IALA buoyage

The IALA Maritime Buoyage System (Recommendation R1001) is the set of rules used all over the world to mark channels and dangers. In the figure you can see the six types of mark: lateral, cardinal, isolated danger, safe water, special and emergency wreck marking, which warns of a new danger. Each mark is recognised by its colour, its shape, its topmark (the figure on top) and, at night, the colour and rhythm of its light.

The world is divided into two Regions, A and B, but only the lateral marks differ: the other five types are the same everywhere. A mark gives information; it does not decide for you. Responsibility for navigation stays with the skipper, who must also check the chart.

The two steps of the figure show the same harbour entrance in the two Regions. Region A covers Europe, Africa, Australia, New Zealand, the Gulf and some countries in Asia; Region B covers the Americas (North, Central and South), Japan, South Korea and the Philippines. The shapes do not change: in both Regions the can is to port and the cone to starboard, and only the colours are swapped.

To know which side is “port” you need the conventional direction of buoyage. As a rule it is the direction of someone arriving from seaward into a harbour, river or estuary; otherwise it is set by the competent authority, in principle clockwise around the land. If the marks are numbered, the numbering follows the same direction.

Where a channel divides, a modified lateral mark shows which branch is the main one. In the first step of the figure, in Region A, the preferred channel to starboard is a red buoy with a broad green band, can-shaped, with a red light; the preferred channel to port is green with a red band, cone-shaped, with a green light. In Region B the colours are reversed.

In every case the light is composite group flashing, Fl(2+1): two flashes, a pause, one flash, in the colour of the buoy's body. This rhythm is reserved for these marks. They are modified lateral marks: the red buoy with a green band in Region A behaves like a port-hand mark, so it is left to port, and shows that the main channel continues to starboard of it; the green buoy with a red band does the opposite.

A cardinal mark shows where the water is safest in relation to a point of interest, and which side to pass: the safe water lies north of a North mark, east of an East mark, south of a South mark and west of a West mark. In the figure the four quadrants around the point are bounded by the true bearings NW-NE, NE-SE, SE-SW and SW-NW (the dashed lines).

Cardinal marks always have yellow and black bands, are nearly always pillar or spar, and carry a black double-cone topmark. Their lights are white and quick flashing. The name tells you on which side of the danger the mark stands, and therefore on which side you pass it.

The lights of cardinal marks are white and quick flashing: “very quick” (VQ, 100 or 120 flashes a minute) or “quick” (Q, 50 or 60 a minute). The number of flashes is remembered with the clock face: 3 for East, 6 for South, 9 for West; North flashes continuously. The long flash of the South mark, of at least 2 seconds, stops the 6 flashes being confused with 3 or 9.

The figure shows the VQ version observed for 10 seconds. The full periods are: North VQ or Q continuous; East VQ(3) every 5 s or Q(3) every 10 s; South VQ(6) plus a long flash every 10 s or Q(6) plus a long flash every 15 s; West VQ(9) every 10 s or Q(9) every 15 s.

The “character” of a light is its rhythm. Fl (flashing) is a flash, with the dark longer than the light; Q is quick flashing, 50 or 60 flashes a minute; VQ is very quick flashing, 100 or 120 a minute; LFl is a long flash, a light of at least 2 seconds. Iso (isophase) has light and dark of equal length; Oc (occulting) has the light on for longer than the dark.

In the figure each row is a light observed for 10 seconds. Morse “A” is a dot and a dash ( ● – ). Fl(2) is two flashes then a pause, and is the light of the isolated danger mark; Fl(2+1) is two flashes, a pause and one flash, reserved for the preferred channel. Iso, Oc, LFl and Morse “A” are the lights of safe water marks; the new danger mark alternates blue and yellow.