Below is a list of the common information that is communicated by recreational boaters using an air horn. The signals must be audible for at least one-half mile.

Note:

  • A short blast = one second.
  • A prolonged blast = 4–6 seconds.

Changing Direction:

  • 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.” or “I am backing up.”

Restricted Visibility:

  • 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 vessels.

Warning:

  • 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.

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