What is the reduction in metacentric height due to free surface when a tank 60 ft. wide and 60 ft. long is partially filled with saltwater? (The vessel's displacement is 10,000 tons.)

Correct Answer: Option B — 3.09 feet

Using the free surface equation FSC = (l × b³) / (12 × W), for a 60 ft by 60 ft square tank on a 10,000-ton vessel, the resulting upward virtual rise of the center of gravity decreases the metacentric height by exactly 3.09 feet.