What is one long blast on a vessel?

One long blast on a vessel is a sound signal used in maritime communication, typically lasting about four to six seconds. It indicates the vessel's presence and is often used in situations where visibility is limited, such as in fog or heavy rain. This signal helps to communicate the vessel's location to other nearby vessels, promoting safety and navigation awareness. Additionally, it can serve specific purposes in certain maritime regulations, such as signaling intentions when maneuvering.