Buoyage Systems

There are two major types of buoyage systems:

  • The lateral system is used for marking the boundaries of navigable channels. The description of each buoy indicates the direction of danger relative to the course of the channel, which is normally followed.
  • The cardinal system is used to indicate isolated obstructions to navigation such as rocks, shoals and islands as well as for isolated dangers in the open sea. The characteristics of each buoy indicates the approximate direction of the danger it marks.
This lateral and cardinal buoyage system is principally used world wide. However, for the lateral buoyage system there exist two different implementations.

The IALA Maritime Buoyage System

Although most of the major maritime nations have used either the lateral or the cardinal systems for many years, details such as the buoy shapes and colors have varied from country to country. With the increase in maritime commerce and traffic between countries, the need for a uniform system of buoyage became apparent.

In 1980, with the assistance of the IMO and IHO the lighthouse authorities from 50 countries adopted the IALA Maritime Buoyage System. IALA is the International Association of Lighthouse Authorities. This IALA Maritime Buoyage System is an international agreement establishing two regions - "Region A" and "Region B" - for the entire world.

Buoyage system "Region A" is used in Europe, Africa, Asia and Australia. Buoyage system "Region B" is used on the American continent as well as in Japan, Korea and the Philippines.

Types of Marks

The IALA Maritime Buoyage System applies to all fixed and floating marks, other than lighthouses, sector lights, leading lights and day marks. Most lighted and unlighted beacons other than leading marks are included in the system. In general, beacon top marks will have the same shape and color as those used on buoys. The IALA buoyage system provides five types of marks which may be used in any combination:

  1. Lateral marks indicate port and starboard sides of navigable channels.
  2. Cardinal marks, named "Eastern marks", "Southern marks", "Western marks" and "Northern marks", indicate that the navigable water lies to the named direction of the mark.
  3. Isolated danger marks erected on, or moored directly over, dangers of limited extend.
  4. Safe water marks, such as mid channel buoys.
  5. Special marks, indicates special features e.g. spoil grounds, or prohibited anchorages. The purpose is determined from the nautical chart or other nautical documents.

Characteristics of Marks

The significance of a mark depends on one ore more features: by day the color, shape and top mark are relevant, by night the light color and the phase characteristics are relevant.

1. color: for daylight navigation, the colors red and green are reserved for lateral marks and yellow for special marks. The other types of marks are painted black and yellow or black and red horizontal bands, or red and white vertical stripes.
When marks are lighted, the colors red and green are reserved for lateral marks and yellow for special marks. The other types have a white light with a specific distinct phase characteristic.

2. shape: there are five basic buoy shapes: can, cone, sphere, pillar and spar.

3. top marks: the IALA system makes use of can, conical spherical and X-shaped top marks only. Top marks on pillar and spar buoys are particularly important and will be used wherever practicable. However, top marks are optional.

4. phase characteristics of lights: red and green lights may have any phase characteristic, as the color alone is sufficient to show on which side they should be passed. Special marks, when lighted, have a yellow light with any phase characteristic not reserved for white lights of the system.
The other type of marks have clearly specified phase characteristics of white light: various quick-flashing phase characteristics for cardinal marks, group flashing (Fl.(2) 2 W) for isolated danger marks and relatively long periods of lights for safe water marks.

Lateral marks

The lateral buoyage system consists of buoys marking the port and starboard side of the navigable water in a channel or sea lane. For clear identification these "lateral" buoys exhibit distinctive characteristics in color, shape, numbering and top marks.

Lateral marks differ in color between Regions A and B. Buoyage system "Region A" uses red colored marks to indicate port side and green colored marks to indicate starboard sides of channels. In Region B these colors are reversed, green colored mark indicate port side and red colored marks indicate starboard side of the navigation channel.

In both systems the respective colors are used by day and night. The conventional direction of buoyage, determining port and starboard side of a channel, is considered to be "entering from seaward".

Buoyage System
port side 
of the navigation channel 
starboard side 
of the navigation channel 
Navigation channel
"entering from seaward"
"Region A" red green +  / ~~~ \  +
"Region B"  green red +  / ~~~ \  +

Other characteristics of the lateral marks such as shape, light phases, numbering system or top marks do not differ between the "Region A" and "Region B" buoyage system:

  • Port side buoys are can shaped (blunt), with optionally rectangular or square top marks and they are numbered with odd numbers;
  • Starboard side buoys are cone shaped (tapered), with optional triangular top marks and they are numbered with even numbers.

Where there may be any doubt, e.g. when a channel can be entered from seaward by more ways, the direction of buoyage may be indicated on charts by the following symbol (see also Chart "INT 1"):

  • direction of buoyage system:

Lighted buoys in the lateral buoyage system will exhibit a colored light according to the IALA-region where they are applied. The light phase characteristics can be anything except for Fl. (2+1). Usually one of the following rhythms is used : Q., Fl., Fl.(2), Oc. or ISO.

IALA Region A Lateral 
IALA Region B
port side starboard side port side starboard side
can cone general shape can cone
square triangle top mark square triangle
QFl. R / Fl. R
Fl. R (2)
Oc. R / ISO R
QFl. G / Fl. G
Fl. G (2)
Oc. G / ISO G
QFl. G / Fl. G
Fl. G (2)
Oc. G / ISO G
QFl. R / Fl. R
Fl. R (2)
Oc. R / ISO R
odd even number odd even

The lateral buoyage system also includes lateral marks for indicating the main channel in case of junctions or branches. In the case of a secondary channel branching on the port side of the primary channel, the first starboard mark of the secondary channel will lie on the port side of the primary channel. The same problem occurs with the first port mark of a secondary channel branching on the starboard side.

For this purpose, the IALA lateral buoyage system includes "preferred channel buoys". They have an horizontal red or green band around the buoy:

Lateral junction marks IALA Region A Lateral Junction Marks IALA Region B
port side junction starboard side junction port side junction starboard side junction

Safe-Water Marks


Safe-water marks indicates that there is navigable water all around and under the mark. They may be used as mid channel or landfall mark. The top mark consist of a single red sphere.

Safe water marks are colored white with one or more red vertical bands. They may be spherical, pillar or spar.

Light, when fitted is a white light, iso-phase, occulting, or signal long flash. As an aid to memory associate single sphere with a single flash.

Cardinal Marks

Cardinal marks are used to mark regions of unnavigable waters e.g. shoals, reefs or underwater crags. The four cardinal marks are named:

  • "Eastern marks",
  • "Southern marks",
  • "Western marks" and
  • "Northern marks".

The name indicates that the navigable water lies to the named direction of the mark. So the cardinal marks should be passed on the side of their name: e.g. an "Eastern mark" should be passed east of this mark - the obstruction lies west of the mark etc.

Cardinal marks are colored in a combination of yellow and black. They may have a top mark consisting of two black cones. The color code and top marks for the four different cardinal marks is shown below:

  Q. W
Q.(9) W
VQ.(9) W
xxx Q.(3) W 
VQ.(3) W
  Q.(6) + LFl. W
VQ.(6) + LFl. W

During the night, cardinal marks show a white flashing light. This may be very quick flashing (VQ.) or quick flashing (Q.). To ensure that there is no confusion between the South mark and the East or West mark, a long flash immediately follows the group of 6 flashes of the South mark.
The light characteristics of the cardinal marks can be made visible by clicking on the buoyage icons above.

Isolated Danger Marks

Fl.(2) W

In contrast to a cardinal mark, an "isolated danger mark" has navigable water all around its position. It an isolated danger of limited extent, e.g. an isolated shoal, rock or reef. The nautical chart may show some information on the extention of the hazard. Otherwise keep an appropriates safety distance to the danger mark.

The top mark consist of two black spheres positioned vertically and clearly separated.

Isolated danger marks are colored black with one or more red horizontal bands. Light, when fitted is a white flashing light showing a group of two flashes (Fl.(2) W).

Special Marks

Special marks are used to indicate a special area or feature such as: traffic separation schemes, spoil ground marks, prohibited anchorages or other restricted areas. The correct meaning is retrieved from the chart or other nautical documents.
The special marks will be yellow can, conical or spar buoys. Top mark, if any, will be a yellow cross. Light, when fitted is a yellow light and may be any rhythm other than those used for the white lights of cardinal, isolated danger and safe water marks.

Use of Buoyage Systems

It is important to remember that buoyage is only a guideline. Local lighthouse or coast guard authorities may occasionally decided to deviate from the IALA recommendations. An experienced navigator will use all his skills to assess how much faith to place in any navigational aids.

There are several aspects that should be remembered:

  • Charts or nautical manuals may not be up to date.
  • Buoyage is only a useful aid to navigation when it is related to an up to date chart.
  • The lights may not be working or occasionally buoys marked as unlit on the chart may be lit!
  • The depth and position of navigation channels may have changed since the last buoyage surveys.
  • Buoys may drift from their original position by strong current or heavy weather.

Cover  <<  Sail Away  <<  Short-Range Aids to Navigation  <<  . .  >>  Buoys last updated: 06-Mar-2003