You are called to the bridge at 0200. The OOW reports a cluster of buoys ahead as you approach an unfamiliar port on the US Eastern Seaboard. Your chart shows a red can to starboard and a green conical to port on the approach. The OOW, trained in Region A, is hesitant — should we leave the red to starboard? This is the moment your understanding of IALA regions earns its keep.
The Two Regions
IALA divides the world into two buoyage regions. The cardinal rule is that lateral marks reverse their colour and shape between regions.
- Region A — Europe, Africa, India, Australia, most of Asia, and surrounding waters. Red to port, green to starboard when entering from seaward.
- Region B — The Americas, Japan, South Korea, and the Philippines. Red to starboard, green to port when entering from seaward.
Your US Eastern Seaboard approach is Region B. The red buoy should be left to starboard — the OOW's instinct was correct for the wrong reason; you must be the one who confirms it with authority.
Lateral Marks — Shape and Light
| Region A (Port) | Region A (Starboard) | Region B (Port) | Region B (Starboard) | |
|---|---|---|---|---|
| Colour | Red | Green | Green | Red |
| Shape | Can/flat | Conical/spar | Can/flat | Conical/nun |
| Light | Red (any rhythm) | Green (any rhythm) | Green (any rhythm) | Red (any rhythm) |
Note: light rhythm does not change between regions for lateral marks — colour is the critical variable.
Cardinal, Isolated Danger, Safe Water and Special Marks
These are identical in both regions — they are not lateral and carry no entering-from-seaward convention. Cardinals (N/S/E/W, yellow/black, Q or VQ flashing) indicate safe water relative to the mark. Safe water marks (red/white vertical stripes, Morse A or isophase) indicate navigable water all around. Isolated danger marks (black/red horizontal bands, Fl(2)) indicate a hazard with navigable water all around it. Special marks (yellow, X topmark, yellow light) delineate areas rather than navigable channels.
Command Decision
As master you must:
- Positively identify which IALA region you are operating in — check the chart, the pilot book, or Admiralty List of Lights. Never assume.
- Brief the OOW explicitly at handover when entering a different region from the vessel's home waters.
- Cross-reference buoy colour with chart symbol and light characteristics — do not rely on shape or colour alone in reduced visibility.
A region mismatch is a classic grounding scenario. The examiner will probe whether you understand the reason for the convention, not just which side to pass.