The system
What is the IALA Maritime Buoyage System?
A worldwide set of rules for marine aids to navigation, so that a mariner anywhere can 'fix their position and avoid dangers without fear of ambiguity', in R1001's words. It also gives the authorities that lay the marks a common standard to work to.
The current text is IALA Recommendation R1001, Edition 2.0, adopted in June 2023. R1001 Edition 1.0 (May 2018) replaced the original 1982 agreement on the system, and R1001 notes that SOLAS Chapter V Regulation 13 requires governments to take IALA's recommendations, including the buoyage system, into account.
What are the six types of mark?
R1001 defines six types of mark, which can be used alone or together. Only the lateral marks differ between the two buoyage regions; 'the other five types of marks are common to both regions'.
Lateral marks show the port and starboard sides of a channel, in red and green.
Cardinal marks show where the safer water lies — north, east, south or west of a point of interest — in yellow and black.
The isolated danger mark sits on or near a danger that has navigable water all around it: black with one or more red bands.
The safe water mark has navigable water all around it and marks no danger: red and white vertical stripes.
Special marks show a special area or feature: yellow.
The emergency wreck mark can mark a new danger: blue and yellow vertical stripes.
Does the system only cover buoys?
No. R1001 describes 'marks', which can be fixed or floating, physical or electronic. It names four applications: fixed, floating, mobile (a Mobile Aid to Navigation, or MAtoN) and electronic (AIS AtoN, racons and radar target enhancers).
It also covers other marks: lighthouses, leading lines (ranges), sector lights, beacons, major floating aids such as lightvessels, and minor auxiliary marks. A beacon is a fixed mark and can take the form of, for example, a cardinal mark.
R1001 is clear that the marks don't navigate for you: responsibility for safe navigation stays with the mariner, using the marks together with official nautical documents and prudent seamanship.
Regions A and B
What is the difference between Region A and Region B?
Only the colours of the lateral marks. In Region A, red marks the port side of a channel and green the starboard side, relative to the conventional direction of buoyage. In Region B 'these colours are reversed': red to starboard, green to port. The preferred channel marks swap the same way.
The shapes do not swap: in both regions a port-hand mark is a can (or a pillar or spar with a can topmark) and a starboard-hand mark a cone (or a pillar or spar with a cone topmark) — and the cardinal, isolated danger, safe water, special and emergency wreck marks are the same everywhere.
Where are Region A and Region B?
R1001 draws the boundaries on a world map rather than listing countries. Its history section describes System A, completed in 1976 and introduced in 1977, spreading through Europe, Australia, New Zealand, Africa, the Gulf and some Asian countries, and System B, completed in early 1980, as suitable for North, Central and South America, Japan, the Republic of Korea and the Philippines.
As we read it, that puts UK and European waters in Region A. Anywhere you are unsure of, take the region from R1001's map and your charts and publications, not from memory.
Why are there two regions?
Before IALA's system there were more than thirty buoyage systems in use, many in direct conflict. The first step was two main systems — one with red to port, one with red to starboard. At a conference in November 1980 the two were found so similar that IALA combined them into one system, leaving authorities the choice of red to port or red to starboard on a regional basis.
Direction of buoyage
What is the conventional direction of buoyage?
The direction that 'port' and 'starboard' on a lateral mark refer to. R1001 gives two ways it is set: the general direction a mariner takes when approaching a harbour, river, estuary or other waterway from seaward; or a direction fixed by the competent authority, which 'in principle' should run clockwise around land masses. Either way, it must be shown on the charts and nautical documents.
In practice: a port-hand mark is on your port side when you are heading in the direction of buoyage. Heading the other way — leaving harbour, say — you keep it on your starboard side.
How are channel marks numbered?
If the marks at the sides of a channel are numbered or lettered, the sequence follows the conventional direction of buoyage. R1001's protocol, especially in confined waterways, is that red marks should carry even numbers and green marks odd.
Identifying a mark
How do you identify a buoy by day?
By colour, shape and topmark, and by its light if you can see it. Lateral marks rely on shape: a can (cylinder) for port-hand marks and a cone for starboard-hand marks. Cardinal and isolated danger marks have no distinctive shape — normally a pillar or spar — so the topmark and colours do the work.
The topmarks, in short: a single can or a single cone, point up (lateral); two black cones (cardinal); two black spheres (isolated danger); a single red sphere (safe water); a yellow 'X' (special); an upright yellow cross (emergency wreck). Where weather or ice make topmarks impractical, the authority may decide not to fit them.
How do you identify a mark at night?
By the colour of the light, then its rhythm. Among the six types of mark: red or green means a lateral mark. White means a cardinal, isolated danger or safe water mark, and each has its own rhythm: very quick or quick flashing for cardinals, group flashing (2) for the isolated danger mark, and isophase, occulting, one long flash every 10 s or Morse 'A' for safe water. Yellow means a special mark. Alternating blue and yellow means an emergency wreck mark.
Lateral lights can have any rhythm except composite group flashing (2 + 1), which is kept for preferred channel marks. Special mark lights never use the rhythms of the white lights, so that a yellow light that looks white in poor visibility can't be read as a cardinal, isolated danger or safe water mark. Unlit marks may carry retroreflective material that shows up in a searchlight.
What are virtual and synthetic AIS marks?
R1001 describes three kinds of AIS AtoN. A physical AIS AtoN is transmitted from a station on a mark that really exists. A synthetic one is broadcast from a station elsewhere for the position of a real mark. A virtual one is broadcast for a mark that does not physically exist: you may see its symbol on ENC/ECDIS with no buoy or beacon in the water.
In the oral
How does buoyage come up in the MCA oral?
Our MCA oral exam and COLREGs pages cover how buoyage is examined, including its Part A pass mark. Examples of the kind of question to be ready for (our wording, not the MCA's):
“What are the six types of mark, and which of them change between Region A and Region B?”
“What is the conventional direction of buoyage, and who decides it?”
“At night you see a white light flashing quickly in groups of three. What is it, and which side do you pass it?”
“What does a virtual AIS mark show you, and what is actually in the water?”
Where can I practise identifying marks?
The free COLREGs quiz on this site has a buoyage drill: what is this mark? Bridgedeck Study's COLREGs drills include buoyage too, free, no card needed. Then go through each mark's page — lateral, cardinal, isolated danger, safe water, special and emergency wreck — until you can give its colour, shape, topmark and light without a pause.
