Vessel Stability

8/13/2019 Vessel Stability

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Vessel Stability


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ncreased resistance in turn drives up fuel consu"ption and operating costs over thelife of the vessel. #s with all good designs! a balance between the design criteria andoperational re7uire"ents "ust be reached.

Weight or Force o !ra"ity

$he hull! "achinery! outfitting! and cargo load deter"ine vessel weight. #s vesselcargo load is increased! the hull will settle deeper in the water until the buoyancye7uals the weight.


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#e initions

Center o Buoyancy :0; is the point at which all vertical upward forces :buoyantforces; are said to act. t is the center of the volu"e of the i""ersed portion of thevessel. . $he 3enter of 0uoyancy "oves in the sa"edirection as the boat5s waterline.

Center o !ra"ity :,; is the center of the total weight of the loaded vessel. t is thepoint where the entire weight of the boat and its contents are concentrated. fadditional excess weight is added to the boat then this point ?,@ will be located higheror lower depending upon if the weight was added above or below ,. $he position of=,= is dependent upon the distribution of weights within the boat. #s the distribution ofweights is altered! the position of =,= will react as followsA

1. =,= "oves towards a weight addition

2. =,= "oves away fro" a weight re"oval9. =,= "oves in the sa"e direction as a weight shift

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#is%lace&ent is the weight of the volu"e of water that is displaced by the underwaterportion of the hull is e7ual to the weight of the boat. $his is 4nown as a boat6sdisplace"ent. $he unit of "easure"ent for displace"ent is the )ong $on :1 )$ B 22>C)0S;.

Force is a push or pull that tends to produce "otion or a change in "otion. nits areexpressed in tons! pounds! ewtons! etc. (arallel forces "ay be "athe"aticallysu""ed to produce one = et +orce= considered to act through one point.

Weight is the force of gravity acting on a body. $his force acts towards the center ofthe earth. nits are expressed in tons! pounds! 4ilogra"s! etc.

'o&ent is the tendency of a force to produce a rotation about a pivot point. $his wor4sli4e a tor7ue wrench acting on a bolt. nits are expressed in foot tons! ewton "eters!etc.

Free sur ace e ect influences the stability of a vessel.


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Stability at Wor,

f an outside force such as a wave caused this boat to heel over to one side! #nd if theweight of the boat and its contentshas not changed! or shifted! then thecenter of gravity :,; will re"ain inplace. 0ut loo4 at the ?0@! it "ovedin the direction of the lower side.$his point is now the center of0uoyancy and the upward forces of0uoyancy will see" to push harderon this lower side. $he result will beto return the hull to its uprightposition.

$he Metacenter ?M@ is a point near the centerline of the boat at rest. t is a point that willnor"ally be stationary and directly over the point of buoyancy regardless of which side?0@ "oves. f you consider ?0@ as the ball at the botto" of a pendulu" then ?M@ is theconnecting point fro" which that pendulu" swings. $he Metacentric %eight then is the

distance between the center of gravity ?,@ and the "etacenter ?M@ and is si"ply called?,M@.

$he ,M is crucial to stability. $he further apart that ?,@ and ?M@ beco"e! the "orestable the boat and the 7uic4er it will right itself. # long ,M also causes anunco"fortable 7uic4 snapping roll. $o provide a "ore co"fortable ride! "ost passengerboats are built with a shorter ,M. $his will allow the vessel to slowly recover. $oo little,M results in a vessel with a long! slow roll that! while co"fortable! could lead tocapsizing. #s long as the weight of a vessel! and the location of that weight! re"ainsconstant! and then the center of gravity would not "ove.

$%& S$#0 ) $ $- # ,)&


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is a good "easure of the boat5s initial stability.

- ,%$ , M*M& $ :-M;$he -ighting Mo"ent is the best "easure of a boat6s overall stability. t describes theboat6s true tendency to resist inclination and return to e7uilibriu". $he -ighting Mo"entis e7ual to the boat5s -ighting #r" "ultiplied by the boat5s displace"ent.

#s long as the , re"ains below the M then there will be available -ighting "o"ent toright the vessel. *nce , is centered over the M then the vessel will capsize.

-ighting energy is the ter" used to describe a vessel6s ability to right itself after beingheeled over. # properly loaded vessel should have positive righting energy to a heel ofat least FC degrees. $he "agnitude of the largest righting ar" is also an indication of avessel6s stability.

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STAB(L(TY CON#(T(ONS

$he positions of ,ravity and the Metacenter will indicate the initial stability of a boat.+ollowing da"age! the boat will assu"e one of the following three stability conditionsA

(*S $ V& S$#0 ) $$he "etacenter is located above the boat5s center of gravity. #sthe boat is inclined! -ighting #r"s are created which tend toreturn the boat to its original! vertical position.

& $-#) S$#0 ) $$he "etacenter and the boat5s center of gravity are in the sa"elocation. #s the boat is inclined! no -ighting #r"s are created:until M starts to "ove below , after the boat is inclined past EJ1CJ;.

&,#$ V& S$#0 ) $$he boat5s center of gravity is located above the "etacenter. #sthe boat is inclined! negative -ighting #r"s :called upsettingar"s; are created which tend to capsize the boat.

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Weight 'o"e&ents

0ecause of the relationship between weight and buoyancy of a given hull shape! both,M and righting energy vary significantly with the weight and center of gravity of theloaded vessel. $his "eans that how a vessel is loaded has the largest i"pact on thestability of the vessel.

#dding a load #dding weight above a boat5s center of gravity will change its stability. f the center ofgravity is raised too "uch! the boat will beco"e unstable. #s a result! less force isre7uired to capsize the vessel.

-e"oval of a load-e"oval of weight fro" below the center of gravity also decreases stability. $he centerof gravity will rise to a higher level decreasing the ,M of the vessel resulting in a vesselwith a 7uic4er roll period.

Shifting a loadShifting weights vertically! no "atter where onboard it is! will always cause the boat5scenter of gravity to "ove in the sa"e direction as the weight shift.


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#a&age Control

$he previous pages have discussed vessel stability characteristics in the intact state.$hey also apply to a da"aged vessel. %owever! the buoyant force and center ofbuoyancy of the da"aged hull will differ significantly fro" that of the intact hull!depending on hull co"part"entation as well as the location and extent of da"age.

#s the unexpected excess weight of flooding wateris added! the boat5s center of gravity will initiallydecrease and the vessel will see" to beco"estable. #t so"e point in ti"e the center of gravitywill start rises. *nce it reaches the "etacenter andgoes beyond the boat will capsize. $his newlocation of the downward force of gravity will nowfight against the righting tendency of the new pointof buoyancy that had shifted previously. $he resultis that the boat will no longer return to the upright..

f an area flooded with the water is only partially

filled! and there is no restriction to the side to side"ove"ent of the water! the result can bedevastating $his free "ove"ent or sudden shifting of water is called ?+ree Surface&ffect@ and has a "a or effect on a vessel5s stability.

f the area is co"pletely flooded or if there are restricting boundaries to act as bafflesthen the water is no longer sub ect to +ree Surface &ffect.

#lso! as the boat develops a list! its center of gravity "ay "ove in the sa"e direction asthe point of buoyancy if there is also a corresponding shift in weight as in the diagra".

# good operational practice is to "ini"ize free surface effect by dividing tan4s withbaffles and fluid cargo holds with bul4heads and by 4eeping the nu"ber of partially

filled tan4s and holds to an absolute "ini"u".

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-essel Stability . Warning Signs/ 0recautions

$he "ost i"portant factors in preventing a boat fro" capsizing are a welldesigned! "aintained! and loaded vessel and an experienced operator and crew.(reventing an unstable vessel condition and being able to recognize the warning signswhen such a condition does occur can save lives. ou should be on constant watch forloss of stability.

# well designed vessel will resist capsizing or foundering in severe conditions ifit is operated properly. $o reduce the li4elihood of these incidents! 4eep theserules in "indA0e aware of external forces L wind! waves! and water depth. #lways chec4 theweather forecast before departure. #void rough weather conditions.

on5t overload your vessel. 0e aware of the a"ount of weight added to yourvessel and available freeboard. istribute the passengers and cargo evenly.(artially filled water ballast and fuel tan4s contribute to instability. +ree surfaceli7uids "ust be contained so their influence will not upset the balance of yourvessel.(revent water fro" entering the interior of your vessel by 4eeping hatches!

doors! and windows closed! as practicable! when underway. -egular"aintenance of gas4ets and fastening devices will help to ensure watertightness.

#ny water shipped on board "ust be re"oved as 7uic4ly as possible. Scuppersand drains "ust "eet design criteria and be 4ept in good wor4ing order.

#d ust course! speed! or both as practicable to "ini"ize vessel "otion! rolling inparticular.

#void sharp turns or turns at high speed when loss of stability is possible.

Stability


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SUB#(-(S(ON AN# #A'A!E STAB(L(TY

f the shell of the ship is da"aged so as to open one or "ore internal spaces to thesea! flow will ta4e place between the sea and these spaces until stable e7uilibriu" isestablished or until the ship sin4s or capsizes. $he loss of watertight integrity could bedue to collision! grounding or internal accident such as an explosion. t is i"practical todesign a ship to withstand any possible da"age. $he degree to which a vesselapproaches this li"it is the true index of its safety. $o reduce the probability of loss! thehull is divided into a series of watertight co"part"ents by "eans of transversewatertight bul4heads extending fro" side to side of the ship.

t is true that the "ore severe the standard adopted for subdivision and stability! thegreater the probability that capital and operating costs will be increased. +or exa"ple!too close spacing of bul4heads "ay unnecessarily increase both the first cost andoperating costs and "ay also seriously restrict the vessel5s usefulness. n addition! it"ight be expected that the "ore bul4heads the safer the ship. 0ut da"age "ay occurentirely between ad acent bul4heads or "ay involve one or "ore bul4heads. %ence! fora given length of da"age! any increase in the nu"ber of bul4heads "ay actuallyincrease the li4elihood of bul4head da"age! which would reduce rather than increasethe chances of survival.

The !eneral E ects o Floo$ing(1) Change of Draft

$he draft will change so that the displace"ent of the re"aining unflooded part ofthe ship is e7ual to the displace"ent of the ship before da"age less the weight ofany li7uids which were in the space opened to the sea.(2) Change of Trim

$he ship will tri" until the centre of buoyancy of the re"aining unflooded part of theship lies in a transverse plane through the ship5s centre of gravity and perpendicularto the e7uilibriu" waterplane.(3) Heel

f the flooded space is unsy""etrical with respect to the centerline! the ship willheel until the centre of buoyancy of the re"aining unflooded part of the ship lies ina fore and Laft plane through the ship5s centre of gravity and perpendicular to thee7uilibriu" waterline. f the GM in the flooded condition is negative! the flooded shipwill be unstable in the upright condition ! and even though the flooded space issy""etrical! the ship will either heel until a stable heeled condition is reached orcapsize. $ri" and heel "ay result in further flooding through i""ersion of openingsbul4heads! side shell or dec4s :downflooding;.(4) Change of Stability

+looding changes both the transverse and longitudinal stability. $he initial"etacentric height is given byAGM = KB + BM - KGSin4age results in an increase in KB. f there is sufficient tri"! there "ay also be anappreciable further increase in KB as a result. BM tends to decrease because ofthe loss of the "o"ent of inertia of the flooded part of the waterplane. %owever!sin4age usually results in an increase in the "o"ent of inertia of the unda"agedpart of the waterplane! thus tending to co"pensate for the loss. #lso! tri" by thestern usually increases the transverse "o"ent of inertia of the unda"aged

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waterplane! and vice versa. +or "ost ocean going ships the co"bined effect ofthese factors is usually a net decrease in GM.

(5) Change of Freeboard

$he increase in draft afterflooding results in a decreasein the a"ount of freeboard.&ven though the residual GM"ay be positive! if thefreeboard is "ini"al and thewaterline is close to the dec4edge! sub"erging the dec4edge at s"all angles of heelgreatly reduces the range ofpositive righting ar" GZ, andleaves the vessel vulnerableto the forces of wind and sea.

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Floatation Calculationsn order to assess the ship5s ability to withstand da"age! it is necessary to deter"ineA

:a; $he da"aged waterline! i.e. the new draft! tri" and heel.

:b; $he da"age stability! i.e. after flooding.

$he floatation calculations can be carried out by either one of two "ethods! the lostbuoyancy method or the added weight method.

12 The Lost Buoyancy 'etho$

n this "ethod the lost buoyancy due to a co"part"ent or co"part"ents being openedto the sea is calculated. $his lost buoyancy and its "o"ents are e7uated to the

buoyancy gain and "o"ents acco"panying sin4age! tri" and heel of the re"ainingintact part of the ship. n this "ethod! it is assu"ed that the displace"ent and theposition of the centre of gravity are unchanged.$his procedure is convenient and si"ple to use if the for" of the vessel andconfiguration of the flooded space are such that the resulting sin4age! tri" and heel donot involve extre"e or discontinuous changes in the re"aining unda"aged part of thewaterline. 3onse7uently! this procedure is often used for "erchant ships.3o"part"ents of ships open to the sea do not fill totally with water because so"espace is already occupied by structure! "achinery or cargo. $he ratio of the volu"ewhich can be occupied by water to the total gross volu"e is called the !ermeability " .+or cargo spaces it is ta4en as ICD! for acco""odation spaces as KFD and for"achinery spaces as 8FD.The ste%s o this &etho$ are as ollo3s4

1. 3alculate the per"eable volu"e of co"part"ent up to the original waterline.

2. 3alculate TPC ! longitudinal and lateral positions of C for the waterplane withthe da"aged area re"oved.

9. 3alculate revised second "o"ents of areas of the waterplane about the C inthe two directions and hence new BM s.

>. 3alculate parallel sin4age and rise of CB due to the vertical transfer ofbuoyancy fro" the flooded co"part"ent to the layer.

F. 3alculate new GM s.

I. 3alculate angles of rotation due to the eccentricity of the loss of buoyancy fro"the new C s.

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$his is best illustrated by an exa"ple.

E5a&%le # co"part"ent having a plane area at the waterline of 1CC " 2 and centroid EC " foreof "idships! 19 " to starboard is bilged. p to the waterline obtained before bilging! theco"part"ent volu"e was 1CCC " 9 with centres of volu"e I8.F " fore of "idships! 12" to starboard and F " above 4eel. $he per"eability was ECD.0efore the incident the ship was floating on an even 4eel draft of 1C " at which thefollowing particulars are givenA

isplace"ent NKGKM : transverse;KB

9CCCC tonnesK.>C "11.>C "F.2F "

KM : longitudinal;F>C " 21 "22C "

3alculate the heel and tri" when the co"part"ent is bilged.1. (er"eable volu"e B C.EC x 1CCC B ECC " 9

2. a"aged F>C 1CC B >>>C " 2

Move"ent of C aft B B 1.FF "

Move"ent of C port B B C.2K "

9. *riginal " T

" T B B " >

a"aged " T :ignoring " of the co"part"ent about its own axis; "# T B 18CCCC L 1CC x 19 2 L >>>C x :C.2K; 2 B 1I2E2E " >

a"aged BM T B F.FI "

*riginal " !

" ! B " >

a"aged " ! "# ! B >.822 x 1C I 1CC x IK2 >>>C x :1.FF; 2 B >.99F x 1C I " >

a"aged BM ! B B 1>8.1 "

>. (arallel sin4age s B C.1I "

-ise of B B C.121 "

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F. a"aged GM T B F.2F O C.121 O F.FI K.>C B 1.F91 "

a"aged GM ! B F.2F O C.121 O 1>8.1 K.>C B 1>>.CE "

I. #ngle of heel P B B B 11.C C

#ngle of tri" Q B B B C.C11F rads

3hange of tri" t B Q x !BP B C.C11F x 22C B 2.F9 "

T B T o O s + t

B B 11.>9 "

T $ B T $o O s - t

B B 8.KC "

62 The A$$e$ Weight 'etho$

n this "ethod the water entering the da"aged co"part"ent can be regarded as anadded weight. $herefore! the resulting displace"ent varies with the increase in draft!tri" and/or heel. 3onse7uently! the position of the centre of gravity of the ship changesas well. Since this "ethod involves a direct integration of volu"es and "o"ents up tothe da"aged condition waterplane! by direct use of 0on ean 3urves! it is ust as welladapted to dealing with co"plex flooding conditions as with si"ple ones. #lso forgreater accuracy this "ethod is reco""ended.C " 2

(arallel sin4age! s B B C.>I "

$he vessel will now tri" about the new centre of floatation! &. $he position of & can befound by ta4ing "o"ent about "idshipsA

:IC x 1C x C; L :8 x 1C x 2I; B :IC x 1C L 8 x 1C; &

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& B > " or > " aft

KG B 2.F " GM ! B 1.E9 O IF.1 2.F B I>.99 "

%dded &eight method Mass added at 9 " draft B 8 x 1C x 9 x 1.C2F B 2>I tonne

(arallel sin4age! s B

ew displace"ent B IC x 1C x 9.> x 1.C2F B 2CK1 tonne

# second calculation considering the "ass of water entering at >.>F " draft will givedrafts forward and aft of F.1> " and 2.CF " respectively. $hird and further calculationswould co"e progressively closer to the lost buoyancy draft values.

#a&age Stability Calculations(a)'nitial Stability

3onsider a ship of displace"ent N ad"itting a weight w having a free surface i asshown in figure.


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%dded eight ethod Lo t *#oyan$y ethod

(b) Stability at Large %ngle

t is now re7uired to deter"ine GZ values after da"age. $o do that cross curves for thevolu"e of flooding water are constructed as followsA

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K. $his procedure is repeated for all angles.

$he GZ curve after da"age will! in general! appear as in the following figureA

$he point at which the curve crosses the P axis! at angle P 1! represents the position ofrotational e7uilibriu"R this will be zero when the flooding is sy""etrical about the"iddle line.


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:c; (robability that the ship "ay survive such flooding.

3hapter 1 of the S*)#S shall apply to ships the 4eels of which are laid on or after 1Tanuary 2CCK. $hese re7uire"ents apply to cargo ships of 8C " in length : ! ; andupwards and to all passenger ships regardless of length. $he degree of subdivisionshall vary with the subdivision length : ! s; of the ship and with the service! in such"anner that the highest degree of subdivision corresponds with the ships of greatestsubdivision length : ! s;! pri"arily engaged in the carriage of passengers.

#e initions1+ S#bdi,i ion Length (L ) - $he greatest pro ected length of that part of the ship

at or below dec4 or dec4s li"iting the vertical extent of flooding with the ship atthe deepest subdivision draft.

2+ id.Length - $he "id point of the subdivision length of the ship.

3+ %ft and For&ard Terminal - $he aft and forward li"its of the subdivisionlength.

4+ Length (L) - $he length as defined in the "nte national Con%ention on !oadlines.

5+ Dee!e t S#bdi,i ion Draft (d ) - $he waterline which corresponds to thesu""er load line draft of the ship.

6+ Light Ser,i$e Draft (d l ) - $he service draft corresponding to the lightestanticipated loading and associated tan4age.

/+ 0artial S#bdi,i ion Draft (d ! ) - $he light service draft plus ICD of thedifference between the light service draft and the deepest subdivision draft.

+ 0ermeability (") - $he per"eability of a space is the proportion of thei""ersed volu"e of that space which can be occupied by water.

+ *#l head De$ - n a passenger ship "eans the upper"ost dec4 at any pointin the subdivision length : ! s; to which the "ain bul4heads and the ship5s shellare carried watertight. $he bul4head dec4 "ay be a stepped dec4. n a cargoship the freeboard dec4 "ay be ta4en as the bul4head dec4.

1 + %mid hi! - #t the "iddle of the length : ! ;.

The e #ired S#bdi,i ion 'nde7 $he subdivision of a ship is considered sufficient if the attained subdi%ision inde4 $ ! is

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not less than the e5ui ed subdi%ision inde4 3 and if! in addition! the partial indices $ s, $ 2 and $ l are not less than C.K 3 for cargo ships.

1+ n case of cargo ships greater than 1CC " in length : ! s;A

2+ n the case of cargo ships not less than 8C " in length : ! s; and not greater than1CC " in length : ! s;A


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watertight horizontal subdivision above the waterline or higher. %owever! if alesser extent of da"age will give a "ore severe result! such extent is to beassu"ed.

Cal$#lation of the fa$tor ! i

$he factor 2 i for a co"part"ent or group of co"part"ents shall be calculated accordingto for"ulae given in 3egulation 7-& of Cha2te ""-& of the S*)#S. $hese for"ulae arebased on the following para"etersA

8B the aft"ost da"age zone nu"ber involved in the da"age starting with o.1at the stern.

n B the nu"ber of ad acent da"age zones involved in the da"age.

9 B the nu"ber of a particular bul4head as barrier for transverse penetration ina da"age zone counted in direction towards the centre line. $he shell has 9 B C

4& B the distance fro" the aft ter"inal of ! s to the aft end of the zone in7uestion.

4( B the distance fro" the aft ter"inal of ! s to the forward end of the zone in

7uestion.

b B the "ean transverse distance in "etres "easured at right angles to thecenterline at the deepest subdivision loadline between the shell and the verticalbarrier extending between the longitudinal li"its of the space. n any case! b isnot to be ta4en greater than B:( .

Cal$#lation of the fa$tor i

1. $he factor s i shall be deter"ined for each case of assu"ed flooding! involving aco"part"ent or group of co"part"ents! in accordance with 3egulation 7-( as followsA

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; e is the e7uilibriu" angle of heel in any stage of flooding! in degreesR

; % is the angle ! in any stage of flooding! where the righting lever beco"es negative! orthe angle at which an opening incapable of being closed weathertight beco"essub"ergedR

GZ ma4 is the "axi"u" positive righting lever! in "etres! up to the angle ; % R

3ange is the range of positive righting levers! in degrees! "easured fro" the angle ; e.$he positive range is to be ta4en up to the angle ; % R

looding stage is any discrete step during flooding process! including the stage beforee7ualization :if any; until final e7uilibriu" has been reached.

$he factor s i for any da"age case at any initial loading condition! d i ! shall be obtainedfro" the for"ulaA

s i B "ini"u" Us inte mediate,i or s inal,i 9s mom,i

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.1.1. M 2assenge is the "axi"u" assu"ed heeling "o"ent resulting fro" "ove"entof passengers! and is to be obtained as followsA

M 2assenge B :C.CEF 26 2; 2 :C.>F 2B; :t";


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B is the bea" of the ship.

#lternatively! the heeling "o"ent "ay be calculated assu"ing thepassengers are distributed with > persons per s7uare "etre on availabledec4 areas towards one side of the ship on the dec4s where "uster stationsare located and in such a way that they produce the "ost adverse heeling"o"ent. n doing so! a weight of EF 4g per passenger is to be assu"ed.

>.1.2. M wind is the "axi"u" assu"ed wind force acting in a da"age situationA

M wind B :P + $ + Z ; / K8CI :t";

.1.9. M su %i%alc a t is the "axi"u" assu"ed heeling "o"ent due to the launching ofall fully loaded davit launched survival craft on one side of the ship. t shallbe calculated assu"ing that all lifeboats and rescue boats fitted on the sideto which the ship has heeled after having sustained da"age shall beassu"ed to be swung out fully loaded and ready for lowering.

F. nsy""etrical flooding is to be 4ept to a "ini"u" consistent with the efficientarrange"ents.


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+or the purpose of the subdivision and da"age stability calculations of the regulations!the per"eability of each general co"part"ent or part of a co"part"ent shall be asfollowsA

S%aces 0er&eability

#ppropriated to stores C.IC

*ccupied by acco""odation C.KF

*ccupied by "achinery C.8F

Void spaces C.KF

ntended for li7uids C or C.KF

+or the purpose of the subdivision and da"age stability calculations of the regulations!the per"eability of each cargo co"part"ent or part of a co"part"ent shall be asfollowsA

S%aces 0er&eability at $ra td

0er&eability at $ra td !

0er&eability at $ra td l

ry cargo spaces C.EC C.8C C.KF

3ontainer spaces C.EC C.8C C.KF

-o ro spaces C.KC C.KC C.KF3argo li7uids C.EC C.8C C.KF

S%ecial :e;uire&ents Concerning 0assenger Shi% Stability

# passenger ship intended to carry 9I or "ore persons is to be capable of withstanding

da"age along the side shell. 3o"pliance with this regulation is to be achieved byde"onstrating that s i is not less than C.K for the three loading conditions. $he da"ageextent is to be dependent on both 6 and ! s such thatA

1. $he vertical extent of da"age is to extend fro" the ship5s "oulded baseline to aposition up to 12.F " above the position of the deepest subdivision draft.

2. CC or "ore persons are to be carried! a da"age length of C.C9 ! s butnot less than 9 " is to be assu"ed at any position along the side shell! in

con unction with a penetration inboard of C.1 B but not less than C.EF "

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"easured inboard fro" the ship side! at right angle to the centerline at the levelof the deepest subdivision draft.

9. " above the topof the tan4! whichever is the greater.

0ea, an$ 'achinery S%ace Bul,hea$s

1. # collision bul4head shall be fitted which shall be watertight up to the bul4headdec4. $his bul4head shall be located at a distance fro" the forwardperpendicular of not less than C.CF ! or 1C "! whichever is the less! and not"ore than C.C8 ! or C.CF ! O 9 "! whichever is the greater.

2. o doors! "anholes! access openings! ventilation ducts or any other openingsshall be fitted in the collision bul4head below the bul4head dec4.

9. 0ul4heads shall be fitted separating the "achinery space fro" cargo andacco""odation spaces forward and aft and "ade watertight up to the bul4head

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dec4. n passenger ships an afterpea4 bul4head shall also be fitted and "adewatertight up to the bul4head dec4.

Sub$i"ision an$ #a&age Stability o Oil Tan,ers

$his topic is dealt with in Cha2te * of the "nte national Con%ention o the P e%entiono Pollution om hi2s /M$3P0!1.

Lo$ation of Damage

a; n tan4ers of "ore than 22F " in length! anywhere in the ship5s length.

b; n tan4ers of "ore than 1FC "! but not exceeding 22F " in length! anywhere inthe ship5s length except involving either after or forward bul4head bounding the"achinery space located aft. $he "achinery space shall be treated as a singlefloodable co"part"ent.

c; n tan4ers not exceeding 1FC " in length! anywhere in the ship5s lengthbetween ad acent transverse bul4heads with the exception of the "achineryspace.

87tent of Damage

Side Damage

1 )ongitudinal &xtent or 1>.F "! whichever is less

2 $ransverse &xtent or 11.F "! whichever is less

9 Vertical &xtent +ro" the "oulded line of the botto" shell plating at

centerline! upward without li"it *ottom Damage

o .)! om .P. o the shi2 #ny other part of the ship

1 )ongitudinal &xtent or 1>.F "! whichever is less or F "! whichever is less

2 $ransverse&xtent or 1C "! whichever is less or F "! whichever is less

9 Vertical&xtent or I "! whichever is less! or I "! whichever is less!

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"easured fro" the "oulded lineof the botto" shell plating atcentreline

"easured fro" the "oulded lineof the botto" shell plating atcentreline

f any da"age of a lesser extent would result in a "ore severe condition! such da"ageshall be considered.

Damage S#r,i,al

*il tan4ers shall be regarded as co"plying with the da"age stability criteria if thefollowing re7uire"ents are "etA

1. $he final waterline! ta4ing into account sin4age! heel and tri"! shall be below

the lower edge of any opening through which progressive flooding "ay ta4eplace.

2. n the final stage of flooding! the angle of heel due to unsy""etrical floodingshall not exceed 2F o! provided that this angle "ay be increased up to 9C o if nodec4 i""ersion occurs.

9. $he stability in the final stage of flooding shall be investigated and "ay beregarded as sufficient if the GZ curve has satisfied the criteria shown on thefollowing figure.

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$he range should be at least 2C o beyond the position of e7uilibriu" inassociation with a "axi"u" residual righting lever of at least C.1 " within the2Co rangeR the area under the curve within this range shall not be less thanC.C1EF ".rad. nprotected openings shall not be i""ersed within this rangeunless the space concerned is assu"ed to be flooded.

>. $he #d"inistration shall be satisfied that the stability is sufficient duringinter"ediate stages of flooding.

Documents

Vessel Stability