inclining experiment
TRANSCRIPT
Inclining Experiment (MAR Rev. 03/01/01)
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INCLINING EXPERIMENTPurposeTo determine the KG of the ship in the light displacement condition.It is essential that it is performed and calculated as accurately as possible because the light KG will be the basis of all subsequent stability calculations.
MethodIf a weight is shifted athwartships on a ship, G will move off the centre-line to G1 causing a list.
wd M
GG1
B1
B
K
GG1 = w × d W
Inclining Experiment (MAR Rev. 03/01/01)
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wd M
GG1
B1
B
If a plumb line is suspended at O such that it crosses a batten at X, then as the ship lists a deflection XY will occur and can be measured.
O
XY
Triangles MGG1 and OXY are similar.
K
Inclining Experiment (MAR Rev. 03/01/01)
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GG1
O
X
Y
M
In MGG1
Tan = OPP = GG1
ADJ GM
In OXY
Tan = OPP = XY ADJ OX
Therefore: GG1 = XY GM OX
and:GG1 = Deflection (m) GM Pendulum length (m)
or: GM = Pendulum length × GG1
Deflection
KG as inclined = KM - GM
where KM is taken from the ship’s hydrostatic particulars for the appropriate True Mean Draught and water density.
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Precautions prior to conducting the experiment
1. Ship to be upright (no list).
2. Moorings slack and gangway landed.
3. No significant wind, especially on the beam.
4. No significant tide.
5. Derricks, cranes etc. secured in normal sea-going position.
6. Minimise free surfaces, tanks ideally should be full or empty.
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Precautions to ensure accuracy of the calculation1. Ship’s displacement to be determined accurately:
(a) Draughts to be read forward, aft and amidships on both sides;
(b) End draughts to be corrected to the forward and aft perpendiculars;
(c) Determine the true mean draught (draught at the LCF);(d) Allowance to be made for any hog/sag of the ship;(e) Density of dock water measured forward, aft and
amidships on both sides and mean density determined;(f) Establish ship’s actual displacement and KM from
hydrostatic particulars accounting for errors due to trim (Hydrostatic data normally calculated for the even keel condition).
2. Two or more pendulums should be used to obtain a mean deflection value.
3. Pendulum to be as long as possible and plumb weight suspended in hydraulic oil to dampen movement.
4. Several successive movements of inclining weights to port and starboard done to provide a number of deflection readings to give a more dependable ‘mean’ deflection value.
5. List to be restricted to a ‘small’ angle to ensure that:
Tan = GG1
GM
remains valid.
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SAQAn inclining experiment is performed on a ship in the following condition:Displacement 12200 t, including 40 t of inclining weights at Kg 16.2 m; KM 13.24 m.
Successive movements of 20 t of weights through a distance of 15 m to port and starboard cause the following deflections of two pendulums each 14 m in length:
Pendulum 1 Pendulum 2Movement to port 30.6 cm 30.2 cmMovement to stbd 29.8 cm 30.0 cm
The following must be accounted for to put the ship in the completed light displacement condition:
(a) Inclining weights to be discharged;(b) 26 t of equipment, Kg 10.4 m, to be discharged;(c) 48 t of contractor’s machinery, Kg 24.0 m, to be
discharged;(d) 16 t of ER machinery to be fitted, Kg 6.0 m;(e) Labour force on board (40 men), Kg 18.0 m (allow 75 Kg
per person).
Calculate the ship’s light KG and displacement.
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Answer
Enter data
KM = 13.24Deflections (cm) w = 20
30.60 d = 1530.20 W = 1220029.8030.00 Using GGh = w x d
Total 120.60 WMean (cms) 30.15 cm GGh = 0.02459 metresMean (m) 0.3015 m
Pendulum length (m) 14.00
Calculate GM as inclined using GM = GGh x lengthdeflection
GM = 1.142 metres
Calculate KG as inclined using KG = KM - GM
KG = 12.098 metres
Take moments about the keel to obtain light KG and displacement
Item w Kg momentsShip as inclined 12200 12.098 147597.7Inclining weights -40 16.200 -648
Equipment -26 10.400 -270.4Machinery -48 24.000 -1152
ER machinery 16 6.000 96Labour -3 18.000 -54
LIGHT DISPL/KG 12099 12.032 145569.3