Section 3: Inclining Test Flashcards
What are the 2 parameters for ship stability?
COG - The centre of gravity is measured from the keel of the ship. You will often be required to find the new position of ‘G’ when cargo is moved. The distance from the centre of gravity (G) to the keel (K) is denoted by KG.
COB - As the location of COB is based on the shape of the underwater of the ship, it can be easily provided to the vessel by the builder/naval architect.
What is the COB for box-shaped vessels and for ship-shaped vessels?
(i) Half the draft from the keel for box-shaped vessels.
(ii) About 0.42 to 0.45 of the draft measured from the water line to keel for ship-shaped vessels.
The difference is due to the shape of the bilge keel.
How do you find the GM at the time of the experiment?
The vessel is made to incline by moving a known weight through a known distance across the deck of the vessel.
The inclination is measured by the movement of a plumb line across a specially constructed batten fixed horizontally in the bottom of a hold. About six such plumb lines are normally erected at different locations.
By measuring the angle of heel using the ship’s inclinometer, and knowing the weight moved and the distance moved horizontally we could find the GM at the time of experiment.
From this GM and the KM provided by naval architect for that draft, we can determine the light ship KG.
M.V. Sample is floating in salt water at a displacement of 30609 t. The vessel’s KG is 11.96 m. The following tanks are slack. Calculate the fluid GM of the vessel.
0.699 m
M.V. Sample is floating in salt water at a displacement of 10,170 t. The vessel’s KG is 13 m. The after peak is the only slack tank and is partially filled with salt water to a sounding of 3 m. The liquid surface at 3 m sounding is rectangular in shape, 16 m long and 7 m wide.
Calculate:
(a) The transverse inertia created by the liquid in the tank.
(b) Fluid GM.
457.333 m4
2.344 m
With reference to the inclining experiment:
(a) State its purpose.
(b) Describe the precautions to be taken before and during the experiment.
(c) When and under what circumstances should a vessel undergo such test?
(a) An inclining test is a test performed on a ship to determine its weight and center of gravity. One way of knowing the location of G in the empty condition is by knowing the material weights that the builder had used throughout the build and then finding the centre of all those weights.
The inclining experiment is the method used to calculate GM for lightship condition. The GM obtained by the test is subtracted from KM to obtain the inclined KG. (KG = KM - GM)
(b) (Intact stability code) The ship should be moored in a quiet, sheltered area free from extraneous forces such as propeller wash from passing ships, or sudden discharges from shore side pumps. The depth of water under the hull should be sufficient to ensure that the hull will be entirely free of the bottom.
(c) This test is usually carried out when the ship is at the completion stages of the building (light ship stage).
From the following results of an inclining test, calculate the KG of the vessel in the Lightship Condition, KM 7.9 m.
A weight of 20 t, already on board, is moved 12 m transversely across the deck. Length of plumb line 8 m and deflection 24 cm.
Present displacement 4200 t (assume that the 20t weight is a part of the lightship).
KG 5.995 m
A vessel, initially upright, is to carry out an Inclining Experiment and is in the following condition:
Displacement 3800 t; KM 4.80 m
Total weight on board:
Stores and sundries: 145 t KG 3.80 m.
Ballast: 385 t (tank is full) KG 2.80 m.
Bunkers: 123 t (tank is full) KG 3.25 m.
Water in the boiler to working level: 23 t (tank is slack) KG 3.10 m.
Free Surface Moment 85 tm.
Fresh water: 56 t (tank is slack) KG 2.56 m. Free surface moments 1560 tm.
Inclining weights 50 t KG 6.80 m.
Personnel: 0.25 t KG 4.80 m.
The plumb lines have an effective vertical length of 6.85 m.
The inclining weights are shifted 5.35 m transversely on each occasion and the mean horizontal deflection of the plumb lines is 0.65 m.
Calculate the KG of the ship in lightship condition.
KG 3.732 m
A vessel, initially upright, is to carry out an Inclining Experiment and is in the following condition:
Displacement 28500 t; KM 7.5 m
Total weight on board during the experiment:
Stores and sundries: 195 t; KG 4.03 m.
Ballast: 433 t (tank is full); KG 3.04 m.
Bunkers: 157 t (tank is full); KG 3.51 m.
Water in the boiler (to working level): 32 t (tank is slack); KG 3.27 m and Free surface moment 109 tm.
Fresh water: 88 t (tank is slack); KG 2.94 m, and Free surface moment 2335 tm.
Inclining weights 65 t KG 7.19 m.
A deck crane weight 23 t; KG 9.24 m is yet to be fitted to the vessel and form a part of her light displacement.
The plumb line effective length is 7.86 m.
The inclining weights are shifted 6.44 m horizontally on each occasion and the mean horizontal deflection is 0.71 m.
Calculate the vessel’s light displacement and lightship KG.
Displacement 27585 t
KG 7.381 m
A vessel at upright condition is to carry out an Inclining Experiment and is. The vessel’s details at the time of inclination are as follows.
Displacement 34000 t; KM 11.8 m
Total weight on board during the experiment:
Stores and sundries: 225 t; KG 7.03 m.
No 1 DB Ballast: 655 t (tank is slack); KG 2.25 m FSM 2300 t-m.
No 5 F/O Tank 325 t (tank is slack); KG 3.21 m FSM 2100 t-m.
Water in the boiler (to working level): 36 t (tank is slack); KG 5.85 m and Free surface moment 109 t-m.
Fresh water: 185 t (tank is slack); KG 7.94 m, and free surface moment 1225 t-m.
Inclining weights 72t; KG 10.5 m.
The ship’s radar mast of weight 50 t; KG 9 m is yet to be fitted to the vessel and forms a part of her light displacement.
The plumb line effective length is 10.2 m.
The inclining weights are shifted 7.45 m horizontally on each occasion and the mean horizontal deflection is 1.21 m.
Calculate the vessel’s light displacement and lightship KG.
Displacement 32588 t
KG 11.82 m
