What is the difference between metacentric height (GM) and center of gravity (CG)?

The distinction between metacentric height (GM) and the center of gravity (CG) is fundamental in understanding vessel stability. GM is a critical parameter that defines the stability of a vessel. It represents the vertical distance between the center of gravity (CG) and the metacenter (M), which is the point at which the buoyant force acts when the vessel is tilted. A larger GM indicates greater stability because it means that the center of gravity is relatively low compared to the metacenter, allowing the vessel to return to an upright position more readily after being heeled over.

On the other hand, the center of gravity (CG) is the point at which the weight of the vessel is effectively concentrated, and it is where the weight is considered to act vertically downward. If the CG is too high, it can lead to instability, as the vessel will be more prone to tipping over.

Understanding these concepts is critical for ensuring safe vessel operation and managing stability under various loading conditions. The performance and safety of a vessel greatly depend on the relationship between its CG and GM.