What must an overtaking vessel indicate before attempting to pass in a narrow channel?

The overtaking vessel must indicate her intention by sounding the appropriate signal before attempting to pass in a narrow channel. This requirement is established in the COLREGs, specifically under Rule 34, which emphasizes the importance of communication between vessels to prevent collisions. The sound signal serves to alert the other vessel of the overtaking maneuver, providing critical information that promotes safety and awareness in the limited space of a narrow channel.

Using sound signals not only helps to clarify the overtaking situation but also fosters mutual understanding between vessels about the actions each intends to take. Adequate signaling is crucial in narrow channels where visibility and maneuverability may be restricted, allowing both vessels to navigate safely amidst the challenges posed by their environment.

The other options, while potentially relevant to communication at sea, do not align with the specific mandatory requirements established in the COLREGs for overtaking situations in a narrow channel. Thus, the requirement to sound an appropriate signal stands as the correct procedure for ensuring safe navigation.