What is the signal for a vessel less than 100 meters in length in restricted visibility?

The signal for a vessel less than 100 meters in length operating in restricted visibility is established by international maritime regulations to ensure safe navigation and to communicate a vessel's presence to others in the vicinity. In this case, the correct signal is one long blast on the ship's whistle.

This long blast, lasting about four to six seconds, serves as a warning to other vessels that a less than 100-meter vessel is in the area. This is crucial in conditions of limited visibility, such as fog or heavy rain, where vessels may not be able to see each other clearly. The long blast is a standardized signal indicating to nearby vessels the presence of the sounding vessel, which is particularly important for preventing collisions.

In restricted visibility, sound signals are critical for maintaining safety at sea, and the one long blast is recognized internationally as a key component of maritime signaling conventions.