Safe Boat Operations – General Characteristics of Short-Range Aids to Navigation (AtoN)

Source: Mariners Learning System, By Capt. Bob Figular

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

Solid red AtoN buoys and beacons bear even numbers and all solid green AtoN bear odd numbers. No other AtoN are numbered. When proceeding from seaward toward the direction of conventional navigation, the numbers increase. Numbers are kept in approximate sequence on both sides of the channel. Letters may be used to augment numbers when lateral AtoN are added to channels with previously completed numerical sequences. For instance, a buoy added between R”4″ and R”6″ in a channel would be numbered R”4A”. Letters will also increase in alphabetical order.

During daylight hours, the color of an AtoN indicates the port or starboard side of a channel, preferred channels, safe water, isolated dangers, and special features. Only red or green buoys, or beacons fitted with red or green dayboards, have lateral significance.

The shapes of buoys and beacons help identify them from a distance or at dawn or dusk, when the color may be hard to see. Like other characteristics of AtoN, mariners should not rely solely on shape to identify an aid.

Lights are installed on AtoN to provide signals to distinguish one navigation light from another, or from the general background of shore lights. AtoN with lateral significance display flashing, quick, occulting, or isophase light rhythms. AtoN with lateral significance display flashing, quick, occulting, or isophase light rhythms. Though there are white and yellow lights, only AtoN with green or red lights have lateral significance.

Sound signals can be identified by their tone and phase characteristics. Horns, sirens, whistles, bells, and gongs produce distinct sound signals. Unless it is specifically stated that a signal “Operates Continuously” or the signal is a bell, gong, or whistle, signals will only operate in fog, reduced visibility, or adverse weather.

Channel Junction or Bifurcation: Red and green, or green and red, horizontally banded buoys and beacons are called preferred-channel marks. They are used to indicate a channel junction or bifurcation (point where a channel divides or where two tributaries meet). They may also mark wrecks or obstructions and may be passed on either side.

Safe Water Marks: Are buoys with alternating red and white vertical stripes, and beacons with red and white vertically striped dayboards. They also mark a mid-channel, fairway, channel approach points and the “In” and “Out” channels of a “Traffic Separation Scheme.” If lighted, they will display a white light with the characteristic Morse Code “A”. Safe water buoys (lighted or not) should be fitted with a red sphere as a visually distinctive top mark. Safe water marks are not laterally significant.

Isolated Danger Marks: Black and red horizontally banded buoys are called “Isolated Danger Marks”. They are used to mark isolated dangers (wrecks or obstructions) that have navigable water all around. Isolated danger marks display a white light with a “group-flashing” characteristic; and are fitted with a visually distinctive topmark, consisting of two black spheres, one above the other.

Special Marks: Yellow buoys and beacons are called “special marks”. They mark anchorages, dredging/spoil areas, fishnet areas, and other special areas or features. When lighted, special marks will display a yellow light with a Fixed (“F”) or Flashing (“Fl”) characteristic. Special marks may also be used to mark the center of the traffic separation scheme.