While underway in fog, a prolonged blast from another vessel indicates what?

A prolonged blast from another vessel while underway in fog signifies that the vessel is actively making way. This sound signal is part of navigation rules designed to enhance safety in reduced visibility conditions. When a vessel makes a prolonged blast, it is communicating its presence to others nearby, indicating that it is moving through the water.

This is crucial for preventing collisions, as all operators must be vigilant in foggy conditions when visual cues are significantly impaired. The sound serves as a warning for other vessels to be aware that they are in proximity to a moving craft, prompting them to navigate with care. This awareness is particularly important as vessels at anchor, adrift, or being towed do not typically signal with a prolonged blast, which helps clarify their status in such conditions. Hence, recognizing this sound as indicative of a vessel making way is essential for maintaining safety on the water.