How does partial flooding of a single ship compartment, with free communication to the sea, affect the free surface effect?

Partial flooding of a single ship compartment, with free communication to the sea, indeed decreases the free surface effect. The free surface effect refers to the tendency of liquid in partially filled tanks to shift and create a dynamic load when a ship rolls or pitches.

When the compartment is only partially flooded, the liquid can slide from side to side as the ship moves, which can cause a shifting center of gravity, leading to a reduction in stability. However, when there’s free communication to the sea, any water that shifts in the compartment can flow out to the open sea, reducing the volume of water acting contrary to the ship's stability. As a result, the re-distribution of weight is less extreme because the water is able to leave, thus mitigating the free surface effect and leading to an overall decrease in instability.

This understanding is crucial for ensuring the safety and stability of the ship during operations, as excessive free surface effect can lead to dangerous tilting or rolling, especially in rough seas.