What sound signal indicates that a vessel is backing up?

The sound signal that indicates a vessel is backing up is three short horn blasts. This specific sound signal is uniformly recognized in maritime communication to convey the intention of a vessel to reverse its direction. The use of three short blasts distinguishes it from other signals, ensuring clear communication among nearby vessels and helping to prevent collisions or misunderstandings about a vessel’s movements.

In contrast, other signals serve different purposes; for instance, a long blast is used to signal the intention to overtake, while a short blast indicates a right turn. Understanding these signals is crucial for safe navigation and compliance with maritime regulations.