A systematic study about the main non-dimensional parameters on the seakeeping behaviour of slender, fast ships

A SYSTEMATIC STJDY AECUT THE MAIN

NON-IMENSIONAL. FARAMETERS ON THE SE(EE?ING

3EHAVIOUF. OF SLENDER, FAST SHIPS

ABS TRACT

During trie p mary stage of the

design rocess, the assessment of the hull

coefficenzs' ffect on the seakeeing

ber.avour of tne snip s of paramount im-pot-tance for a correct prediction and evaluation of sh:p s operat:ve ?erform-antes and fc trie due nowecoe of eventu

al relevant limitations during serv:ce.

This pacer refers to a recent sys-tenatic research carrted out at CANTIERI

NAVALI RIUNITI fr twin screw, slender

and fast naval vessels.

Theoretical studies were carried out with spec:al care ;ver. to tne zaran

etere C , C. , L / 1/S , 3/T

B w o?

LT B% K 'L.

'TV

1. INTRODUCTION

The approacn to trie cesigri cf naval

uri:s was matnlv based, in trie past, on trie octimzatcn cf trie hull forms fit to atnieve the rnr.mum resistance to trie

mo-tior., ir. cairn water, at the maxrnum speed.

A verifcatccn cf trie sntc's cehaviour at trie cru:sng speed was subsecueritiv effect ed. to ascer-ta_r Ine comlance w:th trie en durance contractual prescr:ptions. In trie last years. nowever, due to trie necessity of ensur:ng trie maximum operattonal

effi-A SYSTEMATIC STUDY ABOUT THE :cT OF THE MAIN NON-DIMENSIONAL PARkMETERS ON THE SEAKEEPING EEVIO'JR OF SLENDER, FAST SHIPS

By

F. BAU' ,

G. BELONE

, F. FLAMINGO

cANT:ERI NAVALI RIUNITI - GENOVA (ITALY)

oient>' of trie snip in adverse weather

cori-dzions, trie study of the behav:our in rough sea rias taken on greater and greater

mpertance n the crecmtnary chase of trie

the attainable results are very important and amply uslify the utilisation of suit able resources interns cf time, nasrnuch as its qual:ty is improved r'. a dec:sve manne r.

Trie cas:c Parameters investgatec in th:s type cf study are

CE = Block coefficient

L / 1/3 = Length relative to a:sml.

to

C . =

Water line o-- nt

B/T = Breadtn/draugn: ra::o L 'B = Lengtr./breaztn rat:c OD CM = Midsnip area =nt X% LCB = Longitudtnai position of center cf buoyancy merceritage of ship's lengtn

= Sh:c's free board, at bow

K = PIton gyrat:on radius GM = Metacentric rieicnt

In general, sucr. a study is carr:ed out by mak:ng extensive use of the com-puter, and the flow criart of Fig. 1

'1'

trates schematically trie lterat:ve

proce-dure wnch s followed.

Tne snic, defiried or. tne bas:s of

ner maur. features and the oceanograchic si: uaton of trie " operational trieater ", cna: accented dv the sea matn Parameters, forri

trie nput of most part of trie seaíee:nc Programs adopted at present.

These calculation Programs allow cc obtain provisional values concernimg trie following elements

- criaracceristics of trie sn:p's rigid

mo-tions, namely, piton, ,neave arid roll;

- extent of tne vertical arat:or.s in

ceteririuned POiritS of the snip;

beve.oprneht of a design, :hd er Ic veri-fy, even under heavy operational cond

t:ons, the reua'olty of the chcces.

A parametric study of the ship's

be-havour

n a rough sea, with a view Ic

de-termining the most suitable hull forms and parameters to get good seakeecrig

criarac-terstics, is tnerefore, at this stage, an

essent:al requirement for tne rational ap-proach to a design.

Even if suc.m a systematiC

L

pp

= ienth oeweer1 perpencars

breadtr, rnoulded depth, coulded freeboard at bow draught A =splacener'.t C.. =

blocK

cofcient

=

tsmattc co'rit

cW.

= foating pane coefc.er

= ndsn:pseczor coefficient

X% LOE = center cf buoyancy ong. pos.

= rneta:entr:c heignt

K K = roll and piton gyration radii yy , xx

Shape and dimenons of a?endages

Snape arid d enscns of s ilzer f:ns

Scanitlinz of s:ruc:ura. eernents

'Je:ghz d...s:rb.i::on

enera. operatonai criter:a

Shcs particular operazonal

tasks

OPERAT:v: DOE OGR?KiI SIT2ATION

SL STATE

H,/3 = significant wave neìgnt

T = corresoonding mean oerod

n

-S = direct:onal distribution

P = percen:ae per annum of ari

assumed sea state

7

Ships acceeraton anc motions

Undesired phenomena Power increase

Stresses on structures

Fig. i

SKIPS OPE?ATVTY

S = D = FE = T = SEkEE? INC P ROGFA.M

- frecuency and probab:li:y of undes:red pne-nozcena. such as slamming, deck wetness, pro cellen t:p emergence:

- extent of the added resistance rescect to

trie ' cairn sea

' situatton arid consequent

reouction cf the maximum snps

- extent 3f tne dynam:c loads acting or. trie

structures.

n order to get incicatior.s.on the

sh:ps oerational effnc in various

con-of rough sea, Lt :s necessary to com-pare the obtainec results with performance le veis assumed as " açceptacje or " bearable' by octri the oPerative personnel dr:ving the

Un:: and by trie " subsystems ' ex:st:ng on board.

It :s easy to see how the rat:onal ap-prcach to th: robien is qu:te d:fficult be-cause. Des:des tre ' objective " requirements

essent:al fcr trie ecuiment ceration or the adequacy cf trie structures strength, stab:li ty, etc.), trere are also ' subjec::ve "

ori-:er:a relatec to tne pcysical respor.se cf trie personnel and :ts capabil::v.

To sucn a purose, i: was recently

tin-proved, or. trie :as:s of a s:a:st: c-qual:ta-:lve analy-sis, a sim-va ua::or, sys-cern, essen-t:allv based on :nree rna:n cr:terí a. As sucn an approach

:5

easy to comprehend and slrnp.e to quantify, al tnougn ma:nta:n:ng a ccr.s:cer-able valib ty, :t was adopted :r. tne develop-ment of th:s wcr. Tne a-dopted or:-ter:a con-cern: - Vertical accelera-tion a: bow; L - slamming - deck wetness.

The sea:eep:rig oPt:rnizat:on leads to the following advantages

- igrer sceeds in rough sea

- 3etter operat:onal exloa;ation of the

helicopters

- bess deter:oration of weapon system arid locating sensors scnar)

- setter work performances cf th

person-nel

- Higrier safety degree.

Therefore, trie man urpose of this

Study

is dust to f:rid out tre oo:imal

charac:eni st::sofanaval vessel of a

given d:s:lacemen:, funtrer tc a suitable systematic investigattor..

2

_{GIN?T:0N 0F CH:}

_{TEMAT:C HbLbS}

2..

Eas:o Cr::er:a cr Tre Svs:emrma::c

e se aro r gate Th:s study was carneo out mice, as far :

tRe

aimersìon-- a_ cr.arac:er:s tics of the hull of a fast naval vessel nav:rg a placement of about 4.000 t. Trie maori guice

/ / / lines cf suor / _{' /} a study are j /

'//

the following: wnile the other parao eters, al-ready indi-cated unoer pOirit l,were vari ed; Choice f The ?arane:ens To

-e. 2

The var:a::or rge of tre :rvestgated

des:n oar mecer Values was assumed suf

ficiently wide for rra

easier the

i-derctifica:on of tre behaviour

tender-cies, even if this ras cnvolved,

sorne-t:mes, tre ger.erat:or. of hulls witr. nor

d:mensional ratios somerat beyond tre

usual ones.

Fía.

2

indicates, as an examole, two

hulls placed at tre extremes cf tre

in-vest:zated ranoe.

Every hull

form

exam-:rced was

systemati-caily

de-duced froc

one

basi:

null" by

varvt n

tre _/T ra

t:o from 3

to

4 arid

l/3

troc 7.:

to 3.5.

The

sea-ing

tior.s were

carried

out, for every exam:ned sclut:or,

limit-edy t: the ver::cal mot:or.s

neave arc

p:tcr) amd

i:h read sea.

In fact, the

ooer-attonal lcmctat:or

useful for the

corri-Parison between tre

var:ous soluttons

are ao'

o

:îce-romera )sla.rrrniri,

deck wetness, acce

eratlon at bow)

that, just :r.

sucri

concltions, assume

tre cax:rnum values.

e) The crogran

utiliz-ed for tre

calcula-tions, at CN?'s dis

:osal, based or. tre

stric theory

',

is snort..y

:us-trated ir Acoend:x

A.

MAIN

N2 OP SASC HULL

=

131.56

n

3

=

14.60

= 4270 ç-,

0.43

0.76

Lppi

1/3

5.14

B i 3.27

:':Los

TA5LE

In a2reement with the var:ous

au-tncrs

9ef.) I

,

it was trought acv:sable

to carry cut a first investigation or the

three macn parameters

1/3

Lerght/d:solacemenz ratco

Block co'

Water Line Coeff:tent

by varv:ng such carameters into all ccsz

ole ccm:ina:cons and na:nca:n:r.z çonstar.t

the dtsplacement.

creactr,

/ crauant rat:o

-

LOE =

crg:tuiraL :os:::or cf tre centre

of oucyarcv.

The range of the

nves::-gated values for tre

a-foresa:d tarame:ers :s

:0

dicated in tre acove

Ca-bì

cas::

rc

Cerera::cr- "ccrocc13çv

The basic rull,froc

wh:cn all suosequent hulls

were generated, has the crac

acteristics indicated in

Ca-cle il.

The generation of the

derived nu13s vas rea

by means of tre

' PROSCA

promrarn wcr.ed out by CN

and menticre: in Appendix 3.

- L

¡s

pp

-wz

TA3E

2

Starting

f.'orri tris

EXJ-YThF2 PAANECEFS

f:rst stet

and iim:tei

y to the

C-

0.44

0.48

0.52

hlì

cres-entirm the

t raras

«L

0.73

0.76

0.73

a further

7.50

8.00

8.50

tion vas

carr:ec ou:

3.27

3.60

4 .OC

or cre caram

e te rs

3y maln:aintng ccr'star: tne vaes cf A , 3/7 and X%L05, and varying syaten

atically tne three caranezers L,' A I, 3,

27 hulls were obtained, ilcat

=

-ed by two letters and a number in the fcllcwìng fcrn

_{L, N Lc with}

the follow :ng code meaning :

-= 5ioc cefficient

identifica-tian coos

= 0.44

= C.E

CB = 0.52 (S Slender L ,o case E-_r

-Table g:ves a scnerna:zc

recre-sea:cn of the hulls generated :n the

first :nves::a::cr pflase, wr.cle Taole Cv conzai-s, more in deta:l, the dimens:ons

and zne na:n non dorner.s-_onal o of the aforesa:c nulls.

MAiN c:'1ENs:N5 HE csRA'r:

'.5

Fig. 3 reports, as an exanpie, the verticals cf :ne cody clan cf sorne cf the ahovemen::cnec nulls, cbta:ned by varying

the block :o-n:.

Fig. 3

Examples of 2enera:ed nulls var:a:iorL of parameter C

In order to verify the water-pl coef r'' =n:, tne areas or the transversal

sec-tions were compensacec suon as to eriiare an: reOuce the float:ng f:gure w: chou: mod.fv:ng tre d:scacemen: ano :ne lonz::ucir,al pos:-tian cf :h _{centre cf buoyancy (see Fig.}

_4).

O 5(,

.

SIS SIB 515 12165

I50

450 05-0.44

C066

C.0.67 525 528 i 52R 23'S 15,41 471 535 5.38 537 37.55 14.54 4.5? 51S 5I5 517 2ì55 1523 4.66 C0.4S C:O77

0062

82S 825 827

2B2

1475 451 505 B3B 83 137.55 435

n-:

_{518 12155 53 4.7 CO52} 0.5? 250 2S 52E 7SF 12577 4.33 525 525 53 1375? 13.? 4.20

:'

-"s :-:

:E ' :' s 0 1 O.'12 0.52 cwL 073 0.76 O7 7,73 026 o s 073 0.76 02

750 SiS SI SIE. BIS 218 9I flS 715 IF

SOCi 525 528 52 025 82E 827 72E 72

-

N =

_{0islacern.ert leng:n}

iden-a-tian code (1 1 / cc A 1/3 = 7.50 N = 8.00 = 8.50 = a:erl:ne cation code

oefficen:

ien::f-SI ence r = 0.73 case = 0.76

E-Full

= 0.73

Y Y

:1g.

Z

Atocted method to vary tre oaraoe:er C..

- nL

Suor a croce une was carr:ed ou: or:

ly or tre fcrarc cart of tre ater cisne due to bctr tre corf:gura::or. of tre

bas-:c null, stabli:y reuireoer:s art to

the fact tra: rev: cus works : 2 : rave prov ed trat, for sr:ps :th transom sIerre,

th C cf tre astern part scarcely af-fects tre seaeePir:g berav:our.

The var:a:ior resulted :r. a paseae

from bow forne (ccrresor:c:ng to a

10w value of C ) to V formic

(corre-nL

s;oro:ng cc' htgh values of C.. ).

Trenefcre, It should ce nOted now

th ar.a.veìs of the

caraneter

C. reces-sar:ly a.sc involves the of the

bc forms, crus nespresen::rz a casio dle rent to def:ne the benavour cf a snip Ori

tre waves.

Tre var: at:or cf the 'Olock

-C1Ct

was o:a:rec icdify:r tre form cf tre - r:osection art maing

uni-forrry Irin_ren or larger the wroic r.ull, by means of tre PRZSC.. progran 1see C: Z'

-

-Z

-.1

:1g. o

Varoatior of tre C3

As already mero:oned, t:.e systems tic var:at:on of the parameters E/T aro

X% LC3 was - in a suosecuent

prase of troc study, after raving

al-resoy slnglco out tre most suitable vaI

uc of the OlCk ooefficenI co tre

wa-terpiare coe rt, ant takong aso

orco account Ire fao t trat

cons:dera-tlOrC of resostance, stability arc load dlatr:cut:cr do not alow any too wide

ranoe of trece elements. Tre varlatoori

cf tre S/C ra:o was octaoret for sim1

ar:ty from tre :rev:ouc nulls, by

uti-lIzIng

the two ratios cf somilar::y. bfferert, ori draugrts art creac::s.

The var:a::or of the long:tuc:ra

cs::ior. of tre null centre 103 was

e-crievet by tre compersatoon cf the

transverse sectlor: areas between arcad ant astern sectlors. accordong to wra:

in :z. 6.

la:: ors

7-

'I-Tre sea spectrum core:derec or tre sea keerg calouazoone :s the one recomnenoed by ITTC 17S. Tre relations between sea

state Reaufort Scale), s:r:of:cart wa;e reoght rig. o

Var:a:zon of tre lcnz::udinai position of

tre centre of ouoyancv

3. REFE?ENCE ENVIRONMENTAL CONDITIONS

H 1/3 (n) and average wave per:od Tri. (sec)

are indicated :r the following Table V.

V

The spectral form of tr2e sea state

adopt-ed hereby, is th two variaje

rePresenta-lIon cf :scheiner, Valid for a fully de veloped sea. *ì;h w:de fetch.

3.2. Comoarscn C'::eìa 3e:ween The 2;(a-te: Sc.u::or.s

The orter:a sowing to estad:. a merIt index be:wee-. Inc various ex-aT.:ned nuns, as far as seakee:ng :s cor

cerned, are those generay used a: Pres-ent by CN?.. i.e.:

- Sini.ficanz am:1::ude of the vertical so celeration on the ?cre Pp < 0.4 g

- Proad:li:y of deck wetness a: bow < 7%

-

?roba:ol::y cf s anming a: 3/2CL

f rom the cre Pp < 3%

The Shps mImum attatracle seed

in a certain sea state

:5

the max:murn

speed for wnicr a the abovementioned three limita::cns are verified

simulta-neously.

The exanoned speeds ccvered tne

range of 1:--30 knc:s.

Tne adoverentioned limites were nev er exceeded for sea states lower triar o and therefore Tables VI, VII and VIII, re-fiectir.g tne max. speeds attainable by Inc var:ous nulls, only refer to the sea sta-tes 5 and 6 ?eaufcrt.

A cuic examinatlon of these taDies allows to rriaie the following onmedate cor.

Sì

de ratIons

'C'P s.uo p

AE:o:ry 5' 0.2 0 PPO AP.E2

i::

2E0 POP Ac:zo

r

pC - E.P rTVT2

L

-

the heavier lini:at:on is that imposed cv tne value cf the vertical acceleration a:

bow;

- operational limits due to slanrn:ng phenom - trie maximum altatnable seec :r. rouoh sea cria only occur starting from sea state 6; _{is therefore coinc:der.: w:th tnal imposed}

3,45 052 Cw Cw 073 0.761 0.78 C.73 0.76 0.75 0.77 376 C'S 3.5026.9 30i3C23 26 30

2C724I28

L1 300 25 20 32 22 27.2 30 2071 239127.2 650 26 30 30 229! 27 :c ?O9 2391 2' 0.4 0.46 0.92 073 0.76 0.75 073 0.75 0.78 0.' I 3'S - 078 750 209 207 27.3 20 23 25.9 13.5 22.1 24.5 30G 203 277 238 216 5 27.7 20.9 23.6 262 650 2-2 29.7 30 2321 25 79.9 72.5 25.2 28 OIM! iP11OZ 'll -

-Wi' COS0E.1ON o'..

r. 4'i 3.45 052 072 0,75 375 0.73 0,76 C'S Li i5 7.SC 16.2 19 20:? ?.5 97 14:; 17 186 500 175 I 21 227 6.6 18.7 20e IS 13,7

550 17

224 22 I 7:? 20.2 22.2 17.2 9.2 21

Sea State H113 (m) T (sec)

3 0.9 5

4

1.8

7.3

5

2.7

9.4

by :ne afonesaid lin:: related to the acceleration;

- the nulls having nigner attainable speed are tnose of the ' S ' type

= 0.44) and among tnese,

par-to.6ularly tne S 3 F shows tne 'oest seaeeing criaracterist:cs1L/ 1/3 =

= 3.50 - C,.. = 0.73).

4 _{FIRST FHASE OF THE SYSTEMATIC}

STUOY - EXAMINATION 0F THE

RE-SJLTS RELATE

TO P?_METE?S

-

T

Only the final results of tni.s s:udy are reporteo nere:r.after : the percentage var:a::ons are always refer red to the central values of the var:a tior range cf tne exan:ned parameters,

.l. Effect of Cw.

: is illustrated in Table IX. TABLE

:x

EFFECT OF C.,

ON THE L1M:T S?EE

AS C,, VARES

wherefrom it is deduced that

- the C. var:a::ons produce sIrc:lar

cf-fects' on tne _{aximun atta:naoie speed}

:ndeendently from C and L/ 1/3 as

well as from the ana:zed sea state;

- particularly a 1% increase of C,,, leacs

to a sseed Increase 3-: _4% while a C,,

wL

decrease leads to a worsening of tne

speed in zerns of 3- : -4%.

4.2. Effect cf L/ 1/3

Var:a::ons cf the caraneter L. 1/2 produce acout trie same e' on tne at-tamable speed, fcr eacn exan:neb and

The extCnt cf sucn an effect results from th follow:no statement

sea state t - 1% (L/ 1/3) l.2%V Hl/3=2.70 n - 1% (L/ 1/3) - 1% V sea state o per H: 3=3.30 a - 1% )L/ 1/3) - ,% V 4.2. Effet: of C,,

Tne effect cf C is Practically con-stan: at tne var:ous n:;'s enztns, wn:e

as CWL varies, tne effect of the C varta-::or. on tne limit s:eed

Is

not

con-.,,, as :ncicateo :n

ao.e X.

TABLE X

EFFECT 0F C_

ON THE

_{LM:T SPEE}

AS C. VAF:E3

- .% (Li' 1 / 3) - . 1 %V

'-p

C..

_u

SREZO Sea tate Sea Statet

0.44

1%

-

1% - 3.0% - 4.0% -2.4% 4.0% - 1% + 3.3% + 3.3% O .43

-

-

3.3% - 3.0% - 1% " 4.3% - 3.3% 0.52 - :%

-

3.3% - 3.3% V1O. s "WL L;' 1/3 = = 0.43 0. s.00 r' _{73) V(H, ,,,=3. SC)} - 1% - 0.4% 0.73 - 1% - 1.0% r - 1% I . 4% - 1%

- 0.7%

- 0.7%

-

:.%

-

,O%

0.3%

Therefore, it may be concluded that

- a 1% increase cf 0.. respect to zh

oasc

value leads co a reduction of the

maximum attanabe speed cf about 0.5+1.0%,

wnile a 1% decrease cf C causes a speed

improvement cf about 0.5l.5%.

5. SECONO PHASE 0F THE SYSTEMATIC STUDY

ExAM:NAT:oN OF THE RESULTS RELATEEJ

TO THE FAFkMETEFS S/T AND LC3%

The above reported considerat:ons,

formua:ed tnroun tne first phase of

one systematic researcn, resulted :n the selection of the nulls cnaracter:zed by

the C = 0.79 value, namely, tnpse :den

-tì:ec cy :ne svmocls:

91F 31F F1F

92F 92F

S3F 32F F3F

as the ros: :ace hulls to witnstand one roun sea.

On eaon one of these hulls two cor-versjor.s were oarr:ed out smifting of

tne centre of buovamcv and varoation of the B/T ratio. In sucn a way 36 nulls were obta:ned, as indcaoed in TapIes XI,

xI: and x::z.

9FZ C' TE D!F F

-4

0.48 0.52

As far as the:r :centficatcon ₁₅

concerned, one denominatior. already a-dcpteo in the f:rs: pnase of tne re-search was malnoasned witn tr.e

fcllo-mg additions

- for one nulls ot:acned througn varta-coon of the centre of buoyancy, one

wng AFT ':afterwards) and FWC

0

4t DF DZEFJ,'! LL_F

-(forwards, to sndicate one sn:ft:ng after-wards and forafter-wards respect to Inc central conf:gurs:icn X% LOE = 1.50% AD from

- for the hulls obtained thrcuzn varoatoon cf the S/T parameter one pebtoes A and S oc

it

dicate one va.ues of 3.. T 3.50 ano 4.00 ?eo t o ve . y 052 L.CS LIE LIB 00 CC 220 00 C 220 1.00 1.50 130 7.50 Sl 51F

;l1

s F1F 22° F2'rw 52° 52 ,Î2Ç

aso soi' 53F D3i',

ICC

30 .100

I2 52 O0

:so

si S1A Sì S!. 1F 500 S2 S2A S2 52V 52C B2V, V2V V2F V2 550 23° SJV

57F cr

r3 3F 'o' s o

,.

The riiensons of trie new nulls,

limitedly to those obtained for one varia tior. of EiT, are reoorted tri Table X:::

I:

ould 5e nc ' how

Ofliy

tre breadth

arid tne draugrit are changed.

As for the hulls generated for vari ation of C3, reference should be made to Table :v, reported under cnaoter 2, the new main d:mensor.s of trie new nulls

be-ng same as those of One " basic ' hulls.

5.2. Oalc.azior esu1os

Scm:ary

to wr.at occurred in the first phase of the study, also for trie parameters considered n :n:s second priase, one main or. trie irnìt speec

is determined by the forward vert:cal ac-celeration and, crierefore, the fol:.owinz considerattons only refer to th: aspect of one sn:'s benaviour in rougri sea.

E.2.. .lffec: of

It can be decucec from triC values

of the m. atta:nable

reported ir.

Tables x:v and X7.

LE vrv

sxz: 3C r - r

Th fact, from these tables it re-sults that

- a 1% :ncrease or decrease of trie 3/T ra tic respect to the adopted central

val-ue (3/T = 3.50, Involves a 0.5% seed

crease or decrease for sea state 5 th:s almost irrespective of trie values of 03 or L! 5 1/3;

- the limit seed var:es linear! with trie parameter 3T.

Tnese cor.s:cerat:or.s are summar:zed tri trie following statement

t

t

-.-- -

-Trie resu.ts obta:ned trirougr. trie

researtn are contained Tables XV and

VII, wnerefror It re Its ona: trie effect

of :hcs arame:er 15 practIcally

nezIIz:-ole for trie sea.-eeping.

xv:

'R

.:zxXv:

vr. S C. -

r:i rt

tn8x Xi:: 344 ₀₄₅ 0.52 'T E T 327 360 00 327 360 400 32? 350 400 L,, 750 _{279 23I 30 0H} 29.1 24.5 275 295 30 30 27? 292 30 252 27 2t3 .530 30 30 30 299 30 30 26 29.5 30 04E 0.52 LOE .r5 LOE 100 150 ¿20 1)0 .o ¿20 tOO '.52 020 L, 750 279 275 25 252[256 25 245 243 244 500 29.5 22 299 278 2621 26. 25 050 .30 30 20 22.9 295 295 26 2?Sj?S1

0"

0.49 1.52 S. S. 2, 32? 250 72? 350 400 327 350 400 750 209 207 07' t7 20.3 2:2 15.5 159 600 220! 23 239 205 204 223 9.1' 2C.5 203 ao 22.7! 244J 252! 222 226 23.7 2L7225 T

'.

:..

r vV

04'1 0.49 052 LOB

tOO L5O ¿20 '00 ISO ¿20 lOO LSD ¿20

750 22 2O 2

'4

'27 16 17.7153

500 22.2! 22.1 _{224 21S 204 20} 19.7 19.5

550 23'j 22.5 225 21. 22.0 21 205 2'

5.3. Variation Of The

araneter K

_VV

/L

coragec by tre results ob:anec

from

cre :c previous chases of :ne sys

tenatic study. the variation of K

VV

was et:eotec by

olicw:ng two

-scte

rections.

Namely, by

consider-ing as aopiicabie tre principle cf the

effect superposition, the L/

l/3 =6.00

was mainta:neo at first constant and

trie block ooe

r.t C

was varied;

la:r ori,

the L' il/3 ratio was varied

and the C,.

= C.8 rept constar:.

The results obca:red from tre

K

/

var:a:on calcuLatori are

recor:-v.v

ed in

'..g.

7 and 6.

In such. dia;rans it nay be

observ-ed now, for a var:aton of K

_VV

/L of

a-bout 1%, a 0.5% seed varatìn Wtri

sea state

S and about C.25% w::n sea

state S oar be a:nieved.

.n

irorove-men: of tre maxiou.m

:

occurs

as tre value cf K

¡L decreases.

Yy

0;

2 "S' (C _E 7

ffec: cf K

¡L variation

'¡y 6. CONCLUSIONS

Fr-or th

anaiys:s of the

abcvernen-tioned data the foì.owir.g may be

cecuc-ed

to acnieve a good seakeeping

berav-our, a naval vessel snould nave bow

for-na tending to

' V

',

witri rather

nigh waterp1e coe'-'-=nts:

arrorig the examined Parameters C

ra

presents tre most

mocr:ant

-fac tor, ::s :rmc re ase ov 1% entail

ari

irnorovernerit by accu:

4%

of tre

marcorrium attair.able speed

see 4.1);

o) longer snips are generally

prefer-ab:.e as far their cehavzour in rough

sea ta concerned, ever if tre

engtn

does ro: conSicerablv affect tre 1c

speed (see 4.2);

d) the effect of C.,

not too high

tre tendency

towards lower

40

5

1.5

L/L5

L/5

ao

8.5

o

ffec: cf K

_yy

'L var:a::on

LÌ 5

1/3

=

Constant

=

8.00

03 =

Constant

₌

is however cuite Oosttive, thus io provtng tre proou1sve

perform-a.-ces in talo water (see '.3);

the tncrease of tre S/T parameter causes a mocerate imorovement tn

the rraxtmurt attaInable speed (see 1.2.1);

the variation cf tre longitudinal ocsition of tre tertre of buoyancy does not greatly a''- he sea-wop:htnes cf a snip .see 5.2.2:

g the pnenozranor. which ocre ramoers

one cric a seaway t s tre vert:-cal acoeleratior: at bow (see Tacle VI:). This should ther. :nduoe to

a speed reduction before ire slam-ring ?ressures reacr a hazardous

value. It should be noticed that tre leng:r ras an trfluence Pract. tally reglig:b.e on tre slarn:rg prenorne ron;

h the prcbab:l::v of' deck wetness at bow essentially cepenos or. tre free board. :r the case :n

tIor, tre trresrcic of 7 does not

lead tc an'' speed .im::atior for' the nulls taxer into coreicerattor..

From the follow:ng Table Xv:1, rei evant to tre protacility of deck

wetness

for al.ì exsm:ned hulls, a:

a speed cf 3 ro:s nd sea state I

tre fcllowir,g cand os ceducet

- tre aoopt:cn of tre " '. ' torn

suIte into a cor.stderabe de-crease of tre dec wetness

proba-b:tty (see huls w::n hign C,.

respect cc tre otners);

- an :ncrease :r the ength ras a

cor,sideracle pcs:tive ir.fluer.ce;

- a reduct:cr of C. te pos:t:ve

too.

aithougn

Its

:nfluerce te of a lower extent to tre oth

er exarru.nec arametere;

'At

x::I

EC PRO

y'

. 30 'S JO SE.' ER'E

0.4

ç»

2.12! 052 C. 12 r a;: 153 1.13 '33 217

- an increase of SIT causes an increase

of tre res_stance to cotton. Cc te

however recessary to make a

d:st:nc-ttor bwn ntgn (V,', L

l.1 and

low speed (V,' L 1.0). At low

cre increase of S/T jnvlves a mocee: cower ercen:age increase even consicer:r tre add::::ral ree:scanoe due to the breadtr increase. A: ntgh speec an increase cf S T cuases in-steac a conetcerac'_e :ncrease cf zr cotton res:etan:e. Tnerefore, consid erirg trat tre lim:t speed :n rougn sea (sea state 6) te comparatively low (about 15-2 knots),

t:

mign: ce

desirable to :ncrease tre 3,'? value.

It should be ncwever acv:sable to take also :hto account tre consider-able power :rcreaee requtred at htgh speed :n calm dater. Frbh this it cay be deduced trat

t:

te necessary to con tatn as muon as cose:cle tre va'je cf 3/? compat:bly ':tn tre stacility re-qut renents;

- as fr tre carameter C , from M. 0er:

t

-1ers WorK

tt

ts ' ev:.tent

an op::mal value of C ex:sts for each examIned speed.

The relation C = C X C beIng known,

- o M

tre croste o: ' C

wi_

result from a conromtse betwee tre re

quirenen:s of gooc sea.eeing (low

ç'

low resistance cc mc:ton :n calm water (C def:red aoocrdtr.g to tre de-stgr se:) and ava:laole volume on

board for the irrer arrangement.

71 2133.11

103 122

¿53' ot a :.i

t

a check of hull res:stance ir. calm

water was rate cy utiliz:rg tre Gertier series for' every examined

l'ne crotce of sucr. sertes

was dtctatet by practical reasons, as Lt was :nteres::r.g to make a coo partsor between the various hulls anc no: to get an atsoluce value cf

power. The parameters taken into constderation co exanlre such a

se-rles are, as well kno. C

L/ 1.13 and E.!?.

t

:rocfl tr:s creoio tre :o_ow:ng ::ra_ cons:cerat:-or.s atout tre s or

of tne opt:nal null can os made

- an increase of L," s 1/3 causes a

A

crease of L.." e 1,3 ce termines an aecrease cf the actual power re-cuarec a: all

s?eeds;

the same to improvement in tre sr:p s seakeep-ing features; therefore, tre croice cf a nigh value of the L.' s :/3 ratio is :nO:caced by bc:r requirements of

APPENDX

î

NOTES CN THE SEAMEER NG "

The program used to evaluate the seakeepir.g characterist:cs of the hulls in question was developed by R. T. Scnm:t oke amb M. Mackay at the DREA (Defence Researcr Es:ab.ishment Atlantic -

Cana-da).

Svbsecuently CNR adopted it by

oomactIng Ir. one pacae trie original

Programs ?H}S tPì.tch arid Heave in Head

Seas) ana ROLRFT (Roil Mc:icr. wtn

Rudder. Fins, Tarìis) E

Toether with the normal calcula-tior.s relevant tc the snip's vertical and side motcns based or. the ' STRIP

THEORY " of Korv:n Kroukowsky, as modi-fied by Frank and Salveser. 6 , the

prooram also utilizes some algorithms, related to tne added res:stance calcula tions. to the correc::ons of trie rela-tive motions, to take ir.tc accourit the variation of the wave profile due to

the " cvram:c swell u: ' as weil as to

te uridesred phenomena (slamming and

deck wetness) 7

Particularly, the evaluation, of the slamming pressures was -:ed by

aplying a comtinaton cf two methods,

namely. the one cf Doni arid Mctter B ],

acolicable to ships with higr.

block coe'-nt and trie one of

Stavo-ana Chuamp lO , that, being caseb on experIments carried out or. taPering bodies, :s cuite fit for fast snips.

The adoed r -ance calculation

IS based on the Jinkine and Ferdinande method [Il , with empirical modifica-tions derived from. the exoeriments of Murdey, Strom Telser. and others.

APPENDIX 2.

NOTES ON THE " PROSCA " PROGRAM

This programs allows to operate on the snip's geometry through hull ce-finition, conversion, revision and visu alization procedures, on trie tasis cf data consisting of the hull surveys.

Such surveys contain subs:antal-ly trie values of trie null off sets de-fined for waterlines and frames.

The " PROSCI. " Program cor.s:sts

of groups of Programs allowing the ce-signer

- to cefine trie hull :ri the three space

dmenscns, with specific intervent:ons or. trie geometrical parameters for

carry-ing out hull conversions;

- to carry out prellmlnary calculations of some hydrostatic and geometrical cnarac-teristics useful to the designer;

- to obtain trie drawing cf the three crtnc gonal views;

- to get axonooetr:c and perspCctive vew5 of trie null;

- to set null lines in the th:e orthogonal planes;

- to store trie hull gecmetry so tnat, later on, trie full nydrostatic :nara::er:stics may be calculated.

ith sucn a program, converslcr.s may be

effected

se0

eiy in the :r.ree planes, even repeatedly.

it -c carry out etr.er

conversions

on a smilaritv basis or locai

:zed conversions.

1. " teveloprien: of a Fr:gate Hull form for Super:or Searee::ng ", Schmitice,

Oler., Murcey, 1.975.

7 _{Seakeep:ng and Resistance Trade Offs}

in Fr:gate Hull Form DesIgn. Schmitke, Murdey, DREA.

" Seaxeeping Performances .nd Design Opzimi:at:on Procecures In Use A: Present at CNR's ' - CNM 1973.

" PHHS A FORTRAN Program Far Snip

Pitch. :eave and SeaeePIng Pred:ction"

M. Mackay, F.C. Scrimitcke, CREA, April

1978.

3.

" ROLLRFT:A FORTRAN

Program To

Pre-dict Ship Roll, Sway r.d Yaw Motions in Oblique kaves, Including Trie Effect Of Rudder. Fins d Tank Roll Stabiliz er ", R.T. Schzitke, DREA, Canada, De-cember 197E.

The Franz Close Fit Sh: Motion Com-puter Program ". Frank, Svesen, NSF,DC Repert 3229, June 1970.

sistance Cf Fas: Caro Shos :n head

waves ', Jin<ine, Ferdtnande,

n:erna-:ona

Shipbuildorìo ?roram, Vol. 21,

1574, No.

238.

T

5.

:mproved Si nrnin ?red±cior-is For The ?HHS Corr.puter Progran ', R.T. Schmite, OREA, Oar:mouth N.S. , February 1979.

" Prediczon of Sann Cnaraceristics

And Hull Responses For Ship Design

ACKNOWLEDGEMENTS

The authors

ould Le cc express

their tnan:s to .L.ss. D.H. Ravazzanc

and Mr. S. Morrtisci for navirig

sigrfi-cantly contributed to :ne transìaton

Ochi, Mct:er, TRANS SNkME, Vol. 81, 1973. _{and i1iustraton of croe stud-v.}

9. ' A Method To Estznate Sianmn Character

istics Ror Ship Design ", Ochi, Mutter, Mar:ne Tecnnology, Acrile 1971.

10. ' Anayzical :e:ernination Tif Samm:ng

Pressures For H:gh Seed Ven:cies in

aves ", Stavovy Onuang, Journal cf Ship Researcn, Vol. 20, December 1976.