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Safe Boat Operations – US Aids to Navigation System (AtoN)

Source: Mariners Learning System, by Captain Bob Figular
Edited by Frank Hudson, Jr. – USCG Auxiliary

In the U.S., the Coast Guard is responsible for servicing and maintaining AtoN under federal jurisdiction. This includes both short and long-range navigation systems found in the navigable waters, along the U.S. coast, Intracoastal Waterway (ICW) system, but only those AtoN that are owned by the US Coast Guard. Aids to Navigation that are owned by other Government agencies, commercial corporations, businesses, cities, counties, or individuals are considered private aids to navigation (PATONs) and are maintained by their respective owners, not the Coast Guard. The Coast Guard is responsible to ensure the owners maintain their PATONs to the correct standards. Both Federal and private AtoN make up the complete aids to navigation system.

Buoys, beacons, and other short-range AtoN are used the same way signs, lane separations, and traffic lights guide motor vehicle drivers. Together, these AtoN make up the short-range AtoN system, which uses charted reference marks to provide information for safely navigating waterways.

In the lateral system, buoys and beacons indicate the sides of the channel or route relative to a conventional direction of buoyage. They also mark junctions, a point where two channels meet when proceeding seaward; or bifurcations, the point where a channel divides when proceeding from seaward, or the place where two tributaries meet.

(Incidentally, the Coast Guard has changed the name of “beacons” to “marks”, such as in “day marks” for fixed aids to navigation.)

In U.S. waters, AtoN use the IALA-B system of lateral marks with few exceptions, arranged in geographic order known as the “conventional direction of buoyage”. Under this, the memory aid 3R rule of “red, right, returning” applies when a vessel is returning from seaward. This means, when returning from sea, keep red markers to the right of the vessel from:

  • North to south along the Atlantic Coast.
  • South to north and east to west along the Gulf Coast
  • South to north and east to west along the Pacific Coast.

Aids to navigation have many different characteristics. An aid’s color, size, light, or sound signifies what mariners should do when they see it.

The location and the intended use determine which one of the two types of AtoN will be placed in a spot or waterway:

  • Floating (buoy).
  • Fixed (beacon).

Extending for some 2,400 miles along the Atlantic and Gulf coasts of the U.S. is the Intracoastal Waterway (ICW) that is a largely sheltered waterway, suitable for year-round use. AtoN used to mark the ICW use the same coloring, numbering, and conventional direction of buoyage found in the U.S. AtoN System with the following additional characteristics:

  • Special markings consisting of yellow squares and triangles are used so that vessels may readily follow the ICW.
  • The yellow square shows that the aid should be kept on the left side when traveling north to south/east to west.
  • The yellow triangle shows that the aid should be kept on the right side when traveling north to south/east to west.

Non-lateral aids in the ICW, such as ranges and safe-water marks, are marked with a yellow horizontal band. Where the US AtoN System (IALA B) and Intracoastal Waterway coexist, the yellow triangle and square denote the ICW’s direction of travel, which may be counter to the color/shape of the aid marking the main waterway.

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