the calm water resistance (and the trim and sinkage) it appeared that regression using the three hull form parameters as in the independent variables for a series of fixed values of the Froude-displacement number FUy gave the most accurate results; an example o f t h e accuracy is given in Figure 6.

For the motions and added resistance in head waves the regression was carried out on the speeds for which the experiments were done. Also fixed values of a non-dimensional wave frequency parameter have been used so that the independent variables of the regression are just the hull form parameters. This approach resulted in reasonably accurate predictions, but the

results, motion RAOs or the quadratic added resistance operator, as a function of the wave frequency, are not necessarily smooth lines. An example of the result of the Interpolation formulas is shown in Figure 7.

V s [ k t s ] wave frequency [rad/s]

Figure 6 Example of result of regression Figure 7 Example of result of regression analysis and original data points for the calm analysis and original data points for motions in water resistance. head waves.

Additional studies

Apart from the experiments as described above some additional work has been carried out: • A study into the effect of transom stern wedges for a limited series of hull forms.

• A study into the magnitude o f t h e hull roll damping and the effect of bilge keels at these high speeds.

• A check on the choice of the prismatic coefficient by testing t w o additional hull forms. • Regression analysis for the resistance of an extended database of high speed

FDS - The MARIN Systematic Series 8

Transom stern wedges

The effect of transom stern wedges has been tested on a small series of four models: the parent hull form and the hull forms on the axes of the cube in the low L/B, low B/T and high C B directions. Each model was tested with 9 wedges having a length of 1-2-3% of Lpp and a wedge angle of 5,10 and 15 deg.

As could be expected, the effect of the wedge on the resistance of the L/B - 4 models is quite important due to the fact that these models have a large trim angle at high speed; this is illustrated in Figure 8. The zoom-in shows that the effect on the residual resistance for a speed

Fn^=2.0 is 16%.

Figure 8 Residual resistance coefficient for the L/B = 4, B/T = 4, CB = 0.40 model with a wedge, length 0.02*Lpp, with different wedge angles (wa). Full speed range (right) and zoom-in (left).

Roll damping

As indicated in the introduction, focus of the experiments was on calm water performance and behaviour in head seas. Nevertheless in the course o f t h e 10-year project attention was paid to the prediction of the roll motion; more specific the prediction of the proper roll damping for these high speeds. Roll is a notorious problem; the damping is usually quite low - much lower than the critical damping. The damping increases significantly for increasing speed; the relatively flat aft body of these designs create lift forces that dominate the roll damping at high speeds. Traditional methods to estimate the roll damping, like the one developed by Ikeda (1978) and Himeno (1981), are based on model experiments with merchant ships. The combination o f t h e frigate type hull forms and the high speeds of this systematic series makes the traditional method very inaccurate.

It was therefore decided to develop a new formula to predict the lift damping. A special series of experiments was designed using an oscillator mechanism to force the model into a roll motion while it was still free In the heave and pitch modes. Experiments were carried out with a series of 13 models covering the B/T range in a band from the low Ca low L/B corner to the high Cg -high L/B corner of the "magic cube". Most of the models were tested with and without bilge keels; these bilge keels had a length of 25%*Lpp and a height of 1% of Lpp. This work resulted in a new formula for the roll damping which gave much better predictions of the roll motion at high

HISWA Yacht Symposium 9

speeds as was verified by a series of free running experiments. A detailed description of this work was published by Blok and Aalbers (1991).

Comp. Meas. Vj (F^)

0 1.0 2.0

Figure 9 Roll response of the parent hull form in beam seas at different speeds. Results of calculations using the new method to estimate the roll damping are shown in lines, experimental results by symbols.

Check on the choice ofthe prismatic coefficient

The prismatic coefficient has been fixed from the outset at a value of Cp = 0.63. This value was based on results from existing ships, the results of Series 64, Yeh (1965), the series by Lindgren (1968) and the NPL series. Bailey (1976). Nevertheless It was considered worthwhile to perform a check on the influence of Cp by developing t w o variants o f t h e parent hull form at L/B = 8, B/T = 4 and C B = 0.39. The result of the resistance in calm water is shown in Figure 10; for the higher speeds that are the interest of this series the Cp = 0.63 hull form is confirmed to be the better choice.

Figure 10 Residual resistance / displacement Figure 11 Heave RAO at Fn = 0.57 for the for the prismatic coefficient sub-series. prismatic coefficient sub-series.

FDS - The MARIN Systematic Series to

Regression on an extended database of resistance experiments

Regression formulas t o interpolate in the data of this systematic series have been developed, but on top of this a regression was made on all available calm water data of high speed displacement hull forms. The database consisted of:

• the NPL High Speed Round Bilge Displacement Hull Series, Bailey ( 1 9 7 6 ) , 2 4 hull forms. • the David Taylor Research Centre Series 6 4 , Yeh ( 1 9 6 5 ) , 2 7 hull forms.

• the NRC series, Murdey and Simoes Re ( 1 9 8 5 ) , 3 9 hull forms.

• Non-systematic data from the MARIN database, selected for high speed round bilge hull forms, 3 6 hull forms.

• The MARIN systematic series, 3 3 hull forms.

In total there were 1 5 9 hull forms in this database. The regression of the resistance yields a specialized tool for fast displacement ships that is much more general than the regression of the systematic series only.

A case study

In order to illustrate the possibilities using the data and the computer program, a case study is presented. The base design for the case study is a motor yacht with main dimensions as listed in Table 3 . The hull form belongs to the FDS family. The basis results of the calm water resistance, powering and motions in head waves are presented in Figure 1 2 .

Table 3 Main dimensions and hull form ratios of the motor yacht

Lwl 3 0 . 0 0 m B 6 . 0 0 m T 1.50 m V 9 9 . 9 m^ A 1 0 2 . 4 ton Vs 3 0 kts L/B 5 . 0 0 0 B/T 4 . 0 0 0 CB 0 . 3 7 0 Cwp 0 . 7 7 6 Fn 0 . 9 0 0 6 . 4 6 5

Figure 1 2 shows that the major resistance component is the residual drag for speeds higher than 1 0 kts. There is a clear hump for speeds 1 7 - 2 1 kts after which the relative importance of the residual resistance decreases. Figure 1 3 shows the heave motion in head seas; the peak o f t h e RAO increases for increasing speed and shifts to lower frequencies. The driving parameter behind this is the heave excitation which increases for longer waves. Those longer waves are being encountered at a higher frequency when the speed increases. Since this higher frequency is closer to heave resonance, the response increases. The wave excitation for pitch has a maximum for a wave length about equal t o the ship length (corresponding to a wave frequency of 1.4 rad/s); this is the main reason why the response shows a maximum around this frequency.

HISWA Yacht Symposium 11

Vs IKsl Vs |Ms|

Figure 12 Calm water resistance of ttie motor yacht showing the Total, Frictional, Wave making. Appendage and Wind drag components. The plot on the left gives the absolute values, the plot on the right gives the relative contributions (plotted in a cumulative manner).

The case study concerns the effect of a variation of the beam and draft while keeping the length and displacement constant. If the beam is changed independently of the draft, the block coefficient has to be changed in order to keep the displacement constant. A matrix can be set up with the B/T ratio on one axis and the Cg on the second axis showing either the beam or the draft, see Table 4 as an example. This table shows that the variation o f t h e beam is quite large and also the draft varies a lot more (from 1.05 to 1.95 m) than might be possible in real life. However limits to the ranges can always be added, even after doing the calculations. Calculations were carried out for a matrix of 100 hull forms, 10 steps on the B/T axis and 10 on the C B axis. The results considered are the total resistance at the design speed and the significant heave and pitch motion in the "design" sea state with significant wave height Hs = 2.0 m and average period T i = 6 s. The results are shown in Figure 14. The upper left hand graph shows that there is a maximum difference of 24% between the total resistance of the best and the worst

FDS - The MARIN Systematic Series 12

design. The optimum of the design space is the high block coefficient - low B/T corner. This design has a narrow beam and, since the length is constant, the highest L/B ratio; this design also has the lowest wetted surface, both aspect help in reducing the resistance. The diagram further shows that the penalty in resistance when increasing the B/T ratio is not very large; the total resistance of the Cg = 0.55, B/T = 5.5 hull form is only 5% higher than that of the optimum hull form.

Table 4 Table showing the beam of the motor yacht as a function of the B/T ratio and the Cg

B/T C B ^ \ 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.35 4.877 5.343 5.771 6.169 6.543 6.897 7.234 0.40 4.562 4.997 5.398 5.771 6.121 6.452 6.767 0.45 4.301 4.712 5.089 5.441 5.771 6.083 6.380 0.50 4.080 4.470 4.828 5.161 5.474 5.771 6.052 0.55 3.891 4.262 4.603 4.921 5.220 5.502 5.771

HISWA Yacht Symposium 13

The motions in waves and the added resistance are also shown in Figure 14. The optimum is clearly different to the optimum for the calm water resistance. The ship motions show that having a low value of the B/T ratio is not very good for comfort aspects. Unfortunately the corner in the design space having the highest resistance in calm water also has the highest pitch motion! It seems to be a good compromise to aim for a high B/T and a high C B . The price to pay is the high added resistance in waves, in the design sea state of Hs = 2 m it adds 37% to the calm water resistance. One wonders if this "natural" speed reduction is not a very sensible thing t o do anyway in such a seaway...

This case study shows how the PC program can be used; it can quickly show the consequences of quite dramatic changes in the hull form in a very early stage o f t h e design process. It also shows that naval architecture is about making choices, about finding the right balance between conflicting requirements for a particular design. This balance is dependent on the preference of the owner of the yacht, the use of the yacht and about the wave climate in which the yacht has to operate.

Concluding remarks

As explained in the introduction, no real results of the project were published because of the confidentiality o f t h e project. Permission was granted for some overview publications: Oossanen (1980), Oossanen and Pieffers (1985) and Robson (1987), and for some publications on specific details of the project: Koops (1981), Blok and Beukelman (1984), Aalbers and Blok (1991), Keuning (1990) and a chapter in the PhD thesis of Keuning (1994).

Now all results will be made available, this concerns the definition of the hull forms, the experimental data and the interpolation routines. Together with the book explaining the details of why and how the experiments and the analysis were carried out, we hope that the maritime community will have a useful database of the hydrodynamic behaviour of high speed displacement hull forms.

Nomenclature

B m Maximum beam on the water line T m Draft amidships

Lpp m Length between perpendiculars

LcB m Longitudinal position o f t h e centre of buoyancy forward of St 10 LcF m Longitudinal position o f t h e centre of floatation forward of St 10 CoG m Longitudinal position o f t h e centre of gravity forward of St 10 Cp

-

C B - Block coefficient

Fn

-

Friy

_-

FDS - The MARIN Systematic Series 14

References

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