offshore or an islet separated by a narrow channel from
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 either pillar or spar.
When lighted, a white flashing light showing a
group of two flashes (FL (2)) 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.
A safe-water mark (fig. 9-17) is used to indicate
there is navigable water all around the mark. Such a
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
When lighted, a safe-water mark exhibits a white
light. The phase characteristics of the light will be
occulting, equal intervals, one long flash every 10
seconds, or Morse A. The association of a single flash
and a single sphere in the topmark may help you to
remember its characteristics.
A special mark (fig. 9-18) may be used to indicate
to the mariner a special area or feature. The nature of
the special area or feature may be found by consulting
the chart, Sailing Directions, or Notices to Mariners.
The use of a special mark includes the following:
Ocean Data Acquisition System (ODAS) buoys
carrying oceanographic or meteorological
Traffic separation marks
Figure 9-17.IALA Maritime Buoyage System safe-water marks.
Figure 9-18.IALA Maritime Buoyage System special marks.