A buoy (/ˈbɔɪ, buː.i/; boy, BOO-ee) is a floating device that can have many purposes. It can be anchored (stationary) or allowed to drift with ocean currents.
The ultimate origin of buoys is unknown, but by 1295 a seaman's manual referred to navigation buoys in the Guadalquivir River in Spain. To the north there are early medieval mentions of the French / Belgian River Maas being buoyed. Such early buoys were probably just timber beams or rafts, but in 1358 there is a record of a barrel buoy in the Dutch Maasmond (also known as the Maas Sluis or Maasgat). The simple barrel was difficult to secure to the seabed, and so a conical tonne was developed. They had a solid plug at the narrow end through which a mooring ring could be attached. By 1790 the older conical tonne was being replaced by a nun buoy. This had the same conical section below the waterline as the tonne buoy, but at the waterline a barrel shape was used to allow a truncated cone to be above the water. The whole was completed with a top mark. In the nineteenth century iron buoys became available. They had watertight internal bulkheads and as well as topmarks and might have bells* (1860) or whistles* (1880). In 1879 Julius Pintsch obtained a patent for the illumination of buoys by using a compressed gas. This was superseded from 1912 onwards by Gustaf Dalén's acetylene lamp. This could be set to flash which ensured that buoys could be distinguished from ships' lights and from each other. A later development was the sun valve which shut off the gas during sunlight.
*These additions have one obvious value, they work even in low visibility fog conditions, and the whistling buoys, on at least some models, work via the wave action acting as piston in an open-bottomed chamber with a whistle mechanism in fact making more noise the greater the water's hazards, and without any active input like a fog horn
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Buoys are often used to temporarily or permanently mark the positions of underwater objects:
Several types of marker buoys may be used by divers:
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