Free Surface Effect occurs under which condition?

• A. A compartment is partly filled and the liquid moves unimpeded from side to side as the ship rolls.
• B. A compartment is completely full and the liquid is immobilized.
• C. The hull is dry and sealed.
• D. All compartments are empty.

Answer: (A)

Free Surface Effect shows up when liquid in a partially filled compartment can move freely as the ship rolls. The liquid’s surface stays horizontal, so during a roll it shifts toward the lower side, redistributing weight and effectively lowering the metacentric height. That makes the vessel less stable and increases the tendency to roll. If the compartment were completely full, the liquid cannot move, so there’s no free surface effect. If the hull is dry or all compartments are empty, there’s no liquid to slosh. So the scenario where a compartment is partly filled and the liquid can move side to side as the ship rolls is the situation that produces Free Surface Effect.