Types of Sound Signaling Equipment

Boats used for recreational purposes are required to carry sound-producing devices. Most boating accidents occur as a result of collisions with other vessels. Boaters can avoid collisions by using sound-signaling equipment to communicate their intentions to other watercraft.

A sound signal is required under certain circumstances under the US Coast Guard Navigation Rules, including when a meeting or crossing occurs or when an overtaking occurs.

Below is a list of the sound-producing devices required for each type of vessel:

If the vessel is under 12 meters (39.4 feet), an effective sound-producing device, such as an air horn or whistle, should be installed, and a light signal should also be provided.

image of whistle and air horn

A bell is required for vessels greater than 12 meters (39.4 feet) in length, in addition to an air horn or whistle.

image showing bell, whistle, and air horn

NOTE: The use of sound-producing devices is not allowed on the water except for communicating navigational intention or alerting nearby vessels.

The following table shows basic sound signals used on the water to communicate navigational intention:

Sound SignalMeaning
One short blast“I am altering my course to port (left).”
Two short blasts“I am altering my course to starboard (right).”
Three short blasts“I am operating astern propulsion (moving backward).”
Five short blasts“I am unsure of your intentions or believe we are on a collision course.”
One prolonged blast every two minutes“I am a power-driven vessel underway but not making way (e.g., drifting).”
One prolonged blast followed by two short blasts every two minutes“I am a vessel being towed.”
One prolonged blast at intervals of not more than two minutes“I am a power-driven vessel underway.”
One prolonged, one short, one prolonged, one short blast in that order“I am a vessel restricted in my ability to maneuver (e.g., laying cable, dredging, surveying, etc.).”

The illustrations below show examples of calls and responses between two vessels. Give-Way vessel signals first, Stand-On vessel responds to confirm understanding):

chart showing how to pass

charts showing how to pass from the starboard and port

chart showing give-way and stand-on vessel



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