IALA Buoyage Explained: Cardinal & Lateral Marks
Buoys are the road signs of the sea. This guide makes the IALA system stick — the lateral marks that edge a channel, the four cardinal marks and how to remember them at a glance, and the special marks for dangers and safe water.
The two IALA regions
The IALA Maritime Buoyage System divides the world into two regions. The only difference between them is the colour of the lateral marks:
- Region A — most of the world: Europe, Africa, most of Asia, Australia and New Zealand. Port = red, starboard = green.
- Region B — the Americas, Japan, South Korea and the Philippines. Colours reversed: starboard = red, hence "red right returning".
Everything else — cardinal, isolated danger, safe water and special marks — is identical in both regions.
Lateral marks
Lateral marks show the edges of a channel. Which side is which is defined by the direction of buoyage — generally the direction you travel when approaching a harbour from seaward (and marked on the chart with a magenta arrow where it isn't obvious).
| Region A (e.g. Europe) | Region B (e.g. Americas) | |
|---|---|---|
| Port hand | Red, can (cylinder) shape, red light | Green, can shape, green light |
| Starboard hand | Green, conical shape, green light | Red, conical shape, red light |
In Region A, keep red cans to port and green cones to starboard when entering from seaward; reverse it on the way out. Preferred-channel (junction) marks add a horizontal band of the other colour to show which way the main channel runs.
Cardinal marks
A cardinal mark is placed in relation to a danger and named by the compass quadrant of safe water. They are yellow and black, carry two black cones as a top mark, and show white quick-flashing or very-quick-flashing lights.
| Cardinal | Colours (top→bottom) | Top mark (cones) | White light | Meaning |
|---|---|---|---|---|
| North | Black over yellow | Both point up ▲▲ | VQ or Q | Safe water is to the north — pass to the north |
| East | Black-yellow-black | Base to base ▲▼ | VQ(3) or Q(3) | Pass to the east |
| South | Yellow over black | Both point down ▼▼ | VQ(6)+LFl or Q(6)+LFl | Pass to the south |
| West | Yellow-black-yellow | Point to point ▼▲ | VQ(9) or Q(9) | Pass to the west |
How to remember the cardinals
Two tricks turn the cardinals from memory work into something you read instantly:
- The top-mark cones point the way. North: both cones point up (and black is on top). South: both point down (black on the bottom). East: cones point apart, base to base — like an Egg. West: cones point together, point to point — like a Wineglass.
- The lights are a clock face. East flashes 3, South flashes 6 (plus a long flash so you don't confuse it with West in a tideway), West flashes 9. North is continuous (12 o'clock).
Isolated danger, safe water and special marks
- Isolated danger mark — black with red horizontal band(s), top mark of two black spheres, light Fl(2) white. Marks a small danger with navigable water all round; keep clear of the mark.
- Safe water mark — red and white vertical stripes, single red sphere top mark, white light (isophase, occulting, one long flash every 10s, or Morse "A"). Mid-channel or landfall; safe water all around.
- Special mark — yellow, often an "X" (St Andrew's cross) top mark, yellow light. Marks a special area — cables, spoil grounds, military or recreation zones — not primarily a navigational hazard.
- Emergency wreck marking buoy — blue and yellow vertical stripes, yellow cross top mark, alternating blue/yellow light. A temporary mark for a newly discovered wreck.
Frequently asked questions
What is the difference between IALA Region A and Region B?
Only the lateral-mark colours. Region A (Europe, Africa, most of Asia, Australia/NZ): port red, starboard green. Region B (Americas, Japan, South Korea, Philippines): reversed — starboard red ("red right returning"). All other marks are the same in both.
How do cardinal marks work?
They tell you which side the safe, deep water is by compass quadrant. A North cardinal means keep to the north; East means keep to the east, and so on. They're yellow and black with two black cone top marks and distinctive white flashing lights.
How do you remember the cardinal marks?
Use the cones: North both up, South both down, East base-to-base (egg), West point-to-point (wineglass). For lights, think of a clock: East 3 flashes, South 6, West 9, North continuous.
What does an isolated danger mark look like?
Black with red horizontal band(s) and a top mark of two black spheres; light Fl(2) white. It marks an isolated danger with navigable water all around, so keep clear of the mark itself.
Related reading
- Understanding Tides — depth, chart datum and the Rule of Twelfths
- Free sailing video lessons — buoyage, chartwork, COLREG and more
- COLREG Rule 23 — vessel lights — reading lights at night
- Maritime glossary — navigation and COLREG terms
Practise reading the seaway
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