The design of anchoring systems for merchant ships - A new approach

Leusden, 6 December 1992

THE DESIGN OF ANCHORING SYSTEMS FOR MERCHANT SHIPS A NEW APPROACH by L.Brink, Msc. (TU.Delft) Naval Architect Master MN(Ret) voor -© 1t

):

i

Introdution

The

reconendtioris on.

safe richorir,q of shii:s mzde by the

Mer'nti1e

Mririe Trib'.ri.l

of the Nether1rids

after

the

:jriqury into the disaster of the

mit " Mssiuis", in whi'.h 27

persons

lost

their

life,

prompted the

D:Lretorte-Gerier.1

Shipping IrId

Mritirne

ffirs of the Ministry of Trmsport ;nd

Puhli

works to pro.h the Netherind Shipmsters'

Asso:i;"-t icm w lh Asso:i;"-the

crp ist to n rOr them OTi ho e pc i cni' o I

their

members

with the

methods they use to determine the

required length of .nchor c.hziri.

In order to comply

with the

request, the Netherinid

Ship-masters' Associtioni

requested their members for i.nform;Ltiori. Also ommittee of

four members w.s formed to inivestiqte the

s;.fe

n,hc'riniii of ships

The reommen,dztioris made by the

Mercritile

Marine Tr:i.hun;nJ.

oriernt :

the use of

the "ru 1 CS C) f i'imb '' tn deferm:j. TIC the

requ :1 red I enu1:h oF

r:hor

i ni

.ni i. nivCS....h qat 1 cDri :i. rito the i..ise of the present d;.y

o--puter tehriology to assist

the ship' s master' in om"

piex situt:.onis such

s nichorinq n adverse wethev'

conditions

In the

course

of

the inivestiq.tionis

it

becrne quite

that:

the use of

the "ru 1 CS C) f thumb. " shou 1 d he b.iindoned

in favour of deterrniniin

the required chiru ierith by

rnents 0 the citeniry equ;t:i. ons

-

the desiri philosophy

of nchoririg systems for

mer-chant si-u ps required i..ipdzt :i Tic;

Becus the purpose of

this paper is

highi ii-ut the i.pdtiri

of

the desiqri phi :Losophy of .nichor:i.ntç; systems for mercjarit sluips,

tiic determirit i on of the required cIiiri

lenith by means

of

the cterizry eqijt,ioni will

he de1t with

in .

genuerl wy

;nid not in 3ret depth

The required ].erigth of anchor chain.

Trdition.l ly seaf.rers

used "rules of thumb"

deter--mine -'-ho Lenucth of cL-i;:Lni required for

.mchorin ..bhir

Ships These ru:Les re .enuerl ly based on

ratio

o-F length of

chini CL) niCI

tiic depth

of water' Cd) .

Rtios such

:L/d 3

or 1. C . 'Sd whereby C i; 27 . for U2 ;.nud 38 . 7 for tJ3 ::. ri ;m'e

'..ised . I- nuruber C)f vi' :i. ;t ions C)n these ru :i. be -1-ounid in

v.r:Lous rc fy'pTi('p5 . rhO r;t:i. o :1 s i 1 re -I

'dto.s t hp

scope,

d

Figure No.1.

TIlE ANCIIORLINE CALCULATION MODEL

Is4S- ' - Fg

= Wind force

F =. Wave force

g

F = Current force

Fa = Holding Power Anchor

d = Water depth

'

3

By doing so the following points emerçJe:

the

use of

the

anchor dur1rig

berth

1rig arid i_in

bethirig;

heaviriçj anchor during arJv

'i;e weather conditions;

there must

he sufficient

power to heave

the anchor

home dijrirug adverse weàthr conditions.

ahclioring;

the

nximum -grouridspeed

whih

is

allowed

whiist

arirhor:Lnig

without

running

the

risk

to

break the

anich:r chain

the

permissahie

height

;.bove.

sahed to

drop

the

anchor .

is

often is the practise,

heavy anchors are

heaved CDI....to a few

meters above

seabe.:i arid then

dropped in order to avoid damage to the anchor;

water' depth;

tiie max i mum ater i.:iei:>th the. sJi i p e.ari arii_I-ior

Bear i rig in m i rid these cr i. ter .i. a the ma :1TI items of the mode 1 car

be adressed

The hô1dirg power of the anchor

There are two

aspe_...5 wi :Lch i. ri fluenice the. ciio ice of an anchor

Eor a ship. TI-ic first :is the

holding power arid the second

the

force requL red to break the embedded anchor from

seabed .

-A compieIz

different aspect is ti-ic

influence of

tiie shape of

the anchor on the holding power

Whilst digging itself into tiie seabed,

soil penetrates between

the flukes

arid the shank, Depending

on the

properties of th

soil arid

the

shape of

the

fi....ikes

soil may

become clogged

between shari l f 1 LIkes arid

so obstri.jct the free

rotat I on o f

the flukes,

consequently t-he

anchor becomes

a large

lump of

sol].

which easily breaks

out when

the pull irig

force exceeds

the soil pressure.

The .F;+ tliat

ti-ic free rcyt_tioni of th

flukes may bE hampercd

by badly shaped Fi'.jkes

is considered to be an i..iniwarited

proper-ty of. the anchor

as it directly affects

the holding i°' of

the anchor hence tiie safety of the ship

Generally the

holding

power of

the

ariclior is çji.veri as zini

emp...1. 1

to.'

of

the mass

weight 0.1:

the anchor

:1 ni a:i. r

si_igçest1riçJtiiatt he

holding power is

a function

of the mass

wciqht This :i.s

only partly tr'.e

because in

the firt place

the underwater mass we:i.ciht

is, due to the Archimedes law.

less

V z 0 z F a A 0 A 7 _x 0 x ANCHORLINE SHAPES

Ultimate slack

-W = q.l.. z

-

_l

- --- ___ - --- - -

'

-C

Fully developed

Figure no.2

/

/

I.; V F0

-V x 0 x 0 0 Slack

5

The

"sick" is

common .

It

exists

in modor.to

eriv:Lr'rimorit].

corid:Ltioris.

The chiri

lezds forw;rd

arid down under

s1it

anGle

Part of the chiri rests Or; ebed

The fully developed shipe exists when

the erivirorimerital condi-"

t-ioris h.ve iricre.sed to

such

ni extent that

l 1 of the

ch:iir

is ii fteci from se;ibed ;rud the end

t sehed is t-ricienut tot he

nicIior sh.ckle. It is the 1-rrisitiori between s1ck ;nidt;.ut.

I3otii t.vjt si-ipes

occur when, the erivironrnonit.3. conditions h.ve.

furti-icr irucr'esed .

The ctrtry is pulled tight

;;nid loads ;it:

the

nuchor end ujr,der an niqle

with seabed

. 2orisoquent].y a

vertical component of ti-

NJ1 1 iriti

force attlio

anich'::n' :L

occi_Irs

arid the

process of breaking

the anchor

from the soil

has started .

In the '.i ]. timate taut ;haj:e the ...a :Lri :L s stra :1 ght

arid tiqht.

d'agginiq anchor can be expected

b.ei.wooni the fu]. 3. y developed

arid ultimate taut shapes

Fo ie deL-ermi nat i. on

of the

roclu i rd :j. içjth : f nchor Tha :i.

the f ir ...e sha:.es are of

i riterest si rIce

ti-icy car easily

be calculated.

The ultimate slack shape is

trivia]. arid

bot

others can b.c

cu :1.ated wi tti catoniary

eqiations

The taut

shapes omdriçjer

the ship and must

he avoided

by

fJc:)od;ean1an--ship.

In table

rio, 1 the

results of

a c1c'jlationi of the

cateniary

length for various depths arc given

Frcm ni op('atic)ni;;.]. and dosiqni point: C) v:i.e..' :ii].e rio :1. :i.s oF

interest.

In the first place it

shows the importance of

having reliab].e

data on

ti-ic holding

power of

the .ani:r'

as the

c1culation

iius b L\c_ m do w i I IC' m i 1 'ii' i ho 1 '

oor

i qoo- ho 1 d i i

ground.

] ni

t'he second p3. ace the

tah].e determ:I. rest h max:L ri..im

dept;

:i

whic!i the ship '.:ari safely

and-or with

ava:L lable

length (

In

the third

place the table

cani be

used to

determine the

ml ni mum :1 eni:ith of cl-ia I n w :1 tIi wh :Lch ah :L p must be oq'..i :Lpped :1. ni

order' to anchor :Lni a safe water depth

depth on

which thec aiculationi must be based depenids

very much on the type arid dimensions of the ship.

ri

important

Fact

is that

the

cha i. ni 1. onicith compr :Lsos i:L

Fo 3. 3. ow :i nq three parts

t11e

f:irst part beinig

the length

of the cateniary from

ti-ic anich:r si-iackie to

...e

face

-

the

second part

the lenicjt.i...oiii the

water' su'iace to

6

the third

p.rt the length which

i-s measured from the

erit.wice of

the h.wse p :1. pc, t.ioigh the i..wse p :i. pe,

over the wirid1;ss to

;.

point

n the chiri locker where

the erid of the ch.iri is secured

The first

arid second parts re

v.r:Li:.1e 1erçjths be'se they

depend on

the w.ter depth , ].odirig

condition arid

trim of the

:1. I:

The third pert

is - f:i<cd leriçjth zrid

itis

obvious that

it

musL be lori eriougii to avoid Li ic _hiri bocomi.riq i.ijh in U i locker.

Heric to he

h].e to ci'.ul ...e the minimum lenqth oF chiru

w:Lth wh :Lch . ship -must b eq'.iipped the ía 1 low i rig dt .nre 'e.qu:i. r'ed

safe wziter depth

in order to calcu.izite the cteru.ry

:1.enqt

the b;il ]. st corid:Lt ion nud trim to c;. 3. cuJ. .:ite the 3. ::rith

of chi ri from the water sur f;.ce to the ç%y1'r

f

h;5:iwse pipe;

I:re f ixeci 1nigtii

The

;i.

end of

the chini

vL...ie water' su F;ice .:Lso

follows from the

cteriry equtioris .

By ddirig to

th:is force

tfrie 1 inc fov'cc oF he].ençjth of cheiri from the wziter sur f;ice

to the

chai ni stopI:er or bv' ke of the wi nid1ss t1e f':Dr'c or both items :i.s found

Lip to- now the m.ixi rum ho idi rug power of tiie anichor is entered

into

I-j

c.icu1tion

rid:it:Ls deinicd

thzit in

of

fully devioped cateniry

eqiiilibrium exists between the

han--zorita 1 component Fh arid tlie hold i rig power of the anchor,

± ch on

:i.ts turn I

ckperident

n tli

SC)- 1 cC)nidi t :1. OTiS

Therefore to -coriip.1ete the. problem, the Forces cierierated by

wi rid, c'jrrenits arid waves wh :1. ch can act or

sh I p-.:ticc:r

m'jst be addresse:I

F.e fore address :1. nc; the .nfl i.erce

cf the

ertv :i. rorime.nta]. cond :1.

t i cnis on a ship at archor some atteriti on 1 1 be pa :1 dl: a the

i:art of the ciia :L ri in the mass-spri riq system shi :i. Ti

The mass-spring

ystem ship-chain

It w.s showri

that the ship at anchor

must he considered as a

dynamic system which means

that ti-c

ship at ari.:hor ri be

represented by a mass--spring syst em . The mass compr:i.ses the mass.of the ship arid the chain . The spring constant depends on

the prOperties cf the

hinu nid is rJefinied

i:

(1)

wl-iere

F is

the force

increment produced by the displacement

arid the symbol k denotes the spring cariist-arit which can be

:Lir,er or nonlinear.

The spr irig constant

for the

richor cha i. ri 1:0 liows _{from the} - fore.e--d:Lspiacement plot which is constructed

with the aid

of

the

data of

the fully

dev1oped cateriary arid '.jitim:ite slack case . F :1 guI-c no 3 shows the f'.j 1 i y dcvç I oped catcri.:ry ari

:j.timate slack case

for two

types of cha:in . The data c)f the ci-ia:i.ris ar'c q:iveri in table rio . 2

By d:i v : d:i rig -(is? d:i.

:La11rt:iiItcD :>arts

:i t s pos-.:i. i::L ca

iL-ci iaLe for

caclr part ti-ic Force Fh i'hc esu 1 ts c:f t1i i

cu1t. on

are tiiTi

p :i. otted on the i:asi s where the cl-ia in is fl. Lm- L-e slaci' Th

rsi ilt

s si iowri ii Fi. j' ir iO arid show..

that the spring cc)ristanit is riorii.iniear.

lii a similar mariner

as is done -ía...ic force-disp].acemerit plot an eniergy-di sp 1. acemerit plot can be conistr'.jctcd . TN i s :1. s al so

done

in figi.ire rio, 4.

It

can he shown

that this

curve is the

area uride...ic force<:l:i. si: 3. acement curve . This exp 1 ains ...

similarity between both curves.

flie fiqure No. 4 shows that due to the di ffererice in mass the

energy stored :1 ri the

U 3 ti1 n is io'..ci'thari I nu the

LJ2 clia :1 ri 1i ir 'ii;i I Ti djt; urc rj yen .i Ti T.b1 c no riO ' Ti ii S rnc iTu t1 i-L fc.n

ti-ic choice a f--a ctiairi an eva :LuJatic:r1 between the r-e:Ti.j:i rx:i- force

arid erucrqy is required

Tii eriercJy method is a use ful tool ta compare the ± Ti-F]. ijeruce a-F

tiie ho 1 di rug power

of the

anchor to ti-ic erucrqy tc-rèd In ti-c

cl-ia-in .

This is done in

f:i..:p..ire TiO .

The ericrçjy nietiiod is riot new as it was r.sed by Maddox i1 J for ti-is des I qni of sin le po:i. nit moor i rigs arid can be ijscd

success--fully to assess an anchor arid chain combination.

t.

0

FULLY DEVELOPED ANCIIORLINES GRADE (J2 AND U3

MUTtJAIJLY COMPARED AT TIlE SAME HORIZONTAL FORCE

maximum displacemenL --0 20 40 60 80 100 .120 140 160 180 200 220 240 M 188

-I

l . 216 Figure no.3 U2 tJ2 U3 U3 Si M 30 20 10

- - - kN

-.-FORCE/DISPLACEMENT AND ENERGY-DISPLACEMENT DIAGRAM

kNrn

-5 10 15 20 25 30

m

horizontal displacement

1000 800 600 .1 400 200 0

THE FORCE/DISPLACEMENT CURVES OF AN U3 CHAIN WITH HOLDING POWER OF 412 kN AND 926 kN

differene in displacement 1.34 m

difference in pptential energy : 841 kNm

10 15 20 25 in displacement Figure No.5 b 27,19 926 k 25,8S 30 E kNin 5000 4000 3000 2000 1000 0 .5 0

Tzbie rio 2

( 1. inckJ. = 27, 65 m)

fully &veIoped

teriry

Terisi].e i meI.e

proof ic,d

brekirig lo.id

rnss

1 F

F in

proof 1od

! in.

brekirig load

Poteriti.i Energy,

a

9

wter depth 30 méteP

1.J3 N/mm 2

'9(1()

mm 90 kN 2920 31.60 kN 6090 4.500 kg/rn 189 :1.62. kN 926 26

degrees

18, 2 15,8 rn 188, 0 216, 3 rn :L84,' 21.3,5 kN 974, 0 962, 0 33,.3 3O, 4 23. 8 21., 3 number 6, 8 7, 8 kNrn 2337 2094

Cy Cm 4 to +0.8 +0.6 + 0.6 CX +0.2

fo

-0.2 -0.6 -0.6 -08 - to 1.0 0.8 0.6 0.4 oi +0.05 + 0.04 +0.02 -0.02 -0.06 -0.06 a 0.08 - 0.10 - 0.12 -0.16 -0.15 -14-20 1.0 5Q.;s 00 120 11.0 160 180 2 -....-

.

0 20 40 60 8O100 120 11.0 160 180 200

-I

- - I r - - I I I - -. 20 40 60 80.. 100 120 11.0 160 180 2

AG. 6 Wind Load coètflcteflts

0 00 I botLosted VLCC LNG - corner LPG - corner

Windcoeficients

31aauw(ij.)

method/institute ship type

BSRA I I I

-- -

(sherwood

--NSMB

Rernery. v..Oortm.

-

DHL

- OCIMF -0.18 ₀

WIND-,CURRENT-,WAVE AND HORIZONTAL CHAINFORCE ON A SHIP AT ANCHOR Figure no.7 J wind force. Fc current force Fg : wave force horizontal component chain force V velocity ship length between per.pendicularS breadth a,b coordinates hawse pipe Xg coordinate centre of gravity Course angle attack.waV : 4ind angle w e angle current C

From a design

point of view

the coo diriate b

is of

:i.riterest because

it

.uses

a shearing

effect. This is

especially the

caste

for ships where the hawse

piles are located far from the

centre

line of

the sh. p . TherefcDre the moment cai.ise'.:I by the

location

of

the

entrance

of ti-ic hawse

pipe

cannot be

riegic ted.

By

-piaciriq the

ship

in

a number

of

different orientations

around the

estin ted course of the

equilibrium position

the

forces

rid moment can he calculated.

In the study

by BrinikE 1

on which this

paper is based a

num-ber of calculations were done

to:investa.gate tiue

:Lnufl'..IeTice of

wind, current arid wave

drift forces on a lanikcer,

a bul kcarr:i.cr

and a container ship at anchor.

Figure. no . 8 gives

the outcome of

a clijlaton

For' a J.oaded

tanker which the

e .imatced dimens:Lonis were :310 m x 47, 17 m x

29 . 70 m x 18, 9 m . Inichors with holdiriq

capacity 6 arid

6 were

used . TI"ice cha :Lris had a d :L ameter' ':: :L37 mm arid :1:14 mm arid were

of U3 quality .

i..ierit

was :issi.jmced ...ic sh :1. p was

at

anchor i ri a reasoriab :L i-1 t?r?f.i

ariicracie

w th waves Ti-ic

water depths were

assumed to he

1 . S arid 6

times the

maxim'..im

L oaded

dra ft

The :L :14 mm cha :1 ri was

based on

the equ:i. pmerr!:

number arid the. 137 mr

on the proposed method.

In this example it is assijmed that it is

possible to remain at

anchor' :i ni w i rid force B accord :1TiCs

to

the sca i.e

of Beai_j fort, a

cijrrenit of 2. 5 meters

per second (6 . S knots> in waves provided

the

cha in dimension

is

i. 37 mm aTId the anchor

can cjericratc a

holding power of

2210 RN which is about

2_0 % of

the. breaking

load c t the

cha I1i The ...iter ci.:i :i. r wh:i :i. s

l:ased or

ti-eqi..aipmenit number fai is

because there is little guararitcee

that

the anchor

wiii cii goes w:i. th that chal n can dienieratce much more

holding power ti-ian. 1200 RN

For the. dynamic motiors in

the

hc:rionital

plane

a more

advanced ca icu ].at :Loni method :15

required

Tb 1:s .Ls rio problem

becai.se the

state oF

the art

at present

:Ls

such that

wel

known model bas:Lnis arid iristitijtces ear iianidice the problem

t.astJ. y th fol 1 owi rig two ± ten. are

of 1nit?rest .

The f :1 :1

ti-ic :Lmpact Impact occi.jrs when the sh:Lp :Ls si.rg I rig, sway :1 rig

arid yawl rig .

The second i> ...dynamic force which

15 1nt....

duced

in tie

chain cable wi-icr

the ship

is heaving

, p:i.tciiri

and rolling. Wilsoni[

indicates that fluctuations of

15 % of

tiie i:rca k :1 rig loa:I of the chain are poss :11:>]. ce

in the end o F the

chair

t the water surface

i3oth :1 mpact arid ...ic

dynamic force

have to

be acc oi_lnited fc:r

wi-ten ti"ic ci...i. n di mcenis Loris are detcerm:i. ned . Beca'.ise a di sci.jss:i. on

on these subjects Fails outside

the scope of th:Ls paper

t1cy

are not Furtber addressed

Hav:i ri determ:i.red 1:he Force which .ani

i:e cxi ected

... ic

0f the anchor cha :1 ni ijfldt(.?r van oi_is enivironimenta I cu..id:i. t . onis::he

strength aspect of

ti-ic anchor i rig system can now be adch'cessed

-12

Th:Ls will be. done jr two parts. lThue

f:i.rst part will deal

with

the

hairi arid the seiorid with the windlass,

Strength aspects of the 'anchor chain.

When evluatirucj the Lrericith of

the chain it must i:e realised

that- the

-iain is the

coririectori between the anchor on seaLd

arid

the wi.ridlas

which is p].aced on the

iecastie

of the

shi.p Wi-ic ri tinder e treme weathc.r t:oridi ki r.ri i IC aricho'i

is

I C.) t'ied IC) 1 Is ma i mi im hol di ni. po 'or' thero mi i'.> L c' ' if I i ' CTit

safety in

the chain to prevent

it from

'breakirie under

corr-stanit, variable or impact load.

Neither is the link

or

shack--lé,

which rests or the chafini

1 :Lp of the 1-awse pipe, allowed to de fc:rm

or hrek

The. same app]. :i.es to a 1.1 1 :i niks arid shack 1 es

which form part of

the chain . Lastly ti-ic brake of the wirid].ass

is

riot allowed

to slip arid

both the windlass arid the chain s:)pper, I f fitted, must have su ff1 c:Lcnit-

strenijthi to wi thstnid

11] 1od

1 ii mc.'aIis (h I II ic. d ernn ft i on c I c' d IIii 1I OTu

of the arieior, cha :1 ni, bra ke, stopj:)er arid wi rtdL 1 rite... e3tcd . It also means th ....he des:i.ciri of thies parts must be

art the sanie strength considerations .

Fu rte':c:rc

the ii;nI:e the hawse p :Lpe enitr;;:inuce arid the cha f :i. nic.J l:i.p m'st be

ccith SO that- a :1:1 rik or' e wh :1 :1 s:in contact w :Lth t:he

chafi niq 1 ip cannot be de irrnod when under' 3. ::ad The same app 1 1 G?.St a thiC? WhO 1 C f:)ath F the ci"ia :i. ri t-h' ouçjh Fhe hawse p :1. pe. over the wi nidlass. , thro'.çih the chain p1 p.c :i. rita the chain 1C:cker'

i: ti. s i mp.ortanit to exam:Lnue

the strength

spe't s of

ttie r..h;:i :1 ri i 'anicIc:in C:.;m;\ c: f i.iia :1 ri ar'I :1 ci..i I .nir's i ric to t:

:::ii O.

a chain n niufacturer :15 i Vent I ri tab I rio , 3 .

l'i-ie table siioW

that

imp rovernenit:ini

:ul :ity

from LJ$ to U3

results in a h :Lgher tens I i.e strength arid reduced mass per unti

3. cngth . The proof 3. c)aci of tiie U2 cha:i. r :1 s 71 , 6 % arid that C)

the 1J3 chain 70 % of the l:reakinug load

'.'i-ert (:-)Iipau'ei:i i:c) thie I-uol:i:L nicj po'..er C:) f thie ant':.h cr the 3. ..:j. nu

...i:iu.ies are fci..irud

:i: f.'j ass_med that the ratio i-ia 1 di nq power' liass is 4 :1 nu idea].

SC:) :13. conid :1 t:ic:ris .

I'ci

Uu i :i.t ía L .iows ...at ti-ic estimated

holding power is

( 4 .x. 1.0500 kc .X 9, 80 rn/sec2 ) / 1000 6:12 kN

Hence :10 % of the breakinicj load of the U2 and 9, 15 % of the LI3

chair . Thiese percentages arc very low arid mean a

large satety

:1 ri acja :1 rust breakage

:i: i an anchor i. th irup.ro.'ed ho .Ld:. rig pOW.?r is used arid a ver'y h:i.

atio

of 1-2 is assumed £ 'J then the es... mated hal d:i. rug

power IS:

F _kN 0

23

4 5 LOADED'AR1N TANKER 120 25 ii i2 3U 3'S B U FO AT u/sEc w I n d NOR T H sea ii0° current 1 80° 25 rn/s

wind.:N0RTH

Current 180 2.5 rn/s

/

-/

d: 28.35 d113.40 m U3 _{137 mm} 114 mm / 10 20 30 40 50 8 K C UR S I 0 N 60 7.0 80

Fi'qure no.8

90 m HPF 7 q 0 I0 5 I0 4

/

2400 1800 1200, 800

Hence for the U2 chair. 22, 6 % arid the U3 ch.ini 20, 6 of the

brezk:i nc Lo.id

Tbie

no.3

Data refer to equipment number 3600

i000 i

parti.lars chair.

item dimensions

13

Tcse v

:i. :.jes :1 rd :i. cate that a h icjh ho 1 di r. power' ... t- iL

s-es th

st rerjth propert:i es a f the cha I Ti bette...er ar i:::orive

:Lori.a 1 arucIior

Th:is c;<;;:imp].e si--,o..'s ..he riee.J

fc.r a careFul choice oi-thehoid

'..'or c F U to richor ni I ni1 y ñ c - I Ly p ri t

- D -Frcm a pa i nt a f view a-I st'?rt:ith

Force. or. the windlass, brake and chain stopper

For ti-ue caicijiationi

of the. force

or. ttp

windlass, brake arid ia :i ri itoppe... fain-' wh :i ch I"iese :1 tems are used whci-i

Cal iriçj to anchor vs id:i. riçj at anci-av' arid we:LgI" :i.niçi .irici-i(:n' ave to be addr'essed They are the foil ow i r.

cIrc)l: -itie anchor -Fv'om a cev't.riiri Ici.Tht above seabed ar,d tl-eru hold tIie cha :L r wIth thz. brn ke when t1ie

iici-iov' :1. or. he cde'J , i'idIuaJ. 1 y pay Out ICi' ch.i:LTi

ut :L 1 :L s :1. riçj t:hc: brake wh :1 1st- back i ri' the sh :Lp iri.: '-.1 it :i iiate :i y cuv'i rvj .he cIta:i. ri w i. th (h

L'a e

wi--ini

su ffi

e.j ent chain

is paid

out

to hold

t he ship in :1 t:L c:)ri

sufFicient power' wal k L-he anchor out Lo a :1. i--i

dei:tIi arid Lr-T.ris Icr tite load to the br-: ke ther-, drop

t-e. .aTidI-ic)r' and br:i. nc I.:i-e ;l-- :u p t(:) -aniccir as above

wi-er, we :i. qh i. nidi anchoi- trans -Icr the cl-ia i ri 1 -Ircm the

bri

the w :1. ridi ass, hc;.:vc short, break the .TrhOi' from the seabed so :1. 1 arid then heave i

i'';

-F-li cr1. enit bi'a ke wer tori. dc- at ar .hoi' :1. r

eniv :L ror.menit-al cor.d:i. t:Lonis

U2 U3 Terisi le N/mm 2 690-640 690 mm 90 78

prooF ioid

k N 3 :L 60 i3v'e. k:iTiçj L kN 4090 4 50CJ m.Dss 1 35' 142

1.4.

The four ways

in which the

wirid1zss is used

show the

:Lmpor-t.ricE? 0+ propel' know ].edge C)f

the

Force

on the

brake arid

winsdl.ss. The same

ppi ics to the

ch;.iri stopper

which cni be

used to

re]. ieve the

wi ridi ss In th :Ls respect :i t shou 1. d he

remembered

that

the mc ii rit

the stopper

is opened the. fi..i]. 1

ch; in 1 oad is immedi ;ite ].y trr.s ferred to

br. ke

(s is

mentioned hefoi'e

the

groi.ridt.ck].o

is sometimes

used

during mooriri nud urimooririg nd

:iri rare iristrices

emer'çjericy

stops in close quarter situtioris cri he ecuted.

(2fter the .I:ove genier]. c)bservtionls on the use c:f

the cjroi.rid

tckIe the hrke,

wiridi.ss arid ch;nin stopper wi :1 i be ;ddressed

in more det:i. 1

S showii ;bc:ve .(j.

br ke is

.ru

i mpo'.rt

p i.ece 0+ oqu i pmerit

dur :L rig

the ijse

of the

rchor

arid chi.ri

T1i is is ;.i]. so high-1 :ighted in study by I3roo ks I: 2

:i His stu:Iy ws pI'c:mj::.tod by ni

ccident i.

Ti the w :i. riter i ri 1981 when ;.ini peri;:inieTt Iv moo .-ed rIg

c.rne

dri ft

in ervirc:mmenit;i cord itionil;

less then the

st;:t:i.c

des :L qn conid:i. ti OTis ...ie :i rivEs....L c.t Loris were rot 1 :1. m :1. ted to :i qs

.s

; iso

rznge of ship ss:Lzes

were :1. nc 1....ded . From U-e p.:::irt

c:

the

deals with

the :ehav.o'r'

c:t the winidI;iss

system

it is

obvious that

over the

year's :L ni

the des i

ni of

w I rid]. ass 1 iniear' :1. rcroase of ca:L e

.'asadopt.::! .

The i'esu 1.

wer'e t!-x 11 known prol)]. ems w :ith :he brake when iro;:p niçj

zini Thor

Frinic:Li11y the t:ime

it rEIu:Lr'es

to

p].y thc- brake

a fter

brake re 1 ease arid ...ie coo f f :L :1 enit: c...1. ct Ion of

the

!:r'a ke 1 :ini I rig wer'e the cause C)

f problems

The study a 1SC)

ti-it peak 1....)ads of about 30% C)

f t!i

ia :1-h break i.nig 1 oa.::1 can be

expected when the brake is

su':fdeni lv app 1 :i. ed P 1 1 these prob 1.

ems can be solved

by ftte marl.. tacturer's of the w :1 rid :i ass prov :1

ed ho Is

çjiveni a prOper sot

0+

des:Lqni criteria

wh:icl"i :inicl'..de

hrkC app:L :1 cation - rates arid peak 1 oads

I ri the same pziI:er Brook

1o..:sbhatt he avrage

speed of a sJu :i whilst arichor:L rig can be found I:y eqi..iatiniçj the energy the cha:i. ii

can absorb to the

enuer''.y of the ship arid tI"ie enierqy inii:ut by

tIio env :Lr:Dnimental for'ces on tlie sh :i.p

T1"ic :1 qni ci' :1. i::c:r' :i. a -F or the w I nd .is; . can I:e f'tid :i.ni

the ru I es

and re.iu 1. at: :Ic:nis For

cTst ruct ion an;:I

ci assi f icat :i. on ci -F

stee]. ships pi_ft]. :i. shed

by the

v...- :1. ous we). 1. known soc riot i es

Tak:i. rig those

of Lloyd' s

....eçj i.ster o-F shi pp :iniq

as an

example

: 13.1 the -Fo]. 3. owl ni:i data on w I nidl ass des icri cart be fC)iTi(l

The w:L rid 1 ass :i.

to

have si.. f-F ic I ent power to exert a cant :1 niuous

di_ty pi..]. 3. over a per:Lod Of :0 m:Lniutes ot

1.J2 crade chain 4:1., 68 cL2 J 113 grade cha:iri 66. 60 2

N (3)

:::: di arietor cha :i. ni in mm

fl

table rio 4-

the

va:L ues found fQr the ch;:i ii r

17

Up to now

it has been shown that

it is. possible

to deter'm:Lrie

stati

ca]. ly arid dyriamica]. ].y

the force on the

anchor

chain under

various

erivjrorimertal conditions. Ey

taking as startiriçj point

the reqi_i:i red ho lcti rig power of

the

anchor arid by i. nic].udinig

impa Loa Mid c ..iI' lo id '.JLi L I i r_ ri bc c

pricricod

dur i

the

depi.oymerit of the

anchoring system at is quite possihi.e to

design a good system.

Having set

out what

is

expected of the ar!chor

sy ..cm :it is now

possible

toiàmpare

the method used

at present

with the one

irs.._hi _paper wh:i. ch :i. s based c:m the hc):icii rig power of

tiie nichor arid tiie crivirónimenitai loads

Comparison of the present day and proposed design criteria

Ti-ic peserit day desigri cr :Lter:La

of the

;rc:!"or :1 rig yI.om :Ls

basd

on ic ca]. cu

l;±ion

01 i-c cqt.iip.r1E?nt ni_i b.er

tii

tI-i :1.

riu! her are

determi

ned the niunier arid mass oF anchors arid

)

L1

(C) ( ] 1 c-ni (ii di irnotor rid

ijrdc

o i. ti vi 1 i ni' I uii

for the bower anchors

Ti'ie geriei'a 1 ic)rm a f tIia number Is

Equipment numl:x?r Dispi ' t2' . 1 fl 2

ore

I) :1 sp 1 ' td

:L acemerit ir metric tons

- . 2

raritvers

in m (S)

2

(2 L..onigiti..idi...s;.i.1. (rea i m

Ti"se

p'cc:I des :i. cir

me'thod is based art ti-c

farce cxc -ted on

ti-ic clsa irs by the eriv :i 'orimerta.t FcD's h :1 ch act: or tIie ip t.Iieri aniciiored

The d:i.ffcrerice :1. r: both mct-Iiods cart best be .j udcicd From tab]. c

no . 7 . i ri the

table

the present

day

method is

I rid i. cated as

EC1U:ipmcnt iijmher method arid

the proposed

one as Force - meL-hod .

-L umr i shows ti-sen ire ma I ri I w :1 tIi

the

:1

r

ci :ivis Ioris requl red

for

the des;i.cin fl3. so a

cross ...e f'er

is

gi.esi c- Ti iu n.Tid n :

lculL

LOTS

ei.iilis

1 1, I I

ship s

3. eniclth The cal umri :1. niput...di. cates which :1. terns or

s'..:b-div :Ls :1 on is

required to obtai

ri output . Unmarked i

arc not

needed

or irrelevant,

The compari sari :Lni tiic table SIiC)WS that tIie force methc)d Is the

more

nivo1ved one of tiie o

r- tab]. e a]. SC) shows t1at the e:'dlu :1. jrit nsi.jmber method does rsc:)t

g:Lvc any cju :1.dance on the

forces

which have he

dealt

wi ti-i

ijnidIer various environmental cond:Ltionis nor is any çjuidarice

g:i.vers On the hal...I :1 n ;:awcr' oF the anchor ri-e metI-io::i i:ss :Lca :i.:Ly

dctcrm:inies ...ic anciior wc:Lcht arid the stud 3. :i. ri k cha I ni on tIic

m.ic !.:hcti' arisversc

arid part oF

the _{I org :i ti_id :i nsa1.}

area oF

sh:ip

Tii force meti-sod :i.s more spec I Ii c

beca'isc it

requires a cal

env irorimerit1 corid i. ti oris when . si-up is anchored :i.ri ;.

cert. in

depth of ter . B;ised on tha force, the ho 1 di riq pwev'

of the

anchor, thed imeris ions of the ch.ai ri, the des igru o the w :L

iid-].ass, brake arid cha:i.ri stopper are based, FIeri'

the design of

t-he w i rid 1 ass, brake arid cha i ri stopper :L s

quite di f ferrit

I::o

that according to the eqLi:Lpmerit number method which ori:Ly deaJ.s with the cont :1 nuous duty pu 1 1, short

term pull

arid anchor

break out pull

s mentioned befpr

it is pri.ncipa].ly the lack of

information

ori

the holding power of the

rucIior arid ....ie wh :L ch cart be expected on the archoririg system which prompted this p.apei' .

is

howri in the ompar:L sort the origin of that lack of

iriforma--t lou, I ii ] V] L1 Ic.aI' t I te s 1c op Li on o I I L[ 1hc

iresenit day dcs:Lgni i:iethod wI-i-icl"i takes rio accoi..irt of the

enivi"-rorimental forces or holding power of the anuclior

Reomrnendations and conclusiori5

E?.e fore '.:kI'ess :1 TICI *:he v'ecommenijti C)nis arid c:)r;c ii...1. OnuS :i. i. 1

:1. miJL ru: .1:ç

that ijp

i:o the time the d :Lmeris loris of ...

dramat :f. ca 3. 3. y I nicreased the use. of the ef.:Ii..r.L pment number seemed

suff:Lcierit fo...te des-igru of the anchoring 5y5Ifl

of a

clianiL...tip

is a

result of the trac ic

aicc:Ldenit w :L th

the m/t

Maass3. i_i is Wil :1 ct-i prompte:I the study on archor :1. rig systems, the atterut ion was foc..ised

or the fTact...t for the

desi ri :) fan anchor-i rig

system rio attenit :L on :Ls paid or the holding power of the anchor or the' enivi. ronimenitai. +orces which act on the sh:i. p at aricho...

This is very much in

conitradictior to what is

riorñiai p'ac tise

Ti LI . Ic. (lii r I ,J to moo TtrJt ñ3 LI ioi 'I i LI i I fio '3 1

there , i

is riot applied

... te des:ign of art anchori rig system of a merchant. sIi I p . ls the proposed method Is nuotiu i rig new the

sole 1:ilr' pose of ti-I is paper :i.s çj draw tiuc attenut :i. on to the omi ss :1 on of the ho 1 d:ing power arid env :Lrc:)nimenitaJ. forces ± ni the

design arid urge designiers to adapt tIi force method

-The qizcsti on immed :1. atel y ar :i ses what

to do wIth

the e.qui pmenit number.

TI-ic answer arid recommendation ±5;

use dur I rg a trans itioni period the equiprnenit number

after

transition period

the force method shoi..ild

be required for newly built vessels;

...ge owliers of exist I rug SI"ii ps to detei'm:L re the

capac--i ty of the

anchor :inig system of their ships arid m.:i ke

ti-ic data -zva :i 1 abJ. e to the sI"u :i. p's

rIi conicL us :iar

:i s 'd-at the stal:e of tlic art is

such that it I

feasi Ic to

desi ini ar anchor I nici system w:i. th the force mcthc:d

arid to make the data a-ia i lab ic to the sh :Lp' s st.a fl in this way

cniliaric ± rig the safety of the ships' s at anichor

Tibi no.?.

DESICN COMPARISON

I tem Equ iprnert number

Foo mt"od

method

Output Input Output SHIP' s DT 1 . 1 length

1.2 dr.ft

i.

3 t'ariv .

.zi

1.4 lorigit.

1 . 5 is

1 . 6 iisi morn rit

Tiert 1. ; 1 .7 heiht bow in l;.st ..,'iti I 1 c;.t :i on 2 DE3IcN ROflDS 2 :L o:i 1 cIat.:i 2 . 2 '..ter depth 3 ENVIRONMENTPIL DPiT(i 3. 1 w:ind 2 .... 3.3 waivc .4 DE.SIGN CONDITIONS 4. 1 surv1vL1. 6 . 2 c: '.ticr-; I S COEFFICIENTS S 1 ii ridfoi'c 5 2. '..Irni c:)':': 3 di' :i. ft

FORCE: CLCU!JiT IONS 6 w :1. nid 1.1,1.3,1.4,.

3.1,6, 5.1

. x windforce 6 2 uront

:2

3' . ii.i.1-fo'c 6.3 ve drift 1.1,4 9,3 . wave drift 6 . 6 .:t.:Ln t:it:-:.'. pzrt I 3, 4, 6 . 1 6.2,6.3 x

6.5 chziri

dyrimi

pErt

1 .8, 1. 6, 4., dyrirn:L 6 . 1, 6 2, 6 3 x

ch.iri 1:cr

7 ANCHOR H

7.1 holding PowP

/

2.4,6.4,6.. 5

holding

rnss

x

mss

rii.imbr' x r'.imhv' -w i.ght

-r'oc!i..je:t . on du::L: :i. Oh

S CIIAIN. 8. 1

1rigtli

totzLl. :I.OrCTtI :L . 7, 1.8, 2, 2, 6.4, 7. 1

S . 2 iss

S . 1 irid ri'c.ly h;.::i. i

8.3 cnde

7.1,8.2

x

9 )INDi._ASS, I3RA I<E, cIIA:i:N STOF'F-'ER

- ri'jrnhr

w i rid 1 .ss

1. C)Tit :i rIi..IOuS i.:Iuty

d:i.am har:i. ri Corit . Duty

9 . 2 short term

iu 1 1 (5 . T . P) 9.1. sT.!::, 9 . 3

ek. out

pull

(13.0, P) 7 . 2, S :1. , ci :i. ;.i m !3.O.P.

9 4 ct:i'ztiori;.ul/

s'rv :1. v; 1 ci y (0 . S . C))

4, 6.4,6.5

x

05.0

9.5 Br.ke

itri c:ti.:LTi -6, 6 . 4, 6 . -5 x

1od

9. 6 c:lu;ii:iri -stopp.r 4, 6.4., 6 5 :Lcd

9 . 7 :oritroi system

4,6.4, 6.5,

9 1, Q!5 1-7 . 2 7 . 3 7 . 4

length

ijrit

1 eriith

References

1 lri

erier.y b.sis

for

the design of operr-oce;ri s:i.nigle

point mooriri<

Notley Roger Maddox

Esso ProdUtiori Rerh Co

OTC pzper ro 1536

2. The. dyrimi Behaviour of Single arid

Multiple

Moored

Vessels

Brook, 3 S'.', M . Sr.. .ind 0 . Byriie B ft. S,

Foper no.9

3 on ship J. :L ries in vesond :rrerit... I3si 1 W . W:i isori, F . is.e

rud Dorzld 1b;i:io

.:rji_jv'n1 oF the oi.r's di vi si or

of the

tier:L:.r Sci:::iety of Civ:. :i Ei:Lniee'.:

Novem'er :L969

A. t)'weg I nqeni b :i j L

crtwer'per vr

:ir

C. F.M. Rery en E.G. Kr!..ithof

S G:'ri W

40e. ji'g;r

1973

5 , The role of model tests .nid ...eli' o rr el;.t:Lor with Fi..il I

oziie observtioris

Dr. Ir. J. H. Vugts

Symposi urn on "0 ffshore hydrc:Jyri.nii.:s

'.jcp.st :1971

I<eriiri.:eri The Nethei:rds

6. Wutcr'3.00pkuridig ithoratorium . Nau.jt Ical cC(i tr:i.butioni

ru LL/Jr Lcd 'or I: d 1.ejni H C ' i iw J W Ku i iii

.3 . Stratirig PuLI ic.ijtiori rio 251., febi'uari 1981

Gu I del i rue; arud 'econierudat :Loris For sa moor inig o ]. arge ships at p :L ers arid sea is lards

.Oi 1 compariies Initer'riat lanai M.:r' :L re FOrum

...Pç :i.c)nis al .: i. rid and cu.jrrent I C)i.dS on

II!( I

OCIMF

T.I.!; ICJt'9..iC)I..! .

linri:Lng ;nrid s:i.gni c)1

rrici

.-iri::- tev'ir.s

John Wiley nid Loris

9 . T.rik. .rid L')i. rid turirue 1 tests For' ;.i di' I I ]...h. p. with CIyTIm I i

position contrOl

C). fl. Wise, CEC Electr:i.c;:ul. Pro jects I i m:i.ted

arid .:i . W . Eruql :1 sh, N;.t ioru]. F'hys :1 c;. I Lbor;tory

paper OTC 2345, May 1975

:10 .

Principles of Naval

riI:it:e.jr'e ('evised) Ed.tor .Johri

F

I o....I I I L uc.d by f. _uo r I I y I N v. flr'. I

aiucl Mar' :i. rue Eni I rueers 1%é.7

Het be.)J.c?ri v.fliI d:' ::.TiC:d::.t::;'.1e leri':;to :iTke'ket(:.ruci cor

ru ten .:uTIer' L iav':u.:ig

12 I...'.isrè <.Swc.dish) Ar:hor' i.Ii i ri

13. L.. 1 oyd' s rej: tï' C) f sha. pp iriçj . Rules .md reçiul ;t (DTIS

for