inclining experiment

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


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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


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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

inclining experiment

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