Navigation Skills

The following information was obtained from the Coast Guard.

Aids to Navigation

Caution should be used when relying upon aids to navigation.

The aids to navigation depicted on charts comprise a system of fixed and floating aids with varying degrees of reliability. Prudent mariners will not rely on any single aid to navigation, particularly a floating aid.

The buoy symbol is used to indicate the approximate position of the body and the sinker which secures the buoy to the seabed. The approximate position is used because of practical limitations in positions and maintaining buoys and their sinkers in precise geographical locations. These limitations include, but are not limited to inherent imprecisions in position fixing methods, prevailing atmospheric and sea conditions, the slope of and the material making up the seabed, the fact that buoys are moored to sinkers by varying lengths of chain, and the fact that buoy body and/or sinker positions are not under continuous surveillance but are normally checked only during periodic maintenance visits which often occur more than a year apart. The position of the buoy body can be expected to shift inside and outside the charting symbol due to the forces of nature. The mariner is also cautioned that buoys are liable to be carried away, shifted, capsized, sunk, etc. Lighted buoys may be extinguished or sound signals may not function as the result of ice, running ice or other natural causes, collisions, or other accidents

Lights on Fixed Structures

Lights on fixed structures are aids to navigation placed on shore or on marine sites to assist a navigator to determine his position or safe course, to mark channels and to warn him of dangers or obstructions to navigation.

They are identified by their light color at night or their daymark during daytime. Vessels must keep well clear of fixed aids if there is sufficient water to do so; because there may be dangerous underwater obstructions present in the vicinity of the foundation of the aid.

Unless otherwise stated in the Light List, lights will be displayed from sunset to sunrise. Occasionally in some locations they may be displayed for a short period before sunset and after sunrise due to prolonged twilight or low visibility. The lighting apparatus used on fixed structures is serviced at periodic intervals to assure reliable operations. Lighted aids to navigation (including lighted buoys) are extinguished automatically during daylight hours by switches activated by daylight. These switches are not of equal sensitivity, therefore all lights do not come on or go off at the same time. Mariners should ensure correct identification of aids during twilight periods when some lighted aids to navigation are on while others are not.

The conditions of the atmosphere has a considerable effect upon the distance at which lights can be seen. Sometimes lights are obscured by fog, haze, dust, smoke, or precipitation which may be present at the light, or between it and the observer, but not at the observer, and which is possibly unknown to him. On the other hand refraction may often cause a light to be seen at a greater distance than under ordinary circumstances.

The loom of a powerful light is often seen beyond the limit of visibility of the actual rays of the light. A light of low intensity will be easily obscured by unfavorable conditions of the atmosphere and little dependence can be placed on its being seen. For this reason, the intensity of a light should always be considered when expecting to sight it in thick weather. Haze and distance may reduce the apparent duration of the flashing light.

In some conditions of the atmosphere white lights may have a reddish hue. Colored lights are more quickly lost to sight than are white lights under weather conditions which tend to reduce visibility. It should be remembered that lights placed at great elevations are more frequently obscured by clouds, mist, and fog than those near sea level.

The increasing use of brilliant shore lights for advertising, illuminating bridges, and other purposes may cause marine navigational lights, particularly those in inhabited areas, to be outshone and difficult to distinguish from the background lighting. Mariners are requested to report such cases in order that steps may be taken to improve the conditions.

At short distances some flashing lights may show a faint continuous light between flashes. The distances of an observer from a light cannot be estimated by its apparent intensity. Always check the characteristics of lights to ensure that powerful lights visible in the distance are not mistaken for nearby lights showing similar characteristics of low intensity (such as those on lighted buoys). If lights are not sighted within a reasonable time after prediction, a dangerous situation may exist requiring prompt resolution or action to insure the safety of the vessel. The apparent characteristic of a complex light may change with the distance of the observer. For example, a light which actually displays a characteristic of alternating white and red may, when first sighted in clear weather, show as a simple flashing white light. As the vessel draws nearer the true characteristic of the light is finally recognized.

There is always the possibility of a light being extinguished. In case of unattended lights, this condition might not be immediately detected and corrected. The mariner should immediately report this condition. See Section G for the telephone number of the nearest Coast Guard unit to report any discrepancy in aids to navigation. Emergency lights of reduced intensity are displayed from many major light stations when the main and standby lights are extinguished. These emergency lights may not have the same characteristics as the main light. The characteristics of the emergency lights are listed in column (7) of the Light List if the characteristic is different from the main light.

If a vessel has considerable motion due to pitching in a heavy sea, a light sighted on the horizon may alternately appear and disappear. This may lead the unwary to assign a false characteristic and hence to err in its identification. The true characteristic will be evident after this distance has sufficiently decreased or it can be determined by increasing the observer's height of eye. Sectors of colored glass are placed in the lantern of some lights to produce a system of different colored light sectors. In general, red sectors are used to mark shoals or to warn the mariner of other obstructions to navigation or of nearby land. Such lights provide approximate bearing information since an observer may note the change of color as he crossed the boundary between sectors. These boundaries are indicated in the Light List and by broken lines on the charts.

These bearings, as are all bearings referring to lights, are given as true in from 000 degrees to 359 degrees as observed from a vessel toward the light.

Altering course on the changing sectors of a light or using the boundaries between light sectors to determine the bearing for any purpose is not recommended. Be guided instead by the correct compass bearing of the light and don't rely on being able to accurately observe the point at which the color changes. This is often difficult to determine because the edges of a colored sector cannot be cut off sharply. On either side of the line of demarcation between white and red or green sectors there is always a small arc of uncertain color. Moreover, when haze or smoke is present in the intervening atmosphere, a white sector might have a reddish hue.

The area in which a light can be observed is normally a circle with the light as the center and the range of visibility as bearings, the range may be reduced because of obstructions. In such cases, the obstructed arc might differ with height of eye and distance. When the light is cut off by a sloping hill or point of land, the light may be seen over a wider arc by a ship far off than by one close aboard.

Circles drawn on charts around a light are not intended to give information as to the distance at which it can be seen. In the case of lights which do not show equally in all directions, circles indicate the bearings between which the variation of visibility or obstruction of the light occurs. Lights of equal intensity but of different colors may be seen at different distances. This fact should be considered not only in predicting the distance at which a light can be seen, but also in identifying it. At many lights riprap mounds are maintained to protect the structures against scouring action. There have been collisions with the uncharted, submerged portion of such riprap by vessels attempting to pass the lights extremely close aboard.