(a) State why cargo ships must have a collision bulkhead. (6)

(b) A bilge holding tank of 5m length, 3m width and 1.8m depth has water of density 1.020 t/m3 upto a sounding of 1.3m and oil of density 0.86 t/m3 is floating on top of water upto an ullage of 0.3m. Calculate the mass of water and oil in the tank. (10)