What does a decreased GM indicate for a vessel's stability?

A decreased GM, or metacentric height, indicates that a vessel has less initial stability. GM is a critical factor in determining the stability of a ship; it measures the distance between the center of gravity (G) of the ship and the metacenter (M), the point about which the ship will rotate when tilted.

When GM is decreased, the righting arm (the lever that acts to return the ship to an upright position) is reduced, which means the ship is not as effective in recovering from heeling. This leads to a higher likelihood of the vessel capsizing, especially in rough seas or during sharp turns, where the forces acting on the ship can exceed the reduced righting lever. Consequently, a lower GM signifies an increased risk of capsizing due to diminished stability, making this choice the most accurate answer in regard to vessel stability.

Therefore, understanding the implications of GM on ship stability is vital for ensuring safety at sea and managing navigational risks effectively.