What is the significance of one long blast on a ship's whistle for vessels under 100 meters?

The significance of one long blast on a ship's whistle, especially for vessels under 100 meters, is that it alerts other vessels in conditions of restricted visibility. This sound signal is an important part of maritime communication, particularly when visibility is compromised due to fog, rain, or darkness. It serves as a warning to other vessels that a ship is present and navigating in the vicinity, emphasizing the need for cautious navigation.

In restricted visibility situations, sound signals become critical as they help maintain awareness and prevent collisions. By making a long blast, a vessel communicates its presence to others who may not be able to see it clearly. This is in alignment with the International Regulations for Preventing Collisions at Sea (COLREGs), which establish standardized sound signals for various scenarios at sea to ensure safety.