Why oil tankers have lesser freeboard than a general cargo ship?

Freeboard on Oil Tankers have less freeboard than General Cargo ships of

similar length for several reasons, six of them being:

1. Smaller deck openings in the Upper Deck.

2. Greater sub-division by transverse and longitudinal bulkheads.

3. Density of cargo oil is less than grain cargo.

4. Much larger and better pumping arrangements on tankers to control any

ingress of bilge water.

5. Permeability for an oil-filled tank is only about 5% compared to permeability

of a grain cargo hold of 60-65%. Hence ingress of water in a

bilged compartment will be much less.

6. Larger Transverse Metacentric Height (GMT) values for an Oil Tanker,

especially for modern wide shallow draft tanker designs.