What is an aid to navigation (ATON)?
BUOY
floating, may shift
BEACON
fixed to the bottom or shore
An aid to navigation (ATON) is any device external to your vessel—a buoy, beacon, light, or sound signal—established to help you determine position, follow a safe course, or stay clear of dangers. Buoys float; beacons are fixed to the bottom or the shore.
Related terms
How it works
The two big families differ in how much you can trust their position. Buoys float on moorings: they swing, can be dragged off station by ice, storms, or collisions, and their charted position is approximate. Beacons—from simple daybeacons on piles to lighted structures and lighthouses—are permanently fixed, so they stand where the chart says they do.
Individually, marks carry meaning through colour, shape, topmark, and light rhythm: lateral marks show the sides of a channel, cardinal marks point to safe water, and isolated-danger, safe-water, and special marks each have their own grammar. Lateral colours depend on your IALA region—region B (the Americas) keeps red on the right when returning from sea, region A reverses the colours.
One system, two IALA regions
Until the 1970s, dozens of national buoyage systems coexisted, with fatal ambiguities. The International Association of Lighthouse Authorities (IALA) consolidated them into two regions: region A, used in Europe, Africa, Australia, and most of Asia, and region B, used in the Americas, Japan, Korea, and the Philippines. Only the lateral colours swap between regions—cardinal and other marks are the same everywhere.
On the water
- Returning from sea in IALA region B, the red nun buoys stay on your starboard side—red right returning.
- A daybeacon on a pile stands exactly where charted; the buoy down-channel may be watching slightly off station.
- At night, the rhythm charted beside a mark—Fl(2) 10s—tells you which aid you are actually looking at.
Common mistake
Never treat a buoy as a fixed point—it swings on its mooring and can be off station—and never tie up to one: mooring to an aid to navigation is prohibited. Navigate with the chart and every other available means, not by buoy-hopping alone.
Remember it
Buoys BOB; beacons DON’T.