What does SQUAT refer to in relation to vessel navigation?

SQUAT refers specifically to the effect experienced by a vessel as it moves through restricted or shallow waters, particularly in narrow channels. When a vessel is underway, its forward motion creates a change in water pressure, which leads to the stern of the vessel sinking more than it would in deeper water. This phenomenon can affect the vessel's draft and clearance under the keel, making it essential for navigators to be aware of this effect to prevent grounding or collisions.

Understanding SQUAT is crucial for safe navigation, especially in areas where the water is not deep enough to accommodate the vessel's draft comfortably. In contrast, the other options address different aspects of vessel operation and navigation, such as the overall weight a vessel carries, required distances for safe navigation, or vessel stability in adverse conditions, which do not directly pertain to the specific phenomenon of SQUAT.