Buoys, Markers, and IALA Systems

The IALA Systems: A vs. B

The International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) established a worldwide buoyage system to reduce confusion among mariners navigating foreign waters. The system has two regional variants: IALA-A (red to port on entry) used in Europe, Africa, Asia, and Australia, and IALA-B (red to starboard on entry) used in the Americas, Japan, South Korea, and the Philippines.

This is the single most important fact about IALA: what red means on one side of the Atlantic is reversed on the other. A US sailor visiting European waters, or a European sailor visiting US waters, must mentally flip their color associations or risk navigating into danger.

Within each regional system, the conventions are consistent: lateral marks define channel edges, cardinal marks indicate the safe side relative to a hazard, isolated danger marks sit on top of hazards, safe water marks indicate navigable water all around, and special marks designate specific areas (anchorages, cables, traffic schemes).

Side-by-side diagram showing IALA-A and IALA-B channel entry with red and green buoys on opposite sides — IALA-A: red to port entering. IALA-B: red to starboard entering. Know which system you are in.

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If you sail internationally, confirm which IALA system applies before navigating. Red meaning port in the US (IALA-B) and red meaning starboard in Europe (IALA-A) has caused real groundings by sailors who did not check.

In IALA Region B (United States), when entering a harbor, red buoys are kept to which side?

Port (left) Starboard (right) Red means mid-channel in Region B It depends on the direction of travel

A US sailor is entering a harbor in the UK. Red buoys should be kept to:

Starboard — the UK uses IALA-B like the US Port — the UK uses IALA-A where red is to port on entry Mid-channel — cardinal marks are used instead of lateral Either side — the UK follows international maritime law

Lateral Marks

Lateral marks define the edges of channels and safe routes. In IALA-B (US): red nun buoys (conical top, even numbers) mark the starboard edge of the channel when entering. Green can buoys (flat top, odd numbers) mark the port edge. At night, red marks show red lights and green marks show green lights — flashing, quick, or fixed.

Preferred channel marks (junction marks) are used where channels divide. They are red and green horizontally banded. The top color indicates the preferred channel: red top = preferred channel is to starboard of this mark (keep it to port); green top = preferred channel is to port of this mark (keep it to starboard).

Buoy numbers increase as you proceed from seaward to inland (toward a river or harbor). If you see buoy #3 and then #5, you are heading into the channel correctly. If you encounter descending numbers, you are heading out to sea. This numbering convention also serves as a position check.

Plan view diagram of a channel showing red nun buoys on starboard, green can buoys on port, with numbers increasing toward harbor — In IALA-B: red nuns to starboard, green cans to port — numbers increase going in

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The US memory aid is 'Red Right Returning' — red buoys to the right (starboard) when returning from sea. Flip it to 'Red Left Leaving' to remember the opposite direction.

In IALA-B, you see a red nun buoy with the number '4' to your starboard side while heading toward a marina. You are:

In danger — red should be to port Correctly positioned in the channel Heading out of the channel — numbers should be decreasing In the wrong channel — only green buoys are numbered

You see a buoy that is horizontally banded red and green, with a red top. In IALA-B, this indicates:

A mid-channel safe water mark A preferred channel junction mark — the preferred channel is to starboard of this buoy A temporary mark — the channel is under construction An anchorage boundary marker

Cardinal Marks

Cardinal marks are used in IALA-A waters (and increasingly in IALA-B complex areas) to indicate the safe side to pass a hazard relative to the compass. There are four types — North, South, East, West — each indicating that safe water lies in that compass direction from the mark.

Cardinal marks are yellow and black with distinctive topmark patterns: North = two cones pointing up (both tips up); South = two cones pointing down; East = cones pointing away from each other (diamond shape); West = cones pointing toward each other (hourglass shape). The topmark pattern matches the black band positions — North has black on top, South has black on bottom, East has black at both ends, West has black in the middle.

Each cardinal mark also has a unique light characteristic using quick (Q) or very quick (VQ) flashing: North = continuous; East = 3 flashes; South = 6 flashes + long flash; West = 9 flashes. The pattern can be remembered with the clock: N = 12 o'clock (all flashes), E = 3 o'clock (3 flashes), S = 6 o'clock (6 flashes), W = 9 o'clock (9 flashes).

You are approaching an isolated rocky shoal. A west cardinal mark (yellow over black, hourglass topmark, 9 quick flashes) is positioned near the shoal. This means safe water lies to the west of the mark — pass the mark on its west side, keeping it to your east (or right, if heading north). The mark sits on or near the hazard; do not pass between the mark and the danger it guards.

A cardinal mark with two cones both pointing upward indicates:

East cardinal — safe water to the east North cardinal — safe water to the north South cardinal — safe water to the south West cardinal — safe water to the west

A cardinal mark shows a quick flashing light with 9 flashes in a group. This is a:

North cardinal East cardinal South cardinal West cardinal

Isolated Danger, Safe Water, and Special Marks

Isolated danger marks are placed on, or immediately above, a hazard that has navigable water all around it — an isolated rock or shoal in otherwise clear water. They are black with one or more red horizontal bands and a topmark of two black balls. Their light characteristic is a group of two flashes (Fl(2)). Pass them with care on any side, giving a generous margin.

Safe water marks indicate that there is navigable water on all sides — typically used as a mid-channel marker, landfall buoy, or approach mark. They are red and white vertically striped with a spherical topmark. Their light is isophase, occulting, or single long flash. These are good news — they mean you're in open, navigable water.

Special marks (yellow, X-shaped topmark) designate specific areas that require attention: traffic separation schemes, cable or pipeline crossing areas, spoil grounds, aquaculture areas, or military exercise zones. They don't indicate hazards directly, but the area they mark should be researched before entering.

You see a red and white vertically striped buoy with a spherical topmark. This is:

An isolated danger mark — there is a hazard here A safe water mark — navigable water all around A preferred channel mark — one channel is favored A special mark — an area requiring attention

An isolated danger mark is placed:

At the edges of a channel On or directly above a hazard with navigable water all around it At the centerline of a safe fairway At the boundary of a restricted area

Summary

IALA-A (Europe, Asia, Africa, Australia): red to port entering. IALA-B (Americas, Japan): red to starboard entering ('Red Right Returning').

Lateral marks define channel edges. In IALA-B: red nuns (even numbers) to starboard, green cans (odd numbers) to port when entering.

Cardinal marks indicate safe water by compass direction: North (cones up), South (cones down), East (diamond), West (hourglass). Lights: N=continuous Q, E=3, S=6+, W=9.

Isolated danger marks (black/red bands, 2 balls, Fl(2)) sit on hazards. Safe water marks (red/white vertical stripes, sphere) indicate clear water all around.

Special marks (yellow, X topmark) designate areas of interest or restriction — always research what the specific area designates.

Key Terms

IALA: International Association of Marine Aids to Navigation and Lighthouse Authorities — the body that standardizes buoyage systems worldwide
IALA-A: The buoyage system used in Europe, Africa, Asia, and Australia — red to port when entering
IALA-B: The buoyage system used in the Americas, Japan, South Korea, and Philippines — red to starboard when entering
Lateral mark: A buoy or beacon marking the edge of a navigable channel
Cardinal mark: A mark indicating safe water by compass direction (N/S/E/W) relative to a hazard
Isolated danger mark: A mark placed on or above a hazard with navigable water all around; black with red bands, two-ball topmark
Safe water mark: A mark indicating navigable water on all sides; red and white vertical stripes, spherical topmark
Special mark: A yellow mark with X topmark designating a specific area of interest or restriction
Red Right Returning: The IALA-B memory aid: red buoys are kept to starboard when returning from sea (entering harbor)

Buoys, Markers, and IALA Systems

The IALA Systems: A vs. B

Lateral Marks

Cardinal Marks

Isolated Danger, Safe Water, and Special Marks

Summary

Key Terms

Buoys, Markers, and IALA — Quiz

In IALA-B waters, you are heading upstream in a river. Green can buoys should be kept:

A cardinal mark with an hourglass topmark (cones pointing toward each other) is a:

You see a buoy with a black top half and a red bottom half, with two black balls as a topmark. At night it shows Fl(2). This is:

A US sailor enters a harbor in Australia. Red buoys should be kept to:

Buoy numbers 3, 5, 7 are on your port side as you proceed up a channel in IALA-B. This means:

References & Resources

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