4.Trim n Draft
Transcript of 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