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Bilging and permeability 211
The vertical component of the shift of the centre of buoyancy (B to B1) is due to the increase in the mean draft. KB1 is equal to half of the new draft. The horizontal component of the shift of the centre of buoyancy (B1B2) is equal to X/2.
A trimming moment of W B1B2 by the head is produced and the vessel will trim about the centre of ¯otation (F), which is the centre of gravity of
the new water-plane area.
B1B2 w d
or but
W W B1B2 w d
W B1B2 Trimming moment, ; w d Trimming moment
It can therefore be seen that the effect on trim is similar to that which would be produced if a mass equal to the lost buoyancy were loaded in the bilged compartment.
Note. When calculating the TPC, MCTC, etc., it must be remembered that the information is required for the vessel in the bilged condition, using draft d2 and intact length l2.
Example 6
A box-shaped vessel 75 metres long 10 metres wide 6 metres deep is ¯oating in salt water on an even keel at a draft of 4.5 metres. Find the new drafts if a forward compartment 5 metres long is bilged.
(a) First let the vessel sink bodily.
Fig. 21.4
w x B d 1:025tonnes 1
5 10 4:5 1:025 w 230:63 tonnes
TPC WPA L2 B
97:56 70 10
97:56 TPC 7:175
97:56