Buoy. A buoy is a floating device that can have many purposes. It can be anchored or allowed to drift with ocean currents. Race course marker buoys are used for buoy racing, the most prevalent form of yacht racing and power boat racing. They delimit the course and must be passed to a specified side. They are also used in underwater orienteering competitions. Emergency wreck buoys provide a clear and unambiguous means of temporarily marking new wrecks, typically for the first 24-72 hours. They are coloured in an equal number of blue and yellow vertical stripes and fitted with an alternating blue and yellow flashing light. They were implemented following collisions in the Dover Strait in 2002 when vessels struck the new wreck of the MV Tricolor. Ice marking buoys mark holes in frozen lakes and rivers so snowmobiles do not drive over the holes. Large Navigational Buoys are automatic buoys over 10 m high equipped with a powerful light monitored electronically as a replacement for a lightvessel. They may be marked on charts as a Superbuoy. Lateral marker buoys. Safe water mark or fairway buoys mark the entrance to a channel or nearby landfall. Sea marks aid pilotage by marking a maritime channel, hazard or administrative area to allow boats and ships to navigate safely. Some are fitted with wave-activated bells or gongs. Wreck buoys mark a wrecked ship to warn other ships to keep away because of unseen hazards. Light buoys provide demarcation at night. Buoys are often used to temporarily or permanently mark the positions of underwater objects: Lobster trap buoys are brightly colored buoys making lobster trap locations so lobster fishers can find their lobster traps. Each fisher has a unique colour marking or registration number. They are allowed to haul only their own traps, and must display their buoy colour or license number on their boat so law enforcement officials know what they should be hauling. The buoys are brightly coloured with highly visible numbers so they can be seen in poor visibility conditions like rain, fog and sea smoke. Several types of marker buoys may be used by divers: Decompression buoys are deployed by submerged SCUBA divers to mark their position underwater whilst doing decompression stops. Shot buoys mark dive sites for the boat safety cover of scuba divers so they can descend to dive sites more easily in conditions of low visibility or tidal currents and more safely do decompression stops on their ascents. Surface marker buoys are taken on dives by scuba divers to mark their positions underwater. Dive site demarcation buoys indicate that divers are working in the marked area, to warn passing vessels to stay clear. Lifebuoys are lifesaving buoys thrown to people in the water to provide buoyancy. They usually have a connected line allowing them to be pulled in. Self-locating datum marker buoys are 70% scale Coastal Ocean Dynamics Experiment /Davis-style oceanographic surface drifters with drogue vanes between 30 and 100 cm deep, designed for deployment from U.S. Coast Guard vessels or airframes for search and rescue. They have very little surface area above water to minimize the effects on them off winds and waves. Submarine rescue buoys are released in emergencies and for communication purposes. Profiling buoys are specialized buoys that adjust their buoyancy to sink at a controlled rate to a set depth, for example 2,000 metres while measuring sea temperature and salinity. After a certain period, typically 10 days, they return to the surface, transmit their data via satellite, then sink again. See Argo. Tsunami buoys are anchored buoys that can detect sudden changes in undersea water pressure, and are a component of tsunami warning systems in the Pacific Tsunami Warning Center and Indian Oceans. Wave buoys measure the movement of the water surface as a wave train. The data they transmit is analysed to form statistics like significant wave height and period, and wave direction. Weather buoys measure weather parameters such as air temperature, barometric pressure, and wind speed and direction. They transmit this data, via satellite radio links such as the purpose-built Argos System or commercial satellite phone networks, to meteorological centres for forecasting and climate study. They may be anchored, or allowed to drift in the open currents. Their position is calculated by the satellite. They are also referred to as Ocean Data Acquisition Systems, or buoys. and may be marked on charts as Superbuoys. Mooring buoys keep one end of a mooring cable or chain on the water's surface so ships and boats can tie to them. Many marinas mark them with numbers and assign them to particular vessels, or rent them to transient vessels.