What signal should a vessel intend to overtake to port use?

When a vessel is intending to overtake another vessel to port, the correct signaling maneuver involves using two prolonged blasts followed by two short blasts. This sound signal is designed to communicate the vessel's intent clearly, ensuring safety by notifying other vessels of the planned maneuver.

The protocol for using sound signals is outlined in the COLREGs to prevent misunderstandings at sea. A vessel accorded the obligation to maintain course while overtaking must appropriately signal its intentions to avoid any potential collisions. In this context, the two prolonged blasts followed by two short blasts succinctly convey the message that the overtaking vessel is moving to its port side.

The other options represent different intentions or actions. For instance, one prolonged blast generally indicates that the vessel is going to alter its course to starboard, which is not applicable here. Five short blasts typically signal danger or a need for caution, while one short blast is often used to indicate a turn to starboard. None of these options align with the specific intention of overtaking to port, making the chosen signal the only appropriate one for this scenario.