Question 79Safety & Environmental - 1st Asst/Chief

The correct answer is C) a portion of liquid is removed from a full tank. The presence of free surface effect in a partially filled tank on a vessel can have adverse effects on the vessel's stability. When a tank is not completely full, the liquid inside the tank can shift and move, changing the center of gravity of the vessel and potentially leading to an unstable condition. This free surface effect is most pronounced when a portion of the liquid is removed from a full tank, as the remaining liquid will be able to move more freely, causing the vessel's stability to be compromised. The other answer choices are incorrect because they do not directly relate to the adverse effects of free surface. Decreasing the vessel's draft (A) or increasing the wetted surface area (B) may affect stability, but do not specifically address the free surface issue. Trimming the vessel by the stern (D) is a separate stability consideration not directly related to free surface effects.