What is the purpose of sounding a prolonged blast?

Sounding a prolonged blast serves primarily to communicate a vessel's presence to others in the vicinity, especially in conditions of reduced visibility such as fog or heavy rain. The International Regulations for Preventing Collisions at Sea (COLREGs) outline the use of sound signals to enhance safety on the water. A prolonged blast, which typically lasts for about four to six seconds, signals the vessel's approach and can help others determine the direction from which it is coming.

When in these conditions, it is crucial for vessels to notify each other of their location to prevent collisions and ensure safe navigation. Thus, the purpose of a prolonged blast is fundamentally to alert other vessels to the approaching ship's presence, making it a key safety measure in maritime communication.