4.trim n draft

8/16/2019 4.Trim n Draft

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LESSON TOPIC: 4.4 TITLE: TRIM AND DRAFT

Contact periods allotted this LESSON TOPIC:

Classroo: !." Test: "."

Trainer: "." Total: !."

MEDIA: Classroo lect#re $ith %is#al

edia

TERMINAL O&'ECTI(ES:

)." E(AL*ATE ship+oard sta+ilit, +, anal,-in

$eiht and oent considerations. /'TI 0.!.12 )."2

).12 ).!3

ENA&LIN O&'ECTI(ES:

).15 E6PLAIN $h, tri and loadin a77ect intact

sta+ilit,.

).!" COMP*TE the ipact o7 lonit#dinal $eiht

shi7ts2 additions2 and reo%als on the ship8s tri

and dra7ts.

).!1 i%en a speci7ied loadin condition and dra7t

readins2 CALC*LATE the re9#ired o%eent o7 solid

or li9#id loads to +rin the ship to $ithin

accepta+le liits o7 tri.

).!! i%en a predeterined ao#nt o7 7loodin

daae2 COMP*TE 7inal tri and dra7ts.

).!0 DEFINE dra2 tri2 triin oent2 triin

ar2 lonit#dinal center o7 7lotation2 parallel

rise2 parallel sinae2 and pl#nin.

).!4 DESCRI&E the o%eent o7 lonit#dinal

sta+ilit, re7erence points ca#sed +, $eihtshi7ts2 additions2 and reo%als.


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Lonit#dinal Center o7

Flotation /LCF3:

eoetric center o7 the ship8s

$aterline plane. The ship tris

a+o#t this point.

Ma, +e 7or$ard or a7t o7 the MP

dependin on the ship8s h#llshape at the $aterline.

Center o7 Flotation Distance:

Distance 7ro the LCF to the

MP. Fo#nd #sin the Dra7tDiara and F#nctions o7 For2

as a 7#nction o7 displaceent.

*sed to distri+#te chanes o7

tri +et$een the 7$d and a7t

dra7ts.

Center o7 o,anc, /LC&3:

The point thro#h $hich the

7orces o7 +#o,anc, act2

lonit#dinall,.

Dra:

A desin 7eat#re $here the

dra7t a7t is reater than the

dra7t 7or$ard.

Priaril, done to increase

prop#lsion plant e77ecti%eness.

The di77erence +et$een the


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Tri: 7or$ard and a7ter dra7ts2 in

e>cess o7 desin dra.

Parallel Rise=Sinae /PR=PS3:

;hen $eiht is reo%ed=added

7ro=to a ship at LCF2 the

7or$ard and a7t dra7ts $ill

chane +, the sae ao#nt.

Chane in Tri /CT3:

The s# total o7 the a+sol#te

%al#es o7 the chane in 7or$ard

and a7ter dra7ts. E6AMPLE:

DF;D DAFT Tri

Oriinal: !"FT 1?FT !FT +=+

Final: 1)FT !1FT @FT +=s

Chane:


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or shi7ted.

Moent to Tri One Inch /MT13:

The oent necessar, to prod#ce

a chane in tri /CT3 o7 oneinch. Fo#nd #sin the Dra7t

Diara and F#nctions o7 For.

Tons Per Inch Iersion /TPI3:

The n#+er o7 Lon Tons added or

reo%ed necessar, to prod#ce a

chane in ean dra7t o7 one

inch. /in salt $ater3

LONGITUDINAL WEIGHT SHIFTS

;hen a $eiht is shi7ted lonit#dinall, /7ore 8n8 a7t3 the

net e77ect on a ship is siilar to a see


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0. Calc#late the chane in 7or$ard dra7t /∆dF;D3:

The + or - sign depends on he !o"#ion o$ L%F& I$

L%F is #$ o$ M' (se )+) #nd i$ L%F is $or*#rd o$

M' (se )-)&

4. Calc#late the chane in a7t dra7t /∆dAFT3:

NOTE I$ he *eigh *#s shi$ed $or*#rd, d FWD *i!! e

posii.e #nd d AFT *i!! e neg#i.e& I$ he *eigh *#s

shi$ed #$, d AFT *i!! e posii.e #nd d FWD *i!! e

neg#i.e&

E/#0p!e 'ro!e0

The FO; #st copleted a trans7er o7 )@"" allons o7 diesel7#el /diesel G 0!! allons=LT3. The 7#el is no$ located 10@

FT 7or$ard o7 its oriinal position. Prior to trans7er2 the

ships dra7ts $ere 1)’5" 7$d and 1B’0" a7t. Desin Dra is ".

L&P is 4@" FT2 MT1"G?!@ FT


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0. Calc#late the chane in tri:

4. Calc#late the chane in 7or$ard dra7t:

@. Calc#late the chane in a7t dra7t:

NOTE Sin"e he *eigh *#s shi$ed $or*#rd, he dr#$ "h#nge

# he o* is posii.e, #nd # he sern is neg#i.e&

). Deterine the ne$ dra7ts and tri:

For$ard A7t Tri

Oriinal: 1)85.""" 1B80.""" )."" +=s

Chane: 1.?0" < 1.4B" 0.0" +=+

Final: 1)81".?0 1B81.@0 !.B" +=s

LONGITUDINAL WEIGHT ADDITIONS AND

REMO1ALS


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This step o7 o%in the $eiht to its act#al location is

identical to a $eiht shi7t pro+le. Aain2 to deterine the

chane in the ships dra7ts d#e to tri:

1. Calc#late the Triin Moent /TM3:

!. Calc#late the Chane in Tri /CT3:

0. Calc#late the chane in 7or$ard dra7t /∆dF;D3:

The + or - sign depends on he !o"#ion o$ L%F& I$

L%F is #$ o$ M' (se )+) #nd i$ L%F is $or*#rd o$ M' (se )-)&

4. Calc#late the chane in a7t dra7t /∆dAFT3:


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NOTE I$ he *eigh *#s shi$ed $or*#rd, d FWD *i!! e

posii.e #nd d AFT *i!! e neg#i.e& I$ he *eigh *#s

shi$ed #$, d AFT *i!! e posii.e #nd d FWD *i!! e

neg#i.e&

The 7inal step is to calc#late the total chane in dra7t

7or$ard and dra7t a7t +, considerin +oth Parallel

Rise=Sinae and chane in tri:

E/#0p!e 'ro!e0

D#rin (ERTREP2 all 'P


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!. Deterine the Triin Ar /TA3:

0. Calc#late the Triin Moent /TM3:

4. Calc#late the Chane in Tri /CT3:

@. Calc#late the chane in dra7t 7or$ard d#e to tri /∆dF;D3:

). Calc#late the chane in dra7t a7t d#e to tri /∆dAFT3:

Sin"e *eigh *#s re0o.ed #$, his is # $or*#rd ri00ing

0o0en& The $or*#rd dr#$ *i!! in"re#se #nd he sern dr#$

*i!! de"re#se&


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B. Calc#late the total chane in dra7t 7or$ard /∆DRAFTF;D3:

?. Calc#late the total chane in dra7t a7t /∆DRAFTAFT3:

5. Calc#late the 7inal dra7ts and ships tri:

F;D Dra7t AFT Dra7t Tri

Oriinal: 14’ 6.00" 15’ 0.00" 1’0.00" +, the +o$

Change: +3.25" -5.72" 8.97" +, the +o$

New: 14’ 9.25" 14’ 6.28" 1’8.97" +, the +o$

EFFE%T OF TRIM ON STABILITY

The Dra7t Diara F#nctions o7 For and Cross C#r%es o7

Sta+ilit, are prepared 7or ships +ased on the desin

condition: No Tri0 . For ost s#r7ace ships2 so lon as tri

does not +ecoe e>cessi%e /ore than 1J o7 the lenth3 these

c#r%es are still applica+le.

RULES OF THUMB FOR TRIM

1. Ma>i# accepta+le Tri is 1J L&P

!. Follo$ Li9#id Loadin Instr#ctions


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0. ;atch 7or Hoin and Sain Stresses

'LUNGING

De$iniion ;hen the Triin Moent e>ceeds the

Lonit#dinal Rihtin Moent2 and the ship sins +, the +o$

or the stern.

Loss o7 ships +, pl#nin occ#rs ore o7ten in the erchant

or a#>iliar, t,pe ship than in the co+atant t,pe2 altho#h

soe destro,ers ha%e +een lost in this anner. Merchant

ships ha%e #ch larer copartents2 and the 7loodin o7

these copartents at the +o$ or stern tris the shiphea%il,.

TRIM %AL%ULATION SHEET

It is o7ten desira+le to consider the e77ects o7 se%eral

$eihts at once $hen cop#tin dra7t chanes. The Tri

Calc#lation Sheet is a ta+#lar 7or #sed to calc#late the

net triin oent created +, se%eral $eiht o%eents.

DIRE%TIONS FOR USE

1. In col#ns 1 and !2 descri+e the $eiht2 tan

n#+er2 7looded copartent2 etc. and deterine

the $eiht /Lon Tons3 o7 each o+ect.

!. S# total the $eihts in col#n ! to calc#late

the net $eiht addition or reo%al.

0. In col#n 02 deterine the Triin Ar /TA32

the distance 7ro the center o7 ra%it, o7 the

$eiht to the ships LCF.

4. In either col#n 4 or @2 calc#late the Triin

Moent +, #ltipl,in each $eiht +, its Triin


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Ar. A $eiht chane ca#sin the +o$ to sin lo$er

in the $ater is a 7or$ard triin oent2 a

$eiht chane ca#sin the stern to sin lo$er in

the $ater is an a7t triin oent.

@. S# total the 7or$ard triin oents and a7t

triin oents in col#ns 4 and @. Tae the

di77erence +et$een these totals as the NET

Triin Moent /$ill either +e 7or$ard or a7t

+ased on the reater col#n total.3

). Calc#late Parallel Rise or Parallel Sinae

/PR=PS3. Di%ide the net $eiht addition=reo%al +,

Tons per Inch Iersion /TPI2 7o#nd #sin Dra7t

Diara and F#nctions o7 For and ORIINAL

DISPLACEMENT.3

B. Calc#late the Chane in Tri /CT3. Di%ide the

net triin oent +, the Moent to Chane Tri

+, 1" /MT1"2 7o#nd #sin Dra7t Diara and

F#nctions o7 For and FINAL DISPLACEMENT.3

?. Calc#late the chane in dra7t 7or$ard d#e to

tri /∆dF;D3 and chane in dra7t a7t d#e to tri

/∆dAFT3 #sin the e9#ations. I7 the net triin

oent $as 7or$ard2 ∆dF;D is positi%e and ∆dAFT is

neati%e. I7 the net triin oent is a7t2 ∆dAFT

is positi%e and ∆dF;D is neati%e.

5. Fill in the +o> in the lo$er riht corner +,

appl,in all chanes to the oriinal conditions.

E/#0p!e 'ro!e0 USS STE'HEN W& GRO1ES 2FFG

345

Oriinal Dra7ts: F$d: 1@8"" A7t: 1@80" L&P G 4"? FT

1. !"" LT is added !" FT 7or$ard o7 MP

!. !" LT is reo%ed ?" FT 7or$ard o7 MP


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0. @" LT is reo%ed 0" FT a7t o7 MP

4. 4" LT is shi7ted 7or$ard !" FT

4.trim n draft

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