What sound signal should a vessel use if it is stopped in restricted visibility?

A vessel that is stopped in restricted visibility should use one prolonged blast at intervals to signal its presence to other nearby vessels. This sound signal is essential for ensuring safety in situations where visibility is limited due to fog, rain, or other conditions.

The prolonged blast serves as a warning to others that the vessel is nearby, even if it cannot be seen. In addition, the use of sound signals like this helps to reduce the risk of collisions, as it alerts other vessels to navigate with caution in the area. The intervals between the blasts can vary, but it is important to maintain consistency in signaling to effectively communicate the vessel's presence.

Other sound signals serve different purposes, such as indicating specific maneuvers or intentions, but in the case of a vessel that is stopped, the prolonged blast is the appropriate choice for signaling in restricted visibility.