Question

A lifeboat, when fully laden, displaces 7.2 tonnes. Its dimensions are 7.5 m  2.5 m  1 m, and its block coefficient 0.6. Find the percentage of its volume under water when floating in fresh water.

Answer 1

C_b=0.6=(displacement volume)/(rectangular block volume of equivalent dimensions).

Displacement=7.2t. This is the mass of water displaced which can be converted to a volume assuming the density of fresh water=1 tonne/m³, volume=7.2m³. The displacement volume is subject to the block coefficient C_b. 

The lifeboat volume=7.5×2.5×1=18.75m³. The ratio of the displacement volume to the volume of the lifeboat would be 7.2:18.75 or 7.2/18.75=0.384, 38.4%, before applying C_b.

If C_b is applied to the displacement volume, then the latter=0.6×7.2=4.32m³, which is 4.32/18.75=0.2304 or 23.04% of the volume of the lifeboat. This percentage is 0.6 of 38.4%. I'm not sure if this is what you want.