15. (a) Define TPC and explain its use on ships. (b) Explain clearly why TPC changes with each draft in a conventional merchant ship. (8) (c) A vessel moves from salt water of density 1025 kg/m3 to river water at 1012 kg/m3 If the displacement remains constant at 12250 t and the TPC in salt water is 27.65, calculate the mean bodily sinkage after the ves- (9) sel has moved into the river water.