What signal indicates a vessel's agreement to being overtaken in a narrow channel?

The indication that a vessel agrees to being overtaken in a narrow channel is signaled by one prolonged, one short, one prolonged, and one short blast. This combination of sound signals is specifically prescribed under the International Regulations for Preventing Collisions at Sea (COLREGs) to ensure clear communication between vessels operating in close quarters, particularly in narrow channels where navigation can be challenging.

The prolonged blast indicates the intention to pass, while the subsequent short blasts serve to clarify the agreement and safe intention to proceed with overtaking maneuvers. This sequence effectively communicates to other vessels that the overtaking vessel has their consent to proceed, thereby promoting safety and preventing misunderstandings in such critical navigational situations. It is tailored to avoid confusion in high-traffic areas where ensuring that all vessels are aware of each other's intentions is essential.

In contrast, the other choices are typically used for different situations. For example, five short blasts signal danger or uncertainty about another vessel's intentions, and a prolonged blast is a general warning signal intended for other vessels to be aware of the navigating vessel's presence. Two short blasts indicate a specific maneuver, typically used to signify intent to overtake on the starboard side. Each sound signal has a unique purpose within the COLREG