What does a sound signal of one prolonged followed by two short blasts indicate for a vessel seining or trawling?

A sound signal consisting of one prolonged blast followed by two short blasts is specifically used to indicate that a vessel engaged in fishing—such as seining or trawling—has gear that is fast on an obstruction. This communication is crucial for alerting nearby vessels to the situation, thereby ensuring that they can navigate safely around the fishing operation.

In the context of COLREGs, this signal serves as a safety measure not only for the fishing vessel but also for others in close proximity. By clearly signaling this condition, the crew on the fishing vessel can prevent potential collisions or other hazardous encounters, providing essential information about their operational state.