Page 197 - NAVAL SCIENCE 3 TEXTBOOK

Aids to Navigation

Piloting is olle branch of marine navigation, In traditiollal piloting, the duration of darkness. There are variations of these called fixed
a ship's position is mostly determined by bearings taken 011 visible flIld j1ashillg, with the fixed light intensifying at intervals with two
objects whose exact locations are shown Oil a chnrt. Some of these or more bright flashes; and grollp j1ashillg, in which two or more
objects may be naturallnndmarks, such as hills, rocks, islands, or groups of flashes are shown at regular intervals.
cliffs. Others may be large buildings. smokestacks, television tow- Ocwltillg lights are totally off at regular intervals, the duration
ers, church steeples, ilnd so 011, which arc located close to shore of light always being greater than the duration of darkness. Group
",here they can be casil}' spotted by navigators. occultillg lights have two or 1110re oft· periods ilt regular intervals.
~'Iost aids to navigation, though, are specially constructed to Variations of these principal light characteristics include eqlfnl
assist in the safe navigation of vessels. These include lighthouses, illfen'nl, in which the duration of light equals that of darkness;
light towers, navigation lights, buoys, and da}'beacolls. Most har- lV/orse code, where the light flashes represent a Morse code charac-
bors and well-traveled coasts are well marked with these aids to ter (usuaU)' the letter A); and nltemntillg, in which rhythmic lights
navigation. Elsewhere, these kinds of aids mayor may not be pres- show different colors during each sequence.
ent to assist the navigator. \Vhen specially constructed aids are not
<\\'ailable, or when the}' become inoperative or Ollt of position, then
nnturallandmarks must be used.
This chapter will discliss the major types ofconstrllcted naviga-
tional aids found in international and inland waters. AJI who oper-
ate watercraft in rivers, lakes, harbors, the Intracoastal \Vaterway,
and along seacoasts IllllSt know about these navigation aids, just
ilS one who drives a car or truck on the nation's highways must be
able to interpret road signs.

Lights
Vessels under way operate at night as well as by day. Therefore, nav-
igation lights are important aids to night navigation. These lights
are identified primarily by their color, pattern of flashes, and tim-
ing interval (period). Of these, the timing interval is considered the
1110st valuable for identification purposes, since that is least likely
to be confused if scveralnavigationallights are present in a given
area. These identifying attributes, together with height and nomi-
Ilal visibility, are uSllall}' printed in abbreviated fornl Ilear the light
symbol on the nautical chart. Other details are set forth in publica-
tions called light lists that are a\'ailable for purchase in 1110st nauti-
cal suppl)' stores.

Light Characteristics
There are three principal general patterns of flashes, called
cltnmcteristics, of navigational lights: fi....:ed, flashing, and occult-
ing. Fixed lights burn steadily. Flashillg lights show single flashes
of light at regular intervals, with the duration of light less than
The Fort Story lighthouse, Virginia Beach, Virginia. (Eric Clement)

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