On a vessel of 6500 tons displacement, a tank 30 ft. long, 32 ft. wide and 18 ft. deep is half filled with liquid cargo (S.G. 1.048) while the vessel is floating in saltwater (S.G. 1.026). What is the free surface constant for this tank?

Correct Answer: Option C — 2390

Free surface constant accounts for tank geometry and fluid density relative to saltwater (S.G. 1.048 / 1.026). For a 30 ft long by 32 ft wide tank, applying (L x B^3 / 12) * (SG_oil / SG_water) results in 2390.