Angle of Vanishing Stability (AVS)

The maximum angle of heel at which a vessel can recover to an upright position without capsizing.

The Angle of Vanishing Stability (AVS) is a critical measure of a vessel’s seaworthiness and stability, particularly in rough seas. It refers to the point at which a vessel, when heeled over by wind, waves, or other forces, reaches a tipping point where it can no longer right itself. Up to this angle, the vessel’s design and hull shape allow it to return to an upright position due to the righting moment created by the interplay of buoyancy and gravity. Beyond this angle, however, the vessel’s stability diminishes rapidly, and it becomes increasingly likely to capsize.

The AVS is influenced by several factors, including the vessel’s hull shape, weight distribution, and the centre of gravity. A higher AVS indicates a more stable vessel that can withstand greater angles of heel before becoming unstable. For example, many modern sailing yachts are designed with an AVS of around 120 to 140 degrees, meaning they can heel over significantly before the risk of capsizing becomes critical. 

However, it is important to note that while a high AVS is desirable, it is not the sole determinant of a vessel’s overall safety. Other factors, such as the vessel’s dynamic stability, handling characteristics, and the experience of the crew, also play vital roles in ensuring safe operation at sea.