What signal is used for a vessel that has stopped due to constraints?

A vessel that has stopped due to constraints typically uses one prolonged blast as a signal. This signal communicates the vessel's situation to other mariners, indicating that it is unable to proceed. The use of a prolonged blast serves to alert those nearby to the potential hazard, allowing them to navigate safely around the stationary vessel.

In the context of maritime signaling, one prolonged blast is a common sound signal recognized internationally to indicate a vessel's inability to maneuver or to convey important information about its operational status. This is particularly crucial in areas with high traffic where other vessels need to be aware of potential obstructions.

The other signaling options correspond to different maritime circumstances: one short blast indicates a turn to the starboard, two short blasts signal a turn to port, and three short blasts generally indicate that a vessel is backing up. Each of these signals serves a specific purpose and is used in different scenarios, distinguishing them from the situation of a vessel that has come to a stop due to constraints.