In a narrow channel, what whistle signal does a vessel sound when trying to overtake another vessel on its port side?

In the context of navigating a narrow channel, a vessel that is attempting to overtake another vessel on its port side is required to use a specific whistle signal to communicate its intentions clearly. The correct signal in this scenario is two prolonged blasts followed by two short blasts.

The purpose of this signal is to ensure that the overtaking vessel is effectively informing the vessel being overtaken of its action. The two prolonged blasts indicate that the overtaking vessel intends to pass on the port side and signify a clear and intentional maneuver. The additional two short blasts serve to reinforce the communication, ensuring that the other vessel understands the intent and can respond accordingly.

This whistle signal is established under the International Regulations for Preventing Collisions at Sea (COLREGs) and is designed to promote safety and understanding in scenarios where visibility may be limited, and the movements of vessels are critical. By adhering to these signals, vessels can maintain a safe distance and avoid collisions, which is especially important in the confined conditions of a narrow channel.