What is the primary purpose of a cofferdam on board a ship?

(a) To act as an empty void space separating two compartments so that leakage from one cannot pass into the other

(b) To stiffen the hull girder against longitudinal bending stresses

(c) To provide extra ballast capacity for trim correction

(d) To provide additional reserve buoyancy in the event of hull damage

Briefly justify. (16)