IALA A vs B Overview

IALA's maritime buoyage system groups marks by job. Lateral marks define the sides of a channel in the conventional direction of buoyage. Cardinal marks indicate the named compass side of a danger. Isolated-danger, safe-water, special and emergency-wreck marks each communicate a different relationship or purpose.

Colour alone is not a complete identification. Red and green matter within the lateral system, yellow can identify a special mark or form part of a cardinal pattern, and black can combine with yellow or red. Shape, topmark, light character, sequence and charted position provide the corroboration that a fleeting colour impression cannot.

Even a correctly named mark does not supply the whole route decision. Buoys can be missing, displaced, damaged or temporarily altered, and their charted positions may be approximate. Keep adequate distance, compare the mark with the current chart, depth, surrounding sequence and notices, and retain a safe alternative if the evidence does not agree.

The regional difference belongs to lateral marks. Region A assigns red to port-hand lateral marks and green to starboard-hand lateral marks in the direction of buoyage. Region B assigns green to port-hand marks and red to starboard-hand marks. Preferred-channel marks are also lateral marks, so their predominant red or green colours follow the regional lateral scheme.

The side meaning remains stable: a port-hand mark defines the port side and a starboard-hand mark defines the starboard side when proceeding in the conventional direction. The shapes also remain stable: a port-hand mark is can or cylindrical where shape is used, while a starboard-hand mark is conical. That second cue is especially valuable when colour is difficult to distinguish.

Cardinal, isolated-danger, safe-water, special and emergency-wreck families are not subject to the Region A/B red-green lateral reversal. Their shared IALA patterns still need chart and local context. National implementation, numbering and local direction conventions must be checked in current charts and publications rather than inferred from the region label alone.

Trinity House states that the buoys it deploys around England, Wales and the Channel Islands conform to IALA System A. In the conventional direction of buoyage, a Region A port-hand lateral mark is red and a starboard-hand lateral mark is green.

The Canadian Coast Guard describes Canada as Region B: starboard-hand lateral marks are red and port-hand lateral marks are green in the upstream direction of buoyage. This is the opposite colour assignment, not an opposite definition of port and starboard.

Use a full spoken translation instead of a free-floating colour mnemonic: region, conventional direction, side, colour, then safe action. A slogan such as ‘red right returning’ describes a Region B convention and is unsafe if imported into Region A without first identifying the region and direction.

The competent authority establishes the conventional direction for lateral buoyage and the current chart and publications show how it is applied locally. In many harbour and river approaches the general pattern is from seaward towards the harbour or upstream, but a remembered ‘inbound’ rule cannot resolve every junction, coastwise channel or locally defined waterway.

Direction of buoyage is a reference direction, not an instruction to steer a particular course. Your vessel may be crossing, leaving, turning through a bend or holding clear of traffic while the lateral marks keep the same charted identity. Tide direction, the direction the bow happens to point and compass north do not redefine them.

At a junction, confirm the main direction and identify whether a striped mark is a preferred-channel lateral mark before choosing a branch. The named preferred channel describes the branch relative to the mark in the conventional direction; it does not guarantee sufficient depth, clearance or suitability for your vessel.

In a straight Region A entrance followed in the conventional direction, the red port-hand mark bounds the port side and the green starboard-hand mark bounds the starboard side. If the boat later follows the exact reciprocal track outward, the same red port-hand mark is normally seen on the boat's starboard side and the same green starboard-hand mark on its port side.

Region B follows the same viewpoint logic with its regional colours. Inward, green port-hand lies to port and red starboard-hand lies to starboard. On the exact reciprocal outward track, the fixed green port-hand mark appears to starboard and the red starboard-hand mark appears to port.

This is a geometry aid, not an instruction to make every outbound passage a mirror image. Bends, junctions, crossing traffic, one-way directions, preferred channels, off-station aids and the actual safe-water geometry can defeat a cockpit-side mnemonic. Navigate the charted channel and circumstances, not a slogan.

Begin with family rather than a memorised action. Ask whether the pattern is lateral, cardinal, isolated danger, safe water, special or emergency wreck. Only a lateral candidate triggers the region-and-direction translation. A cardinal candidate instead uses its black-and-yellow pattern, paired cone topmarks and white-light rhythm to name a compass side of safe water.

Then corroborate the identity. Daylight shape and topmark can remain readable when paint is faded, while a distinctive light character can support the identification at night. The expected charted position and the order of neighbouring marks test whether those observed cues form the scene you planned for.

Finish with the action, not just the name. A north cardinal indicates safe water to the north of the mark, but the navigator must still check the charted danger, position, depth, traffic and whether the northern route is usable for this vessel. Recognition informs pilotage; it does not replace it.

The Canadian Coast Guard warns that aids may fail, be out of position or altered without immediate notice, and that charted buoy positions are approximate. The operational lesson applies more widely: never make a close-quarters route depend on one floating aid being exactly where or how you expect.

When the observed mark does not fit the planned picture, reduce the rate at which risk is developing. Slow, stop, hold, turn away or move to known safe water as the vessel and traffic allow. Preserve lookout and control before spending attention on a chart, display or publication search.

Cross-check an independently established position, depth and trend, charted hazards, the sequence of other aids, visual or radar cues, and current notices or warnings. If the discrepancy remains unexplained, do not chase the buoy or squeeze past its assumed side. Use the safe alternative and report the defect to the responsible authority once immediate navigation is under control.