What is the reduction in metacentric height due to free surface when a tank 60 feet long and 30 feet wide is partially filled with salt water, and is fitted with a centerline bulkhead? (The vessel has a displacement of 10,000 tons.)

Correct Answer: Option A — 0.1 foot

The free surface effect of slack liquid in tanks creates a virtual rise in the vessel's center of gravity ($GG' = i / \nabla$), reducing the transverse metacentric height ($GM$) and impairing righting arm ($GZ$) energy.