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Aids to Navigation

The term aids to navigation, or navaids, includes lighted and unlighted beacons, buoys, and ranges. A beacon is a stationary visual navaid such as a lighthouse or a small single-pile structure. Lighted beacons are often called lights, and unlighted beacons are known as daybeacons. All beacons also have a daymark identification of one sort or another.

Ranges   A range consists of pairs of beacons or lights that indicate a specific line of position when they are visually lined up. Ranges are shown on the chart by a black dashed line. The rear beacon or light is higher and located behind the lower front light. When you see the lights vertically in line, you are on the range line and directly in the center of the intended channel. If the front light appears left of the rear light, you are off course to the right of the range line – if the front mark moves to the right of the taller rear beacon, you are drifting off course to port.

Range lights usually have both a high intensity lighting system and dayboards, but you will often encounter only the dayboards. Lining up these striped marks is similar to lining up the sights on a rifle.

Buoys  Buoys are floating aids to navigation used to mark channels and warn of dangers such as shoals or obstructions. On the chart, lighted buoys are indicated by a purple flare from the buoy symbol or by a small purple disk centered on the position circle. Buoys are distinguished by color, shape, topmark, lights, and sounds. The colors red and green are used for lateral marks or to delineate the edge of a channel. These can be colored all red or all green, but they can also be horizontally banded red and green or vertically banded red and white. Yellow is reserved for special buoys which may be used to indicate an unusual area or feature such as traffic separation, spoil ground, military exercise zone, cable, pipeline, or recreation zone. When you shine a searchlight on buoys at night, reflective tape helps identify them, and the color of the reflective material agrees with the color of the buoy.

There are five basic buoy shapes: can, cone, sphere, pillar, and spar. Topmarks can be cone, spherical, cylinder, or X-shaped. Red and green lights are used to match the colors on lighted lateral marks while yellow is reserved for special marks. White lights are used on safe water aids with an occulting, isophase, a single long flash or Morse code A flashing sequence. Cans are cylindrically shaped, are usually colored green, and have odd numbers. The conical shaped buoys, usually called Nuns, are red and have even numbers. The numbers are lowest at the seaward end of the channel and increase moving upstream toward land. Often, you see a buoy with both a number and a letter such as "9A." This usually happens when an additional buoy has been inserted in the channel and the USCG doesn't want to change the numbering sequence. Any buoy may use just a letter for identification. The number or letter appearing on a navaid will be identified in quotation marks on the chart. If the buoy is lighted, the color of the light will usually be the same color as the buoy and will usually be a flashing light.

Buoys often have other features noted on the chart. Marks may have sound-producing gear including horns, whistles, gongs, bells, or diaphones, each having a distinctive tone. A buoy referenced as "RaRef" on the chart has a radar reflector that enhances its visibility to radar equipped vessels. A buoy labeled "RACON" emits its own independent radar signal that identifies it, usually a Morse code letter, on any radar screen within range.

Red and green horizontally banded buoys are used at junctions in a channel to show the preferred channel or to mark obstructions that may be passed on either side. If you want to stay in the preferred channel, consider the buoy to be all the same color as the top band and position your boat accordingly; for example, if the top band is red, keep the buoy to your starboard coming in toward land, and you will take the preferred channel.

We have all heard the mnemonic "Red-Right-Returning", which refers to the International Association of Lighthouse Authorities (IALA) lateral mark system of buoyage used in the US. In order to remain in the correct channel when returning to harbor, the red buoys, called Nuns, are kept to starboard. But Red-Right-Returning is also used when proceeding along the US coast in a clockwise direction from Maine to Florida, around the Gulf Coast and northward from California to the Canadian border. This is called the "general direction of buoyage." It is important to know if a buoy is used to mark the return from seaward, the coastal route around the US, or to mark an isolated dangerous area. Usually a quick look at the location on the chart, the numbering sequence of the buoy, or the proximity of a hazard to the buoy will give you the answer.

Remember, there are two major types of buoyage systems: the lateral system and the cardinal system. The lateral system is partially explained above and is best suited for well-defined channels and the general direction of buoyage. The US navaid system is a lateral system. The cardinal system is best suited for coasts with numerous isolated rocks, shoals, islands, and for dangers in the open sea. The cardinal system is explained in Bowditch and should be reviewed before venturing into waters where it is used.

Chart No. 1 is a book containing a key to chart symbols. It contains a listing of all chart symbols used by the National Ocean Service (NOS), the Defense Mapping Agency (DMA), the International Hydrographic Organization, and on foreign charts reproduced by DMAHTC. Subjects covered include general features of charts, topography, hydrography, and aids to navigation. There is also a complete index of abbreviations and an explanation of the IALA buoyage system.

Lights  Lights on beacons and buoys also have distinctive characteristics to differentiate them from other lights, or to convey specific information. Every light displays a distinctive sequence of light and dark intervals with the dark intervals called eclipses. There are numerous types of light sequences ranging from continuous fixed to quick flashing, from single to group flashing, and almost everything in-between. An occulting light is eclipsed at regular intervals and the duration of light is always greater than the duration of darkness. A flashing light is also eclipsed at regular intervals, but the duration of light is always less than the duration of darkness. Needless to say, you need to know the various kinds of lights and their abbreviations displayed on the chart in order to identify them, determine your location in relation to them, and then maneuver your boat properly.

On large scale charts, the legend elements of lighthouses and other navigation lights are shown in this order: Characteristic, Color, Period, Height, Range, and Designation. For example, Fl (2) R 10s 80m 19M "6" is a lateral mark with the number 6 on it, has group flashing lights that present two red flashes every 10 seconds, has a height of 80 meters (261 feet), and is visible for 19 nautical miles under normal conditions.

Reliability  Wise sailors don’t rely entirely on floating navaids. These are often displaced or destroyed by storms or are removed for repair. They are also occasionally re-numbered or changed by the USCG, and if you haven't updated your charts with the Local Notices to Mariners, you can become disorientated. When you are depending on a particular navaid for your position, and it isn't there, or the numbering is different, don't panic. Immediately determine your position using radar, loran, GPS, or by bearings from other identifiable landmarks before you take any action that could place you in harm’s way.

We will cover more of this aspect of navigation later on in the section on coastal navigation. See you here at SailNet.

Jim Sexton is offline  
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