What does three short blasts signify?

Three short blasts of a vessel's whistle are used to signal that the vessel is operating astern propulsion, meaning it is moving backward. This sound signal is part of the International Regulations for Preventing Collisions at Sea (COLREGS), which help maintain safety and avoid misunderstandings between vessels navigating close to one another.

In this context, operating astern is an important maneuver, especially in crowded or narrow waterways. It clearly communicates to other vessels that your boat is moving in reverse, allowing them to take appropriate action to avoid a collision. This signaling system is crucial for safe navigation, as it helps ensure that all nearby vessels are aware of each other's intentions and maneuvers.

The other options represent different signals that are not associated with three short blasts. For instance, going full speed ahead would typically be indicated by one long blast, while changing course to starboard uses two short blasts. Anchoring does not have a specific sound signal, as the process is usually more visual and depends on the context of other vessels nearby.