Kuliah-8 TBK Stabilitas Memanjang
-
Upload
panji-wahyu-bimantoro -
Category
Documents
-
view
219 -
download
0
Transcript of Kuliah-8 TBK Stabilitas Memanjang
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 1/15
© Adi Wirawan Husodo2012
Kuliah-8 Teori Bangunan Kapal
Stabilitas Memanjang (TRIM)
Dosen : Adi Wirawan Husodo, ST, MT
1
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 2/15
© Adi Wirawan Husodo2012
• Trim is also known as ‘longitudinal stability’
• Trim is measured as the difference between the draft forward and
aft.
– If difference is zero ship is on even keel
– If forward draft is greater than aft draft trimming by bow
– If aft draft is greater than forward draft trimming by stern
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 3/15
© Adi Wirawan Husodo2012
• Consider a ship to be floating at rest still water and on an even keel(fig 15.1)
• Now let a weight w, already on board, be shifted aft through adistance d. The center of gravity of the ship will shift from G to G1,parallel to the shift of center of gravity of the weight shifted.
GG1= (w x d)/WW x GG1=w x d…….trimming moment
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 4/15
© Adi Wirawan Husodo2012
• When trimmed (fig 15.2), the wedgeof buoyancy LFL1 emerges andwedge WFW1 is immersed
• The volume of immersed wedge =the volume of emerged wedges
• F , the point which the ship trim, is
the center of gravity of water planearea (center of flotation or tippingcentre)
• ML (longitudinal metacentre) is thepoint of intersection betweenverticals through the longitudinal
positions of centre of buoyancy. Thevertical distance between the center of gravity and the longitudinalmetacentre is called longitudinal metacenrric height (GML)
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 5/15
© Adi Wirawan Husodo2012
Moment to change Trim one cm (MCT 1 cm)
• Moment required to change trim
by 1 cm
• MCT 1 cm = (W x GML)/100L
W : vessel’s displacement, ton
GML
: long. Metacentric height, m
L : Vessel’s length, m
• Fig 15.3 (a) ship in equilibrium
• Fig 15.3 (b) weight w is shifted
through d distance. The center of
gravity will shift from G to G1
• Causing the trimming moment of
W x GG1
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 6/15
© Adi Wirawan Husodo2012
Moment to change Trim one cm (MCT 1 cm)
• See fig 15.3 (c)
• The ship will trim to bring thecentre of gravity and buoyancy int
othe same vertical line the ship isagain in equilibrium
• The tipping centre (F) is l metrefrom aftGG1 = (w x d)/W = GML tan θ
tan θ =(w x d)/(W x GML)
tan θ = t/L…….fig 15.4.(b)
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 7/15
© Adi Wirawan Husodo2012
Moment to change Trim one cm (MCT 1 cm)
• Let the change of trim due to shifting is 1 cm
• Then w x d is the moment to change trim 1 cm
• tan θ= 1/100 L
But
• tan θ=(w x d)/(W x GML)
• tan θ= MCT 1 cm/(W x GML)
• MCT 1 cm/(W x GML) = 1/100 L
MCT 1 cm = (W x GML)/100 L
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 8/15
© Adi Wirawan Husodo2012
To find the change of draft due to change of
trim
• Trim will cause a change in the draft forward and draft aft. One will be
increased and one will decreased.
• A is a new draft aft, F is a new draft forward. Trim = A-F
• x is the change of draft aft, y is the change draft forward
• See the triangles WW1F1 and WW1C
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 9/15
© Adi Wirawan Husodo2012
To find the change of draft due to change of
trim
• Change of draft aft in cm
= (l /L) x Change of trim in cm – l = distance F from aft, m
– L = ship’s length, m
– x + y = t
• Change of draft F in cm = Change of trim – Changeof draft A
mL
cmx tmcmx
mLcmt
mcmx
l
l
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 10/15
© Adi Wirawan Husodo2012
The effect of shifting weight already on board
A ship 126 m long is floating at draft of 5.5 m F and 6.5 m A. The centre of flotation is 3 m aft of amidships. MCT 1 cm = 240 ton. m, displacement 6000 tons. Find the new drafts if a weight 120 ton already on board isshifted forward a distance of 45 m.
Trimming moment = w x d= 120 x 45
= 5400 ton m by the head
Change of trim = trimming moment/MCT 1 cm
= 5400/240
= 22.5 cm by the headChange of draft aft = (l /L) x Change of trim
= (60/126) x 22.5
= 10.7 cm
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 11/15
© Adi Wirawan Husodo2012
The effect of shifting weight already on board
Change of draft Forward = Change of trim – Change of draft Aft
= 22.5 – 10.7
= 11.8 cm
Original draft 6.500 m A 5.500 m F
Change due trim -0.107 m +0.118 m
New draft 6.393 m 5.618 m
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 12/15
© Adi Wirawan Husodo2012
The effect of loading and/or discharging weight
• When a weight is loaded at the centre of flotation it will produce no trimming
moment, but the ship’s draft will increase uniformly so that the ship displaces
an extra weight of water equal to the weight loaded. If the weight is now
shifted forward or aft away from the center of flotation, it will cause a change
of trim. cause both the bodily sinkage and a change of trim
• When a weight is being discharged, if the weight is first shifted to the centre of flotation it will produce a change of trim, and if it is then discharged from the
centre of flotation, the ship will rise bodily.
TPC = the mass which must be
loaded or discharged to change
the ship’s mean draft by 1 cm
(ton)
WPA = water plane area, m2
ton97.56
WPATPC
cmTPC
w riseor sinkageBodily
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 13/15
© Adi Wirawan Husodo2012
The effect of loading and/or discharging weight
A ship 90 m long is floating at drafts 4.5 m F and 5.0 m A. The centre of flotation is 1.5 m aft of amidships. TPC 10 tons. MCT 1 cm is 120 ton m.Find the new drafts if a total weight of 450 tons is loaded in a position14 m forward of amidships
Bodily sinkage = w/TPC Change of trim = trim moment/MCT 1
cm= 450/10 = (450 x 15.5)/120
= 45 cm = 58.12 cm by the head
Change of draft aft = (l /L) x Change of trim
= (43.5/90) x 58.12
= 28.09 cm
Change of draft Forward = Change of trim – Change of draft Aft
= 58.12 – 28.09
= 30.03 cm
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 14/15
© Adi Wirawan Husodo2012
The effect of loading and/or discharging weight
Original draft 5.000 m A 4.500 m F
Bodily sinkage + 0.450 m + 0.450 m
5.450 m 4.950 m
Change due trim - 0.281 m + 0.300 m
NEW DRAFT 5.169 m A 5.250 m F
7/28/2019 Kuliah-8 TBK Stabilitas Memanjang
http://slidepdf.com/reader/full/kuliah-8-tbk-stabilitas-memanjang 15/15
© Adi Wirawan Husodo2012
TERIMA KASIH
15