What does one long blast of a horn typically indicate?

One long blast of a horn is primarily recognized as a signal indicating the presence of a vessel and serves as a warning to other nearby ships to be cautious and maintain a safe distance. This action plays a critical role in maritime safety, helping to prevent collisions by alerting other vessels of a ship’s position and intentions.

The choice signaling for other vessels to acknowledge their presence aligns with the practice of using sound signals in situations where visibility may be limited or in busy waters, ensuring that all parties are aware of potential movements and actions. This communication is part of the navigational conventions outlined in maritime rules, promoting cooperative and safe encounters at sea.