cramping during prolonged swimming. Although the detachable coupling converting the separate swimming fins into a monofin-like design is granted US patent 3165764A on 19 January 1965, it does not appear to have entered the production stage. 1967: In his review of the range of fins available in France during that year, J. Larue mentions how unnamed experts are experimenting with the use of a single swim fin accommodating both feet of the swimmer, who deploys the butterfly stroke to progress in the water. Although the experiment yields relatively satisfactory results for swimmers, Larue concludes that this fin is unsuitable for divers. 1969: Franco Pavone constructs his "Matrimoniale" monofin in the Italian city of Bologna. After designing a high-speed monofin with a metal-reinforced rubber blade, Boris Porotov (Kazakh Soviet Socialist Republic) builds an entire blade out of fibreglass-reinforced plastic. 1970: On 10 December 1970, Spanish underwater diving equipment company Nemrod-Metzeler patents a monofin-like device for swimmers incorporating both feet, but it never enters production. 1971: Nadejda Turukalo (URSS) arrives at European Finswimming Championship (1970, Barcelona, Spain) with a monofin constructed from two titanium branches, joined by a "sail". She beats all comers. Monofins have been used ever since for finswimming competitions, allowing monofin swimmers to reach speeds of 12 km/h. Traditional monofin 50 m apnea world record is as fast as 13 km/h. Construction Monofins can be made of glass fiber, carbon fiber, or aluminum, and rubber. The diver's muscle power, swimming style, and the type of aquatic activity the monofin is used for determine the choice of size, stiffness, and materials. Most monofins consist of a single, wide, glass or carbon fiber reinforced composite blade with graded flexibility, attached to the diver by two rubber foot pockets. The leading edge may be thickened and faired. The blade flexibility is generally controlled by tapering the amount of fibre and thickness of the blade to make the trailing edge thinner and more flexible. See also References External links Good monofin technique with the Lunocet Rick Waldock: Monofin - freediving in Bonaire Monofin Manufacturers Underwater sports Diver propulsion equipment Swimming equipment Sports footwear