Aids to Navigation


There are a variety of things we can use to find our way around on the water. Known landmarks such as the mouth of a river or an island certainly help. In addition to these natural landmarks we have lighthouses, buoys, and beacons known collectively as aids to navigation or ATON for short.

Some of the most of these aids are the familiar channel markers or buoys. Each one will have unique characteristics so that it cannot mistaken for something else. These characteristics include color, shape, and number or lettering displayed on them. In the US we use the lateral system meaning that the sides of channels are marked. When entering a harbor our rule of thumb is always: Red Right Returning. We are returning whenever we enter a smaller body of water from a larger body. Mariner's will often say this as: Leave the red buoys to starboard when returning. In other words, we pass by the buoy while keeping it on our right hand side.

There is another convention also used. The numbers on buoys increase as we travel toward a harbor or smaller body of water. Also, all green buoys are odd numbered and reds are even numbered. So, we start at the entrance to a channel with #1 green to port (left) and #2 red on starboard (right). These numbers will increase the further we go along.

There are basically four different types of buoys we might encounter in US waters: Red, green, red and green horizontally striped, and red and white vertically striped. We will talk about special buoys further below. Each one may or may not have a light. The light color will be green, red, or white. Lights are often used where greater caution must be exercised such as a bend or narrowing of a channel. Also, especially in areas where fog may exist, some buoys make sounds such as a whistle, bell, or gong.

Lighted green buoy Red lighted buoy Red green horizontally striped buoy Red and white vertically striped buoy

Green and red buoys. The greens will mark the port (left) side of a channel when entering a smaller body of water (returning) and reds mark the starboard (right) side while returning. The greens and reds come in two varieties; They can be lighted as above or they can be unlighted as below. An unlighted green buoy is called a can because of its flat top and an unlighted red is called a nun because of its pointed top resembling a nun's cap. Greens and reds will have numbers on them and all other buoys will have letters. These two are illustrated below:

Green can buoy Red nun buoy

The unlighted green and red buoys above would be represented on a chart as small diamond shapes of the appropriate color:

Chart symbol used to indicate a can buoy

Chart symbol to indicate a nun buoy R
N "6"


If the buoys have lights, they would be represented on a chart as the diamond above but with an additional solid magenta (purple) circle below:

Chart symbol indicating a lighted green buoy Chart symbol for lighted red buoy


Let's talk about some of the other things indicated above. We notice that all lighted buoys on charts are marked with by a solid magenta (purple) circle at the location of the buoy. We also notice that the lighted buoys say Fl G or Fl R; this stands for flashing green or flashing red. These designations will be accompanied by the number of seconds between flashes such as: Fl G 2s meaning it flashes green every 2 seconds. Also look at the buoy number in each one of the four chart symbols above. You will see that it is surrounded by quotation marks. Just as we would use quotation marks to quote someone we use these same marks to quote what the buoy 'says' on it. This applies to all buoys and other aids to navigation.

Red and green junction buoyRed and green horizontally striped buoys. These are junction buoys which also might indicate an obstruction with two different ways around the obstruction. These buoys will indicate the preferred and secondary channel to be taken. By studying the chart in advance you will be able to determine which channel you want to take.

Lighted red junction buoyHere is the rule to follow: The top band indicates the preferred channel. If you want the preferred channel then simply read the top color of the buoy and ignore the lower color altogether. So, if the top color is red, you are returning, and you want the preferred channel; read the junction buoy as a solid red buoy and leave it to starboard. However, if you have decided that you want the secondary channel you would read the second color down from the top (green) and treat the buoy as a solid green leaving it to port when returning. One thing to note: These buoys will have a letter instead of a number. Numbered buoys are always solid green or red; all others have letters. On the chart they will look like these:

Chart symbol for red junction buoy Chart symbol for lighted red junction buoy

The one on the left is for an unlighted red green junction buoy with the letter 'C' on it. The 'N' stands for nun buoy which we discussed above. The one on the right is for lighted junction buoy 'B'. Let's see what else there is to the lighted one. In this instance we read that it is Fl (flashing) 2+1 (meaning it flashes twice, pauses, then flashes once) its color is R (red) and it repeats the 2+1 flashing sequence every 6 seconds.

Safe water buoyRed and white vertically striped buoys. These are safe water or mid-channel buoys indicating good depth of water all around. They may be left to either side when returning or leaving. The entrance to major sea ports is often marked with a sea buoy that is red and white vertically striped. This sea buoy is so called because it is the first buoy of the port that one would pass by, it is further out than even the first red and green buoys. These buoys are not numbered but will often have a letter(s). When used as a sea buoy they will have a letter that stands for the channel leading into that particular port. The sea buoy for Miami has an 'M' on it. Other safe water, mid-channel buoys may be small and round simply marking the middle of a channel. The rule for red and white vertically striped buoys is good water, leave it to either side.

Yellow lighted buoyYellow buoys. Yellow represents caution on these buoys. Usually meaning to stay away from them. They are used to indicate pipes, dredge lines, traffic schemes, an isolated danger. They do not usually indicate which side to leave them on. Reading the chart may tell you their significance if they are marking a permanent hazard such as a shoal area. Yellow buoys, if lighted, will flash a yellow light. The rule for yellow buoys: Stay away. Special note on the meaning of the color yellow: While yellow means caution on these buoys yellow is also the designated color for identifying Intracoastal aids to navigation. As we will see later, all buoys and other aids on the Intracoastal Waterway will have at least some yellow on them.

Green daybeaconDaybeacons. In shallow water channels are often marked with a piling that has been driven into the mud bottom and topped with a daymark also called a dayboard. These use the same colors, lights, and numbering system as buoys.

Red and green daymarks. The red daymarks will be triangular, red, and even numbered while the greens will be square, green, and odd numbered. The chart symbol for the red is a triangle and for green is a square. These are illustrated with their chart symbols below:

Green daybeacon Red daybeacon Lighted green daybeacon Lighted red daybeacon
Chart symbol for green daybeacon Chart symbol for red daybeacon Chart symbol for lighted green daybeacon

Chart symbol for lighted red daybeacon "2"
       Fl R 2s

You may notice the above chart symbols for lighted daybeacons are different than for buoys. As you will recall lights for buoys are indicated by a solid circle of magenta (purple) but here the lights are indicated by tear drop shapes of magenta (purple). The general rule about lights on NOAA charts is if the navigation aid is floating then the chart symbol will be a circle; if the aid is attached to land (either by a pile or on solid land as in a lighthouse) its light will be indicated by a tear drop shape.

Red and green horizontally striped daybeacons. These are preferred channel (junction) daybeacons and used just like their counterpart buoys (see above). Shown below with their chart symbols:

Green junction daybeacon Red junction daybeacon
Chart symbol for green junction daybeacon Chart symbol for red junction daybeacon

Safe water daybeaconRed and white vertically striped daybeacons. These are octagonal shaped and mean safe water or mid-channel and can be passed safely to either side. They are direct counterparts to the red and white vertically striped buoys. The chart symbol for these daybeacons is a white square with the letter "A" in quotation marks. These may have lights and, if so, it would be white and flash Mo (A). This is Morse code "A" or; one short flash followed by a longer flash. The sequence would repeat after an interval of a few seconds.

ICW green daybeaconIntracoastal Waterway Aids. The Intracoastal Waterway (also known as the ICW) runs just inside and parallel to the east and gulf coasts of the US. Since this waterway never leaves smaller bodies of water or returns from larger bodies of water we use the aids in a slightly different way. All red buoys and daybeacons are on the mainland side of the Intracoastal while all green buoys and daybeacons are on the ocean/gulf side of the Intracoastal. This arrangement is consistent throughout the waterway so we can remember like this: Red means stop, on the mainland side of the Intracoastal is dry land; don't go there. Green means go, on the ocean side of the Intracoastal is deep water. Since the Intracoastal has land, albeit a relatively narrow strip, between it and the ocean the analogy is only partially correct but works for many to remember the arrangement of buoys.

ICW red daybeaconYellow is the color used on the Intracoastal Waterway to distinguish the buoys and daybeacons so they won't be confused with the red right returning buoys of a channel that crosses the Intracoastal. Whenever you see a small swatch of yellow on a green or red buoy you know you're on the Intracoastal. The only problem with this is that often the yellow has become faded due to sun or has disappeared behind bird guano. So, consult the chart often.

Below are some other buoys that have their own distinct meanings.

Mooring buoy
Mooring buoy or ball

Obstruction buoy
Obstruction, do not pass between this and shore.
Regulatory buoy
Regulatory buoy
Rock marker
Rock marker
Speed limit buoy
Speed limit buoy
Swim area marker/buoy
Swim area buoy

Light phase characteristics. Lights displayed by buoys, beacons, and lighthouses come in a wide variety to facilitate identification. For instance, two red lighted buoys, close to each other in a channel, will need to flash at different rates so they can be identified at night. The following are some of the common ones you'll run into:

Fixed light

Fixed. The light is on all the time.

Flashing light

Flashing. The light flashes once then is off for a period of seconds. This period will be stated on the chart.

Quick flashing light

Quick flashing. Abbreviated Q on the chart. This light flashes once every second.

Occulting light

Occulting. The light is on for a longer period of time than off.

Isophase light

Isophase. The light is on for the same period of time it is off.

Group flashing light

Group flashing. The light flashes in a group, here it is 2.

Composite group flashing light

Composite group flashing. The light flashes in two different groups, here a group of two followed by a group of one.

Morse code "A" flashing light

Morse code "A". The light flashes one short followed by one long then off for a period of seconds as stated on the chart.

Blue Water Sailing School Logo



If you are ready to find out for yourself what it's like to sail a 35-50' boat, receive meaningful sailing lessons, and get a taste of the sea then check out an excellent resource: Blue Water Sailing School. All sailing lessons lead to ASA certification and are taught by experienced instructors who are licensed by the U.S. Coast Guard (Captain's license).