Sound producing devices have become a bit antiquated since so many boats now carry VHF radios and communicate verbally rather than through sound. However, there are sounds that the recreational boater needs to be aware of, especially when their boating environment includes commercial vessels, which always seem to transmit their intentions with sound. There are two sound signals or blasts used on the water: one short blast which lasts about one second, and one prolonged blast which lasts from four to six seconds.
Most relevant of all sounds is the danger signal. Five or more short horn blasts in a row indicate danger. If you hear them, respond immediately by finding the source of the hazard. If you become aware of an immediate peril, you must initiate the five blast signal to warn other boaters of the danger.
Sound signals can become confusing when explained in minute details. When studying for my captain’s license, I was somewhat overwhelmed by the inland rules and the international rules, and who was conveying what. On a practical level, I figured out that the first vessel to sound one short blast is going to move to his right or starboard, and the first vessel to sound two short blasts is going to move to his left or port.
At the Boating Safety Class, the Instructor will elaborate with many more details on the rules that guide sound producing devices.