The Principle Method for Calculation of Freeboard Distribution

UeIft University of

TechnclOy

SI2 HyromecflS

Laboratrj

Library

Meketweg 2 - 2628 CD Deift The Nethertands

Phone: 3115 785373 -Fax: 31 15 781 82

TECHNICAL REPORT

STUDY ON REVIEWING FREEBOARDS

OF ICLL

(1)

Report NO.1 The Principle Method for Calculation of

Freeboard Distribution

Report No.2 Probability Criteria for Determination of

Freeboard Distribution and Analysis on

Practical Ships

Report No.3 Computations of Freeboard Distribution

for Reference Ships and Typical Ships

Report No.4 A Seakeeping Experiment Research on

Flokstra Container Ship Model

CHINA CLASSIFICATION SOCIETY

Study on Reviewing Freeboards of IICLL

Report No.1 The Principle Method for

Calculation

of Freeboard Distribution

Abstract

This report has provided the method of calculating freeboard distribution (JPCM) which is based on probability calculation of deck wetness, according to the principleof revising freeboards

ofICLL presented by 1MO LL Working Group. In this method, the freeboards at seven positions that are distributed equally along the ship length are computed and atforward perpendicular. it is called bow height, at amidship, it is called basic freeboard. The research is the expansion of minimum bow height research presented by China. After taking into account the items affecting

the computation of freeboards listing in Appendix I of 1966 ICLL and analysing the ocean wave data of North Atlantic and other typical sea areas, the report has presented the principles of freeboard distribution calculation. As the instance of application of the principle method, the computation of two typical ships (Flokstra and Bulkcarrier) have been made according to the

procedure ofcomputation.

1. The Principle of reviewing freeboards of ICLL by 1MO

1.1 The SLF 37/25/8.6 of 1MO has decided to remain the following factors in the future ICLL. that

is,

Deck wetness.

Intact reserve buoyancy,

Intact stability and damaged stability. Watertight integrity,

Strength of construction, Protection of the crew,

1.2 The 1MO SLF Sub-Committee has confirmed the following fundamental factors in reviewing freeboards of ICLL at SLF 37/25/8.11,

Providing the performance criteria for conventional ships and new type ships, Determining environmental criterias,

Remaining freeboard table for conventional ships. revising

if

necessary, Simplifying the procedure of determining freeboard,

Allowing to determine freeboards of conventional ships and new type ships through theoretical calculation / model test.

Coordinating the requirement of damaged stability with probability method or other

requirements of damaged stability of 1MO, such as MARPOL 73/78, Other suggestions provided by SLF Sub-Committee.

1.3 Decisions made by LL Working Group in further reviewing freeboard since 1MO SLF Sub-Committee's 32nd meeting

(i) Applying linear strip theory as the fundamental calculation tool,

Using ITTC wave spectrum, long-crested wave, head seas and a seriesof ship speeds and

significant wave heights as the calculation condition.

wetness,

(4) Determining a loading condition (Summer Load Line).

2. Review of bow height research made by China

2.1 According to the fundamental principle of reviewing 1966 ICLL presented by 1MO. China has taken into account the questions in research of bow height as follows:

Providing the method (Joint Probability Criterion Method JPCM) of calculating bow

height based on the concept of probability according to the progress of research in ship seakeeping theory( details in SLF 40/6/2),

Taking into account the fact that the deck wetness is most severe at head seas, it is determined

to use head seas as computing wave direction,

Choosing ship speed corresponding to Fn0. I as the calculating speed throughinvestigation of

practical ships and hearing the comments of the masters that the speed is decreased in general at head seas in severe sea conditions. So the assumption is suitable for both large and small ships.

The minimum bow height formula does not include parameter about speed, this is favourable to

simplify the calculating procedure,

ITTC wave spectrum with two parameters and North Atlantic wave statistics are fully used in JPCM,

Obtaining the reasonable probability criteria value Ps-Pc of deck wetness (risking level)

through parameter analysis and computation of practical ships, Using severa! principles of 1966 ICLL in JPCM as follows,

Determine the height of deck flooding according to Regulation 15 and Regulation 16 of

Appendix I,

Calculate the minimum bow height corresponding to winter freeboard, applying North

Atlantic winter wave data, taking into account the concept of season freeboards,

The related parameters in calculating minimum bow height corresponding to Regulation

39 of Appendix I are consistent with the definition of Regulation 3 of Appendix I.

2.2 The research of bow heigth by China has realised the following goals presented by 1MO SLF

Sub-Committee,

Providing a new formula (see SLF 37/8/1) for minimum bow height of 1966 ICLL, and, Developing the direct computing program of minimum bow height required by ICLL. 2.3 The principle method of bow height research in fact is applicable for the research of freeboard

distribution of ICLL. So the finished research in how height could be the rea!iable basis for the

research in revising freeboard of ICLL.

3. The principle method of calculating freeboard distribution

linear Strip Theory and Calwlatiori of Relative Motions + Ps-Pc Joint Probability Criteria Method Fig. 3.1.1 3.2 Instructions of input.

Head seas. it is the ideas of 1MO LL Working Group, Fn0. 1. it is the results of investigation shown in 2.1 (3),

ITTC wave spectrum with two parameters, it is also the ideas of 1MO LL Working Group. North Atlantic ocean wave statistics, see 4,

Probability criteria value Ps-Pc. details see Report No.2,

Main dimensions and hull lines, providing table of offsets of2l stations,

The height of deck flooding H. according to Regulation 15 and Regulation 16 of Appendix 1,

1966 ICLL.

height of coamings of hatchway + loads on hatchway covers in Position I"

This value is related with criteria Ps-Pc. Now H=0 is determined on the basis of ideas of

1MO SLF LL Working Group.

Height of bow wave swell up ft. determined by Tasaki formula on the basis of ideas of 1MO SLF LL Working Group (In fact, HO for position L/3 after the forward perpendicular).

3.3 Strip theory and calculation of relative motions

(1 Factors in strip theory and calculation of relative motions

Calculating motions with 5 degrees of freedom according to S.T.F. method,

Calculating hydrodynamic coefficients with multi-expansion precision fitting method, Calculating statistical values in irregular waves with the linear superposition method.

(2) Figs. 3.3.1 to 3.3.7 show the relative motion results of two typical ships (Flokstra ship and Bulkcarrier) calculating with factors described above, comparing with the results provided by other countries. lt can be seen that the results of our research are consistent with that of other

countries. Freeboards at: AP. (1!6) froni AP. (113)L from AP. Amidships (1/3) from F.P. (1!6)L from F.P. F.P.

INPUT

_PROCESSOR

_OUTPUT

Wave Direct ion of

Head Seas

Speed Corresponding To Fn = 0.1

ITTC Wave Spectrum

With Two Parameters North Atlantic Winter Wave Statistics Probability Criteria for

Type A & Type F] Ships Hull Form

Height of Green Water

above the Ded 11w = O

Statical Swell-up Tasaki Formula)

2

t

5 4 E E o

Relative motions at bow

CaknjLatons based on deat waves. 25 Jan. 1996

Fkdtstra Cb 0.6, Fn = 0.245. Head seas Location 2.56%L fwd of EPP

Flokstra Cb = 0.6. Fo = 0,245. Head Leas Locabon' 3.93%L ted of APP

da/L

Fig. 3.3.1

Reatíve motions at stern

Cafculatíons based on inadant waves, 25 Jan. 1996

0.5 da / L Fig. 3.3.2 l's 2 Expenmeni A Germany a Netherlands e Canada Ç Japan Poland , Crdna E.xpertrnent o Germany a Netherlands O Canada Ç' Japan Poland Chora o 0.5 1,5 2

E (V E E 2 2 E E 2 2 5

PIo1stra Cb 0.6, Pn 0.17, Head aecs LacaSen: FPP

FIok.stra Cb = 0.6. Fr = 0.17, Head SOa LacaSen: O.7SxL ted 04 APP

Relative motions at bow

C&JlSitonS based on ncdent waves. 23 May 1996

Fig. 3.3.3

Relative motions at bow quarter

Caidaabons based on dent waves, 23 May1996

Fig. 3.3.4 O Germany Poland $ Cenada Netherlands Clvna O Germany O. Poland & Canada Netherlands COana o 05 I.5 2 2.5 3 Lambda IL o 1.5 Lambda I L 0.5 2.5

Helative motions at L)ow

Cabjlatjors based on inadenl waves, 23 May 1996

Bulkcarrlor, n 0.155, 'seed seas Location FPP 0.5 e Canana ' Japan , Netherlands e Poarid Chsna Fig. 3.3.5 E

Bulkcaroer, Fn = 0.155, Heed sees Locahan' 95% L ted cl APP

Relative motions at bow quarter

Calculations based on irsadent waves. 23 May 1998

& Canada Japar e Netherlands e PoLand Cnera o 0.5 15 2.5 3 Lambda IL 3 2.5 1.5 Lambda I L 2

Relative motion at bow (RMS values)

Cacu1atons based on nciderd waves. 3 Jurie 1996

0.6 r-. ;1o4L 02 F 6 8 10 12 14 Mean pehod Ti (s)

Floknira t. = 270 rn. Cb = 0.6, Fn = 017. ilead soaz Spectrum:PM.,Ms1w

Fig.3.3.7

(3)Non-linearity in prediction of relative motion

In studying deck wetness, nowadays the strip theory is frequently used. Although the flow field and resulting motions of a ship advancing in waves are nonlinear, three-dimensional boundary value problem, for design purpose, the traditional engineering solution is to use a strip theory, in which the frequency is assumed to be high and the geometry of the body to be long and slender so that a solution can be approximated by a series of two-dimensional problems in the

cross-flow plane. Strip theory gives rather accurate predictions for slender ships and ships moving at low speed, however, since in strip theory, the three-dimensionality of the flow field is neglected and the forward speed effects are taken into account only in a simplistic manner, therefore for high

speed ships or for ships and ocean structures of complex geometry, the strip theory is not

theoretically correct for prediction purposes.

All calculations of the deck wetness are based on the prediction of relative motion. The main influence of nonlinearity in predicting relative motion comes from following three factors.

First factor is the effect of flare hull above waterline. On using strip theory. the transfer functions of relative motions provided the necessary information for statistical evaluation. The transfer functions for ship motions and relatìve motions at selected stations were calculated

modeling the ship hull only up to the designed load waterline.

Normally, the calculations of ship motion and relative motion to waves by strip theory are confined to light and moderate sea states, since nonlinear effects generally dominate the response

in severe wave conditions. For relative motions, in particular higher incident waves, the effect 01 the non-vertical sides(flare) between waterline and deck contour of the ship and time varying

A Nalheriandu o PoLand Q Canada o ChIna 7 0.8

ç-hydrodynamic coefficients were considered a major effect on the ship response in severe wave

conditions.

However. in most case of light and moderate sea states, the accuracy of prediction by strip

theory is enough to use in engineering.

The second nonlinear factor is the effect of dynamic swell-up due to the hull geometry. In

predicting relative motion, for high speed container ship, a dynamic swell-up should be taken into account in bow part of ship.

The third nonlinear factor is undisturbed incident wave elevation. Hong et aI (1993) concluded from their experiments with a S-175 container ship model in head seas that the strip theory underestimates the deck wetness at the bow, If the prediction method made use of the measured relative motion a very good agreement was obtained with the directly measured deck

wetness.

Their results demonstrated that to predict the relative motion accurately the motion components resulting from the diffracted and radiated waves should be considered. These components are, however, usually not taken into account by the strip theory methods. 1fthe disturbed wave surface is taken into account, there is a difficulty of phase prediction accurately.

Although there are three nonlinear factors, for the time being it may be concluded that the prediction of relative motion nowadays is enough accurate in engineering, by using strip theory

with considering dynamic swell-up coefficient. 3.4 Calculation method of freeboard distribution

JPCM can be used to obtain the freeboard at any positon of ship. lt is a long term prediction

method for determining freeboard required by deck wetness at any position of ship in irregular wave, using strip theory, wave spectrum with two parameters and sea wave statistics with two

parameters.

Taking the determination of the statistics of bow height in irregular sea waves as an example, JPCM could be described as follows:

(1) Assumptions and known conditions

The target ship sails in irregular waves with a constant speed and the wave direction of

head seas, the relative motion of the ship is considered by coupling pitch and heave ofthe ship.

The relative motion follows the narrow-band normal distribution and its amplitude follows Rayleigh's distribution.

The amplitudeofrelative motion can be determined by using strip theory.

The ocean wave statistics with two parameters (H, T1 )

for the sea area under

consideration is given, where H is significant wave height, T1 is average period.

The ocean wave spectrum with two parameters (H, w )

for the sea area under

consideration is given, where w is wave frequency.

The height of bow wave swell-up at the forward perpendicular can be calculated

according to Tasaki's formula.

(2) Marginal deck wetness probability and minimum bow height

For the given bow height Fb and irregular wave of combination of parameters (H.T1 ) and

height H , the probability Ps which is the height of wave surface above the exposed deck

exceeding the height H. can be calculated according to the following formula:

(Pb - Hs Hw)2

Psexp{-

_2mos(H,T1) I (I)

Where,

ft

is height of bow wave swell-up at F.P.

H is the height of the coamings of hatchway + load on hatchway in "Position 1"

=2.35 m

mos (H, T1 ) is variance of the relative motion of the bow for the given wave

parameters (H, T ), can be expressed as follows:

Ao 2

mos (H, T1 ) =

S ( H ,w)() dw

(2)

where, - _{is amplitude of the relative motion corresponding to the wave}

parameters(H, T1 ),

S(H, w) is ocean wave spectrum with two parameters (H, w).

Reversely, when the wave parameters (H, T1 ) and criterion probability Ps, height H, and H,

are given, the minimum bow height Fb can be calculated according to the following formula:

Fb=

-2lnPsmos(H,Tl) +Hs-Hw

(3)

(3) Plane q and plane F

For the sea area under consideration, the long-term ocean wave statistics can be presented by

plane q as follows: H _qij q2j qj H_1 q . q2.l q1_1 - qj-H2 q12 q22 q.12 q H1 q q q11 () T1 I T17

T_

T1, Fig.3.4.l p!aneq

Where, q,j is occurrence frequency of the wave with parameter conibination (H , T11).

For the criterion probability Ps = 5%, the minimum bow height can be calculated by using the

formula (3) for each combination (H. T1) in plane q, thus the corresponding plane F can be

obtained as follows: H F1 F2 _F H_1 F11 F2I F_1 H2 F12 F22 F112 F2 H1 F11 F,1 F11 F1 T1 i T1, T111 T11 Fig. 3.4.2 plane F

combination (H, T1 ) and the given constant criterion probability Ps. (4) Probability statistics of bow height

In order to find the probability statistics of minimum bow height in plane F, second criterion

probability Pc is to be given. Then the required minimum bow height Fmin can be determined by

finding out an area in plane F. In such area, each element F, complies with the relation of F Fa

(an assumed bow height ) and the sum of all elements in the corresponding plane q equals to criterion Pc.. Here Fa is the required minimum bow height Fmin. The principle of determining

Fmin is shown in Fig. 3.4.3

H

>

lo

H

T T

Fig. 3.4.3 Principle of determining Fmin

Note: Each element F, in the shadowed area of plane F complies with the relation of F,

FaFmin, and the sum of all elements in the shadowed area of plane q equals to Pc.

To sum up. Pc is a criterion probability in the nature of long-term probability, by which the risk level can be controlled, and its value is defined as the sum of occurrence frequencies of such sea waves that the probability of deck wetness Ps of the considered ship will reach 5% or above.

Here Pc is taken as 1.5%.

(5) The procedures of numeral evaluation of probability statistics of minimum bow height Assuming a group of bow height in ascending order of its values:

Fai, Fa2, ,Fak

For each element of the group Fa, calculating the probability Pc according to the

following formula:

Pc= P (4)

where, P1 = q1 F > Fa

=0

F<Fa

(5)

Thus obtaining a group of Pc for the assumed group of bow height of Fa.

Drawing the curve of Fa-Pc as shown in Fig.3.4.4. and the required minimum bo height

the statistics of minimum bow height Fmin can be found by taking the constant criterion probability as Pc1.5% in the curve.

Fmin

F42

Pc =1.5%

Fig. 3.4.4 Determination of Fmin

3.5 Instructions of output

The freeboards in seven positions which seperates the ship length into six parts, the length of each part is L/6, are computed in the research according to the positions of standard profile in Regulation 38 of Appendix 1. 1996 ICLL. At FR it is called bow height and at amidship it is

called basic freeboard. The distribution curve which meets the requirements of deck wetness can be obtained from this seven freeboards value. Thus the minimum forecastle length could be

obtained for given moulded depth.

4. Wave statistics

4.1 Selection of wave statistics

The great progress in research of wave spectrum and wave statistics since 1960s has made it possible to calculating bow height and freeboard distribution under the given probability criterion of deck wetness based on concept of probability. In 1985 N.Hogben presented the global wave statistics, here we select it as environment data in calculations. The following contents are chosen

from this book,

(1) North Atlantic winter wave data

Tab.4.1.1 lists winter wave data in Zones No.8, 9, 15, 16 that are considered as unrestricted navigating area ( simplified as NAW 1985).

(2) Typical restricted navigating area winter wave data

Tab.4.1.2 lists winter wave data in Zones No. 10, 11. 17. Tab.4. 1.3 lists winter wave data in Zone No. 40.

SUM = 100

*

Obtained from combination of wave data of Zones of No. 8,9, 15. 16 (N. l-logben 1985).

**

Relation hcveen zero uperossing period Tz and characteristic period TI:

Ti = I .086Tz. I-Is (ni) 4.5 5,5 6.5 7.5

Zero uperossing period 8.5

9.5 10.5 Tz (s) 11.5 12.5 135 14.5 15.5 12.5 0

-() 0 1) 0 0.025 0.050 0.075 0 (I 11.5 0 O 0 0 0 0.050 0.100 0,100 0.075 0 0 (1 10.5 0 0 0 0 0.025 0.125 0.175 0.175 0.100 0.025 1) 0 9.5 0 0 0 0 0.100 0.250 0.325 0.275 0.125 0.045 0.020 0.010 8.5 0 0 0 0 0.200 0.525 0.625 0.425 0.175 0.070 0.025 0.005 7.5 0 0 0 0.100 0.475 1.050 1.150 0,700 0.275 0.090 0.010 0 6.5 0 0 0 0.250 1.100 2.050 1.875 0.975 0.300 0.080 0.020 0 5.5 0 0 0.050 0.650 2.425 3.725 2.800 1.225 0.350 0.080 0.020 0 4.5 0 0 0.175 1.600 4.725 5.625 3.350 1.175 0.275 0.075 0 0 3.5 0 0 0.525 3.475 7.400 6.450 2.875 0.800 0.151) 0 0 1) 2.5 0 0.075 1.350 5.700 7.725 4.500 1.400 0.275 0.025 0 0 1.5 0 0.275 2.375 4775 3.425 1.125 0.225 0.025 0 0 0 0.5 0.025 0.325 0.825 0601) 0.150 0 0 0 0 0 0 0

Wave Data for Zones ofNo. 8, 9. 15. 16

(North Atlantic Winter)

Table 4. I

.

SUM = 100

Obtained from combination of wave data of Zones of No. 10, 11. 17 (N. Hogben 1985). Relation between zero uperossing period Tz and characteristic period Ti:

TI 1 .086Tz. Hs (in) 3. 4. 5.5

Zero uperossing period

6.5 7.5 8.5 Tz (s) 9.5 10.5 11.5 l2 12.5 0 0 0 0 0 0 0 0.033 0 0 .5 0 0 0 0 0 0 0.033 0.033 0.033 0 10.5 0 0 0 0 0.033 0.067 0.067 0.033 0.033 0 9.5 0 0 0 0.033 0.033 0.100 0.133 0.100 0.067 t) 033 8.5 0 0 0 0.033 0.133 0.233 0.233 0.200 0.100 0.033 7.5 0 0 0.033 0.067 0.233 0.367 0.433 0.333 0.167 0.067 6.5 0 0 0.033 0.233 0.500 0.833 0.800 0.567 0.267 0.100 5.5 0 0 0.100 0.467 1.067 1.600 1.433 0.867 0.333 0.100 4.5 0 0.033 0.267 1.100 2.267 2.933 2.300 1.167 (.).400 0.133 3.5 0 0.067 0.700 2.400 4.433 4.800 3.133 1.333 0.400 0.067 2.5 0 0.167 1.633 4.833 7.200 6.000 3.000 1.000 0.233 0.067 1.5 0 0.567 3.500 7.233 7.300 4.067 1.400 0.333 0.067 0 0.5 0.133 1.500 3 400 3.267 1.60)) 0.467 0.067 0 0 0

Wave Data for Zones of No. 10, Ii, 17

(North Atlantic Winter)

L

SUM

100

**

*

Obtained from combination of wave data of Zone of No. 40 (N. Hogben 1985). Relation between zero uperossing period Tz and characteristic period TI:

TI = I.086Tz.

Wave Data for Zone of No. 40

(South China Sea Winter)

Table 4. 1 .3 I 1-Is I (m) F-3.5

r

T

4.5 5.5

Zero uperossing period

6.5 7.5 8.5 Tz (s) _9.5 10.5 11.5 9.5 0 0 0 0 0 0,100 0 O O 8.5 0 0 0 0 0.100 0.100 0.100 O O 7.5 0 0 0 0.100 0.200 0.200 0.100 0.100 0 6.5 0 0 0.100 0.300 0.600 0.500 0.300 0.100 0 5.5 0 0 0.200 0.900 1.400 1.100 0.500 0.200 0 4.5 0 0 0.600 2.300 3.100 2.100 0.900 0.200 0.100 3.5 0 0.100 1.800 5.100 5.600 3.200 1.100 0.300 0.100 2.5 0 0.500 4.300 9.200 7.700 3.400 1.000 0.200 0 1.5 0 1.600 7.800 10.400 5.800 1.800 0.400 0.100 0 0.5 0.300 2.800 4.800 3.000

0.900

0.200 0 0 0

4.2 Comparison of wave statistics data

Fig. 4.2.1 shows curves relating significant wave height H113 with frequency f and Fig. 4.2.2 shows uperossing-zero period T with frequency f. According to them. it can be seen that,

j.

(7,)

f

25-a ç.O 5_0 3.0 2S 0 -5,-O AO 5.' o N Fig. 4.2.1 LO So -O Zone No.40

(For Winter Seasonal)

15

Statistics Characteristic ofH113 - f

òa 80 Zone No.8 9 ± 15 16 ZoneNo.10 + Il + 17 0-O

\

\

00

Fig. 4.2.2 Statistics Characteristic of Tz - f

a

2.0 4'.O

H1,3 (rn)

16

(For Winter Seasonal)

Tz(s)

\

Zone No.8 + 9 + 15 + Zone No.10 + 11 + 17

Significant wave height, the appearing frequency of which is the largest, in unrestricted

navigating area is larger than that in restricted navigating area. The appearing frequency of bigger

waves in former is also larger than that in latter. But the appearing frequency of smaller waves in

former is obviously less than that in latter.

Wave period, the appearing frequency of which is the largest, in unrestricted navigating area is

larger than that in restricted navigating area. The curves of T - f show some trend of translation.

4.3 Application of wave statistics

According to the comparison in 4.2 and the opinions of N.Hogben to wave statistics data presented in "Global Wave Statistics", the wave statistics in the book are chosen in the research.

Although there would be some effects in computing freeboards of different dimensional ships

with different wave statistics from the role of deck wetness, these effects would be no sense on the

whole when taking into account the ship type, using specialty, navigating area and environment condition, etc. So it is acceptable to use unique wave statistics in research of freeboard. Here we

select the winter wave data of unrestricted navigating area, i,e. that of North Atlantic Zones No.8. 9. 15. 16 (NAW wave data, see Tab.4.1.1) in the research.

5. Analysis of computing results of typical ships

5.1 Flokstra ship (1) Main dimension: L 2700m B = 32.2m d = l0.85m Cb = 0.60

Fig.5.l.1 shows the body plan.

16

6,'

-(2) Fig. 5.1.2 shows a group of freeboard distribution curves corresponding to probability criterion Pc=0.015 and Ps=0.1, 0.2. 0.3. 0.4, 0.5 respectively. .z / 5.2 Bulkcarrier (1) Main dimension: L = 247.Om B 406m

d= 161m

Cb = 0.827

Fig.5.2.1 shows the body plan.

17

Fig. 5.1.2

'2

(m)

L = 270.Om Head Sea 0(0

I00 B = 322m d= 1085m Fn 0.1 Hw =0 o.2

_c:

Cb = 0.60 Pc 1.5%

/

Flokstra Ship (N.A.W. wave data) p

2.0 SbG

-a...

c \ 0r

\

, Qo

I

o \ O

/

. i- .- -G ro Ö

rri

Fig. 5.2.1 Bodyplan of Bulkcarrier

(2) Fig. 5.2.2 shows a group of freeboard distribution curves corresponding to probability criterion

Pc0.015 and Ps0.1. 0.2, 0.3, 0.4. 0.5 respectively.

Bu!kcarrier (N.A.W. wave data)

LL S

----

-=----Fig. 5.2.2 18 o(o 0,2

/

-L = 2470m Head Sea B = 406m

Fn0.1

d= 161m Hw =0 Cb = 0.827 Pc= 1.5% F Cm)

-AP F, F.

5.3 Analysis of computing results

Determination of freeboard depends on the determination of probability criterion value. There

will be a special research to determine them.

The curves of freeboard distribution have provided the basis for determination of freeboard at

amidship. minimum bow height and minimum forecastle length.

The standard profiles of 1966 ICLL for ships of Type A and Type B are also given in Fig.

5.1 .2 and Fig. 5.2.2 . They are useful to analyse probability criterion.

6. Conclusions

The report has expanded the research of bow height to that of freeboard distribution, provided the theoretical method to calculate freeboard distribution based on concept of probability for reviewing freeboards of ICLL according to the principles presented by 1MO SLE

Sub-Committee's LL Working Group.

JPCM using strip theory for calculations of relative motions, wave spectrum with two

parameters and wave statistics with two parameters, is the core of the research.

The calculation conditions such as height of deck flooding, wave statistics and calculating ship

speed. etc, have been established on the reasonable basis according to the relative Regulations of

ICLL and analyses.

The method can be used to calculate freeboards in seven positions regulated by ICLL, thus the

curves of freeboard distribution under given probability criterion be obtained. The minimum forecastle length can also be obtained when the moulded depth is given for determined curve of

freeboard distribution.

The calculating results of two typical ships indicate that the probability criterion Ps-Pc should be determined before the calculation of freeboards in reviewing freeboard of 1996 ICLL. This

research would be presented in Report No.2.

References

(I) International Convention on Load Lines, 1966. SLF 37/25/8, 1MO 1993.

SLF 37/8/1, 1MO 1993. SLF 37/8/2. 1MO 1993. SLF 39/WP.S, 1MO 1995.

Nils Salvesen, E.O.Tuck, Odd Faltinsen: Ship Motions and Sea Load. SNAME Vol 78, 1970. F.Tasai: Formula for Calculating Hydrodynamic Force of a Clylinder Heaving on a Free

Surface (n-Parameter). Rept. of Research Institute for Applied Mechanics. Vol 111 Number 31, 1960.

Yu Jiapeng, Da Rongting: Conformal Transformation of Sections and its Application on Calculation of Ship Motions. Jal. of Shipbuilding of China. No.1.1979.

Jorgen Strom - Tejsen. Huge Y.H. Yeh, David D.Moran: Added Resistance in Waves. Trans SNAME. Vol 81. 1973.

N.Hogben, F.E.Lumb: Ocean Wave Statistics, Her Majesty's. Stationary.

N.Hogben, N.M.C.Dacunha, G.F. 011iver: Global Wave Statistics. British Maritime Technology, Feitham, Middlesex, England 1985.

C.Flokstra: Comparison of Ship Motion Theories with Experiments British Maritime Technology, Feltham, Middlesex, England 1985.

Zhou Z.Q., Miao GP., Liu Y.Z. and Gao H.Q. : The Theoretical Prediction of Ship Motions, Jal. of Shipbuilding of China, Vol 114,1991.

Zhou Z.Q., eta! Large-amplitude Ship Motions in Time Domain. CSSRC Technical Report. Aug.1996.

Hong S.Y., Lee P.M., Gong D.S.: Experimental Study on the Deck Wetness of a Container Ship in Irregular Head Waves. Selected Papers of the Society of Naval Architects of Korea. Vol 1, pp37-44,1993.

SLF4O/6/3. 1MO. 1996. SLF 40/WP.4, 1MO, 1996.

Study on Reviewing Freeboards of ICLL

Report No. 2

Probability Criteria for Determination of Freeboard

Distribution and Analysis on Practical Ships

Abstract

According to the calculating principle method presented in Report No.1 and the unique requirement of 1MO LL Working Group, the probability criteria value Ps of JPCM which was defined as the limited value of severe deck wetness has been replaced with that of the upper

acceptable deck wetness probability based on the research of bow height formula presented in SLF

37 I 8 / 2. It has been used to determine the freeboard distribution of Type A ships, for Type B ships it is defined as the function of the position of ship along the ship length, taking into account the construction characters and the protection of the crew. In addition, the probability criteria value Pc has also revised taking into account the reasonable difference of safe criteria between large and small ships. Through a series of computations for practical ships. the length of which

ranges from 34m to 264m, the Ps, Pc values have been determined as follows for Type A and B,

forTypeA, Pc =1.5%

L ) 100m,

= (l.5+(100L)*3.5/76)% 24m L 4 100m Ps=40%

04X4L

forTypeB, Pc =1.5% L 100m, (1.5+(100L)*3.5/76)%

24m 4 L

100m Ps=40%

0.9L 4 X 4L,

=(50X/L-5)% 0.5L < X < 0.9L =20% X 4 0.5L

The bow heights calculated from above probability criteria are consistent with that of the proposed formula in SLF 37 / 8 I 1.The freeboards at amidship show the difference required by Type A and B ships by calculation of freeboard distribution. Although the freeboards at amidship of calculating ships meet the requirements of above Ps, Pc criteria, it is necessary to revise the

relevent provisions about freeboard and forecastle length of ICLL.

1. Review

SLF 37 / 8/1 and SLF37 / 8/2 indicate the suggested formula of calculating the minimum

bow height and its research contents. In this research, the probability criteria values Ps, Pc used in

JPCM for calculating bow height are corresponding to the severe deck wetness condition, in which the height of deck flooding is conducted according to the requirement of ICLL and such

happening of severe deck wetness is regarded as small probability event. Thus, the assumed Ps, Pc values may be considered as the critical values,in fact that,

Pc1.5%;

Ps=5%.

An acceptable deck wetness probability Ps corresponding to the height of deck flooding h, >

0. has been suggested to be adopted for calculating the bow height and freeboard at 1MO LL Working Group meeting in Jan. 1996 and 1MO SLF 40 in Sep.1996. lt is larger compared with above severe deck wetness probability and difficult to determine in an adquate level. This report

2. Probability criteria values Ps, Pc of Type A and B ships

2.1 Definition

Type A ship lt is designed to carry only liquid cargoes in bulk, has a high integrity of the exposed deck with only small access openings to cargo compartments, closed by watertight gasketed covers of steel or equivalent materials and has low permeability of loaded cargo

compartments.

Type B ship All ships which do not come within the provisions regarding Type A

ships shall be considered as Type B ships.

Ps An acceptable deck wetness probability at which the height of deck flooding h,

> 0.

Pc A probability, its value is equal to the wave occurring frequency at which the

deck wetness probability encountered exceeds the given Ps in above (3) 2.2 Probability Criterion Pc

Pc was taken as a small probability value to consistent with the research of bow height in SLF 37/8/1 and SLF 37/8/2. In that research, the height of deck flooding h, corresponding to the value of Ps depends on the position along the ship length according to ICLL. Now h is equal to

zero, so the determination of Fc should be related to ship length to reflect the reasonable

difference of safe criteria between large and small ship. Similar to the requirements of ICLL, when

ship length L is greater or equal to 100m, Pc is equal to 1.5%, when L is equal to 24m, Pc is equal to 5%, when L is between 24m and 100m, Pc is obtained by linear interpolation, see Fig.

2.2.1. lt means that, because the probability of entering unrestricted navigating area for small ships

is less than that for large ships, the Pc value for small ships is allowed to exceed that for large

ships. Pc (Z) 50 40 3.0 2p-

Pc=5%

200 250 300 Fig. 2.2.1.

2.3 Probability Criterion Ps at F.P. (ship bow)

(I) Choosing a group of practical ships in random shown in Tab. 2.3.1; 1.5%

o

Assuming a group of Ps values shown in Tab. 2.3.2;

Tab. 2.3.2

3

I'ab.2.3H

Computing the bow heights of practical ships listing in Tab. 2.3.1 with JPCM method presented at report No.1, using Pc given in 2.2 and Ps given in Tab. 2.3.2. The results are shown

in Tab. 2.3.3; Tab. 2.3.3 i Ship No. L x B D X d

( m )

Cb n A 34 7.6 x 3.15 2.0 0.588 13.0 B 49.8 9.0 4.0 3.5 0.615 12 X C 62.0 12.0

49

3.8 0,705 53 D

680 x

12.8 6.2 x 4.8 0.709 6.4 E 84.0 15.6 x 8.4 6.8 0.590 9.5 F 03.0 ¡90 8.5 65 _{0.705 30} G ¡29.7 20.8 8.7 6.25 _{0,744 5.1} H 175.0 32.0 15.4 9.5 _{0.837 09} j 215.0 * 32.2 x 18.7 12.5 _{0.830 .0} K 260.0 44.6 24.2 16.1 _{0.829 ¡.0} 264.0 32.2 215 12.5 _{0.651 8.1} Ship No. Fb I m I Ps20°/o Ps30% _{Ps=40% Ps=50%} A 2.16 .92 ¡.66 .47 B 3.47 3.02 2.77 2 32 C 3.98 3.48 2.99 2.81 D 4.48 3.98 3.48 _2.98 E 5.75 5.16 4.28 3.78 1 _{6.64 5.80 4.96} 4.56 G 6.43 5.73 493 4 41 H 8.16 7.14 6.48 571 J 8.16 7.I3 6.20 5.71 K 8.51 7.46 6.46 5.92 L 8.6! _{7.55 6.77 5.84} Ps I atbow 1°/o) _{20 30 40 50}

(4) Calculating the bow heights of practical ships listing in Tab. 2.3.1 with the suggested formula presented at SLF 37/8/1. Tab. 2.3.4 shows the results and the bow height given by 1966

ICLL;

Tab. 2.3.4

4

(5) Making variance analysis for data shown in Tab. 2.3.3 and Tab. 2.3.4. The results are

shown in Tab. 2.3.5 and Fig. 2.3.5;

Tab. 2.3.5 Ship No. Fbp ( SLF37/8/l ) ( m ) Fb66 ( m A 2.45 1.82 B _{3.04 2.59} C 3.81 2.98 D 3.79 3.23 E 4.33 4.01 F 5.12 4.50 G 4.99 5.13 H 5.80 5.72 J 5.83 6.16 K 6.06 6.24 L 6.27 6.95 Ship No. o ( Fbp

lb

Ps20%

l's=30%

ls40%

Ps50°/b A 0.0841 0.2809 0.6241 0.9604 B 0.1849 00004 0.0729 0.5184 C 0.0289 0 1089 0.6724 1 .0000 D 0.476 I 00361 0.0961 0.6561 E 2.0164 0.6889 0.0025 0.3025 F 2.3104 0.4624 0.0256 0.3136 G 2.0736 0.5476 0.0036 0.3364 1-1 5.5696 I 7956 0.4624 0.0081 J 5.4289 1 6900 0 1369 0.0144 K 6.0025 I 9600 0.1600 0.0196 L 5.4756 1.6384 0.2500 0.1849 29.6510 9.2092 2.5065 4.3144

2.0 30 20 Io

j

20 30 40 ₀₀ Fo 'X) Fig. 2.3.5 2 Ps

(6) Taking Ps which is corresponding to the minimum

a

2

(Fb-Fb)2 according to Tab. 2.3.5 as the probability criteria value at F.P. That means, Ps = 40%. Fig. 2.3.6 shows the bo

heights with this Ps, comparing with that obtained by SLF 37/8/1 and 1966 ICLL;

o 50 ¡00 50 5

z

I-V'

1966 ICLL JPCM(Ps = 40%) SLF37/8/1 Fig. 2.3.6 200 250 300 L ('lU

(7) Being unique to bow height for Type A and Type B ships of ICLL. the probability

criterion value Ps at F.P. may be used in all ships including Type A and B. 2.4 Probability Criterion Ps of Type A ship

According to the definition of Type A ships, there are gangway for walking on the exposed deck and the crew do not operate on deck in general at sailing, so it is suitable that the probability criterion value Ps for freeboard along the ship length is determined as that for F.P., that

's,

Ps40%

O X L

Where, X The distance of the considered position from AP. along ship length. (m)

Fig. 2.4.1 to Fig.2.4.1 I show the curves of freeboard distribution for practical ships listed in Tab.2.3.1, with the probability criteria values given in 2.4(1).

-o PzoZ 40 Z AF çp 6 SHIP A Fig. 2.4.2 Fig. 2.4.3 o S. FR Fig. 2.4.1 0-SHIP C Lbp 620m Freeboard(JPCM) N.A.W. '° F B 12.Om S.S. profile (1966 ICLL)

D 49m 1m)

d 38m

Cb 0.705 3.0

Lbp 34.Om Freeboard(JPCM)N.A.W.

B 76m ---S.S. profile (1966 ICLL) D d 35m 20m ° F _{Cb 0.588} .0-Al) o (01) PS 1.0 -. SHIP B Lbp 498m Freeboard (JPCM) N.A.W. B 90m - - S.S. profile (1966 ICLL) D 46m d 35m Cb 0.615

-.-

i

(n) - 20 F -AP Ap Fig. 2.4.6 40Z Lbp 680m B 128m D 62m d 4.8m Cb 0.709 = Lbp 840m B 156m D 84m d 68m Cb 0.59 9=. SHIP D Fig. 2.4.4 SHIP E Fig. 2.4.5 Freeboard (JPCM) N.A.W. S.S. profile(1966 ICLL) S. L Freeboard (JPCM) N.A.W. S.S. profile(1966 ICLL) ,pe O -SHIP F Lbp 030m Freeboard(JPCM)N.A.W. B 190m ---S.S. profile (1966 ICLL) (m D 85m d 65m Cb 0.705

A

AP Fig. 2.4.7

-4F Lbp 1297m B 208m D 87m d 625m Cb 0.744 Ps o4 34 Lbp 2150m B 322m D 18.7m d 125m Cb 0.845 SHIP G Fig. 2.4.9 8 Pec SL Type 5 Freeboard (JPCM) N.A.W. - - S.S. profile (1966 ICLL) EF Fig. 2.4.8 SHIP J ¡ 'J L SHiP H - _{p Lbp 1750m Freeboard(JPCM)N.A.W.} (ml B 320m --S.S. profile (1966 ICLL) D 54m d 9.5m Cb 0.837 A

4

/

Freeboard (JPCM) N.A.W. - - S.S. profile (1966 ICLL) Dec . L

-

_F - ¿. o - 2.0

-.5

-b

AP AP Lbp 2642m B 3222m D 2150m d 1250m Cb 0.651 F' Pz 3 z 24 9 Fig. 2.4.10 SI-HP L Fig. 2.4.11 Type. «A tech S. L Freeboard (JPCM) N.A.W.

7

- -

S.S. proflle (1966 ICLL)

/ /

7/

/

FP

2.5 Probability Criterion Ps of Type Bship

(1) According to the definition of Type B ships, there are big weathertight openings on deck

after the F.P. The crew operate on deck in general at sailing. So the Ps level for freeboard along the ship length should be higher than that at F.P., taking into account the safe operation and the

protection of the crew. It is assumed that Ps value is the function of the position along the ship

length. This function is shown in Fig. 2.5.1, that is,

Ps = Psi = 40%

0.9L « X « L

X - 0.5 L

= (Psi-Ps2) +Ps2 0.SL K X K 0.9L

0.4 L

= Ps2 X « 0.5L

Thus, the determination of Ps value for Type B ship is converted into the problem of

,,

L 2-1 SIUP K Lbp 2600m Freeboard(JPCM)N.A.W. B 446m ---S.S. profilc(1966 ICLL) D 242m d 161m F _{Cb 0.829}

/

/

Lm1f De(

/

determining Ps2 value, see Fig. 2.5.1.

Fs

Type A

Type B

Fig. 2.5.1

(2) Assuming a group of Ps2 value shown in Tab. 2.5.1.

Tab. 2.5.1 o. IL

Computing freeboard at amidship of practical ships listed in Tab. 2.3.1 with probability

criteria value Ps, Pc given in 2.2 and 2.5.(2). The results are listed in Tab. 2.5.2. Fig.2.4. i to Fig.

2.4.11 show the freeboard distribution curves corresponding to Ps2=20%, 30%, 40%. Among

them, Ps=40% is also the probability criterion value for Type A ships.

Comparing the computed freeboard distribution curves with the practical freeboard of ships, it can be seen that the partial deck line and forecastle length of ships which is less than

100m do not meet the requirement, and with the increase of L, the freeboard and forecastle length

of practical ships are obviously richer than that of computed.

Through above comparison, it can be considered adquate to determine Ps2 with 20%. Although the freeboards at amidship of computed ships meet the requirements of above Ps. Pc

criteria, it is necessary to revised the LL freeboard and forecastle length which is practically used.

Ps2

(%)

20 25 30

F. P

2.6 Analyses

(1) Fig. 2.6.1 compares the deviation of computed freeboard at amidship of Type A and Type B ships with the deviation of freeboard at amidship of Type A and Type B ships given in 1966

ICLL. nl) b 2 0 A F66 = FB66 - FA66 (1966 1CLL) A Fm) = Fm20 - fm4O (PsI = 40%. Ps2 = 20%) A Fm2 = Fm25 - Fm40 (Psi = 40%, Ps2 =25%) A Fm3 = Fm30 - Fm40 (Psi = 40%, Ps2 30%)

,

N N

7

'S

's-

-

-"S Fig. 2.6.1 11 Tab. 2.5.2 O=°,3 (AF,,1) O-- O26 (Fm) Ship No.

Fm ( m )

Ps=40% Ps,=20% Ps2=25% Ps2=30% Ps2Ps1=40% A 0.73 0.54 0.49 0.43 B 0.89 0.88 0.84 0.69 C 0.99 0.97 0.96 0.91 D 1.21 1.08 0.98 0.94 E 1.36 1.30 1.19 0.99 F 1.75 1.64 1 .49 1 .40 G 2.26 1.98 1.94 1.74 H 2.81 2.54 2.43 1.98 J 2.95 2.83 2.74 2.45 K 3.42 3.16 2.96 2.74 L 3.39 2.98 2.90 2.72 o 50 00 IrO 2Q0 2Ç0 3O L Un)

(2) Fig. 2.6.2 shows the comparison of freeboard at amidship required by deck wetness in

determined probability criteria values with that required by 1966 ICLL.

Freeboard (1966 ICLL) Freeboard (JPCM) 12 v0 50 300 L

(m)

Fig. 2.6.2

For Type B ships, when the ship length L is less than 150m, the freeboard required by

deck wetness is higher than that by 1966 ICLL. especially for small ships, on the contrary, when L is larger than 150m, the freeboard required by deck wetness is lower than that by 1966 ICLL. This is consistent with the explanation of traditional reserve buoyancy factor.

For Type A ships, when the ship length L is less than 130m, the freeboard required by deck wetness is higher than that by 1966 ICLL, on the contrary, when L is larger than 130m, the

3. Conclusions

3.1 According to the unique requirement of 1MO LL Working Group, the probability criterion

value Ps of JPCM which was defined as the critical value of severe deck wetness has been replaced with the upper acceptable value of deck wetness probability based on the bow height

formula presented in SLF 37 / 8 / L

3.2 The probability criterion value Ps for F.P. of ships has been introduced according to the

definition of adjusted Ps. It can be used by all ships in ICLL, including Type A and Type B ships.

3.3 The probability criterion value Pc has been revised according to the adjusted Ps taking into

account the reasonable difference of safe level between large and small ships.

3.4 Taking into account the deck construction, integrety. tightness, operation and protection of the crew in sailing for Type A ships, the Ps. Pc values have been determined as follows,

Pc 1.5% L 100m,

= (I .5+(100L)*3.5/76)% 24m L 100m

Ps = 40% 0 X L

3.5 Through analysis of computed freeboard distribution of a group of practical ships, the Ps, Pc

values of Type B ships have been determined as follows, taking into account the deck construction. integrety, tightness, operation and protection of the crew in sailing,

Pc1.5%

L 100m,

(1.5+(100L)*3.5/76)% 24m L 100m

Ps40%

0.9L ( X (L,

= (5OXIL-5)% 0.5L < X < 0.9L

=20%

X ( 0.5L

3.6 The research of probability criteria values Ps, Pc for Type A and Type B ships has provided all details of the principle computational method of reviewing freeboard of ICLL presented in Report No.1.

INPUT

Statical Swell-up

Tasaki Formula

Study on Reviewing Freeboards of ICLL

Report No. 3

Computations of Freeboard Distribution

for Reference Ships and Typical Ships

Abstract

This report has given the freeboard distribution of Type A and Type B ships for two typical ships (Flokstra ship and Bulkcarrier) determined by 1MO LL Working Group, calculated by using the method presented by the Report No.1 and the probability criteria presented by the Report No.2.

Then, two groups of systematically varied hull forms, one of 12 slender ships and the other of 12

full bodied ships, based on parametric variations L/B and BIT have been designed according to the

two reference ships given by 1MO SLF 40. The bow height, freeboard at amidship and length of

forecastle of Type B for slender ships and the bow height and freeboard at amidship of Type A for

full bodied ships have been computed. All computation results have shown agreeable regular relations with parameter LIT. According to the characteristrics of freeboarddistribution curves of computed ships, it is suggested that the freeboard about L16 after amidship be as the required

freeboard at amidship.

1. Computation procedure of freeboard distribution

According to the Report No. i and Report No.2, the computation procedure of freeboard

distribution is shown in Fig. 1.1.1.

Wave Direction of

Head Seas

Speed Corresponding

To En 0.1

111G Wave Spectrum

With Two Parameters

North Atlantic Winter

Wave Statistim

Probability Criteria for

Type A & Type E] Ships Hull Forni

Height of Green Water above the Deck 11w = O

PROCESSOR

linear Strip Theory and Cakjlation of Relative Motions + Ps-Pc Joint Probability Criteria Method Fig. 1.1.1

OUTPUT

Freeboards at: AP. (1!6)L troni .P. (1I3) troni f..P. Amidships (113)L troni F.P. (1!6)L from F.P. 1. F.P

2. Freeboard distribution of the typical ships

2.1 Flokstraship

The computation results of freeboard distribution of Type A and Type B are shown in Tab.

2.1.1 and Fig. 2.1.1.

-_LhQ -2 2 A.P Fig. 2.1.1 B Type

Freeboard distribution ut I ÌoLstra ship

A Type L = 270m

B = 322m

Flokstra ship

Freeboard distribution Standard sheer profile

T= 1085m Cb=0.60 2 I ¿ib. 2 I I

//

/

L B

B/I

I: ( ni ) A P-' / 13 1 PC

L/T

LP (116)L (2/6)L mid (4/6)L 56)1. AP. 8.38 2.97 7,29 4.46 4.62 .97 2.29 230 2.97 2.92 3.85 2.28 2.91 290 3.78 24.88

-

2.0-2.2 Bulkcarrjer

The computation results of freeboard distribution of Type A and Type B are shown in Tab.

2.2.1 and Fig. 2.2.1.

Freeboard distribution of Bulkcarrier Tab. 2.2.1

- f0,0 F (.m)

-,.p

A Type

Bulkcarrier

Freeboard distribution

- -

Standard sheer profile L = 247m B = 406m 3 Fig. 2.2.1 T= 160m Cb=0.82 B Type

/

/

/

7'\

-

//

\,/

\ifl)

/

/

8P-j F. F 6. ,0

-LIB

BIT

F(m)

AType/BType

LIT

F.P. (1/6)L (2/6)L mid (416)L (5/6)L AP. 6.08 2.54 6.84 4.10 4.45 2.86 2.98 2.74 3.40 2.83 359 2.80 3.50 3.29 4.17 15.43

3. Freeboard distribution of slender ships (L= 150m, Cb= 0.68 at 0.85D)

3.1. Systematically varied hull forms

(I) The main dimensions of the reference ships (L/B=7.5, B/T=2.5) L=150m

B20m

T8m

Cb0.650 (T8m)

Cw0.785 (T8m)

Cm0.976 (T8m)

LCB-O.497%L (T=8m) n=6.6 (T8m)

Fig. 3.1.1 shows the body plan of this ship.

I: .5 5 IS S I.

t'

s I I I ( S ¿ 5. ¿ f S. é r I lia S Si I e I t I I I tS il O' O 5 _{f f f} / t O. .. , _I I I .5

5

I _f f ¿ ¡ _/

I'!

'i OSI t I t ¡ I . SI s S- _{f f /} t I I I I j f III t- I I i i f t

'

₁

_f

_f « j te S,

'

I t e : / _s . / :3 * I I I .. ' I . .' s. .' t S, f I I 1 'S / _{Ç H} .5 / .. /O - s. I.t 5., s I I I / _{e' ..- . -} .-- 5/ i e I r t .' . . .. I f t t I

j

'

t /0 _{,/ /} .5' SS tt Fig. 3.1.]

(2) The parameters of systematically varied hull forms L/B=5.5. 6.5, 7.5, 8.5

B/T= 2.50, 2.75, 3.00 Totally about 12 ships. 3.2 Freeboard distribution

(1) Tab. 3.2.1 shows the values of the freeboard distribution of 12 Type _{A and Type B ships}

each;

(2) Fig. 3.2.1 and Fig. 3.2.2 show the freeboard distribution curves of 12 Type A and Type B ships each.

L/B

B/I'

'n ) A Type! 13 type

L F

IP.

(1/6) L (2/6] L mid (4/6) L (56) L AP.

3.94 1.97 ¡.91 ¡.99 1.96 2.96 2.50 6.48 3.97 2.43 2.43 2.83 2.54 3.94 i 3.75 3.35 1.90 1.94 ¡.98 ¡.92 2.96 5. 2 75 5.92 3.69 ¡ .96 2.43 2.81 2.42 3.91 IS ¡25 2.99 1.78 1.95 1.99 1.91 2.95 3.00 5.60 3.46 1.90 2.34 2.83 2.27 3.84 16. 3.60 ¡.90 ¡.91 1,98 1.92 3.20 2.50 5.94 3.78 1.96 2.43 2.80 2.44 4.17 ¡6.25 2.99 1.76 1.95 1 99 1 9] 2.98 6.5 2.75 5.60 3.46 1.90 2.5! 2.81 2.27 3.97 17.873 2.91 1.44 1.96 1.99 1.91 2.96 3.00 5.44 2.98 1.78 2.74 2.83 2.27 3.94 19.50 3.22 1.76 1.94 1.99 ¡.91 3.39 2.50 5.73 3.50 ¡.89 2.51 2.81 2.27 4.39 18.75 2.95 1.42 1.96 1.99 1.91 3.16 7.5 2.75 5.49 2.98 1.78 2.74 2.83 2.27 4.07 20.625 2.81 1.42 1.99 1.99 1.90 2.98 3.00 4.96 2.87 1.76 2.81 2.83 1.99 3.97 22.50 2.98 1.42 _1.96 1.99 1.91 _3.39 2.50 5.60 2.99 1.76 2.54 2.83 2.27 4.44 21.25 2.83 1.27 1.99 1.99 1.90 3.39 8.5 2.75 4.96 2.90 1.76 2.81 2.83 2.00 4.37 23.375 2.76 1.42 1.99 1.99 1.90 3.17 3.00 4.94 2.81 1.78 2.83 2.83 1.98 4.17 25.50

F

Em

D Lt.o 30 2.0 Lo

-F ()

50

30

-2.0

LO -A Type Ships B Type ships L = 150m Cb = 0.68 (0.85D) L / B =8.5 B / T = 2.50. 2.75, 3.00 L / B =7.5 B / T = 2.50, 2.75. 3.00 L / B =6.5 B / T = 2.50, 2.75, 3.00 6 L / B =5.5 B / T = 2.50, 2.75, 3.00 Fig. 3.21 FF F Cm)

-

7.c - 6.0 - 5O F Cm) c.c 30 20

I O

- 3,0

Fm

2.O 70 i.G -F Cm)

-

7.0 5TO - 40

3

-2 o-. 0 -(m) -3D. 2.0 1.0-Fm -. 3.0-. 70.0 -(rn) co -

4,0

-20-1 J 300 300 L / B =8.5 B / T = 2.50, 2.75. 3.00 2.75 L / B =6.5 L / B =5.5 "J = 50m. Cb = 0.68 (O.85D), L / d = 15 Freeboard distribution - - - - Standard sheer profile

I /R=7c

-

..-.

n/T=')cfl

.-, 76 IflÛ

_-

DL(300) B / T = 2.50, 2.75, 3.00 3 00 AP _Fp Fig. 3.2.2 300 B Type 2So) B/T = 2.50, 2.75, 3.00

/

(2 '

r

B _2.5

-L(3.ao) F m) - co 3ao 3 0

3.3 Data analyses

(I) Fig. 3.3.1 shows the relations of bow heights, freeboards at amidship and freeboards at

L/6 after amidship with parameter L/T;

:-

Fb,F,n±tP (m) 2.2 e) e) o L = i 50m

0Fb

F,,, Fui,, 6 Cb0.68 (at 0.85D) Bow height Freeboard at midship Freeboard at L/6 aft midship

e)

Fig. 3.3.1

_L/T

_{Fh, F21, Frn}

(2) Fig. 3.3.2 shows the relations of the ratio of L and freeboard at amidship. the ratio of L

and freeboard at L/6 after amidship with LIT;

L = 150m _{Cb0.68 (at 0.85D) L / D = 15}

.L\

Freeboard at midship

".D1rnc.x

Freeboard at L/6 aft midship

o a L T i I j I J S 2C 22 ¿t,C 26 o L/D 8 Fig. 3.3.2 I i i L

L__L___t

'6 20 22 . 24

(3) Fig. 3.3.3 shows the relations of the ratio of the forecastle length (L/D=15, sheer height'0) and L with L/T.

o

G o L -r J I I I I 2.1 22 23 2 2Ç Fig. 3.3.3

4. Freeboard distribution of full bodied ships (1= 200m, Cb=0.8 )

4.1 Systematically varied hull forms

(1) The main dimensions of the reference ships (L/B=6.0, B/T=2.5)

L=200m

B33.33m

T 13.33 m Cb0.80 (T=13.33m) Cw0.88 (T=13.33m) Cm0.996 (T°°13.33m) LCB2.0% L (T13.33m) n2.1 (T=13.33m)

Fig. 4.1.1 shows the body plan of this ship.

i t i J I i I-,- i r '_ ,,I r . I

il

i ( r I

II

j II I I I I VI I j :1

a'

al I ¿ , II . .. 4

II

I .' .1 '

t.t

I.I I I i I - t e I 1 /I I.. . . .. .. I . .. .- . -V ,V S. V-- --

.-

.__

tri

I-.

-. .... ..-

....i

. --- -- -: --

.

... -. Fig. 4.1.1 -F

(/L)

L= 150m Cb=0.68 (at 0.85D)

L/D= 15

o o 200 10.0 o 2°

1,

(2) The parameters of systematically varied hull forms L/B=5.0, 5.5, 6.0, 6.5

B/T= 2.50, 3.00, 3.50 Totally about 12 ships. 4.2 Freeboard distribution

(1) Tab. 4.2.1 shows the values of the freeboard distribution of 12 Type A and Type B ships

each;

Frechoad disrihuiion of thc lull boWed ship lab. 4.2 I

IO L I R: I F n A Type / B lype L/ i F.P. (1/6) L (2/6) L mid (4/6)1. (5/6)1. AP. 4.11 2.87 2.74 2.83 2.81 2.95 2.50 6.60 4.54 3,37 3.50 3.59 3.52 3.89 12.50 3.91 2.62 2.48 2.71 2.50 2.85 5.0 3.00 6.20 3.92 2.91 2.97 3.38 2.97 3.68 15.00 3.70 2.37 2.44 2.55 2.14 2.84 3.50 6.11 3.84 2.78 2.95 2.99 2.88 3.63 17.50 4.10 2.78 2.48 2.78 2.55 2.93 2.50 6.58 4.43 2.98 2.99 3.47 2.99 3.85 13.75 3.82 2.45 2.21 2.54 2.25 2.89 5.5 3.00 6.12 3.92 2.81 2.91 2.99 2.91 3.72 16.50 3.69 1.99 2.00 2.54 1.99 2.89 3.50 6.11 3.77 2.53 2.91 2.99 2.84 3.72 19.25 3.92 2.55 2.37 2.55 2.50 2.95 2.50 6.58 4.20 2.90 2.95 2.99 2.97 3.89 15.00 3.70 1.99 2.00 2.53 1.99 2.90 6.0 3.00 6.11 3.82 2.54 2.87 2.98 2.84 3.84 18.00 3.39 1.96 2.00 2.55 1.99 2.90 3.50 5.92 3.68 2.43 2.91 2.99 2.83 3.84 21.00 3.91 2.45 2.00 2.53 2.29 2.99 2.50 6.24 3.94 2.79 2.87 2.99 2.92 3.97 16.25 3.56 1.97 _2.00 2.53 1.99 2.94 6.5 3.00 5.96 3.72 2.43 2.87 2.99 2.83 3.88 19.50 3.17 1.94 2.33 2.55 1.99 2.93 3.50 5.82 3.39 1.99 2.91 2.99 2.83 388 22.75

I

(2) Fig. 4.2.1 and Fig. 4.2.2 show the freeboard distribution curves of 12 Type A and Type B ships each. 30_ 30 20 -L / B =6.5 B IT = 2.50. 3.00. 3.50 A Type Ships B Type ships L=200rn

Cb0.80

11 L / B =5.5 _{B / T = 2.50, 3.00, 3.50} -L / B =5.0 _{B IT = 2.50, 3.00, 3.50} Fig. 4.2.1 Fcm

-

7.0 F1m) -7.0

r

r

r

- 3 - 2,o Frn)

-2.o -7

.-.}.0 -é.O - 30 i 0

-Fn)

ç.0 1 L / B =6.0 B / T = 2.50, 3.00, 3.50 40 -4 .P F. P

I,

I,

2o 0 1 30- 2."- 0-1 (ni)

- 4.0-3. -F )m)

- 1.0-3. ° 3 Ö 3 Ç0 2. 12

¶

Fig. 4.2.2

/

T

/,

- (.0 -Wi-Fi")

-

7." F. P ¿.0 A Type

/

-

7,0 L = 200m .Cb = 0.80 Freeboard distribution

- - Standard sheer profile

2.co T 300 3.5o L / B =6.5 B / T = 2.50, 3.00, 3.50 B / T = 2.50, 3.00. 3.50

L/B=6.O

B / T = 2.50. 3.00, 3.50 L/B =5.5 30_ 20-3ÇC

4.3 Data analyses

(1) Fig. 4.3.1 shows the relations of bow heights, freeboards at amidship and freeboards at

L/6 after amidship with parameter L/T;

L = 200m Cb=0.80

C) Fb Bow height

A F,,, _{Freeboard at midship}

FITIa Freeboard at L/6 aft midship

Ag

A

6

Fig. 4.3.1 L / T Fb F11, Fm

(2) Fig. 4.3.2 shows the relations of the ratio of L and freeboard at amidship, the ratio of L

and freeboard at L/6 after amidship with L/T.

L = 200m

Cb0.80

A _{Freeboard at midship}

Freeboard at L/6 aft midship

A L 1 P 211 Fig. 4.3.2 13 AA A 2G o A L T 22 2«

2-

_pim4X

p

i6 o 'z '4

- Fb

F _.F (m 2.0 'e '0

5. Conclusions

5.1 The computed bow heights. freeboards at amidship, freeboards _{at L/6 after amidship and}

the forecastle length at given LID value have shown agreeable regular relations with parameter

LIT.

5.2 The freeboard at L16 after amidship is equal to or greater than that at amidship. So from the role of practical use, it seems reasonable that the freeboard about L/6 after amidship be as the

required freeboard at amidship.

5.3 The computed freeboard distribution results of two systematically varied hull forms groups

have shown that for given L and Cb, with the increase of L/T. the minimum bow height, freeboard at amidship and freeboard at L/6 after amidship that meet the required criteria are tend to constant.

5.4 For slender ship, when L/D=15, the minimum L/T which meets the required criteria is

approximately equal to 20.6.

Study on Reviewing Freeboards of ICLL

Report No. 4

_{A Seakeeping Experiment Research}

On Flokstra Container Ship Model

by

ZHENG-QUAN ZHOU DE-CAl ZHOU

NAN XIE

( July20

,

1996 )

Notes: Being entrusted by China Classification Society (CCS), this experiment research has been made by China Ship Scientific Research Center (CSSRC) according to the contract.

LIST OF SYMBOLS

Aa

Vertical acceleration amplitude at i 7 station

B Breadth

CB Block coefficient C.G. Center of gravity

F

Froude number

g Acceleration due to gravity GM

Metacentric height

H13 Significant wave height

k

Wave number

Transverse gyradius

_{( in roll direction )}

Longitudinal gyradius (in pitch direction )

L Length between perpendiculars L.C.G. Longitudinal center of gravity

S0 Relative motion amplitude

S (co)

Wave spectrum in fixed point

S (co e)

Encounter wave spectrum

S, (co e) _{Response spectrum of relative motion}

S0 (coe) Response spectrum of pitch motion SA (cor) Response spectrum of acceleration

S (co ,)

_{Response spectrum of heave motion}

S (cor)

Response spectrum of roll motion

S),! _{Significant value of relative motion}

T _Draught

t Time

Natural pitch period Natural roll period

Wave characteristic period

V Speed

Xg

_{Longitudinal center of gravity aft of}

_{station 10}

Z,,

_{Significant value of heave} Incident wave amplitude

ea

Pitch amplitude

e

,, _{Significant value of pitch}

?. / L _{Wave numberíLength between perpendiculars} Wave direction

Non-dimensional roll damping coefficient Roll motion amplitude

Significant value of roll motion

w _{Wave circular frequency}

s

A Seakeeping Experiment Research

On Flokstra Container Ship Model

by

ZIJENG-QUAN ZHOU

DE-CAl ZHOU NAN XJE

( July 20

,

_{1996 )}

ABSTRACT

An experiment is carried out to investigate the effect of

_{wave direction and rolling}

motion on deck wetness and on the relative motion for

_{a large fast container ship.}

The experiment results of regular waves and irregular waves are presented. From

this experiment, it is evident that the wave direction and rolling motion have a

considerable influence on relative motion at midship.

INTRODUCTION

Technical developments in the ship building and shipping industry, demand reexamination

of the " International Convention on Load Lines 1966 " ( ICLL 1966 ) with the aim of

developing a tool for the assignment of freeboard which needs to be flexible enough to dea! with conventional as well as unconventional ships.

The goal of this research project is to develop freeboard_{tables conditioned on deck wetness}

and setting up respective requirements for load

line _{calculations, which will support}

International Maritime Organization " ( 1MO ) activities to revise the 1966 convention for a year 2000 release.

According to the requirement of the _{" SLF Load Lines Working Group ", The Register of}

Shipping of the People's Republic of China_{arrange an experiment to investigate the effect of}

wave direction and rolling motion on deck wetness and on the relative motion for a large fast

container ship . _{China Ship Scientific Research Center undertake this ship model experiment}

This paper is reporting the experiment results and analyzing the phenomena revealed by this experiment.

DESCRIPTION OF THE MODEL TEST

2.1 Selection of Wave Directions

largely concerned on head seas. This approach is rational since it has been confirmed that the bow relative motion is largest in head seas when determine the freeboard height_{at bow . Due to} the combined effect of the vertical and lateral motion, however, higher relative motion at

midship may occur in oblique waves.

For container ships having a large natural roll period can lead to large motion due to near-synchronous conditions in oblique waves. Therefore, in the present study, measurements of

relative motion and deck wetness were carried out at midship and at oblique wave directions.

Summarizing it may be concluded that for a larger container ship the _{highest relative} motion due to vertical _{lateral motion may be expected in 30 to 60 degree wave directions,}

either approaching from the bow or from the stern. Within this _{range no priority can be given to}

a certain heading. For the present research the model tests were conducted initially in bow and stern quartering waves e.g. approaching 45 degrees off the bow and the stern. Preference_was given to 45 degrees heading since in stern quartering _{waves largest roll angles due to}

near-synchronous conditions will occur in the wave length and ship speed range tested. It follows that the relative motion was considerably influenced by the roll motion.

2.2 Seakeeping Basin

This ship model experiment is carried out in the seakeeping basin of China Ship Scientific Research Center from June lO to July 6, 1996.

China Ship Scientific Research Center (CSSRC) is a research and development organization in ship engineering. It offers service in R&D _{model experimentation and}

consultation iii concept design for various marine structures.

CSSRC's headquarters is located at WuXi, JiangSu province, _{with a branch office at} Shanghai. CSSRC has more than 40 years of history, and has tested and given consultations to

most of the large marine structures in China.

Seakeeping basin is one of main facilities in CSSRC. The dimensions of the seakeeping basin are 69mx 46mx 4m (water depth), wave makers on two adjacent sides, capable of

generating regular and irregular waves. A bridge _{spans the diagonal of the basin and is rotatable} 45°. Model running_{or towed by a carriage under the bridge (max. speed 4m/s) may be tested at} any required angle with respect to the waves. Wind and current effect also may be simulated.

2.3 Ship Model

The tested ship is a container ship provided by _{" SLF Load Lines Working Group}

referred to as the _{" Flokstra-Ship " . The main particulars of the ship are listed in Table I and a}

body plan is reproduced in Figure 1 as well as the stem and stern outlines in Fig.2, two ship

model photo in Fig. 3 and Fig. 4.

The ship model has an integral hull form including _{the hull form above waterline, an}

integral deck form, _{as well as a set of appendages: bilge keels, propeller shafts, shellbossing,} two propellers, a rudder.

The ship model constructed to a scale of ito 80 of glass reinforced polyester

The scale was mainly determined by the capacity_{of the irregular wave generator installed} in the Seakeeping Laboratory of the CSSRC

The model was fitted with bilge keels

Table I

Principal Ship Dimensions

2.4 Model Preparation And Calibration

The weight distribution in the model was adjusted on a low - mass trimming table , by

means of which the exact position of the center of gravity in the _{vertical and horizontal} directions was obtained

The longitudinal radius of gyration in pitch direction was adjusted on the trimming table, whereas the transverse radius of the gyration in_{roll direction was adjusted and verified by a roll}

heeling experiment in still water.

2.5 Test Content

The primary aim of the present experiment is to investigate the effect of wave direction wave height .. period and ship speed, as well as rolling motion on relative motion and deck

wetness at midship.

The main test contents are rolling decay test, regular wave test and irregular wave test. The main measurements in this ship model experiment are

Determining the roll damping in still water

Measuring the heave .. pitch and roll motion of ship model in regular and irregular

4

No. Denomination _{Symbol Full Scale Ship}

Model

i

Total length

_{LOA 284.Om 3.55m}

2

_{Length between perpendiculars}

_{270.Om 3.375m}

3

Breadth

_{32.2m 402.5mm}

4

Total height

_{H 18.662m 233.3mm}

5

Displacement volume

V _{56097m3 0.1096m3}

6

Displacement weight

_{A 57499t. 109.6kg}

7

Draught even keel

_T

_1085m

_135.6mm

8

Block coefficient

_{C 0.598 0.598}

9

Center of gravity above base

_{Zg 13.49m 168.6mm}

IO

L.C.G. aft of station 10

Xg

-1O.12m -125.6mm

il

Transverse gyradius in roll direction

_0.375B1

_0.375B1

0.248L1

12

Longitudinal gyradius in pitch direction

_0.248L\v!

13

Metacentric height

_{GM 1.15m 14.4mm}

14

Natural roll period

T _{24.9s 2.78s}

15

Natural pitch period

T0 _{8.6s 0.96s}

16

Length of bilge keel

I 47.Om _587.5mm

17

Breadth of bilge keel

_{b 0.48m 6.0mm}

waves

Measuring the relative motion in several stations

Measuring the frequencies of deck wetness in several stations Measuring the vertical acceleration at bow part of the ship

2.6 Test Procedures

During the tests the model was self propelled by_{two stock propellers The model was} completely free in its motions _{It was kept on course by an auto}

_{- pilot ,}

_{controlling the} rudder _{in such a way that a straight course through the middle of the basin was maintained by} small rudder angles The model was connected by a light _{weight vertical rod in the} center of gravity of the _{model to a low - mass and low- friction subcarriage ,}

So that no appreciable forces or moments _{were transmitted on the model}

Each test run contained simultaneous recordings of the following quantities by data

recording computers

- Heave

pitch and roll angles recorded by a six _{degreefreedom motion measuring}

system connected to the light - weight rod

- Relative motion (with respect to the wave surface ) at the bow and_{the stern as well as} at amidship _{obtained by resistance wire wave probes attached vertically on the model}

at the station of 17 14 .. 10 and 5 on the weather-side

Vertical acceleration at the station 17 _{measured by a 2g accelerometer}

- Model speed _{measured by a slotted disc with photo cell pick-up}

Wave height _{determined by two wave probes one fixed to the moving carriage in front}

of the ship model, another fixed on the center at basin . The wave probes were calibrated

before the tests.

In irregular wave case , the frequency and probability of deck wetness at station 17 14

10 and 5 , recorded by a computer

The requirement of velocity simulated in model test is listed in Table 2

Table 2

Velocity Simulated of

Ship Model

3. ANALYSIS OF TEST

_{RESULTS IN ROLL DAMPING TEST}

Roll damping tests were first performed_{in calm water at a speed of0.0,}

10.0, 22.0 and 27.0

knots to determine the roll damping coefficients. During test, a transient_{moment acting on the} ship model, then, recording the curve of declining roll angle history. _{Analysis the declining}

curve, measuring the period of roll motion and the roll damping coefficients.

No. _{Full scale (knot)}

_{Ship model (nils)}

Fn

i

_{o o} o 2 10 _{0.575 0.10} 3 _{22 1.265} 0.22 4 _{27 1.553} 0.27