Sound signals must be audible for at least one-half mile. Some common sound signals that you should be familiar with as a recreational boater are as follows.
- A short blast lasts one second.
- A prolonged blast lasts 4–6 seconds.
- One short blast tells other boaters, “I intend to pass you on my left (port) side.”
- Two short blasts tell other boaters, “I intend to pass you on my right (starboard) side.”
- Three short blasts tell other boaters, “I am operating astern propulsion.” For some vessels, this tells other boaters, “I am backing up.”
- One prolonged blast at intervals of not more than two minutes is the signal used by power-driven vessels when underway.
- One prolonged blast plus two short blasts at intervals of not more than two minutes is the signal used by sailing boats.
- One prolonged blast is a warning signal (for example, used when coming around a blind bend or exiting a slip).
- Five (or more) short, rapid blasts signal danger or signal that you do not understand or that you disagree with the other boater’s intentions.