Characteristics of Lighted Aids to Navigation, Continued
Some aids, such as safe-water marks always use the same rhythm
(Morse "A"), while others may display one of several different rhythms.
Figure 4-2 on the previous page gives a description and definition of
light characteristics (rhythms) as well as their chart symbol
abbreviations. Abbreviations are used on charts because of space
When working with composite light abbreviations, you must carefully
distinguish between the meanings of the numbers in parentheses
following a composite-flashing light. In the case of the
composite-flashing light, the numbers refer to the pattern of the flashes
of light. On the contrary, when the light is a composite-occulting light,
the numbers within the parentheses denote the pattern of the eclipses in
The "Light Cycle," or period of a light, is the time it takes a light to
complete one full cycle of ON and OFF changes. By varying the length
of the cycles, a clear distinction can be made between numerous aids in
the same area.
All solid red and solid green ATONs are numbered. Red aids have even
numbers; green aids have odd numbers. The numbers for each increase
from seaward, proceeding in the conventional direction of buoyage.
Numbers are kept in approximate sequence on both sides of the channel
by omitting numbers where necessary.
Letters may be used to augment numbers when lateral aids are added to
channels with previously completed numbering sequences. If letters are
used, they will increase in alphabetical order from seaward and will be
added to numbers as suffixes.
No other aids are numbered. Preferred-channel, safe-water, isolated
danger, special marks, and information or regulatory aids may be
lettered, but not numbered.