In 1979, a body called International Association of Lighthouse Authorities (IALA) was formed to unify the World's buoyagesystem. They were largely successful, except we now have two similar systems, IALA 'A' and IALA 'B'.

The areas that use the 'B' system, are North and South America, Japan and the Philippines. The remainder of the World uses the 'A' system. We will concentrate on the 'A' system first, then look at the differences in the 'B' system.

The IALA systems are made up of five types of buoys, lateral cardinal, safe water, isolated danger and special.

In addition to the marks used in the IALA system, you will encounter navigation marks that do not follow this pattern. These will include: Lighthouses, Lightships, LANBYs (Large Automatic Navigation Buoys, generally replacing lightships), Light-floats (like a small light ship), Sectored lights and Leading lights.

Due to the change in the charts and practical almanac being used for RYA courses I am in the process of re-writing all the examples and questions. For those people who have the old charts (Chart 1 and 2 and PNT follow the Archive link where they exist to access the old questions. The charts referred to here are being changed to the RYA Training Almanac Northern Hemisphere and Practice Charts 3 and 4. These are the charts used for the Day Skipper and Coastal Skipper/Yacht master theory courses, unfortunately at present I only plan to create examples for the northern hemisphere version of these charts.

A lateral buoy, lateral post or lateral mark, as defined by the International Association of Lighthouse Authorities, is aseamark used in maritime pilotage to indicate the edge of achannel.Each mark indicates the edge of the safe water channel in terms of port (left-hand) or starboard (right-hand). These directions are relative to the direction of buoyage; this is usually a nominally upstream direction. In a river, the direction of buoyage is towards the river's source; in a harbour, the direction of buoyage is into the harbour from the sea. Where there may be doubt, it will be labelled on the appropriate chart. Often the cardinal mark system is used instead, when confusion about the direction would be common.

the main channel should:

keep port marks to its port (left) side, andkeep starboard marks to its starboard (right) side

Region Acomprises nations in Europe, Australia, New Zealand, parts

of Africa and most of Asia other than the Philippines, Japan and Korea.

port marks are red and may have a red flashing light of any rhythm.

starboard marks are green and may have a green flashing light of any rhythm.

(Port) (Left) (Red) (Starboard) (Right) (Green)

Region B comprises nations in North America, Central America and South America, the Philippines, Japan and Korea.

port marks are green and may have a green flashing light of any rhythm.

starboard marks are red and may have a red flashing light of any rhythm.

(Port) (Left) (Green) (Starboard) (Right) (Red)

A cardinal mark is a sea mark (a buoy or other floating or fixed structure) used in maritime pilot age to indicate the position of a hazard and the direction of safe water.Cardinal marks indicate the direction of safety as a cardinal (compass) direction (north, east, south or west) relative to the mark. This makes them meaningful regardless of the direction or position of the approaching vessel, in contrast to the (perhaps better-known) lateral mark system.The characteristics and meanings of cardinal marks are as defined by the International Association of Lighthouse Authorities.

A cardinal mark indicates one of the four compass directions by:

the direction of its two conical top-marks, which can both point up, indicating north; down, indicating south; towards each other, indicating west; or away from each other, indicating east

its distinctive pattern of black and yellow stripes, which follows the orientation of the cones - the black stripe is in the position pointed to by the cones (e.g. at the top for a north cardinal, in the middle for a west cardinal)

optionally, its distinctive sequence of flashing light, which consists of a sequence of quick or very quick flashes whose number gives the clockface position which corresponds to the direction of the cardinal (e.g. three for an east cardinal, nine for a west; north has continuous flashes, and south may be augmented with a long flash, to help distinguish it from a west in difficult conditions)

A cardinal mark may be used to accomplish the following:

Indicate that the deepest water is an area on the named side of the mark

Indicate the safe side on which to pass a danger

Draw attention to a feature in a channel, such as a bend, junction, branch, or end of a shoal

Draw attention to a new danger such as a grounded ship. In such cases two equal marks are often placed together to indicate that it's a newly marked danger and is not yet printed in official charts.

Isolated danger marks are placed on, or moored above, an isolated danger of minimal area below the water around the mark. The water around the mark is safe to navigate. The colors are red and black horizontal stripes and the mark is, when practicable, also fitted with a black top mark of two vertically aligned spheres.

Isolated danger marks are not always positioned centrally over a danger so to be safe do not pass too close to the mark.

If the mark is lit, the light will be white showing a group of two flashes. Two white flashes of light = two spheres.

The safe water mark is the only one with vertical stripes.

The stripes are red and white and it will also have a red sphere as the top-mark.

They indicate that water is safe for navigation all around the mark.

They may be used to mark fairway approaches or forks in a chanel.

When fitted with a light it is usually white however it may be isophase, occulting (rhythmic flashes of equal length where the period of light is longer than the dark) or flashing the Morse code letter "A".(dot dash).

A Special mark indicating an outfall pipe in the Irish Sea off Helen's Bay,Northern Ireland. It has the flashing sequence Fl.(2).Y meaning it flashes yellow twice, this is called group flashing. A Special Mark, as defined by the International Association of Lighthouse Authorities, is aseamark used in maritime pilotage. It is recognisableby its yellow colour and X, (often referred to as a St. Andrews Cross) top-mark. It has a distinctive sequence of various flashes that does not match any other navigational mark flashes in its vicinity.