Whether you are a sailor, a fisherman, a kayaker, or someone who just enjoys being on the water, it is important to be familiar with the basic Aids to Navigation. These structures allow you to identify hazards, set a course, and locate your position while on the water. You can use Aids to navigation with or without the use of a nautical chart.

Aids to navigation include lighthouses, beacons, buoys, etc and are located around the world. There are two main systems in place: IALA A (Europe, and most of the world) and IALA B (Americas, Japan, Korea, and the Philippines). In general the differences between these systems are minimal, with the important exception of the direction you should pass the buoys. This article will describe the IALA B system.

Each Aid to navigation is identified using 4 elements: the shape, color, topmark, and light and an option sounds signal.

Color, Shape and Topmark

During the daytime, each Aid to navigation can be identified using the color, the shape, and the topmark. These three characteristics allow the mariner to identify the Aid as well as its purpose. The most basic, and most common, Aids on the water are colored green and red.

  • Red buoys - red buoys are generally conical and have red lights and even numbers. The topmark (the shape on top) is square. Red buoys are often referred to as 'nuns.' When you are returning to a harbor you should leave red buoys on your starboard (right) side. To remember this, use the saying - red, right, returning.
  • Green buoys - green buoys have green lights, odd numbers, and a triangular topmark. Green buoys are commonly called cans. When you are returning to a harbor, leave the green buoys on your port or left side.
  • Green and red buoys - buoys with horizontal stripes of red and green indicate that two channels are joining. The color that appears on the top indicates which channel is preferred. For example, a buoy with a red stripe on top indicated that you should choose the channel by leaving the buoy to the right.
Look at the following marks. The black line indicates the path you would take through the buoys. Notice that you leave the red marks to your right when you head in to the harbor and the green buoys to the left.
  • Red and black horizontally striped buoys - these buoys indicate isolated danger. The top mark is two circles stacked on top of each other.
  • Red and white vertically striped buoys - these buoys indicate safe water
  • Yellow buoys - these buoys are special purpose. If you see a yellow buoy you should look at a chart to determine its purpose.

Cardinal Marks

In addition to the lateral green and red marks described above, cardinal marks are also used. These marks indicate what cardinal direction (north, east, south, west) you should pass the buoy on. This system is less common then the above system and is not fully described here.

Light Characteristics

During the night time hours, Aids to Navigation can only be observed using lights. The lights on these marks vary in color, period, and phase characteristics. Lights can be white, red, green, or yellow. If it is not indicated, the light is assumed to be white. The period refers to how long the light takes to complete each pattern. The phase characteristics are the pattern of lights during each period. Some of the most common phase characteristics are labeled on a chart as:

F = fixed

Fl = flashing

Q = Quick flashing

VQ = Very quick flashing

IQ = Interrupted quick flashing - quick flashing with a pause

Iso = Isophase - equal periods of light and dark

Gp Fl (x+x) = Group flashing - 2 separate groups of different flashes

Occ = Occulted - mostly lighted with flashes of dark

Al - Alternating - changing color

For an example of light characteristics: look at the aid to navigation located in the chart below marked with the arrow. Now look at the writing above this mark. This first information tells the name of the structure: Cuttyhunk North Jetty. Next the text uses the information: Fl R 6s. This means that the light signal is a flashing (Fl) red (R) light that flashes every 6 seconds (6s).

The additional information lets you know how tall the structure is (29 ft) and how far the light is visible on a clear night (6M or 6 nautical miles). The number in parenthesis indicates that the number "8" is written on the structure.

buoy example 1


Many buoys are also given a sounds signal. These signals include bells, horns, whistles, gongs, etc. Some of these sounds are electronically controlled, and some are controlled simply by the movement of the water.

Aids to Navigation on a Chart

Nautical charts contain many different Aids to navigation and include information on each aid. The buoys, lighthouses, etc are marked with a variety of different symbols depending on exactly the type of Aid. These symbols also appear on GPS. These symbols are listed in the publication Chart One that can be downloaded for free here.

Here are some general guidelines for translating the most common information on a chart that describes each Aid to navigation, with an example of each piece of information.

  • The first letter indicates the color of the buoy: R = red, G=green, Y=yellow, etc
  • If there is a light on the Aid, the light characteristic appears first. This is followed by the color and then the period. If the light color is R, the buoy will also be red: Fl R 3s (Flashing red every 3 seconds)
  • Any number or letter that appears in quotes is painted on the buoy: "4"
  • Any sounds associated with the Aid to Navigation are written in all capital letters: GONG, BELL, etc
  • A number followed by ft indicates the height of the Aid to Navigation. This is typically included for lighthouses, but not for buoys. 25 ft
  • A number followed by a capital M indicates the range of the light: 8M (the light has a range of 8 nm on a clear night). It is important to note that this number is the nominal range. The distance you can see the light from depends both on the nominal range and the height of the light.

Here are some examples of Aids to Navigation on charts and what they mean:

buoy example 2