IALA System of Buoyage

(IALA is the International Association of Lighthouse Authorities)

Buoys and beacons are used for the purpose of marking points of interest to the mariner. Beacons are fixed structures, driven into the sea bed or standing on concrete footings in shallow water. Buoys are floating chambers of various shapes, anchored to the seabed where it is too deep for a fixed structure.

There are several methods of constructing and mooring navigation buoys. The one sketched below is commonly found around the Australian coast. At low tide the anchor chain is lying at random around the dump. From this we can see that it would be inadvisable to anchor near a buoy because the vessel’s anchor might foul the mooring, and also because the buoy might become obscured from view of other vessels. It is normally illegal to tie up to buoys used in the IALA system.

The position of a buoy as marked on a chart (or listed in other publications) is only correct if the dump has landed in the exact position and remained there without subsequently moving.

It is possible for buoys to be dragged off location by a very significant distance. As well, the tide causes the buoy to swing in a large circle on the surface.

The radius of this circle is known as the “excursion radius” and even if the dump is located precisely, the position of the buoy varies according to the excursion radius, which in turn depends on the depth of water and length of chain and strength of tide. A very strong tide can even drag a buoy below the surface. 

                     
                       Buoy arrangement