In periods of reduced visibility or whenever a vessel operator needs to signal his or her intentions or position, a sound-producing device is essential. The navigation rules for meeting head-on, crossing, and overtaking situations are examples of when sound signals are required.
The following requirements apply to vessels operating on Missouri state waters.
- Vessels that are 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 to vessels operating 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.