When your vessel is underway and you can see other vessels, you can use sound signals to let other vessels know your intended movements. For example, if you plan to alter course or are slowing down. These signals can help prevent collisions.
Powerboats and sailing boats must carry a sound signal device – such as an air horn, bell or whistle – as part of their safety equipment.
The signals can be in short or long blasts. A short blast is about 1 second and a long blast is 4 to 6 seconds.
You can accompany these sound signals with light signals.