Seamanship & Navigation, September 2021
Buoys have been used by mariners since the 1500s to guide them been past shoals and rocks, with early buoys being no more than large pieces of timber strapped together, topped with a marker, and anchored in position.
Modern buoys are brightly painted and labeled, can show a variety of light characteristics, can produce distinctive sounds. In the U.S., the Coast Guard is responsible for buoy placement and maintenance, and it uses a prescribed procedure for determining where buoys will be placed and what shape, light, sound and electronic signature they show.
Buoys come in a wide range of shapes and sizes to meet the needs of both marking a channel or hazard and surviving the environmental conditions of the area where they are placed. Generally, the more exposed a location the larger the buoy and the longer the mooring chain.
Buoys fall into two groups, lighted and unlighted, with these two groups broken down into five types: lateral, isolated danger, safe-water, special, and information buoys. Buoys are located to supplement natural and manmade landmarks and are used in conjunction with other navigation information. They should not be used as a single means of navigation.
In the US, buoy placement follows a lateral system, meaning buoys are generally used to define port and starboard sides of channels or routes. However, they are also used to show dangers, safe water, and special areas. Lateral channel buoys are placed as near to a channel’s edge as possible, and buoys marking obstructions are placed on the channel side of the obstruction.
Buoys used to mark isolated dangers are placed on or immediately next to the danger and may be passed on all sides. These marks are painted black, with one or more horizontal red bands, and have a topmark of two black spheres, one above the other. When lighted, isolated danger marks display a white, group-flashing (two) light (flash, flash, dark, flash, flash) with a period of five seconds
Safe-water buoys indicate that there is navigable water all around the mark, and they are commonly found in midchannel or offshore approach points to harbors. These buoys are either spherical in shape or display a spherical topmark and when lighted show a white light coded with the Morse letter A (dit-dah), They are often called Morse alpha buoys.
Special-purpose buoys are not intended for navigation, though they certainly can be used for such, but for marking areas such as anchorages, cable or pipeline crossings, traffic separation schemes, and military exercise zones. These buoys are colored yellow and show yellow flashing lights.
Buoys are often supplied with sound signals to provide mariners with information during restricted visibility. However, the human ear is not good at accurately determining direction, so sound signals are useful only for warning of buoy proximity.
There are four types of audible signals: gongs, bells, whistles, and electronic horns. Gong, bell, and whistle sounds are produced by buoy movement and so are useful on buoys in exposed locations. Electronic horns are battery-powered and are often used on buoys in protected locations without much wave action.
In deciding how to deploy sound signals the following rules of thumb are used:
• Where two or more channels meet or are near each other, different sound signals are used for each waterway, to aid in channel differentiation.
• Midchannel buoys and buoys at the approaches to harbors and channels are usually equipped with whistles.
• Gongs, bells, and whistles do not carry lateral significance and so assumptions cannot be made concerning leaving them to port or starboard.
Sound signals generally do not have a range greater than two miles, under the best conditions.
A buoy’s light has two qualities: color and rhythm. Possible colors are red, green, white, or yellow. Rhythm choices include fixed, flashing, isophase, and occulting
• Fixed lights are on all the time.
• A flashing light is on for a shorter period of time than the time the light is off. There are several types of flashing lights single flashing, group flashing, slow flashing, quick flashing, and Morse code.
• An isophase light has the light on for a period of time equal to the time the light is off.
•An occulting light has the light on for a longer time than it is off.
A light’s characteristic is determined by the aid’s function. Quick flashing (60 or more flashes per minute) is the most conspicuous and is used on buoys designating turns or marking shoals or wrecks. A Morse alpha light always indicates a safe water buoy.
Flash intervals of 25, four, and six seconds are commonly used on lateral channel makers because they are not multiples of each other, eliminating the situation in where if a flash on a particular buoy is missed, it might be mistaken for different buoy
Exposed location buoys (ELB) are frequently found offshore near pilot boarding areas. They are often equipped with both flash tubes and incandescent lights. Flash tubes provide greater range than an incandescent light but it is difficult to obtain a bearing on or to judge the distance of flash tubes, so the incandescent light allows bearing and range measurements to be taken as a vessel nears the buoy.
When the Coast Guard places buoys to mark a channel or harbor they first determine the direction of flood and ebb tide in that area so buoys can be located with the proper lateral significance: red buoys to the right when entering from seaward or following a flood tide; green buoys to starboard when departing or following an ebb tide
Buoy placement in a waterway is normally designed for the largest vessel that will be transiting that area, but if there is a significant amount of smaller traffic the Coast Guard gives this fact consideration in buoy placement.
If there is to be more than one channel in a particular harbor then channels are ranked by order of importance, with width, depth, and predominant traffic flow as a means of comparison. Channel importance will determine the quantity and spacing of buoys and the other navigation aids used to mark it.
Once a channel is designated, its length is divided into regions, based on three navigation tasks: turns, turn recovery, and track keeping. Turn regions generally extend a half mile
on either side of a turn’s apex, with three types of turns possible: cutoff, non-cutoff, and bends.
Buoys are used at turns to enclose the area in which the turn can be made without the vessel’s entering shallow water or nearing a danger. Since turning is the most difficult task in channel navigation turn areas are heavily marked. A turn’s inside edge is always prominently buoyed or otherwise marked to assist vessels in not turning too tightly.
Recovery regions immediately follow turns and are needed by large vessels to regain a steady heading, which usually takes 3/4 to 1 1/2 miles. The larger the vessel, the longer the recovery region. Since a vessel tends to slide to the outside of a turn, the recovery region has prominent buoys along the outboard edge, usually within 1/2 mile of the turn’s apex.
Track keeping regions make up the remaining segments of a waterway. Buoys are placed here in one of three arrangements: gated, staggered, and one-sided. Spacing is usually ½ to 11/2 miles.