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IALA Buoyage

Buoyage

One worldwide system of marks — and the lights actually blink here. Lateral marks flip colour between Region A and B; cardinals, dangers and safe water look the same everywhere.

Showing IALA Region A (Europe, Africa, most of Asia, Australia & New Zealand). Switching regions flips the lateral colours below, live — everything else is identical worldwide.

You can also change the region in language and regional settings in the site header. It applies everywhere on boatrules.com.

Lateral marks

The edges of the channel, read in the direction of buoyage (normally from seaward into harbour). These are the only marks whose colours differ between IALA regions — the can/cone shapes keep their meaning everywhere.

Port-hand lateral markRegion A shown · differs A/B
Fl R 4sOne flash every 4 s — dark longer than light. Colour: red.

Going with the direction of buoyage (e.g. entering harbour), leave this mark on your port side. Leaving harbour, keep it to starboard.

Starboard-hand lateral markRegion A shown · differs A/B
Fl G 4sOne flash every 4 s — dark longer than light. Colour: green.

Going with the direction of buoyage (e.g. entering harbour), leave this mark on your starboard side. Leaving harbour, keep it to port.

Preferred channel to starboardRegion A shown · differs A/B
Fl(2+1) R 10sComposite group 2 + 1 every 10 s. Colour: red.

To follow the preferred channel, leave this mark to port, exactly as you would a normal port-hand mark. Leave it to starboard only to take the secondary channel.

Preferred channel to portRegion A shown · differs A/B
Fl(2+1) G 10sComposite group 2 + 1 every 10 s. Colour: green.

To follow the preferred channel, leave this mark to starboard, exactly as you would a normal starboard-hand mark. Leave it to port only to take the secondary channel.

Cardinal marks

Black-and-yellow marks named for the side you pass on: safe water lies north of a north mark, east of an east mark, and so on. Identical in both regions.

N · 12 o’clockQcontinuous — pass northW · 9 o’clockQ(9) 15s9 flashes — pass westE · 3 o’clockQ(3) 10s3 flashes — pass eastS · 6 o’clockQ(6)+LFl 15s6 flashes + long — pass south
Danger
Read the flashes off a clock face: East flashes 3 (3 o’clock), South 6 plus a long flash, West 9, North is continuous at the top. Safe water is always on the side the mark is named for.
North cardinal mark
QContinuous quick flashing.

Pass to the north of the mark.

East cardinal mark
Q(3) 10s3 quick flashes every 10 s.

Pass to the east of the mark.

South cardinal mark
Q(6)+LFl 15s6 quick flashes followed by one long flash every 15 s.

Pass to the south of the mark.

West cardinal mark
Q(9) 15s9 quick flashes every 15 s.

Pass to the west of the mark.

Isolated danger

Placed on a small danger that has navigable water all around it.

Isolated danger mark
Fl(2) 5sA group of 2 flashes close together every 5 s.

Do not pass close aboard. Identify the extent of the danger on the chart, then keep well clear on either side.

Safe water

Navigable water all around — fairway, mid-channel and landfall marks.

Safe-water mark
LFl 10sOne long flash (at least 2 s) every 10 s.

You may pass on either side. In a fairway, standard practice is to keep it to port so you stay on the starboard side of the channel.

Special marks

Yellow marks for special areas and features — the chart tells you what they protect.

Special mark
Fl Y 4sOne flash every 4 s — dark longer than light. Colour: yellow.

The mark itself does not tell you which side to pass — consult the chart for the area it protects, and keep clear of any activity it marks.

Emergency wreck

The temporary blue-and-yellow buoy placed over a new, still-uncharted wreck.

Emergency wreck-marking buoy
Al Bu/Y 3sAlternates blue → yellow every 3 s.

Give it a wide berth and slow down — the wreck may extend well beyond the buoy, and its exact position may still be uncertain.

Colours, shapes, topmarks and rhythms follow the IALA Maritime Buoyage System as published by the USCG Navigation Center (U.S. Aids to Navigation System). All artwork is our own. Rhythms are explained on the light characteristics page.