12 December 2001
used in areas of lesser importance or as intermediate aids to supplement
lighted buoys in the more important areas.
Daybeacons. Although all aids, whether lighted or unlighted, serve as a
daymark to the mariner, daybeacons are specifically designed as
unlighted structures used to mark isolated dangers, channels, edges, or
Sound Signals. Sound signals are sound-producing devices operated
mechanically or by the action of the sea, consisting of horns, sirens, diaphones, bells,
gongs, and whistles. They are installed on shore structures and on buoys.
Operation. Most sound signals on structures are attended. Sound signals
on a few minor shore structures or on buoys shall be automatically
operated. Other signals on buoys shall be operated by action of the sea.
Purpose. Sound signals are intended to warn of danger and provide the
mariner with the best practicable means of determining his position. This
is in relation to the sound signal station at such times as the station, or
any light that it might display, is obscured from view by fog, haze, smoke,
or generally poor visibility.
Range. To be effective, sound signals must be capable of a useful range,
and they must be of such characteristic duration as to permit their
direction to be judged with reasonable accuracy by ear. It must be
remembered that due to the uncertainty of passage of sound through the
atmosphere, the range of sound signals cannot be depended upon or
specifically fixed. Major fog signals shall have a minimum range of 2.4 km
Lights. Due to the increase in shore illumination along navigable waters,
the usefulness of fixed white lights is limited to areas where the usable range is short or
where the natural background includes few other lights.
Length of Period. The period of a flashing or occulting light is the time
required to go through a full set of changes. The limiting basis for the period of light
characteristics is 60 seconds, since it is considered that the mariner cannot always
safely watch the light to the exclusion of everything else for a longer period. Light
characteristics that are so similar as to require careful timing in order to differentiate
between them should not be established in close proximity to one another.
Colors. White, red, yellow, and green are used for navigational lights.
Other colors are not used.
Means of Obtaining Color. The light source in all illuminating apparatus is
white. Color is produced by the addition of colored-glass shades or