Table of Contents

Download the PDF Version

It's the Law

Sound-Producing Devices


The following requirements apply to vessels operating on Missouri state waters.

  • Vessels more than 16 feet but less than 40 feet in length are required to carry on board a whistle or horn to make an efficient sound to signal intentions or positions.
  • Vessels that are 40 feet or more in length are required to carry on board a whistle or horn and a bell.

The following requirements apply under federal laws on federally controlled waters.

  • Vessels less than 39.4 feet (12 meters) in length, which includes PWC, must have some way of making an efficient sound signal. Examples are a handheld air horn, an athletic whistle, an installed horn, etc. A human voice is not acceptable.
  • Vessels that are 39.4 feet (12 meters) or more in length must have a sound-producing device that can produce an efficient sound signal. The sound signal should be audible for one-half mile and should last for 4 to 6 seconds.

Sound Signals

Sound producing devices

Some common sound signals that you should be familiar with as a recreational boater are as follows.

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 sailboats under sail.

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.