Figure 14-01 Buoys, daybeacons, and minor lights all follow a systematic pattern of shapes and colors, whereas primary lights, such as lighthouses, are more distinctive and diverse.
• Buoys • Daybeacons • Lights of All Sizes & Types • Sound Signals Ranges & Directional Lights—All Vitally Necessary for Safe Navigation
Unlike the roads and highways that we drive on, the waterways we go boating on do not have road signs that tell us our location, the route or distance to a destination, or of hazards along the way. Instead, the waterways have AIDS TO NAVIGATION, all those man-made objects used by mariners to determine position or a safe course. These aids also assist mariners in making landfalls, mark isolated dangers, enable pilots to follow channels, and provide a continuous chain of charted marks for precise piloting in coastal waters. An aid-to-navigation system is designed and intended to be used with a nautical chart. The exact meaning of an aid may not be clear to a navigator unless the appropriate chart is consulted, as the chart illustrates the relationship of the individual aid to channel limits, obstructions, hazards to navigation, and to the total aids to navigation system.
The term “aid to navigation” includes buoys, daybeacons, lights, lightships, radiobeacons, and sound signals. (The United States no longer has any lightships, marine radiobeacons, or a Loran system, but these may be found in some foreign waters.) Also included are the Global Positioning System (GPS) and other electronic systems that are covered in Chapter 16. The term covers all the visible, audible, and electronic signals that are established by government and private authorities for piloting purposes. The U.S. Coast Guard uses the acronym ATON.
Note that the term NAVIGATION AID is far broader, including charts, instruments, and methods that assist in marine navigation.
Aids to navigation are shown on the appropriate charts. Good piloting starts with the ability to correlate what appears on the charts with what you see on the water.
Aids established by the federal government are placed only where the amount of traffic justifies their initial cost and continuing maintenance. Within bounds of necessity and cost, each aid is designed to be seen or heard over the greatest possible area.
Operating Agencies
The U.S. Coast Guard is the agency responsible for maintaining aids to navigation on U.S. waters that are under federal jurisdiction or that serve the needs of the U.S. armed forces. Each Coast Guard District has supply and buoy depots, and special vessels for maintaining the aids.
State-Maintained Aids
On bodies of water wholly within the boundaries of a single state and not navigable to the sea, the state is responsible for establishing and maintaining aids to navigation.
Although each state keeps authority over its waters, a uniform system of aids and regulatory markers was established, but this has now been phased out in favor of aids conforming to the system used in coastal waters.
“Private” Aids to Navigation
With prior approval, aids may be established in federal waters by individuals or agencies other than the Coast Guard. Commercial, naval, scientific, sporting, or other private organization may establish aids for their own specific purposes. These might consist of such diverse activities as lights on loading docks, data-gathering devices for oceanographers, or racing marks for regattas. These PRIVATE AIDS must be patterned after federal aids, and any fixed structure planned for navigable waters requires a permit from the Army Corps of Engineers. See any USCG District Headquarters for details and procedures.
All such aids to navigation—whether established by an individual, a corporation, a state or local government, or even a federal agency other than the Coast Guard, such as the Navy—are private aids. They must have the same appearance as Coast Guard–maintained aids but are specially designated in the Light Lists.
Protection by Law
Whether or not established by the Coast Guard, all aids to navigation are protected by law. It is a criminal offense to cause any damage or hindrance to the proper operation of any aid. Do not deface, alter, move, or destroy any aid to navigation. Never make your boat fast to a buoy, daybeacon, or light structure. Avoid anchoring so close to a buoy that you obscure the aid from sight of passing vessels. If you should unintentionally or unavoidably collide with or damage an aid to navigation, report the fact to the nearest Coast Guard unit without delay.
Suggestions for improvements to aids to navigation should be submitted in writing to the Commander of the Coast Guard District concerned; see Appendix C.
TYPES OF AIDS TO NAVIGATION
The term “aid to navigation” encompasses a wide range of floating and fixed objects (“fixed” meaning attached to the bottom or shore), ranging from a small buoy or a single pile of wood, concrete, or metal with a sign, to lighthouses with an array of visible, audible, and electronic signals. Informal aids such as bush stakes marking natural channels or hazards in a creek are not a part of the organized system of aids to navigation.
Prominent buildings, cupolas, smokestacks, and other structures ashore, as well as unique land features, also can be used as signposts for navigation. These are LANDMARKS, as distinguished from aids established solely for navigation.
Major Types
BUOYS are floating objects—other than lightships—that are anchored to the bottom as aids to navigation. They have distinctive shapes and colors as determined by location and purpose, and may have visual, audible, and/or electronic signals.
BEACONS are structures that are permanently fixed to the earth’s surface, on shore or in the water; they may be of any size, from a lighthouse to a single pile. Lighted beacons are called LIGHTS; unlighted beacons are called DAYBEACONS.
Beacons are equipped with one or more DAYMARKS of a distinctive shape and color for daytime identification. Lights are classified by the U.S. Coast Guard and other authorities as PRIMARY SEACOAST LIGHTS, SECONDARY LIGHTS, or MINOR LIGHTS, as determined by their location, importance, and physical characteristics. A light’s range and intensity vary with its classification. The shape and color of its supporting structure may be distinctive to identify it, but these characteristics do not convey information as they do for buoys. The term LIGHTHOUSE is often applied to primary seacoast lights and to some secondary lights; see Figure 14-01.
SOUND SIGNALS are audible signals to assist mariners during periods of low visibility. They may be stand-alone aids but are generally part of a buoy, light, or other aid to navigation.
RANGES are pairs of unlighted or lighted fixed aids that, when observed in line, show the pilot to be on the centerline of a channel. The front aid of a pair may also serve to mark a turn in a channel.
LIGHTSHIPS are specially equipped vessels anchored at specific locations to serve as aids to navigation. They are of distinctive shape and color and have lights, sound signals, and radiobeacons. In U.S. waters, lightships have been replaced by permanent towers and large, specially equipped buoys, as explained later in this chapter.
RADIOBEACONS are transmitters broadcasting a characteristic signal specifically to aid navigation at night, in fog, or at distances exceeding normal visibility. These are usually with another aid, such as a major light, but may be separate. Marine radiobeacons are no longer operated along the U.S. coasts.
RADIONAVIGATION SYSTEMS are radio transmitters ashore and on satellites that emit special signals for use in navigation. The systems include the now-ubiquitous Global Positioning System (GPS) operated by the Department of Defense, the Coast Guard’s Differential Global Positioning System (DGPS), the Wide Area Augmentation System (WAAS) under the FAA, and aeronautical radiobeacons and Omni stations run by the Federal Aviation Administration. There are also some private systems, but these will seldom be available to recreational boaters.
BUOYS
Buoys are anchored to the bottom at specific locations, and are shown on charts by special symbols and lettering that indicate their shape, color, and visual and/or sound signals (if any). They vary widely in size. Buoys are anchored with chain to heavy concrete “sinkers” weighing up to six tons or more. The length of the chain will vary with the location, but may be as much as three times the depth of the water.
The buoyage system adopted for United States waters consists of several different types of buoys, each kind designed to serve under definite conditions. Broadly speaking, all buoys serve as daytime aids; many have lights and/or sound signals so that they may be used at night and in periods of poor visibility.
A buoy’s shape, color, and light characteristics, if any, give a navigator information about his location and the safe guidance of his vessel. A buoy’s size is usually determined by the importance of the waterway and size of vessels using it, and the distance at which the buoy must be seen.
Buoy Characteristics
Buoys may be unlighted or lighted, sound buoys, or combination buoys (having both an audible and a visual signal). The Coast Guard maintains about 20,000 unlighted and 4,100 lighted and combination buoys in waters under its jurisdiction. Additional buoys are maintained by state and private agencies in nonfederal waters.
Buoy Shapes
Unlighted buoys may be further classified by their shape.
Figure 14-02 A can buoy is cylindrical in shape with its long axis vertical. On this buoy, the upper part is made of metal plates at right angles to each other, making it an excellent radar reflector. Most, but not all, can buoys are constructed in this manner.
CAN BUOYS have a cylindrical above-water appearance, like a can or drum floating with its axis vertical and one flat end upward; see Figure 14-02. Two lifting lugs may project slightly above the flat top of a can buoy, but they do not significantly alter its appearance.
NUN BUOYS have an above-water appearance like that of a cylinder topped with a cone, pointed end up; see Figure 14-03. The cone may come to a point or be slightly rounded. Smaller nun buoys have a single lifting ring at the top; larger buoys have several lugs around the sides.
Figure 14-03 A nun buoy is cylindrical up to just above the waterline; from there it tapers to form a conical top. The upper part of some nun buoys, as here, consists of metal plates at right angles to reflect radar signals. The lifting ring at the top of this buoy (viewed side-to in this photo) has no navigational significance.
Unlighted buoys come in standardized sizes; a nun’s above-water portion may vary from 30 inches (0.76 m) to 14 feet (4.27 m); can buoys range from roughly 18 inches (0.46 m) to nearly ten feet (3.05 m) above the waterline. Boaters should remember that a considerable portion of a buoy is underwater, so that it is actually much larger and heaver than would appear from casual observation. Some smaller buoys are now made of plastic materials.
SPHERICAL BUOYS are used in the revised U.S. lateral system for information and regulatory purposes.
Other buoys of special shapes will sometimes be found in use as markers, but these are not regular aids to navigation. The Coast Guard has now eliminated the use of SPAR buoys, but they may be used in some other nations or in private systems. They are usually large vertical logs, trimmed, shaped, and appropriately painted; they are anchored at one end by a chain.
Lighted, sound, and combination buoys are described by their visual and/or audible signals rather than by their shape, as discussed below; see Figure 14-04.
Figure 14-04 Buoys with lights or sound signals, or both, have no significant shape, although most will appear similar to the Winwah Bay sea buoy shown here. Lifting lugs are at the base of the superstructure. Note the topmark above the solar-powered light.
Sound Buoys
A separate category of unlighted buoys includes those with a characteristic sound signal to aid in their location in fog or other reduced visibility. Different sound signals are used to distinguish between different buoys that are within audible range of one another.
BELL BUOYS are steel floats surmounted by short skeleton towers in which a bell is mounted; see Figure 14-05. They are effective day and night, and especially in fog or other conditions of reduced visibility; their use is favored because of their moderate maintenance requirements. Bell buoys are operated by motion of the sea using four tappers, loosely hung externally around the bell. When the buoy rolls in waves, wakes, or ground swells, a single note is heard at irregular intervals. Bell buoys, and other types that require some sea motion to operate, are not normally used in sheltered waters; a horn buoy is used there instead if a fog signal is needed.
Figure 14-05 A bell buoy has four tappers that are outside the bell. These strike the bell, making similar sounds in an irregular pattern as the buoy rocks due to the motion of the sea.
GONG BUOYS are similar in construction to bell buoys, but they have multiple gongs instead of a single bell. They normally have four gongs of different tones, with one tapper for each gong. As the sea rocks the buoy, the tappers strike against their gongs, sounding four different notes in an irregular sequence.
WHISTLE BUOYS have a whistle sounded by compressed air that is produced by sea motion. Whistle buoys are thus used principally in open and exposed locations where a ground swell normally exists.
HORN BUOYS are rather infrequently used. They differ from whistle buoys in that they are electrically powered; they are placed where a sound signal is needed and sea motion cannot be depended upon.
Lighted Buoys
Buoys may be equipped with lights of various colors, intensities, and flashing characteristics (called RHYTHMS). Colors and characteristics of the light convey specific information to the mariner. Intensity depends upon the distance at which the aid must be detected, as influenced by such factors as background lighting and normal atmospheric clarity.
Lighted buoys are metal floats with a battery-powered light atop a short skeleton tower; see Figure 14-06. Lighted buoys can operate for many months without servicing and have “day -light controls” that automatically turn the light on and off as darkness falls and lifts. The lights are powered by storage batteries that are kept charged by panels of solar cells near the top of the buoy.
Figure 14-06 A lighted buoy has a light at its top that flashes in one of several regular patterns. Power is obtained from a battery that is kept charged by a solar panel. Power-efficient light emitting diode (LED) arrays are replacing conventional incandescent lamps.
Lights on buoys may be red, green, white, or yellow according to the specific function of the buoy; the use of these colors is discussed later in this chapter.
Combination Buoys
Buoys with both a light and sound signal are designated COMBINATION BUOYS. Typical of these are lighted bell buoys, lighted gong buoys, and lighted whistle buoys. There will be only one type of sound signal on any buoy; see Figure 14-07.
Figure 14-07 This combination buoy has both a light and a whistle. The light is powered by solar cells at the top and a battery within the hull; the whistle is operated by the motion of the seas. The red-and-white vertical striping and red spherical topmark on this buoy indicate that it’s a safe-water mark.
Offshore Buoys
As a replacement for lightships and for use at important offshore locations, the U.S. Coast Guard developed LARGE NAVIGATIONAL BUOYS (LNBs). These aids—sometimes referred to as “super buoys”—were roughly 40 feet (12.2 m) in diameter with a superstructure rising to 30 feet (9.1 m) or more. Because of their high initial cost and considerably greater maintenance costs, however, LNBs have been replaced with EXPOSED LOCATION BUOYS (ELBs). These are still quite large, being 9 feet (2.74 m) in diameter. ELBs are equipped with lights and sound signals as well as weather and electronic navigation devices. Power is supplied by batteries kept charged by solar cells and a generator powered by wave motion; see Figure 14-08.
Figure 14-08 Exposed location buoys (ELBs) are usually equipped with a RACON (radar transponder), light, and sound signal; some will have meteorological sensors. These typically have both solar and wave-actuated power sources.
Buoy Colors
Buoys may be of one solid color or have a combination of two colors in horizontal bands or vertical stripes. The colors used in the IALA system are red, green, yellow, white, and black. The specific application of colors is discussed later in this chapter in connection with the uses of various buoys.
Optical Reflectors
Almost all unlighted buoys are fitted with areas of reflective material to help boaters find them at night by using searchlights. The material may be red, green, white, or yellow in banding or patches, and it has the same significance as lights of these colors. White reflective material may be placed on the numbers or letters of lighted and unlighted buoys of all types.
Radar Reflectors
Many buoys have RADAR REFLECTORS—vertical metal plates set at right angles to each other so as to greatly increase the echo returned to a radar receiver on a vessel. The plates are shaped and mounted to preserve the overall characteristic shape of an unlighted buoy or the general appearance of a lighted buoy; refer to Figures 14-04, 14-06, and 14-07.
CAUTIONS IN USING BUOYS
Do not count on floating aids always maintaining their precise charted positions or unerringly displaying their characteristics. The Coast Guard works constantly to keep aids on station and functioning properly, but obstacles to perfect performance are so great that complete reliability is impossible.
Buoys are heavily anchored but may shift, be carried away, or sunk by storms or ships. Heavy storms may also cause shoals to shift relative to their buoys.
Lighted buoys may malfunction and show no light, or show improper light characteristics. Audible signals on most buoys are operated by action of the sea, and may be silent in calm water, or they may fail to sound because of a broken mechanism.
A buoy does not maintain its position directly over its sinker, as it must have some scope on its anchor chain. Under the influences of current and wind, it swings in small circles around the sinker, which is the charted location. This swinging is unpredictable, and a boat attempting to pass too close risks collision with a yawing buoy. In extremely strong current, a buoy may even be pulled beneath the water surface.
Buoys may be temporarily removed for dredging operations, and/or in northern waters they may be discontinued for the winter or changed to special types in order to prevent damage or loss from ice flows. The Light Lists show dates for changes or for seasonal buoys, but these are only approximate and may be changed by weather or other conditions.
Temporary or permanent changes in buoys may be made between editions of charts. Keep informed of existing conditions through reading Notices to Mariners and/or Local Notices to Mariners.
All buoys (especially those in exposed position) should, therefore, be regarded as warnings or guides, and not as infallible navigation marks. Whenever possible, navigate with bearings or angles on fixed aids or objects on shore (see Chapter 18), and by soundings, rather than by total reliance on buoys.
Light Rhythms
The lights on lighted buoys will generally flash in one of several specific rhythms, for these reasons:
• Flashing conserves the energy source within the buoy.
• A flashing light can be more easily detected against a background of other lights.
• The light can signal specific information during hours of darkness, such as the need for special caution at a certain point in a channel.
• Different flashing patterns can be used to distinguish clearly between buoys of similar functions that are within visible range of each other.
FLASHING lights are those that come on for a single brief flash at regular intervals; the time of light is always less than the time of darkness. Coast Guard–maintained flashing buoys will flash their light not more than 30 times per minute; this is the more generally used characteristic. It is sometimes referred to as “slow flashing,” but this is not an official designation.
QUICK FLASHING lights will flash not less than 60 times each minute. These buoys are used for special situations where they can be more quickly spotted and where particular attention to piloting is required.
GROUP FLASHING (2+1) lights show two brief flashes, a brief interval of darkness, a single brief flash, and then an interval of darkness of several seconds duration.
MORSE CODE (A) FLASHING lights have a cycle of a short flash, and a brief dark interval, then a longer flash and a longer dark interval, repeated every eight seconds. This is the “dot-dash” of the letter “A” in Morse code.
The above light rhythms are shown diagrammatically in Figure 14-09. The PERIOD of a light is the time it takes to complete one full cycle of flash and dark interval, or flashes and dark intervals. A light described as “flashing 4 seconds” has a period of four seconds. One flash and one dark interval lasts just that long before the cycle is repeated. Three standard periods are used for flashing lights—intervals of 2.5, 4, and 6 seconds.
The term CHARACTERISTICS as applied to a lighted aid to navigation includes the color as well as the rhythm, and may also cover physical features, such as nominal range.
Figure 14-09 Characteristic light patterns identify buoys. They are named (as indicated in these schematic patterns) and identified on charts by abbreviations. One period is indicated by (quick flashing is continuous and does not have a period).
DAYBEACONS
DAYBEACONS are unlighted aids that are fixed, rather than floating like buoys. They may be either on shore or in waters up to about 15 feet (4.6 m) deep.
Daybeacons vary greatly in design and construction, depending upon their location and the distance from which they must be seen. Daybeacons in U.S. waters, and their chart symbols, are illustrated in the ATON Light List plates.
Daybeacon Construction
The simplest daybeacon is a single pile with signboards, called DAYBOARDS, at or near its top, usually two, facing in opposite directions; see Figure 14-10. The pile may be wood, concrete, or metal.
Figure 14-10 Most daybeacons consist of a single pile with two square or triangular dayboards, corresponding to a can or a nun and marked with a number or number and letter. At some locations, such as channel junctions, where the daybeacon can be approached from more than two directions, there will be an additional dayboard.
A larger, more visible, and more sturdy daybeacon is the “three-pile dolphin” type: three piles a few feet apart at their lower ends, bound tightly together with wire cable at their tops. There are also some five-pile dolphins (four piles around one central pile.) The Coast Guard maintains approximately 10,000 daybeacons.
Dayboards
Dayboards usually bear identification in the form of a number, a letter, or a number plus a letter, and are normally either square or triangular, corresponding to can and nun buoys. Square dayboards are green with green reflective borders. Triangular dayboards are red with red reflective borders. Rectangular dayboards are used in range marks as well. In special applications, a dayboard may be octagonal (eight-sided) or diamond shaped, carrying a brief warning or notice.
Dayboards used as marks in the Intracoastal Waterway (ICW) display unique square, triangular, or horizontal-band yellow symbols to distinguish them from aids marking other waters.
The Uses of Daybeacons
For obvious reasons, daybeacons are restricted to relatively shallow waters. Within this limitation, however, a daybeacon is often more desirable than a buoy because it is firmly fixed in position and taller, thus easier to see and identify. Daybeacons also require less maintenance than buoys.
Daybeacons are used primarily for channel marking, and they serve in the same manner as buoys in the buoyage systems to be described later in this chapter.
MINOR LIGHTS
Just as daybeacons are sometimes substituted for unlighted buoys, so may lighted buoys be replaced with MINOR LIGHTS. These are fixed structures of the same overall physical features as daybeacons, but equipped with a light generally similar in characteristics to those found on buoys; see Figure 14-11. Most minor lights are part of a series marking a channel, river, or harbor; also included, however, are some isolated single lights if they are of the same general size and characteristics. The term “minor light” does not include the more important lights marking harbors, peninsulas, major shoals, etc.; these have lights of greater intensity and/or special characteristics—these are designated as “secondary” or “primary seacoast” lights and are discussed in detail later in this chapter.
Figure 14-11 Most minor lights are little more than a daybeacon to which has been added a light, with its battery box and solar panels. The minor light seen here has a more elaborate structure and has three dayboards.
Features of Minor Lights
Minor lights are placed on single piles, on multiple-pile dolphins, or on other structures in the water, or on shore; see Figure 14-11. Minor lights carry dayboards for identification, and reflective material for nighttime safety should the light be extinguished.
Light Characteristics
A minor light normally has the same color and flashes with the same phase characteristics as a lighted buoy; refer to Figure 14-09. Intensity will generally approximate that of a lighted buoy, but visibility may be increased by its greater height above water and its more stable platform. A combination of storage batteries and solar cells is used in the same manner as on lighted buoys.
Sound Signals
Minor lights may, in some locations, have an audible sound signal—an electrically operated horn or siren. In some cases, the signal operates continuously for months when reduced visibility conditions can be expected.
Figure 14-12 An articulated light is a rigid, buoyant structure fixed (with an articulated coupling) to the seabed. It provides a more precise location than an anchored lighted buoy. Without the light, it would be an articulated daybeacon.
BUOYAGE SYSTEMS
Most maritime nations use either a LATERAL SYSTEM OF BUOYAGE or a CARDINAL SYSTEM, or both. In the lateral system, the buoys indicate the direction to a danger relative to the course that should be followed. In the cardinal system, characteristics of buoys indicate location of the danger relative to the buoy itself; see Figure 14-13. The term “cardinal” relates to the cardinal points of the compass.
Figure 14-13 Cardinal marks indicate that the navigable water lies to the named side of the mark—i.e., to the north of the north mark, to the east of the east mark, etc. The marks are distinguished from one another by their color banding and topmarks.. If lighted, the color is white.
The IALA Systems of Aids to Navigation
The INTERNATIONAL ASSOCIATION OF MARINE AIDS TO NAVIGATION AND LIGHTHOUSE AUTHORITIES (formerly the International Association of Lighthouse Authorities and still known as the IALA) had the goal of establishing a single global system of aids to navigation, but was unable to do so and had to settle for two regional systems. These systems have many identical characteristics, but also one fundamental difference—the colors used for the lateral marks. Both systems have provisions for the use of topmarks; these are small shapes, such as spheres and triangles, placed atop the buoy.
THE IALA-A SYSTEM OF AIDS TO NAVIGATION
The IALA-A system uses the same cardinal marks, isolated danger marks, safe water marks, and special marks as the IALA-B system. The difference is that the lateral marks are directly opposite in color—marks left to starboard when entering from the sea are colored green, those on the port side are colored red. The shapes of the lateral marks are the same in both systems; only the color is different.
The IALA-A system is used in all waters worldwide that are not covered by the IALA-B system. This, of course, includes European, African, and nearly all Asian waters.
The IALA-B System
The full name is “System B—The Combined Cardinal and Lateral System (Red to Starboard).” System B uses five types of “marks”—those of lateral and cardinal systems, plus three different marks for isolated dangers and safe waters, and for special indications. These are all of a designated design, but may vary in size. Nations using this system must use aids conforming to the basic designs, but need not use all types. As indicated by the title, lateral marks on the starboard side of channels entering from the open sea are colored red, with the port side being marked by green aids. Table 14-1 summarizes the IALA-B System.
The IALA-B system is used in the Western Hemisphere, Japan, Korea, and the Philippines.
IALA-B LATERAL SYSTEM OF BUOYAGE
Table 14-1 This table summarizes the color numbering, shape, and lights or buoys used in the IALA-B system of buoyage. Be aware of the “clockwise direction” rule in the coastal waters of the United States, see text.
The U.S. Aids to Navigation System
The United States has long used a “lateral system” of buoyage; this has now been converted to conform, as noted above, to the colors and shapes established by the International Association of Lighthouse Authorities (IALA) for “System B.” Wherever you travel in the navigable waters of the United States, Canada, and other countries of the Western Hemisphere, the basic system is the same; you needn’t learn a new system for new waters. (The IALA-A system is used in U.S. possessions west of the International Date Line and south of 10°North latitude; see sidebar.)
In the United States, the lateral system of buoyage is uniformly used in all federal-jurisdiction areas and on many other bodies of water where it can be applied. In this system, the shape, coloring, numbering, and light characteristics of buoys are determined by their position with respect to the navigable channel, natural or dredged, as such channels are entered and followed from seaward toward the head of navigation. This is termed the “conventional direction of buoyage.”
Since not all channels lead or appear to lead from seaward, certain arbitrary assumptions are used in order that the lateral system may be consistently applied. In coloring and numbering offshore buoys along the coasts, the following system has been adopted: proceeding in a southerly direction along the Atlantic Coast, in a northerly then westerly direction along the Gulf Coast, and in a northerly direction along the Pacific Coast will be considered the same as coming in from seaward. This can be remembered as proceeding around the coastline of the United States in a clockwise direction.
Thus there’s a very important exception to red-right and green-left. As noted above it occurs in the United States when a channel that appears to come from the sea has in fact been designated by the U.S. Coast Guard as part of the “clockwise direction” rule. It happens in coastal waters including rivers and especially in the Intracoastal Waterway. Many unexpected groundings have occurred because the navigator did not study the charts or does not understand the clockwise rule.
On the Great Lakes, offshore buoys are colored and numbered as proceeding from the outlet end of each lake toward its upper end. This will be generally westerly and northward on the lakes, except on Lake Michigan where it will be southward. Buoys marking channels into harbors are colored and numbered just as for channels leading into coastal ports from seaward.
On the Mississippi and Ohio rivers and their tributaries, characteristics of aids to navigation are determined as proceeding from seaward toward the head of navigation, although local terminology describes “left bank” and “right bank” as proceeding with the flow of the river.
Not all types of marks are used in all waters, but those that are used will conform to the IALA-B system with respect to shapes, colors, topmarks, and light color and rhythm (characteristic). The U.S. system does not use cardinal buoys, but does use safe-water buoys and a few isolated-danger buoys. The IALA-B system makes no mention of sound signals such as bells, gongs, or whistles on buoys, and the previous U.S. usage has not been changed. The U.S. system also includes daybeacons and lights on fixed structures, aids that are not covered by either IALA system.
The U.S. system of lateral aids to navigation is supplemented by nonlateral aids where appropriate; see Figure 14-14.
Coloring
All buoys are painted distinctive colors to indicate on which side you should pass them, or to show their special purpose. In the lateral system the significance of colors is as described below; the traditional phrase “red, right, returning” helps in remembering the system.
Red buoys mark the starboard (“right”) side of a channel when entering (“returning”) from seaward, or a hazard that you must pass by keeping the buoy to starboard.
Green buoys mark the port (left) side of a channel when entering from seaward, or an obstruction that must be passed by keeping the buoy on the left hand.
Red-and-green horizontally banded buoys are used to mark the “preferred” channel (usually the major channel) at junctions, or hazards that you may pass on either side (but check your chart to be sure). If the topmost band is green, the preferred channel is with the buoy to port of your boat—it is treated as if it were a can buoy. If the topmost band is red, the preferred channel is with the buoy to starboard. (Note: When proceeding toward the sea, it may not be possible to pass such buoys safely on either side. This is particularly true in situations where you are following one channel downstream and another channel joins in from the side; see Figure 14-15. When such a buoy is spotted, be sure to consult the chart for the area.)
Figure 14-15 A junction buoy, painted with red and green bands, must be treated differently depending upon whether you are proceeding toward the sea or away from it. Upstream, either course is safe; downstream one course is dangerous.
Figure 14-14 There are some circumstances in the IALA-B system where yellow buoys that have no lateral significance are used. Generally, these mark anchorages, exclusion areas, artificial reefs, and dumping grounds, etc.
Red-and-white vertically striped buoys are “safe-water marks”; they are used as offshore approach points (often called “sea buoys”) and to mark a fairway or midchannel. If lighted, there will be a single red spherical TOPMARK above the light that is roughly one-fifth the diameter of the buoy. If unlighted, the buoy may be spherical or it may be similar in construction to a sound buoy and will have a red spherical topmark.
Red-and-black horizontally banded buoys are used to mark isolated dangers (those not along the side of a marked channel); the top band will be black and there will be two black spherical topmarks.
Note carefully that areas of color running horizontally are “bands”; if the areas are arranged vertically, they are “stripes.” These terms are used in other color combinations in the case of special-purpose buoys.
Shapes of Buoys
In the lateral system of buoyage, unlighted buoys have definite shape characteristics that indicate which side of the channel they mark. The ability to distinguish shapes is particularly essential when you first sight a buoy in line with the sun and can see only its silhouette, not its color.
Can buoys, painted green, mark the port (left) side of the channel when returning from seaward, or a hazard that you must pass by keeping the buoy to port.
Nun buoys, painted red, mark the starboard (right) side of channels, or hazards that must be passed by keeping the buoy to starboard.
Channel junction buoys may be of either can or nun shape as determined by which is the primary channel. If the buoy is a nun, the uppermost band is red; if the buoy is a can, the uppermost band is green; see Figure 14-15.
No special significance is to be attached to the shape of sound, lighted, or combination buoys. The purpose of these is indicated by their coloring, number, or the rhythm of the light. Special caution must be exercised when a buoy is first sighted under conditions that its color cannot be determined, such as when proceeding in a direction toward a sun low in the sky.
Numbering
Most buoys have “numbers,” which actually may be numbers, letters, or a number-letter combination to help you find and identify them on charts. In the lateral system, numbers serve as yet another indication of which side the buoy should be passed. The system is as follows:
Odd-numbered buoys mark the port (left) side of a channel leading in from seaward. In accordance with the rules stated above, these will be green buoys, cans if they are unlighted.
Even-numbered buoys mark the starboard (right) side of a channel; these will be red (nun) buoys or buoys with red lights.
Numbers increase from seaward and are kept in approximate sequence on the two sides of a channel by omitting numbers as appropriate if buoys are not uniformly placed in pairs. Occasionally, numbers will be omitted on longer stretches without buoys, to allow for possible later additions. Numbers followed by letters, such as “24A” and “24B,” are buoys added to a channel after the initial numbering system was established, and with the series not yet renumbered.
A buoy marking a wreck will often carry a number derived from the number of the buoy next downstream from it, preceded by the letters “WR.” Thus, a buoy marking a wreck on a channel’s left-hand side between buoys 17 and 19 would be “WR17A.” A wreck buoy not related to a channel may be designated by one or two letters relating to the name of the wrecked vessel or a geographic location.
Letters without numbers are sometimes used for red-and-white vertically striped buoys marking fairways or harbor entrances, and for green-and-red horizontally banded buoys.
Numbers followed by letters may be used on aids to navigation marking offshore dangers. For the buoy marked “1JR,” the number has the usual sequential significance and the letters “JR” indicate that it is off “Johnson Reef.”
Color of Lights
For all lighted buoys in the IALA-B lateral system, the following system of colors is used:
Green lights on buoys mark the left-hand side of a channel returning from seaward; these are on green odd-numbered buoys, or green-and-red horizontally banded buoys with the green band uppermost.
Red lights on buoys mark the right-hand side of a channel when entering from sea (red even-numbered buoys) or red-and-green horizontally banded buoys with the red band uppermost.
White lights in the IALA-B system are used only on safe-water marks with the Morse letter “A” rhythm, and on marks at isolated dangers with a group flashing (2) rhythm. (Some white lights remain in use on the Western Rivers but will eventually be eliminated.)
Yellow lights are used only on special marks; the rhythm may vary, but usually is flashing or fixed.
Light Rhythms
Flashing lights are placed only on green or red buoys, or on special-purpose buoys.
Quick flashing lights are placed only on channel edge–marking green and red buoys; these are used to indicate that special caution in piloting is required, as at sharp turns or changes in the width of the waterway, or to mark hazards that must be passed only on one side.
Group flashing (2 + 1) lights are used only on buoys with red-and-green horizontal bands. These are the buoys at channel junctions and at obstructions that can be passed on either side.
Morse code “A” flashing lights are placed only on red-and-white vertically striped buoys that mark a fairway or midchannel; these are passed close-to on either side, and are always white.
Fixed lights show continuously; they are rarely used because of excessive power requirement as compared with flashing lights.
Daybeacons & Minor Lights
The lateral system of buoyage has been described in terms of unlighted and lighted buoys, but the descriptions apply fully to comparable daybeacons and minor lights.
Daybeacons with red triangular dayboards may be substituted for nun buoys, and ones with green square dayboards may replace can buoys. Minor lights may be used in place of lighted or combination buoys. Structures subject to being repeatedly struck by vessels may be set back from the channel edge, as noted in the Light List.
If a daybeacon is used to indicate the preferred channel at a junction or an obstruction, the dayboard will be red-and-green horizontally banded, with the color of the uppermost band indicating the main or preferred channel. The dayboard shape will be either square or triangular as determined by the color of the top band, as with a can or nun buoy used for this purpose.
Safe-water daybeacons marking fairways or the midchannel have an octagonal dayboard, painted red and white, divided in half vertically down the middle.
A diamond-shaped dayboard has no significance in the lateral system. A typical application might be to increase the daytime detectability of a minor light that is not a part of a channel or waterway series. These are often used to mark a shoal, rock, submerged object, or other hazard; they are also used to mark prohibited areas where boats must not enter.
Minor lights, and the lights on buoys, are equipped with electronic DAYLIGHT CONTROLS that automatically turn the light on during periods of darkness and off during daylight. These controls are not of equal sensitivity; therefore all lights do not go on and off at the same time. Take care to identify aids correctly during twilight periods, when some may be on and others are not.
Wreck Buoys
Buoys that mark dangerous wrecks are generally lighted, and placed on the seaward or channel side of the obstruction and as near to it as possible. Wreck buoys are solid red or green if they can be safely passed on only one side; horizontally banded otherwise, and numbered as previously discussed. Be careful around wreck buoys, because sea action may have shifted the wreck since the last Coast Guard visit. Wreck buoys are also used in some instances where a fixed aid to navigation has been knocked down, but the remains have not been removed.
Isolated Danger Marks
In addition to the widespread lateral system of buoyage, the U.S. Coast Guard maintains a few aids to navigation in the cardinal system of buoyage. Such an aid is erected on, or moored above or near, an “isolated danger” that has unobstructed water on all sides. These marks should not be approached closely without special caution. Colors are red and black, horizontally banded; if lighted, the light is always white and group flashing (2), 6 seconds. A topmark of two black spheres vertically arranged is used on lighted and unlighted buoys; no numbers are used, but they may be lettered.
Seasonal Buoys
In some areas subject to severe icing during winters, the normal buoys are removed to prevent damage or loss. These are temporarily replaced with ICE BUOYS, lighted or unlighted buoys of special sturdy construction. The placement and removal of such buoys are announced in Local Notices to Mariners and Light List changes. In some instances, lights on shore may be activated to guide vessels in the absence of buoys.
Racons
Some major aids to navigation are equipped with RADAR BEACONS, commonly shortened to RACONS. When a racon is triggered by pulses from a vessel’s radar, it transmits a reply that results in a better-defined display on that vessel’s radarscope, thus increasing accuracy of range and bearing measurements.
The reply may be coded to facilitate identification, in which case it will consist of a series of dots and dashes (short and/or long intensifications of the radar blips beginning at and extending beyond the racon’s position on the radar screen). The range is the measurement on the radarscope to the dash nearest its center. If the racon is not coded, the beacon’s signal will appear as a radial line extending from just beyond the reflected echo of the aid, or from just beyond where the echo would be seen if detected. Details of racon coding will be found in the Light Lists. The coded response of a racon may not be received if the radar set is adjusted to remove interference (IF) or sea clutter from the scope; interference controls should be turned off when reception of a racon signal is desired.
Special-Purpose Aids
The Coast Guard also maintains several types of special-purpose aids with no lateral significance to mark anchorages, fish net areas, dredging limits, etc.
In the IALA-B system of buoyage, these are all yellow, regardless of the use to which they are put. These may be of can or nun shape, and, if lighted, the light will be yellow with any rhythm, fixed or slow flashing preferred. (Some are equipped with xenon discharge tube lights that flash very brightly but very briefly.) Dayboards on a daybeacon or minor light will be diamond shaped and yellow in color.
Reporting Discrepancies
All boaters should realize that the U.S. Coast Guard cannot keep the many thousands of aids to navigation under constant observation, and it is impossible to keep every light, buoy, daybeacon, and fog signal operating properly and on its charted position at all times. The safety of all who use the waters will be enhanced if every person who discovers an aid missing, off station, or operating improperly notifies the nearest Coast Guard unit of the situation that has been observed. Use radio, land telephone, e-mail, or postal mail as dictated by the urgency of the report. You can also use the Coast Guard's Boating Safety Mobile App, available for free download at www.uscgboating.org.
Variations in the Basic U.S. System
Although all U.S. waters are marked by the basic U.S. Aids to Navigation System, there are some areas in which additional or modified markings are used to meet local needs.
Buoyage on the Western Rivers
Buoyage on the “Western Rivers”—the Mississippi River and its tributaries above Baton Rouge, LA, and on some other rivers that flow toward the Gulf of Mexico—differs from the basic U.S. system in several ways:
• Aids to navigation are not numbered.
• Any numbers on aids to navigation are of no lateral significance, but show mileage (statute) from a fixed point—usually the river mouth.
• Diamond-shaped crossing dayboards, red-and-white or green-and-white as appropriate, are used to indicate where the river channel crosses from one bank to the other.
• Lights on green aids to navigation show a single-flash characteristic, which may be green or white.
• Lights on red aids to navigation show a group (2) flashing characteristic, which may be red or white.
• Isolated-danger and safe-water marks are not used.
In an effort to eliminate white lights from the lateral buoyage system, the U.S. Coast Guard is attempting to restrict their use to crossing daymarks.
Intracoastal Waterway Aids to Navigation
The Intracoastal Waterway (ICW) runs parallel to the Atlantic and Gulf coasts from Norfolk, Virginia, to the Mexican border. The purpose of the ICW is to provide a protected route for vessels making coastwise passages. Distances along the ICW are measured in statute miles, as the waterway is maintained by the U.S. Army Corps of Engineers.
Distinctive ICW markings Aids to navigation on the ICW are conventional buoys, daybeacons, and minor lights, but with added identification of yellow triangles on “red” aids and yellow squares on “green” aids; see Figure 14-16.
The conventional direction of buoyage in the ICW is generally southerly along the Atlantic coast, and first northerly then westerly along the Gulf of Mexico coast. Intracoastal Waterway aids are numbered in groups, with the numbers rarely exceeding “99” and beginning again with “1” or “2” at specified natural dividing points.
Buoy lights follow the standard system of red lights on red buoys and green lights on green buoys. Colors of minor lights fit the same pattern. Range lights, not being a part of the lateral system, may be of any standard color.
Figure 14-16 The dayboards on daybeacons and minor lights on the Intracoastal Waterways carry the usual numbers but also a yellow triangle or square. Buoys also have such a mark.
Dual-purpose aids The ICW was stitched together out of local rivers, channels, and fairways (with some additional land cuts created), which are marked in the conventional manner of the basic U.S. system. Some aids to navigation on these local waterways may also serve the
Intracoastal Waterway. If they have this DUAL PURPOSE, some portion of them is identified with either a yellow square (indicating a can buoy) or a yellow triangle (indicating a nun buoy). In some cases, a green can buoy marking a local channel may carry a yellow triangle for the ICW.
No matter what its basic shape, any aid of any shape carrying a yellow triangle should be left to starboard when following the ICW from north to south and on the Gulf Coast. Similarly, any aid with a yellow square should be left to port. Where dual markings are employed, the ICW skipper disregards the basic shape and coloring of the aid on which the yellow square or triangle is placed and pilots his craft solely by the shape of the yellow markings. The numbers on the aids will be those of the local channel’s lateral system, and in some instances where the southward ICW proceeds down a river, the numbers will be temporarily decreasing rather than increasing.
Nonlateral aids in the ICW—such as safe-water marks, isolated-danger marks, and ranges—will have a horizontal band or bar in yellow.
INLAND WATERS OBSTRUCTION MARK
To meet the needs of boaters on inland waters after the elimination of the United States Waterway Marking System, one new aid to navigation was created. On inland navigable waters designated by the Commandant of the Coast Guard as “state waters,” and on waters of a state where there is no defined head of navigation, such as lakes, the INLANDWATERS OBSTRUCTION MARK is used to indicate that an obstruction extends from the nearest shore out to that location. This buoy will have black-and-white vertical stripes, and its meaning is “Do not pass between this buoy and the shore.” If lighted, it will have a quick-flashing white characteristic.
Canadian Aids to Navigation
In Canadian waters, the lateral system of buoyage is essentially the same as in the United States, but there may be minor differences in the physical appearance of some buoys. Cardinal aids of the IALA-B system are used in some areas. Boaters should learn the appearances and meanings of such aids. Chart symbols may be slightly different from those used on U.S. charts. Responsibility for aids to navigation in Canada resides with the Canadian Coast Guard under Transport Canada. The Canadian Coast Guard has embarked on a new project, Aids To Navigation of the Twenty-First Century (AToN 21). Information about the program can be found at http://www.ccg-gcc.gc.ca.
Bahamas Aids to Navigation
The buoyage system in the Bahamas is essentially identical to the lateral system used in U.S. waters. Responsibility for the system resides with the Royal Bahamas Defence Force. The RBDF solicits reports on the condition and operation of ATONS including dayboards, buoys, lighthouses, beacons, and towers, and operates lighthouses with nominal ranges between 5.5 and 22.6 miles. Captains should take care to rely on their own navigational skills when operating in the Bahamas.
Information & Regulatory Markers
Although not derived from the IALA-B system, the U.S. Aids to Navigation System also includes INFORMATION & REGULATORY MARKS, often called “markers.” These are used to alert skippers to various warning or regulatory matters. The markers may be either buoys or beacons.
These marks have orange geometric shapes against a white background. The meanings associated with the orange shapes are as follows:
• An open-faced diamond signifies danger.
• Avertical diamond shape with a cross centered within it indicates that vessels are excluded from the marked area.
• A circular shape indicates that certain operating restrictions are in effect within the marked area.
• A square or rectangular shape contains directions or instructions lettered within the shape.
When a buoy is used as an information or regulatory mark, it must be white in color with two horizontal orange bands placed completely around the buoy circumference. One band must be near the top of the buoy body, with the other just above the waterline; both bands must be clearly visible.
PRIMARY SEACOAST & SECONDARY LIGHTS
PRIMARY SEACOAST and SECONDARY LIGHTS in the U.S. are so designated because of their greater importance as aids to navigation. They differ from the minor lights previously considered in their greater physical size, intensity of light, and complexity of light characteristics. These lights are more diverse than minor lights and buoys; only broad, general statements can be made about them as a group.
Primary seacoast lights warn the high-seas navigator of the proximity of land. They are the first aids seen when making a landfall (except where there may be a light tower or exposed location buoy). A coastwise navigator can use these lights to keep farther offshore at night than by using other visual aids. These are the most powerful and distinctive lights in the U.S. system of aids to navigation.
Primary seacoast lights may be located on the mainland or offshore on islands and shoals. Offshore, they may mark a specific hazard or they may serve merely as a marker for ships approaching a major harbor.
Many primary seacoast lights are classified according to the importance of their location, the intensity of light, and the prominence of the structure. Other aids are classed as secondary lights because of their lesser qualities in one or more of these characteristics. The dividing line is not clear, however, and lights that seem to be more properly in one category may be classified in the other group in the Light Lists. The difference in classification is of no real significance to boaters and can be ignored in practical piloting situations.
Figure 14-17 New London Ledge Light, Connecticut.
Structures
The physical structure of a primary seacoast light and of many secondary lights is generally termed a LIGHTHOUSE, although this is not a designation used in the Light Lists. The structure’s principal purpose is to support a light source and lens at a considerable height above water. The same structure may also house a sound signal or other equipment, and quarters for the personnel who operated the LIGHTSTATION and equipment before all functions were automated and responsibility for the structures was turned over to local communities.
Lighthouses vary greatly in outward appearance depending on where they are, whether they are in the water or on shore, the light importance, the ground they stand on, and the prevalence of violent storms; see Figures 14-17, 14-18, and 14-19.
Lighthouse structures also vary with the range of visibility they need; a lengthy range requires a tall tower or a high point of land, with a light of high CANDLEPOWER—the standard measure of brightness. At points intermediate to principal lights, however, and where ship traffic is light, long range is not so necessary, and a simpler structure can be used.
Figure 14-18 Split Rock Lighthouse State Park, Lake Superior, Minnesota.
Figure 14-19 Kilauea Point Lighthouse, Kauai, Hawaii.
Figure 14-20 Bands or stripes of various colors are often used to help in distinguishing lighthouses from their background, and as an aid to identification.
Coloring of Structures
Many lighthouses and other light structures are marked with colors, bands, stripes, and other patterns to make them stand out against their backgrounds and to assist in their identification; see Figure 14-20.
Light Characteristics
Primary seacoast and secondary lights have distinctive light characteristics—lights of different colors, and lights that show continuously while others show in patterns. Their three standard colors are white, red, and green.
Light Rhythms
Varying the intervals of lights and darkness in both simple and complex ways yields many different rhythms for major lights.
Fixed A light is termed “fixed” if it is always on, with no periods of darkness.
Flashing The term “flashing” has already been defined as a light that is on less than it is off in a regular sequence of single flashes occurring less than 30 times each minute. Some primary seacoast and secondary lights will “flash” in accordance with this definition, although their characteristics will have no relation to the flashes of buoys and minor lights. In general, a flashing major light will have a longer period (time of one complete cycle of the characteristic) and may have longer flashes—for example, Yaquina Head (Oregon) Light has a 20-second period with two flashes, each of 2 seconds duration.
In most instances, however, the light source is constant, and the “flashes” are produced by a rotating set of optical lenses; at close ranges, a weak steady light may be seen. Although a few major lights have a “fixed” characteristic (a continuous light without change of intensity or color), the light phase characteristics of primary seacoast or secondary lights are generally more complex, as described below (with current abbreviations).
Group Flashing (Fl [n]) The cycle of the light characteristic consists of two or more flashes separated by brief intervals and followed by a longer interval of darkness. (The “n” in the abbreviation will be replaced by the number of flashes for the light in question.)
Table 14-2
The light phase characteristics of primary and secondary lights permit rapid identification at night. One full cycle of changes is the light’s period. Light phase characteristics can be combined—fixed and flashing, for example. Eclipses refer to periods of darkness.
Alternating Flashing (Al Fl) Flashes of alternating color, usually white and red or white and green.
Occulting (Oc) The light is on more than it is off; the interval of time that the light is lighted is greater than the time that it is ECLIPSED—its period of darkeness.
Isophase (Iso) Intervals of light and darkness are equal; the light is described in the Light List or on charts in terms of the period, the lighted and eclipsed portions each being just half of that time. This was formerly known as an “equal interval light.”
Group Occulting (Oc [n]) Intervals of light regularly broken by a series of two or more eclipses. This characteristic may have all eclipses of equal length, or one greater than the others. (The “n” in the abbreviation will be replaced by the number of eclipses for the light in question.)
Complex Characteristics
The above light phase characteristics may be combined. Examples might include Gay Head Light “Alternating White/Red 15 seconds (Al W R 15s)” where there is a white flash for 0.2 seconds, an eclipse (period of darkness) for 7.3 seconds, a red flash for 0.2 seconds, and an eclipse of 7.3 seconds, for a total period of 15 seconds; or Minots Ledge Light “Group Flashing White 45 seconds (Fl W (1+4+3) 45s)” where 1.5-second white flashes occur with 1.5-second eclipses in groups of one, four, and three separated by 5-second intervals and followed by a 15.5-second longer interval to indicate the proper starting point of the 45-second period; or other characteristics of a generally similar nature.
Sectors
Many lights will have SECTORS—portions of their all-around arc of visibility in which the normally white light is seen as red or green. These sectors mark shoals or other hazards or warn of land nearby.
Lights so equipped show one color from most directions, but a different color or colors over prescribed arcs of the horizon as indicated on charts and in the Light List. A sector changes the color of a light when viewed from certain directions, but not the flashing or occulting characteristic. For example, a flashing white light with a red sector, when viewed from within the sector, will appear as flashing red; see Figure 14-21,.
Sectors may be a few degrees in width, as when marking a shoal or rock, or wide enough to extend from the direction of deep water to the shore. Bearings referring to sectors are expressed in degrees as they are observed from a vessel toward the light.
You should almost always avoid water areas covered by red sectors, but you should also check your chart to learn the extent of the hazard. Some lights are basically red (for danger) with one or more white sectors indicating the direction of safe passage, but a narrow white sector of another light may simply mark a turning point in a channel.
Lights may also have sectors in which the light is obscured—cannot be seen. These will be shown graphically on charts—see Figure 14-21,—and are described in the Light Lists.
Figure 14-21 A hazardous area is often covered by a red sector of a light, and this sector (or sectors) is indicated by words along the arc on a chart (left). Aside from being red, the sector shows the same characteristics as the normal white sector of the light. A light may also be obscured over a sector, and this, too, is indicated on the chart. Note: The colors used here are for clarity and do not actually appear on a nautical chart.
The Visibility of Lights
A light’s theoretical visibility in clear weather depends on two factors: its intensity and its height above water. Its intensity fixes its NOMINAL RANGE, which is defined in the Light Lists as “the maximum distance at which the light may be seen in clear weather (meteorological visibility of 10 nautical miles).”
Height is important because of the earth’s curvature; height determines the GEOGRAPHIC RANGE at which the light can be seen. It is not affected by the intensity (provided that the light is bright enough to be seen out to the full distance of the geographic range).
The nominal range of major lights is generally greater than the geographic, and the distance from which such aids can be seen is limited only by the earth’s curvature. Such lights are often termed “strong”; a light limited by its luminous range is a “weak light.”
The glare, or LOOM, of strong lights is often seen far beyond the normal geographic range, and under rare atmospheric conditions the light itself may be visible at unusual distances. The range of visibility is obviously lessened by rain, fog, snow, haze, or smoke.
U.S. Coast Guard Light Lists show the nominal range for all lighted aids except private aids, navigation ranges, and directional lights, and show how to convert nominal range to LUMINOUS RANGE—the maximum distance at which a light may be seen in specific existing visibilities. Both nominal and luminous ranges take no account of elevation, observer’s height of eye, or the curvature of the earth. (Any height of eye on board the vessel increases the effective geographic range for that specific situation.) For lights of complex characteristics, nominal ranges are given for each color and/or intensity.
The geographic range of lights is not given in the Light Lists but can be determined from the given height of the light source. The distance to the horizon may be taken from a table in the front pages of each Light List volume, or calculated using the equation D = 1.17 (where H is the height in feet and the distance is in nautical miles) or D = 2.12
here H is in meters and distance is still in nautical miles). For distances in statute miles, the factors are 1.35 and 2.44.
For any situation, the light’s range, as limited by the earth’s curvature, will be the distance to the horizon for the light plus the distance to the horizon for your height of eye—determine each distance separately, then add; do not add heights and make a single calculation. Boaters should know their height of eye when at the controls of their boat (and the height of any other position on board to which they can climb to see farther).
Lights on inland waters, where their radius of usefulness is not great, are frequently “weak” lights whose intensity need not reach the full limit of their geographic range.
Identification of Lights Charts can only briefly describe the characteristics of a primary seacoast or secondary light by means of abbreviations and a notation of the total period of the light cycle. You will often need to consult the Light Lists for details of the characteristics to help you identify it positively.
When you first see a light, note its color and time its full cycle of light changes. If color, period, and number of flashes per cycle match the Light List information, the light has been identified. As a precaution, however, check the charts and Light Lists to be sure that no other light in the vicinity has similar characteristics.
Emergency Lights
Emergency lights of reduced nominal range are displayed from many light stations when the main light is inoperative. These standby lights may or may not have the same characteristics as the main light. The existence of the standby light (if any) and its characteristics (if different) are noted in the Light Lists.
CAUTIONS IN USING LIGHTS
Complex lights with several luminous ranges may appear different at extreme distances where, for example, a white fixed (or flashing) light can be seen but a red flash of the same light is not yet within luminous range. Examination of a Light List will show that the nominal range of a red or green light is usually 15 percent to 30 percent less than that of a white light from the same aid. Be cautious when identifying lights like these.
The effects of fog, rain, snow, and haze on the visibility of lights are obvious. Colored lights are more quickly lost to sight in poor weather than are white lights. On the other hand, refraction may also cause a light to be visible from a greater distance than normal.
Be cautious also when using light sectors in your navigation. The boundaries between the colors are not so distinct as the chart suggests; the lights shade gradually from one color into another.
Note, too, that the increasing use of brilliant shore lights for advertising, illuminating bridges, and other purposes may cause marine navigational lights, particularly those in densely populated areas, to be outshone and difficult to distinguish from background lighting.
A light can also be extinguished for some reason. Unattended lights that are broken may not be immediately detected and corrected. If you do not see a light reasonably soon after your course and speed suggest that you should, check the situation carefully. Do not rely on any one light, except perhaps for making a landfall. For positive identification, use several lights together as a system, checking each against the others.
SOUND SIGNALS
Any sound-producing instrument operated in time of fog or other condition of reduced visibility from a definite point shown on a chart serves as a useful sound signal. To use it effectively as an aid to navigation, you must be able to identify it and know its location.
As mentioned, the simpler sound signals used on buoys are operated by sea action, and thus you may have difficulty identifying them. Sound signals at all lighthouses and other lights are electrically or mechanically operated on definite time schedules, however, so are easier to identify positively.
Signal Characteristics
Sound signal characteristics consist of the length of a total cycle of one or more BLASTS of specific length and one or more SILENT INTERVALS, also of definite lengths. These times are shown in the Light Lists to aid in identification. (Normally, only the type of sound signal, without further details, is indicated on charts.) When you are counting the blasts and timing the cycle, refer to the Light Lists for its details.
Sound Signal Equipment
Sound signals also differ from each other in tone, which helps in identification. The signal type for each station is shown in the Light Lists and on charts.
Diaphones produce sound by means of a slotted reciprocating piston activated by compressed air. Blasts may consist of two tones of different pitch, in which case the first part of the blast is of higher pitch and the latter is lower. These alternate-pitch signals are termed “two-tone.”
Diaphragm horns produce sound by means of a disc diaphragm vibrated by compressed air or electricity. Duplex and triplex horn units of different pitch are sometimes combined to produce a more musical signal.
Sirens produce sound by means of either a disc or cup-shaped rotor actuated by compressed air, steam, or electricity. These should not be confused with “police sirens”; these aids may produce a sound of constant pitch much like a diaphragm horn or a whistle.
Whistles produce sound by compressed air emitted through a slot into a cylindrical bell chamber.
Operation of Signals
Sound signals at stations where a continuous watch is maintained are placed in operation whenever the visibility decreases below a limit set for that location; typically, this might be five miles.
Sound signals at locations without a continuous watch may not always be sounded promptly when conditions of reduced visibility occur, or may operate erratically due to mechanical difficulties.
Where sound signals are operated continuously on a seasonal basis or throughout the year, this information will be found in the Light Lists.
On buoys where sound signals are operated by sea motion, the signals may be heard in any condition of visibility.
CAUTIONS IN USING SOUND SIGNALS
Sound signals obviously depend upon the transmission of sound through the air. As aids to navigation, they thus have inherent limitations that you must consider. Because sound travels through air in a variable and unpredictable manner, you should note that:
• The distance at which a sound signal can be heard may vary at any given instant with the bearing of the signal, and may be different on different occasions.
• Under certain atmospheric conditions you may hear only part of a sound signal that is a siren or that has a combination of high and low tones.
• There are sometimes areas close to a signal where you will not hear it, perhaps when the signal is screened by intervening landmasses or other obstructions, or when it is on a high cliff.
• The apparent loudness of a sound signal may be greater at a distance than in its immediate vicinity.
• A patch of fog or smoke may exist at a short distance from a manned station but not be seen from it. Thus the signal may not be placed in operation.
• Some sound signals require a start-up interval.
• You may not hear a sound signal with your boat’s engine on, but you may hear it suddenly when it is off or if you go forward on board away from its noise.
In summary, sound signals are valuable as warnings, but do not place implicit reliance upon them in navigating your vessel.
Based on the above established facts, you must not assume:
• That you are out of the ordinary hearing distance of a sound signal because you do not hear it.
• That because you hear a sound signal faintly, you are at a distance from it.
• That you are near to the sound signal because you hear it clearly.
• That the sound signal is not sounding because you do not hear it, even when you know that you are nearby.
• That the detection distance and sound intensity under any one set of conditions is an infallible guide for any future occasion.
RANGES & DIRECTIONAL LIGHTS
Ranges and directional lights serve to indicate the centerline of a channel and thus aid in the safe piloting of a vessel. Although they are used in connection with channels and other restricted waterways, and shown on all the appropriate charts, they are not a part of the lateral system of buoyage.
Ranges
A RANGE consists of two fixed aids to navigation so positioned with respect to each other that when seen in line they indicate that the observer’s craft may be in safe waters; see Figure 14-22. The aids may be lighted or unlighted as determined by the importance of the range.
The conditional phrase “may be in safe waters” is used because observation of the two markers in line is not an absolute determination of safety. A range is “safe” only within specific limits of distance from the front marker. A vessel too close or too far away may be in a dangerous area. The aids that comprise the range do not in themselves indicate the usable portion of the range; check your chart and other aids.
Ranges are described in the Light Lists by first giving the position of the front marker, usually in terms of geographic coordinates—latitude and longitude—and then stating the location of the rear marker in terms of direction and distance from the front marker. This direction, given in degrees and minutes, true, need not be used in ordinary navigation, but is useful in making checks of compass deviation. The rear dayboard (and light, if used) is always higher than the one on the front aid; see Figure 14-23.
Because of their fixed nature, and the accuracy with which a vessel can be positioned by using them, ranges are among the best aids to navigation. Use a range whenever one is available, and use a buoy only to determine the beginning and end of the usable portion of the range.
Figure 14-22 Lighted ranges are often used to mark channels in rivers, particularly where cross-currents exist. This range is on the St. Clair River on a true bearing of 207¼°. Range front light structures sometimes have all-round “passing lights” lower than the range light. The crossed-dashed line is the international border between Michigan and Ontario.
Ranges are used outbound just as they are inbound, by sighting over the stern. Make sure you do not meet head-on a vessel using the range in the opposite direction to your own.
Figure 14-23 A skipper can keep within a narrow channel by following a range. At A, the front and range marks are in line, with the higher rear mark directly over the lower front mark. If he gets “off range,” the markers will not be aligned, as shown in B. The channel may turn before reaching the range front marker, as in C; the turning point is normally marked by a buoy.
Unlighted Ranges
Although any two objects may be used as a range, the term is properly applied only to those pairs of structures built specifically for that purpose. Special shapes and markings are used for the front and rear aids of a range for easier identification and more accurate alignment. Differing designs have been used in the past, but the Coast Guard has now standardized the use of rectangular dayboards, longer dimension vertical, painted in vertical stripes of contrasting colors. The design of specific range dayboards will normally be found in the Light Lists.
Lighted Ranges
Because of their importance and high accuracy in piloting, most range markers are equipped with lights to extend their usefulness through the hours of darkness; they may or may not have the usual dayboards. Entrance channels are frequently marked with range lights; the Delaware River on the Atlantic Coast and the Columbia River on the Pacific Coast are examples of this.
Range lights may be of any color used with aids to navigation—white, red, or green—and may show any of several characteristics. The principal requirement is that they be easily distinguished from shore backgrounds and from other lights. Front and rear lights will, however, normally be of the same color (white is frequently used because of its greater visibility range), with different rhythms. Since both lights must be observed together for the proper steering of the craft, range lights often have a greater “ON” interval than other lights do. Range rear lights are normally on more than their front counterparts; many ranges now show an isophase (equal interval) rear light and a quick-flashing front light.
Many range lights are fitted with special lenses that give a much greater intensity on the range centerline than off it; the lights rapidly decrease in brilliance when observed from only a few degrees to either side. In some cases, the light will be visible only from on or very near the range line; in other cases, a separate, lower light of lesser intensity may be seen all around the horizon—this can be either from the main light source or from a small auxiliary “passing” light. Light is shown around the horizon when the front aid also serves to mark the side of a channel at a turn of direction.
Historically, most ranges have had dayboards for daytime operations and lights for night use. With advances in technology, more and more ranges are being converted to lights for both day and night use. If the active portion of the range is of moderate or short length, and the near end is not too far from the front light, a single light may be used on each structure, burning 24 hours a day. If the usable portion of the range is considerable and/or its near end is some distance from the front structure, there will be two lights on each structure, as a light strong enough to reach out the required distance by day may be too bright for nighttime use. These pairs of lights may have different colors, but both lights, front and rear, of each pair will have the same color. The light rhythms of the two pairs may be different—the daytime lights are often fixed white; the nighttime lights are colored red or green with typical flashing patterns as described above. The arcs of visibility may be different for the day and night ranges. Each range is evaluated on its specific situation, and lights are installed as appropriate. Typically, these day/night ranges do not have dayboards; this permits lower and less expensive structures because of lesser wind loading, and simplifies maintenance that is costly and hazardous to servicing personnel.
Directional Lights
The establishment of a range requires suitable locations for two aids, separated adequately both horizontally and vertically. In some areas, this may not be possible, and a single light of special characteristics will be employed.
A DIRECTIONAL LIGHT is a single light source fitted with a special lens so as to show a white light in a narrow beam along a desired direction, with red and green showing to either side. Width of the sectors will depend upon the local situation, but red will be seen if the pilot is to the right of the centerline as he approaches the aid from seaward, and green if he is to the left of the desired track.
A typical example is the Thames River Upper Directional Light (Connecticut) that shows an isophase 6-second white light over an arc of 3 degrees, with green and red sectors 3 degrees wide on either side; it cannot be seen from any other direction. A quite different light is the Kailua Bay Entrance Directional Light (Hawaii), which shows an occulting 4-second white light, 3 degrees either side of the correct heading of 023 degrees True, with a green sector 34 degrees wide and a red sector 70 degrees in width.
An interesting use of a directional light is seen at Port Everglades, Florida. The front range light is sometimes obscured by a tanker discharging its cargo. A special type of directional light, known as a Pell Sector Light, is used for the range rear light. It functions as a range rear light if the front light can be seen; if that light is blocked, the rear light alone is used as a directional light, with very complex characteristics, to mark the entrance channel.
Directional lights will normally have an occulting or isophase characteristic, so that they are easily followed.
Caution Regarding Directional Lights
A skipper should not place too great a reliance on the various colors of a directional light for safe positional information. As noted for light sectors, the boundaries between colors are not sharp and clear; the light shades imperceptibly from one color to the other along the stated, and charted, dividing lines.