SeaMemo
Channel markers and buoys explained: lateral marks, cardinal marks and IALA A or B
Channel markers and buoys show you where the safe water runs and where the dangers are. Lateral marks mark the sides of a channel: entering from sea in Europe and the Mediterranean (IALA Region A), keep red to port and green to starboard. In the USA and the rest of the Americas (Region B) it is the other way round. Cardinal marks are yellow and black and name the side with the deepest water: pass north of a north cardinal.
All the marks at a glance
Almost everywhere in the world, buoys follow the system set by IALA, the international association of lighthouse authorities. By day you identify a mark by colour, shape and topmark, at night by the colour and rhythm of its light.
| Mark | Looks like | Light | Meaning |
|---|---|---|---|
| Lateral mark | Region A: red can, green cone | red or green | sides of a channel |
| Cardinal mark | yellow and black, two black cones | white, quick flashing | deepest water on the named side |
| Isolated danger mark | black with red band, two black spheres | white, Fl(2) | small danger, navigable water all around |
| Safe water mark | red and white vertical stripes, red sphere | white, Iso, Oc, LFl or Mo(A) | navigable water all around |
| Special mark | yellow, yellow X | yellow | area or feature shown on the chart |
| Emergency wreck marking buoy | blue and yellow vertical stripes, yellow cross | alternating blue and yellow | new danger, possibly not yet charted |
Lateral marks: red and green channel markers
Lateral marks always follow the direction of buoyage. That is the direction you travel when approaching a harbour, river or estuary from seaward. Where this is not obvious, the authority sets it, in principle clockwise around land masses, and the chart shows it.
The shape stays the same in both regions, only the colour changes. If a mark is not itself a can or a cone, it should carry the matching topmark where practicable. Its light is the same colour as the mark. If marks are numbered, the count starts from seaward, usually with even numbers on red and odd numbers on green. Heading out to sea, everything flips. (Diagrams are simplified.)
Where a channel divides, a modified lateral mark shows the preferred route. It has the shape and main colour of a normal mark plus one broad band in the other colour, and its light flashes Fl(2+1). In Region A, a red mark with a green band means the preferred channel is to starboard. A green mark with a red band means it is to port.
Port is the left side of the boat when facing the bow, starboard the right. Memory aids and the sidelight colours are in our guide to port and starboard.
IALA Region A or B: where does which apply?
Only lateral marks differ. All other marks look the same worldwide.
| Region A | Region B | |
|---|---|---|
| Port, coming from sea | red | green |
| Starboard, coming from sea | green | red |
| Where | Europe including the Mediterranean, Africa, the Gulf, Australia, New Zealand, many Asian countries | North, Central and South America, Japan, South Korea, the Philippines |
So a charter in the Caribbean or Florida uses Region B, where "red right returning" is the rule of thumb. Bring that phrase to Croatia or Greece and it is wrong.
Cardinal marks: north, east, south, west
A cardinal mark tells you that the deepest water lies on the side it is named after. Pass north of a north mark, south of a south mark. They are always banded in yellow and black and carry two black cones.
| Mark | Colour | Cones | Light (white) | Pass |
|---|---|---|---|---|
| North | black over yellow | both up | VQ or Q, continuous | to the north |
| East | black, yellow, black | points away from each other | VQ(3) 5 s or Q(3) 10 s | to the east |
| South | yellow over black | both down | VQ(6)+LFl 10 s or Q(6)+LFl 15 s | to the south |
| West | yellow, black, yellow | points towards each other | VQ(9) 10 s or Q(9) 15 s | to the west |
Two memory aids come straight from the IALA booklet. The cones point at the black bands. And the light follows a clock face: 3 flashes for 3 o'clock in the east, 6 in the south, 9 in the west. The long flash on the south mark ensures you cannot mistake 6 for 3 or 9. A north mark only tells you it is safe to the north. Whether there is deep water east and west as well is on the chart.
Isolated danger, safe water, special marks and wrecks
These four marks are the same in both regions:
- Isolated danger mark: placed on or near a small danger with navigable water all around. How far to stay off is in the chart and pilot book, not on the buoy.
- Safe water mark: navigable water all around, for example mid channel or as a landfall mark. It does not mark a danger.
- Special mark: points to an area or feature described on the chart. Its light is always yellow.
- Emergency wreck marking buoy: blue and yellow stripes can mark a newly found danger that may not yet be charted. Check the latest notices to mariners.
Buoy lights at night: reading the light codes
The chart lists a code next to every lit mark. Count the flashes and compare them with the chart. These are the most useful abbreviations:
| Code | Meaning | Typical on |
|---|---|---|
| Q | quick flashing, 60 or 50 flashes a minute | cardinal marks |
| VQ | very quick flashing, 120 or 100 flashes a minute | cardinal marks |
| LFl | long flash, at least 2 seconds | south cardinal, safe water |
| Fl(2) | group of 2 flashes | isolated danger |
| Fl(2+1) | group of 2 flashes, then 1 | preferred channel |
| Iso | equal light and dark | safe water |
| Oc | light longer than dark, with short eclipses | safe water |
| Mo(A) | Morse A: short, long | safe water |
Buoys talk with color and shape, ships also talk with flags. You'll find the meaning of every signal flag in the guide nautical flags.
Using marks under way
- Plan before you leave. Check the region and the direction of buoyage on the chart and note the key marks on your route.
- Identify the mark. By day look at colour, shape and topmark. At night note the light colour and count the flashes, ideally with a stopwatch.
- Compare with the chart. Find exactly that mark on the chart or plotter, by name or number, and check your position.
- Choose your side. Lateral marks follow the direction of buoyage, so swap sides when heading out. Cardinal marks stay the same.
- Keep clear. Current and wind set you sideways, and floating marks can drift. Never pass close by, and never rely on a single mark.
Marks help at anchor too: a cardinal nearby warns of a shoal before you drop the anchor. If you sail at night on a mile building trip, learn the light codes first. Check the wind on the Beaufort scale as well, because marks are far harder to spot in waves. According to IALA, responsibility for safe navigation always stays with the mariner.
Who gives way in a channel, when a sailing boat must not impede large ships and what port tack and starboard tack mean is explained in our guide to COLREGs right of way.
Record every passage with SeaMemo
SeaMemo does not replace a chart or a plotter. It is your logbook: the app records route, sea miles, duration and speed of every leg by GPS, offline at sea. Keep notes such as a tricky harbour approach in the travel journal. What else belongs in there is in our guide on how to keep a sailing logbook.
Sources
- IALA: Maritime Buoyage System (PDF via Irish Lights): the official rules, memory aids, lights
- Trinity House: IALA Buoyage System: overview from the UK lighthouse authority
- IALA Region A vs Region B: regions and colours
- Wikipedia: Cardinal mark: overview
- Wikipedia: Lateral mark: overview
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Frequently asked questions
What is the difference between lateral and cardinal marks?
Lateral marks show the left and right edges of a channel and follow the direction of buoyage. Cardinal marks work with your compass: they tell you in which direction the deepest water lies, and they are often placed at shoals or wrecks.
Which side do I keep a red buoy on?
In Region A, including Europe and the Mediterranean, keep red to port when entering from sea. In Region B, including the USA, keep red to starboard when returning from sea. Leaving harbour reverses both.
How do I remember the cardinal marks?
The two cones point towards the black parts of the buoy. For the light, think of a clock face: east 3 flashes, south 6, west 9, and north flashes continuously.
What does a yellow buoy mean?
It is a special mark. It indicates an area or feature described on the chart or in nautical publications and is generally not meant to mark a channel or an obstruction.
What does red right returning mean?
It is the memory aid for Region B: when you return from sea, red marks stay on your right. It is correct in the USA and wrong in Europe, where red stays on your left.