What must vessels indicate once the risk of collision exists?

When vessels are in a situation where the risk of collision exists, one of the critical responsibilities they have is to communicate their intended maneuvers to other vessels. Using sound signals is essential for this communication, as it helps ensure that both vessels are aware of each other's intentions, particularly in low visibility conditions where visual signals may not be effective.

The use of sound signals to indicate maneuvers, such as altering course or speed, promotes safety by helping to prevent misunderstandings that could lead to collisions. Proper signaling establishes clear intentions on the part of both vessels and helps in coordinating movements to avoid conflict.

Maintaining the current course or altering course without signals does not adequately communicate intentions and could lead to confusion among vessels. Speeding up can also lead to an increased risk of collision, as it reduces reaction time and may not convey a clear signal to other vessels. Therefore, indicating maneuvers using sound signals is the appropriate action when the risk of collision is present.