IALA Buoyage Regions A and B: what actually changes

Sailors crossing between Europe and the Americas meet one of the great quirks of marine navigation: the buoys swap sides. Or more precisely, the colours do.

The one change that matters

The IALA Maritime Buoyage System divides the world into two regions. Region A covers Europe, Africa, Australasia and most of Asia. Region B covers the Americas, Japan, South Korea and the Philippines.

The difference between them affects lateral marks only - the buoys that mark the sides of a channel:

• Region A: port-hand marks are red (can shapes), starboard-hand marks are green (cones). Entering from seaward, you keep red to port.
• Region B: the colours swap. Port-hand marks are green, starboard-hand marks are red - the famous "red right returning".

The shapes keep their meaning in both regions: can to port, cone to starboard when entering from seaward. If you learn the shapes as your primary cue, the colour swap loses most of its sting.

What does not change

Everything else is identical in both regions:

• Cardinal marks - yellow and black, topmarks of two cones, indicating where the safe water lies relative to the mark
• Isolated danger marks - black with red bands, two black spheres
• Safe water marks - red and white vertical stripes, single red sphere
• Special marks - yellow, optional yellow X topmark

That is worth repeating, because it is a favourite exam question: a west cardinal mark looks exactly the same in the Solent as it does in Chesapeake Bay.

Keeping it straight

Two habits help. First, learn shapes before colours - they are constant worldwide. Second, drill recognition until it is instinct rather than recall. The IRPCS app's buoyage drill shows you photoreal marks from either region and scores your recognition, so the knowledge holds up at six knots with spray over the bow, not just at a desk.

FAQ

Which region does the UK use? Region A - red to port entering from seaward.

Does the direction of buoyage ever change locally? Yes. Around continuous coastlines and in some channels the conventional direction of buoyage is defined on the chart - always check the chart's buoyage arrows rather than assuming.

Are cardinal marks really identical in both regions? Yes. Only lateral marks (and preferred-channel marks, which follow their region's lateral colours) differ between A and B.