What is the effect of a reduction in a vessel's GM on stability measures?

A reduction in a vessel's GM, or metacentric height, leads to a decrease in the vessel's overall stability measures. GM is a critical factor in determining a ship's ability to right itself after being tilted by external forces, such as wind or waves. When GM decreases, the vessel's righting arm becomes less effective, which directly impacts several stability measures.

Specifically, the righting moment – the force that tends to bring the vessel back to an upright position – will decrease as GM reduces. This change can lead to a lower angle of heel at which the righting moment is maximized, thereby reducing the vessel's overall stability. In contrast, the angle of deck edge immersion, which is concerned with the danger of water entering the ship through openings on the deck, may remain unchanged depending on the specific design of the vessel.

The overall impact of reduced GM can result in decreased static stability, which is the vessel's ability to remain upright when at rest, and dynamic stability, which relates to the vessel's behavior when in motion and responding to external forces. Hence, while angles such as the maximum righting arm and the angle of heel at which maximum stability occurs diminish, the angle of deck edge immersion does not inherently change due to