What condition indicates that a vessel is unstable?

The condition that indicates a vessel is unstable is when the height of the metacenter is less than the center of gravity. In naval architecture, stability is fundamentally linked to the relative positions of the metacenter and the center of gravity. The metacenter is a point where the buoyant force is applied when a vessel is tilted, and it plays a crucial role in determining a vessel's stability. When the metacenter is below the center of gravity, the righting arm—the force that restores a vessel to an upright position—becomes negative, which leads to instability and a tendency to capsize.

The center of buoyancy, which is the center of the underwater volume of the vessel, being below the center of gravity does not directly indicate instability. Instead, it suggests that the vessel may have sufficient buoyancy but does not account for the overall stability unless paired with the metacenter position. An excessive draft can indicate a heavy load or something amiss but does not solely determine the stability of the vessel. Similarly, an uneven load can contribute to a vessel's list or trim but does not inherently define stability. The critical factor remains the relationship between the metacenter and the center of gravity.