Isolated Danger Marks
Isolated danger marks (fig. 5-30) are erected on, or
moored above, an isolated danger of limited extent. The
isolated danger mark has navigable water all around it.
The extent of the surrounding navigable water is not
important. The isolated danger mark, for example,
indicates either a shoal that is well offshore or an islet
separated by a narrow channel from the coast.
A black double-sphere topmark is, by day, the most
important feature of an isolated danger mark. Whenever
practical, this topmark will be carried with the spheres as
large as possible, mounted vertically, and clearly separated.
Black, with one or more red horizontal bands, is
used for isolated danger marks. The shape of an isolated
danger mark is not significant, but, in the case of a buoy,
it will be a pillar or spar.
When lighted, a white flashing light showing a
group of two flashes (F1 ) is used to denote an
isolated danger mark. The association of two flashes and
two spheres in the topmark may be a help in
remembering these characteristics.
Safe Water Marks
Safe water marks (fig. 5-31) are used to indicate that
there is navigable water all around the mark. Such a
Figure 5-30.IALA Maritime Buoyage System isolated danger
mark may be used as a centerline, midchannel, or
Red and white vertical stripes are used for safe water
marks. The vertical stripes are used to distinguish them
from the black-banded danger marks. Spherical, pillar,
or spar buoys may be used as safe water marks.
Whenever practical, a pillar or spar buoy used as a safe
water mark will carry a single red sphere topmark.
When lighted, a safe water mark exhibits a white
light. The phase characteristics of the light will be
occulting, equal interval (isophase), one long flash
every 10 seconds, or Morse A. The association of a
single flash and a single sphere in the topmark may help
to remember these characteristics.
Special marks (fig. 5-32) may be used to indicate a
special area or feature. The nature of the special area or
feature may be found by consulting the navigational
chart being used.
Notice to Mariners. The uses of a special mark
include the following:
Ocean Data Acquisition System (ODAS), buoys
carrying oceanographic or meteorological sensors
Traffic separation marks
Spoil ground marks
Military exercise zone marks
Cable or pipeline marks, including outfall pipes
Recreation zone marks
Another function of a special mark is to define a
channel within a channel (for example, a channel for
deep-draft vessels in a wide approach area where the
limits of the channel for normal navigation are marked
by red and green lateral buoys).
Figure 5-31.IALA Maritime Buoyage System safe water marks.