Swimfin
Swimfins, swim fins, diving fins, or flippers are finlike accessories worn on the feet, legs or hands and made from rubber, plastic, carbon fiber or combinations of these materials, to aid movement through the water in water sports activities such as swimming, bodyboarding, bodysurfing, float-tube fishing, kneeboarding, riverboarding, scuba diving, snorkeling, spearfishing, underwater hockey, underwater rugby and various other types of underwater diving.
Swimfins help the wearer to move through water more efficiently, as human feet are too small and inappropriately shaped to provide much thrust, especially when the wearer is carrying equipment that increases hydrodynamic drag. Very long fins and monofins used by freedivers as a means of underwater propulsion do not require high-frequency leg movement. This improves efficiency and helps to minimize oxygen consumption. Short, stiff-bladed fins are effective for short bursts of acceleration and maneuvering, and are useful for bodysurfing.
History
Early inventors, including Leonardo da Vinci and Giovanni Alfonso Borelli, toyed with the concept of swimfins, taking their inspiration from ducks' feet. Benjamin Franklin made a pair of early swimfins when he was a young boy living in Boston, Massachusetts near the Charles River; they were two thin pieces of wood, about the shape of an artist's palette, which allowed him to move faster than he usually did in the water.Modern swimfins are an invention by the Frenchman Louis de Corlieu, capitaine de corvette in the French Navy. In 1914 Corlieu made a practical demonstration of his first prototype for a group of navy officers, Yves le Prieur among them who, years later in 1926, invented an early model of scuba set. Corlieu left the French Navy in 1924 to fully devote himself to his invention. In April 1933 he registered a patent and called this equipment propulseurs de natation et de sauvetage.
After struggling for years, even producing his fins in his own flat in Paris, Louis de Corlieu finally started mass production of his invention in France in 1939. The same year he issued a licence to Owen Churchill for mass production in the United States. To sell his fins in the U.S., Owen Churchill changed the French Corlieu's name to "swimfins", which is still the common English name. Churchill presented his fins to the US Navy, which decided to acquire them for its Underwater Demolition Team. American UDT and British COPP frogmen used the "Churchill fins" during all prior underwater deminings, thus enabling in 1944 the Normandy landings. During the years after World War II had ended, De Corlieu spent time and efforts struggling in civil procedures, suing others for patent infringement.
In Britain, Dunlop made frogman's fins for World War II, but after the war saw no market for them in peacetime, and, after the first supply of war-surplus frogman's kit was used up, the British public had no access to swimfins, until Oscar Gugen began importing swimfins and swimming goggles from France.
In 1946 Lillywhites imported about 1,100 pairs of swimfins; they all sold in under 3 months.
In 1948 Luigi Ferraro, collaborating with the Italian diving equipment company Cressi-sub, designed the first full-foot fin, the Rondine, named after the Italian word for swallow. A distinctive feature of Cressi's continuing Rondine full-foot fin line is the embossed outline of the bird on the foot pockets and the blades.
After The Amphibians Club, the UK's first post-war sport diving club, was founded by Ivor Howitt and friends in 1948 in Aberdeenshire, "swim fins were made by wiring stiff rubber piping each side of a flap of inner tube rubber. Very uncomfortable, but they worked. As secretary of The Amphibians, wrote to the Dunlop Rubber Company in February 1949, as they had made the naval frogmen's fins during the war. Incredibly, they replied that they could see no commercial market for swim fins in peacetime. This response reflected the virtual non-existence of sport diving in the UK at that time."
Standards
Seven military, national and international standards relating to swimfins are known to exist: US military standard MIL-S-82258:1965; USSR and CIS standard GOST 22469—77 ; German standard DIN 7876:1980; Polish Industry Standard BN-82/8444-17.02.. Austrian standard ÖNORM S 4224:1988; Malaysian standards MS 974:1985; MS 974:2002 ; and European standard EN 16804:2015.Types
Types of fins have evolved to address the requirements of each community using them. Recreational snorkellers generally use lightweight flexible fins. Free divers favour extremely long fins for efficiency of energy use. Scuba divers need large wide fins to overcome the water resistance caused by their diving equipment, and short enough to allow acceptable maneuvering. Ocean swimmers, bodysurfers, and lifeguards favour smaller designs that stay on their feet when moving through large surf and that make walking on the beach less awkward. Participants in the sports of underwater hockey or underwater rugby use either full-foot or open-heel fins, and the chosen fin style is usually a compromise in performance between straight-line power and turning flexibility - carbon fibre blades are popular at higher levels of competition, but the over-riding requirement is that the fins must not have sharp or unprotected edges or points, nor buckles, which could injure other competitors. Structurally, a swimfin comprises a blade for propulsion and a means of attaching the blade to the wearer's foot.Fins vs monofins
The vast majority of fins come as a pair, one fin is worn on each foot. This arrangement is also called bifins, to distinguish it from monofins. A monofin is typically used in finswimming and free-diving and it consists of a single fin blade attached to twin foot pockets for both the diver's feet. Monofins and long bifin blades can be made of glass fibre or carbon fibre composites. The diver's muscle power and swimming style, and the type of activity the fins are used for, determine the choice of size, stiffness, and materials.Full-foot vs open-heel
Full-foot or closed-heel fins fit like a shoe and are designed to be worn over bare feet or soft neoprene socks; they are sometimes called "slipper" fins. Most fins with complete foot coverage have toe openings for comfort and for ease of water drainage inside the foot pocket. If a larger size is chosen, however, full-foot fins can also be worn over thicker neoprene socks or thin-soled booties. They are commonly used for surface swimming, and come in non-adjustable sizes.Open-heel fins have a foot pocket with an open heel area, and the fin is held to the foot by springs or straps which are usually adjustable and so will fit a limited range of foot sizes. They can be worn over boots and are common in diving, in particular where a diver has to walk into the water from a shore and requires foot protection. Some manufacturers produce fins with the same blade architecture but a choice of heel type.
Paddle vs split
Paddle fins have simple plastic, composite, or rubber blades that work as extensions of the feet while kicking. Some paddle fins have channels and grooves claimed to improve power and efficiency though it has been shown that the desired effect does not usually occur. Relatively stiff paddle fins are widely believed to be the most versatile and have improved swimming economy in men. Tests in women showed a more flexible fin to be more economical, most likely due to lower leg power. Stiff paddle fins are required for certain types of kicks — such as back kicks and helicopter turns — performed by scuba divers trained in cave diving and wreck diving to avoid stirring up sediment.Some swimfins have a split along the centreline of the blade. The manufacturers claim that split fins operate similarly to a propeller, by creating lift forces to move the swimmer forwards. The claim is that water flowing toward the center of the fin's "paddle" portion also gains speed as it focuses, creating a "suction" force. A 2003 study by Pendergast et al called this into question by showing that there was no significant change in performance for a particular split fin design when the split was taped over. The technology used in most commercial split fin designs is patented by the industrial design firm Nature's Wing, and is used under license.
Paddle variations
Vented
Vented fins were first designed in 1964 by Georges Beuchat and commercialised as Jetfins. The Jetfin tradename and design were sold to Scubapro in the 1970s. Vented fins are generally stiff paddle fins that have vents at the base of the foot pocket. The vents are intended to allow for the passage of water during the recovery stroke, but prevent passage during power strokes due to the blade angle, attempting to lessen effort during recovery and improve kick efficiency. A review and study by Pendergast et al in 2003 concluded that vented fins did not improve economy, implying that water does not pass through the vents. The study is only partially significant because it only considers the flutter kick, whereas the jetfin is mostly used with frog kick in the technical diving community. There is a risk of objects snagging in the vents.Freediving
These are very similar to paddle fins, except they are far longer, and designed to work with slow stiff-legged kicks that are claimed to conserve oxygen and energy. The vast majority are made in the "full-foot" design with very rigid footpockets, which serves to reduce weight and maximize power transfer from the leg into the fin. Freediving fin blades are commonly made of plastic, but are also often made from composite materials using fibreglass or carbon fibre reinforcement. The composite blades are more resilient and absorb less energy when flexing, but are relatively fragile and more easily damaged.Image:Schwimmflossen.jpg|thumb|left|Swimfins designed for swim training.