On a vessel of 7000 tons displacement, a tank 35 ft. long, 30 ft. wide and 4 ft. deep is half filled with fuel oil (S.G. 0.962) while the vessel is floating in saltwater (S.G. 1.026). What is the free surface constant for this tank?

Correct Answer: Option A — 2,109

Free surface constant is calculated using tank length, cubed breadth, and the specific gravity ratio between the fuel oil (0.962) and saltwater (1.026). For a 35x30 ft tank, this formula correctly produces 2,109.