What occurs to the free surface effect when a compartment located below the waterline is completely flooded?

When a compartment located below the waterline is completely flooded, the free surface effect vanishes completely. The free surface effect refers to the impact that the liquid surface inside a tank or compartment has on the stability of a vessel. This effect is significant when the liquid can move freely within the tank, creating a shifting center of gravity that can adversely affect the vessel's stability.

When a compartment is flooded and the liquid reaches a level above the waterline, that liquid is in equilibrium with the surrounding water, which eliminates any free surface movement within that specific compartment. Consequently, there is no longer a shifting weight contribution from that compartment, which means the destabilizing influence of the free surface effect is mitigated entirely.

In contrast, if the flooding were only partial or if the compartment were above the waterline, the free surface effect could still impact stability, as the liquid would be able to move and shift, affecting the stability of the vessel. Thus, the complete flooding of a compartment below the waterline leads to the total elimination of the free surface effect within that compartment.