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Page Title: Isolated Danger Marks
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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 [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. Safe  Water  Marks Safe water marks (fig. 5-31) are used to indicate that there is navigable water all around the mark. Such a C69.223 Figure 5-30.–IALA Maritime Buoyage System isolated danger marks. mark may be used as a centerline, midchannel, or landfall buoy. 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 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). C69.224 Figure 5-31.–IALA Maritime Buoyage System safe water marks. 5-34

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