What direct, negative effect does a large, partially filled tank of liquid have on a ship's stability?

A large, partially filled tank of liquid has a direct, negative effect on a ship's stability primarily through a phenomenon called the free surface effect. Ship stability is its inherent ability to return to an upright position after being tilted or heeled by external forces. When a ship heels, which is its rotational movement about its longitudinal axis, the liquid in a partially filled tank does not remain stationary. Instead, it flows or sloshes to the lower side of the tank, seeking to maintain a level surface parallel to the waterline. This movement of liquid within the tank creates an internal heeling mome....