What does a negative GM value indicate for a vessel?

A negative GM value indicates that the metacenter is located below the center of gravity of the vessel. This configuration signifies that the vessel is in an unstable condition. When a ship is heeled (tilted) due to external forces like wind or waves, the center of gravity does not return to its original position after the force is removed; instead, the ship continues to lean further over. This phenomenon can lead to situations where the vessel may capsize, as it lacks the necessary stability to right itself. Therefore, a negative GM value directly correlates with potential instability and an increased risk of capsizing.