Special marks are used to mark areas of no navigational significance but have a special nature. The chart needs to be consulted to indicate the purpose of the buoy as there will normally be extra information available.
Special mark, that can be treated as a starboard hand mark.
For example, as race buoys, water-skiing area or the end of sewerage pipes.
Another use of special marks is to mark a channel within a channel. For example, a channel for deep-draught vessels in a wide estuary, where the limits for the channel for normal navigation are marked by red and green Lateral buoys, may have the boundaries of the deep channel indicated by yellow buoys of the appropriate Lateral shapes, or its centerline marked by yellow spherical buoys. Yellow buoys may also mark the limits of Traffic Separation Schemes.
Special marks can be any shape; normally they will be spherical or pillar with a cross-shaped topmark. If they are in a position where they can be treated as a navigational mark (near a channel), they will be conical or can shaped as appropriate.
The light will be yellow but because of the difficulty of identifying the difference between a yellow and white light, the sequence will always be different to any of the white sequences. A common pattern is Fl (4)10s. An example of special mark use is the firing danger area on Chart 4F (46° 15.73'N 05°351.05'W).
Particular care should be taken in popular yacht racing areas at night as many yellow race buoys are unlit or have damaged lights, especially near the end of the season. Remember to treat an unlit buoy with the same care you would a rock.
O.D.A.S. (Ocean Data Acquisition System) buoys normally exhibit the following sequence: Fl (5) 20s.
ODAS buoys can be found moored in deep oceans, with the tendency of yachtsmen to keep a very relaxed watch keeping system when in deep water these types of buoy can present an occasional hazard to small craft as they may be found in areas that you may expect to be completely clear of hazards. Typically the buoys are recording weather, tide and wave information.
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