What defines the actual range of stability for a vessel at sea?

The actual range of stability for a vessel at sea is defined by the angles through which the vessel can safely tilt or roll before capsizing or losing its upright position.

The angle of maximum list being at the deck edge refers to a condition where the vessel is inclined significantly, causing the deck to become submerged at the edge. However, this does not accurately represent the vessel's stability, as stability is concerned with the forces and moments acting on the ship as it rolls and how they contribute to restoring the vessel to an upright position.

Similarly, the angle of maximum roll being at the vanishing point pertains to the concept of the center of gravity and the metacenter, but it does not effectively determine the actual safety or stability of the vessel. The vanishing point is more related to visibility and perspective rather than a measure of stability.

A comprehensive understanding of stability involves concepts such as the metacentric height, the center of gravity, and the righting arm, which are essential in assessing how a vessel will behave in an array of sea conditions. Therefore, neither the angle of maximum list being at the deck edge nor the angle of maximum roll being at the vanishing point accurately describes the criteria that define a vessel's stability in a seaway.