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Official Massachusetts Boating Handbook

Boating Basics: On the Water

U.S. Aids to Navigation System (ATON)

Buoys and markers are the “traffic signals” that guide vessel operators safely along some waterways. They also identify dangerous or controlled areas and give directions and information. As a recreational vessel operator you will need to know the lateral navigation markers and non-lateral markers of the U.S. Aids to Navigation System.

Lateral Markers

These navigation aids are used to mark the edges of safe water areas; for example, to direct travel within a channel. They use a combination of colors and numbers that may be applied to buoys or permanently placed markers.

Illustrations
What the Markers Mean
Red buoy with light and number
Red colors, red lights, and even numbers indicate the right side of the channel as a boater enters from the open sea or heads upstream.
Green buoy with number
Green colors, green lights and odd numbers indicate the left side of the channel as a boater proceeds from the open sea or heads upstream.
Buoy with green stripe on top, red below, and light on top
Red and green colors and/or lights indicate the preferred (primary) channel. If green is on top, the preferred channel is to the right; if red is on top, the preferred channel is to the left.
Green buoy with light on top
Lighted Buoys use the lateral marker shapes, colors and numbers discussed above; in addition, they have a matching colored light.
Red cone shaped "nun" buoy
Nuns are cone-shaped buoys marked with red colors and even numbers.
Green cylindrical-shaped "can" buoy
Cans are cylindrical-shaped buoys marked with green colors and odd numbers.
Red triangle daymark with even number, green square daymark with odd number
Daymarks are permanently placed signs attached to structures such as posts in the water. Common daymarks are red triangles (equivalent to nuns) and green squares (equivalent to cans) and may also be lighted.

Red Right Returning is a reminder of the correct course when returning from open waters or heading upstream.

Boat entering channel: red buoy on starboard, green on port
Boat entering open water: red buoy on port, green on starboard
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Online boating safety handbook last modified: April 22, 2008
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