What characterizes the initial transverse metacentric height (GM) of a vessel?

The initial transverse metacentric height, often denoted as GM, is defined as the vertical distance between the center of gravity (G) and the metacenter (M) of a vessel. This measurement is crucial because it directly relates to the vessel's stability in a transverse direction. A higher GM indicates greater stability, as the center of gravity is farther from the metacenter, which results in a stronger righting moment when the vessel is tilted or heeled.

Understanding GM is essential for ensuring that a vessel remains upright and stable under various conditions, such as changes in cargo load or external forces like wind and waves. This aspect of stability management is critical in naval architecture and maritime operations, guiding decisions about safe loading and cargo distribution.

The other options discuss various aspects of naval architecture but do not accurately describe the concept of GM. The distance from the keel to the waterline pertains to the vessel's draft, while the horizontal distance between the center of buoyancy and center of gravity relates to stability but does not define GM. The angle of heel at which a vessel becomes unstable is a concept associated with the limits of stability but does not denote the initial transverse metacentric height. Thus, the first choice is the most accurate characterization of GM.