A buoy is a floating device that can have many different purposes, which determine whether the buoy is anchored (stationary) or allowed to drift. The word is most commonly pronounced ([bɔɪ]) (as in buoyant), but in American English it's often pronounced [ˈbu.i].

Types

• Sea mark - aids pilotage by marking a maritime channel, hazard and administrative area to allow boats and ships to navigate safely.
• Lifebuoy - used as a life saving buoy designed to be thrown to a person in the water to provide buoyancy. Usually has a connecting line allowing the casualty to be pulled to the rescuer
• Submarine communication buoys - used for release in case of emergencies or for communication
• Communication buoy for a bottom pressure sensor, for tsunami detection.
• DAN buoy - has two meanings:
  
  • a large maritime navigational aid providing a platform for light and radio beacons
  • a lifebuoy with a flags used on yachts and smaller pleasure craft
• Sonobuoy - used by anti-submarine warfare aircraft to detect submarines by SONAR
• Surface Marker Buoy - taken on dives by scuba divers to mark their position underwater
• Decompression buoy - deployed by submerged scuba divers to mark their position underwater whilst doing decompression stops
• shot buoy - used to mark dive sites for the boat safety cover of scuba divers so that the divers can descend to the dive site more easily in conditions of low visibility or tidal currents and more safely do decompression stops on their ascent
• Mooring buoys - used to keep one end of a mooring cable or chain on the water's surface so that ships or boats can tie on to it
• Tripping buoys - used to keep one end of a 'tripping line' on the water's surface so that a stuck anchor can more easily be freed
• Weather buoys - equipped to measure weather parameters such as air temperature, barometric pressure, wind speed and direction and to report these data via satellite radio links to meteorological centres for use in forecasting and climate study. May be anchored (moored buoys) or allowed to drift (drifting buoys) in the open ocean currents. Position is calculated by the satellite.
• Tsunami buoys - anchored buoys that can detect sudden changes in undersea water pressure are used as part of tsunami warning systems in the Pacific and Indian Oceans.
• Profiling buoy - specialised models which adjusts its buoyancy so that it'll sink at a controlled rate to 2,000 metres below the surface while measuring sea temperatures and salinity. Then after typically 10 days it returns to the surface and transmits its data via satellite before sinking again.
• Ice marking buoys - used for marking ice holes in frozen lakes and rivers, so that snowmobiles don't drive over the holes.
• Marker buoys - used in naval warfare, particularly anti-submarine warfare, is a light-emitting or smoke-emitting, or both, marker using some kind of pyrotechnic to provide the flare and smoke. It is commonly a 3-inch (76 mm) diameter device about 20 inches (500 mm) long that's set off by contact with seawater and floats on the surface. Some markers extinguish after a set period and others are made to sink.
• Lobster trap buoys - brightly colored buoys used for the marking of lobster trap locations so the person lobster fishing can find their lobster traps. Each lobster fisherman has his or her own color markings so they know which one is theirs. They are only allowed to haul their own traps and must display their buoy color on their boat so law enforcement officials know what they should be hauling. The buoys are brightly colored so they can be seen under conditions when there's poor visiblity like rain, fog, sea smoke, etc.
• Waverider buoy - used to measure the movement of the water surface as a wave train. The wave train is analysed to determine statistics like the significant wave height and period, and wave direction.
• Target buoy - used to simulate target (like small boat) in live fire exercise by naval and coastal forces, usually targeted by weapons (medium size) like HMG's, rapid fire cannons (20 or so mm), autocannons (bigger ones up to 40 and 57mm) and also anti-tank rockets.

Other uses