What may occur if a vessel is running in a trough?

When a vessel is running in a trough, it is positioned between two waves, which can significantly affect its stability and handling. The correct outcome associated with this scenario is broaching. Broaching occurs when a vessel turns sideways to the waves, which can happen easily when there are significant wave actions, such as when trailing down the face of a wave or when in a trough.

In this position, the force of the waves can cause the vessel to rotate uncontrollably, potentially leading to a loss of control. This is particularly dangerous because as the vessel is broached, it can expose a larger surface area to the waves, increasing the likelihood of capsizing or swamping if not managed properly.

The other possibilities, such as swamping, capsizing, or rolling, are related but describe different scenarios of instability. Swamping involves waves breaking over the sides of the vessel, capsizing refers to the vessel overturning completely, and rolling describes the side-to-side motion that can occur due to wave action. However, in the specific context of running in a trough, broaching is the most critical concern due to the angle and force exerted upon the vessel.