IALA Maritime Buoyage System

The need for the establishment of a unified buoyage system became crucial the last decades, because of the great extend of the international navigational traffic, the accidents and, finally, because of the variety of the buoyage systems that were locally applied by the States. It has to be highlighted that during 1975 more than 30 systems were in use, provoking confusion and creating anarchy in the field of maritime buoyage.

A few years ago, the International Association of Lighthouse Authorities (IALA), the non-governmental body which brings together representatives from the aids to navigations services in order to exchange information and recommend improvements to aids to navigation based on the latest technology, decided that a unified Maritime Buoyage System has to be applied, based on the contemporary Maritime Buoyage equipment and the acquired experience.

Thereby, two International Regions of Buoyage were created, the Region A and the Region B. The only difference between them is the vessels’ lateral marking.

Region A: Combination of cardinal and lateral marking (red port).

Region B: Combination of cardinal and lateral marking (red starboard).

This system is applied in Greece and is represented in IALA by the Service of Lighthouses. Greece belongs to the Region A.

The System’s aim is to aid the mariner to both recognize and interpret easily the buouyages, even if it is not registered to the maps, and to decide correctly about the course he has to follow. However, nautical maps and other navigational aids are still necessary.

The System applies to all fixed and floating marks, other than lighthouses, sector lights, leading lights and marks, lightships and ‘lighthouse buoys’, and serves to indicate:

The sides and centerlines of navigable channels; Natural dangers and other obstructions, such as wrecks (which are describes as ‘New Dangers’ when newly discovered); Areas in which navigation may be subject to regulation ; or other features of importance to the mariner.

Types of Marks

The system provides five types of marks which may be used in any combination:

Lateral marks indicate the port and starboard hand sides of the channel; Cardinal marks used in conjunction with the compass, indicate that navigable water lies to the named side of the mark; Isolated Danger marks erected on, or moored directly on or over dangers of limited extend; Safe Water marks, such as mid-channel buoys; and Special marks, the purpose of which is apparent from reference to the chart or other nautical documents.

The concept of the system’s signaling derives from one or more of its characteristics and more specifically:

By Day- Color, shape and topmark

Lateral Marks Region A

By Night- Colour and rhythm of light

Lateral Marks

Lateral marks are generally used for well-defined channels; they indicate the port and starboard hand sides of the route to be followed, and are used in conjunction with a conventional direction of buoyage. This direction is defined in one of two ways:

Local Direction of buoyage- the direction taken by the mariner when approaching a harbor, river estuary or other waterway from seaward; or

General Direction of buoyage- In other areas, a direction determined by the buoyage authorities, following a clockwise direction around continental land masses, given in Sailing Directions, and, if necessary, indicated on charts by a symbol (see Diagram).

Characteristics of Marks

A port hand mark is colored red and its basic shape is can, for either buoy body or topmark, or both.

A starboard hand mark is normally colored green and its basic shape is conical, for either buoy body or topmark (point up), or both.

Cardinal marks

A cardinal mark is used in conjunction with the compass to indicate where the mariner may find the best navigable water. It is placed in one of the four quadrants (north, East, South, West), bounded by the true bearings NW-NE, NE-SE, SE-SW, SW-NW, taken from the point of interest. A cardinal mark takes its name from the quadrant in in which it is placed.
The mariner is safe if he passes N of a North mark, E of an East mark, S of a south mark and W of a West mark.


A Cardinal mark may be used to:

a) Indicate that the deepest water in an area is on the named side of the mark;

b) Indicate the safe side on which to pass a danger;

c) Draw attention to a feature in a channel such as a bend, junction, bifurcation, or end of a shoal.


Black double-cone topmarks are the most important feature, by day, of cardinal marks: the arrangement of the cones must be memorized.
More difficult to remember than North and South are the East and West topmarks: ‘W for Wineglass’ may help.

Cardinal marks carry topmarks whenever practicable, with the cones as large as possible and clearly separated.


Black and yellow horizontal bands are used to colour a Cardinal mark. The position of the black band, or bands, is related to the points of the black topmarks, thus:


North-Points up: Black Band above yellow band.

South- Points down: Black band below yellow band.

West- Points inward: Black band with yellow bands above and below.

East- Points outward: Black bands above and below yellow band.


The shape of a Cardinal mark is not significant, but in the case of a buoy will be pillar or spar.


When lighted, a cardinal mark exhibits a white light; its characteristics are based on a group of quick or very quick flashes which distinguish it as a Cardinal mark and indicate its quadrant.

The distinguishing quick or very quick flashes are:

North- Uninterrupted.

East- 3 flashes in a group.

South- 6 flashes in a group followed by a long flash.

West- 9 flashes in a group.

To aid the memory, the number of flashes in each group can be associated with a clock face (3 o’clock-E, 6 o’clock-S, and 9 o’clock-W).

The long flash (of not less than 2 seconds duration), immediately following the group of flashes of a South Cardinal mark, is to ensure that its 6 flashes cannot be mistaken for 3 or 9.

The periods of the East, South and west lights are, respectively, 10, 15 and 15 seconds if quick flashing; and 5, 10 and 10 seconds if very quick flashing.

Quick flashing lights flash at the rate of either 60 or 50 flashes per minute: very quick flashing lights flash at the rate of either 120 or 100 flashes per minute.

It is necessary to have a choice of quick flashing or very quick flashing lights in order to avoid confusion if, for example, two north buoys are placed near enough to each other for one to be mistaken for the other.

Isolated Danger Marks


An Isolated Danger mark is erected on, or moored on or above, an isolated danger of limited extend which has navigable water all around it. The extend of the surrounding navigable water is immaterial: such a mark can, for example, indicate either a shoal which is well offshore, or an islet separated by a narrow channel from the coast.


Isolated Danger Marks

On a chart, the position of a danger is the center of the symbol or sounding indicating it: an Isolated Danger buoy will inevitably therefore be slightly displaced on the chart.


A black double-sphere topmark is, by day, the most important feature of an isolated Danger mark and, whenever practicable, this topmark will be carried, with the spheres as large as possible, disposed vertically, and clearly separated.


Black with one or more red horizontal bands are the colors used for Isolated Danger marks.


The shape of an Isolated Danger mark is not significant, but in the case of a buoy will be pillar or spar.


When lighted, a white flashing light showing a group of two flashes is used to denote an Isolated Danger mark. The association of two flashes and two spheres in the topmark may be a help in remembering these characteristics.

Safe Water Marks


A Safe Water mark is used to indicate that there is navigable water all around the mark. Such a mark may be used as a centerline, mid-channel or landfall buoy.


Red and white vertical stripes are used for Safe Water marks, and distinguish them from the black-banded danger-marking marks.


Spherical, pillar or spar buoys may be used as Safe Water marks.


A single red sphere topmark will be carried, whenever practicable, by a pillar or spar buoy used as a Safe Water mark.


When lighted, Safe Water marks exhibit a white light, occulting, or isophase, or showing a single long flash. If a long flash (i.e. a flash of not less than 2 seconds) is used, the period of the light will be 10 seconds.

The association of a single flash and a single sphere in the topmark may be a help in remembering these characteristics.

Special marks


A Special mark may be used to indicate to the mariner a special area or feature, the nature of which is apparent from reference to a chart, sailing directions of notices to mariners.

Uses include:

a. Ocean Data Acquisition Systems (ODAS), i.e. buoys carrying oceanographic or meteorological sensors;

Lateral Marks Region A

b. Traffic separation marks;

c. Spoil ground marks;

d. Military exercise zone marks;

e. Cable or pipeline marks, including outfall pipes;

f. Recreation zone marks.

Another function of a Special mark is to define a channel within a channel. For example, a channel for deep draught vessels in a wide estuary, where the limits of the channel for normal navigation are marked by red and green Lateral buoys, may have the boundaries of the deep channel indicated by yellow buoys of the appropriate Lateral shapes, or its centerline marked by yellow spherical buoys.


Yellow is the color used for special marks.


The shape of a Special mark is optional, but must not conflict with that used for a Lateral or a Safe Water mark. For example, an outfall buoy on the port hand side of a channel could be can-shaped but not conical.


When a topmark is carried it takes the form of a single yellow X.


When a light is exhibited it is yellow; the rhythm may be any, other than those used for the white lights of Cardinal, Isolated Danger and Safe Water marks. i.e.

Cardinal Marks

North Mark- Quick (or very quick) flashing

East Mark- Quick (or very quick) flashing (3) 10 seconds (or 5 seconds).

South Mark- Quick (or very quick) flashing (6) + long flash 15 seconds (or 10 seconds).

West Mark- Quick (or very quick) flashing (9) 15 seconds (or 10 seconds).

Isolate Danger mark : Occulting- Isophase- Long flash 10 seconds.