What signal indicates that a vessel is altering course to port or intends to leave another vessel to starboard?

The correct signal indicating that a vessel is altering course to port or intends to leave another vessel to starboard is three short blasts. This is defined within the COLREGs as a maneuvering signal to communicate intentions clearly to other nearby vessels. The use of three short blasts specifically conveys that the vessel is making a turn to port.

In maritime navigation, effective communication between vessels is crucial for safety and to avoid collisions. The signaling system established by the COLREGs helps ensure that vessels understand each other's maneuvers. The other signals referenced (such as one long blast, one short blast, and two short blasts) indicate different intentions or maneuvers, but they do not correspond to altering course to port or leaving another vessel to starboard. Therefore, recognizing and understanding the specific context for each sound signal is vital for safe navigation.