A monofin is a type of swimfin used in underwater sports such as finswimming, free-diving and underwater orienteering. It consists of a single or linked surfaces attached to both of the diver's feet; the diver's appearance is reminiscent of a mermaid or merman. The arrival of the monofin in the early 1970s led to the breaking of all finswimming world records by the end of the decade due to the improved performance possible when used instead of two ordinary swimfins. To differentiate between the use of monofins and conventional fins, the latter are sometimes referred to as stereo fins or bi-fins; the monofin swimmer extends arms forward, locking hands together, locking the head between the biceps. The undulating movement starts in the shoulders, with maximum amplitude towards the hips, the legs don't bend to transfer the movement to the monofin; this technique is called the dolphin kick. By oscillating the surface of the monofin when submerged, divers can generate large amounts of thrust with small or slow movements.
This preserves energy. 1949. Kurt Schaefer, who invented an underwater film camera during wartime military service in Italy, designs a pair of homemade swimming fins, which he proceeds to fasten together with straps and cords to create what is the world’s first monofin; the artefact is on display in the Aquazoo-Löbbecke Museum in the German city of Düsseldorf. 1955-1961. On 19 September 1955, Kurt Ristau and Hans Joachim Bergann, who founded the underwater diving equipment manufacturing company Barakuda in the early 1950s in the German city of Hamburg after serving as combat swimmers during World War II, file a patent for a monofin-like device for swimmers incorporating both feet. Although the invention receives German patent 1085798 on 12 January 1961, it never enters the production stage. 1962-1965. On 15 October 1962, James S Christiansen files a patent for a device enabling a pair of swimming fins to be coupled together to reduce fatigue and 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.
1969. Franco Pavone constructs his "Matrimoniale" monofin in the Italian city of Bologna. 1969-1970. After designing a high-speed monofin with a metal-reinforced rubber blade, Boris Porotov builds an entire blade out of fibreglass-reinforced plastic. 1971. On 16 August 1971, Spanish underwater diving equipment company Nemrod-Metzeler patents a monofin-like device for swimmers incorporating both feet, it never enters the production stage, however. Monofins were introduced in 1972 by a Soviet finswimming club and have been used for finswimming competitions since, allowing monofin swimmers to reach speeds of 12 km/h. Traditional monofin 50 m apnea world record is as fast as 13 km/h. Monofins can be made of carbon fiber or aluminum and rubber; the diver's muscle power, swimming style, the type of aquatic activity the monofin is used for determining the choice of size and materials. Most monofins consist of a single, glass or carbon fiber reinforced composite blade with graded flexibility attached to the diver by two rubber foot pockets.
The leading edge may be faired. The blade flexibility is controlled by tapering the amount of fibre and thickness of the blade to make the trailing edge thinner and more flexible. Mermaiding Good monofin technique with the Lunocet Rick Waldock: Monofin - freediving in Bonaire Monofin Manufacturers
A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport the high pressure breathing gas required by a scuba set. It may be used for surface-supplied diving or as decompression gas or an emergency gas supply for surface supplied diving or scuba. Cylinders provide gas to the diver through the demand valve of a diving regulator or the breathing loop of a diving rebreather. Diving cylinders are manufactured from aluminium or steel alloys, are fitted with one of two common types of cylinder valve for filling and connection to the regulator. Other accessories such as manifolds, cylinder bands, protective nets and boots and carrying handles may be provided. Various configurations of harness may be used to carry the cylinder or cylinders while diving, depending on the application. Cylinders used for scuba have an internal volume of between 3 and 18 litres and a maximum working pressure rating from 184 to 300 bars. Cylinders are available in smaller sizes, such as 0.5, 1.5 and 2 litres, however these are used for purposes such as inflation of surface marker buoys and buoyancy compensators rather than breathing.
Scuba divers may dive with a single cylinder, a pair of similar cylinders, or a main cylinder and a smaller "pony" cylinder, carried on the diver's back or clipped onto the harness at the sides. Paired cylinders may be manifolded together or independent. In some cases, more than two cylinders are needed; when pressurised, a cylinder carries an equivalent volume of free gas greater than its water capacity, because the gas is compressed up to several hundred times atmospheric pressure. The selection of an appropriate set of diving cylinders for a diving operation is based on the amount of gas required to safely complete the dive. Diving cylinders are most filled with air, but because the main components of air can cause problems when breathed underwater at higher ambient pressure, divers may choose to breathe from cylinders filled with mixtures of gases other than air. Many jurisdictions have regulations that govern the filling, recording of contents, labelling for diving cylinders. Periodic inspection and testing of cylinders is obligatory to ensure the safety of operators of filling stations.
Pressurised diving cylinders are considered dangerous goods for commercial transportation, regional and international standards for colouring and labelling may apply. The term "diving cylinder" tends to be used by gas equipment engineers, support professionals, divers speaking British English. "Scuba tank" or "diving tank" is more used colloquially by non-professionals and native speakers of American English. The term "oxygen tank" is used by non-divers, they contain pure oxygen, except when used for rebreather diving, shallow decompression stops in technical diving or for in-water oxygen recompression therapy. Breathing pure oxygen at depths greater than 6 metres can result in oxygen toxicity. Diving cylinders have been referred to as bottles or flasks preceded with the word scuba, air, or bailout. Cylinders may be called aqualungs, a genericized trademark derived from the Aqua-lung equipment made by the Aqua Lung/La Spirotechnique company, although, more properly applied to an open circuit scuba set or open circuit diving regulator.
Diving cylinders may be specified by their application, as in bailout cylinders, stage cylinders, deco cylinders, sidemount cylinders, pony cylinders, suit inflation cylinders, etc. The functional diving cylinder consists of a cylinder valve. There are one or more optional accessories depending on the specific application; the pressure vessel is a seamless cylinder made of cold-extruded aluminium or forged steel. Filament wound composite cylinders are used in fire fighting breathing apparatus and oxygen first aid equipment because of their low weight, but are used for diving, due to their high positive buoyancy, they are used when portability for accessing the dive site is critical, such as in cave diving. Composite cylinders certified to ISO-11119-2 or ISO-11119-3 may only be used for underwater applications if they are manufactured in accordance with the requirements for underwater use and are marked "UW". An common cylinder provided at tropical dive resorts is the "aluminium-S80", an aluminium cylinder design with an internal volume of 0.39 cubic feet rated to hold a nominal volume of 80 cubic feet of atmospheric pressure gas at its rated working pressure of 3,000 pounds per square inch.
Aluminium cylinders are often used where divers carry many cylinders, such as in technical diving in water, warm enough that the dive suit does not provide much buoyancy, because the greater buoyancy of aluminium cylinders reduces the amount of extra buoyancy the diver would need to achieve neutral buoyancy. They are sometimes preferred when carried as "sidemount" or "sling" cylinders as the near neutral buoyancy allows them to hang comfortably along the sides of the diver's body, without disturbing trim, they can be handed off to another diver or stage dropped with a minimal effect on buoyancy. Most aluminium cylinders are flat bottomed, allowing them to stand upright on a level surface, but some were manufactured with domed bottoms; when in use, the cylinder valve and regulator add mass to the top of the cylinder, so the base tends to be buoyant, aluminium drop-cylinders tend to rest on the bottom in an inverted position if near neut
Finswimming is an underwater sport consisting of four techniques involving swimming with the use of fins either on the water's surface using a snorkel with either monofins or bifins or underwater with monofin either by holding one's breath or using open circuit scuba diving equipment. Events exist over distances similar to swimming competitions for both swimming pool and open water venues. Competition at world and continental level is organised by the Confédération Mondiale des Activités Subaquatiques; the sport's first world championship was held in 1976. It has been featured at the World Games as a trend sport since 1981 and was demonstrated at the 2015 European Games in June 2015. Competitors are described within the International Rules as'swimmers' rather than as finswimmers or divers. Competition is divided in two classes: long distance. A swimming pool must be 50 m long by 21 m wide and 1.8 m deep, i.e. an Olympic-size swimming pool suitable for the holding of swimming races for either the Olympic Games and a FINA world championships.
The International Rules do not permit the use of 25m length pools although these are used in regional and national competition. Long distance sites include both the sea and natural water bodies such as freshwater rivers and lakes. Site selection criteria include'low current and tides' and water quality'appropriate for swimming' as certified by a local authority; the site, when in use for competition, will be marked by buoys, patrolled by safety boats and will have observation points for judges to oversee any turns present in the course. Surface swimming is swimming on the surface of water using mask and monofins. SF races are held for distances of 50, 100, 200, 400, 800, 1500, 4 × 100 relay and 4 × 200 relay in swimming pools and over various long distances in the open water environment. Swimmers must remain on the surface of the water at all times for the duration of the race except when starting or make a turns at the end of a swimming pool where an immersion over a distance of 15m is permitted.
Apnoea finswimming is underwater swimming in a swimming pool using mask and holding one's breath. AP races are held for the distance of 50m. A swimmer's face must be immersed for the duration of the risk disqualification. AP races are not conducted in open water for'safety and security reasons'. Immersion swimming with breathing apparatus is underwater swimming using mask and underwater breathing apparatus conducted in a swimming pool. While there are no requirements on how a breathing apparatus is carried, it cannot be exchanged or abandoned during a race. IM races are held for distances of 400 m. A swimmer's face must be immersed for the duration of the risk disqualification. IM races are not conducted in open water for'safety and security reasons'. IM swims were conducted in openwater up to distances of 1000m. Bi-fins is swimming on the surface of water with mask, snorkel and a pair of fins using a crawling style. BF races are held for distances of 50, 100 and 200 m in swimming pools and over various long distances in the openwater environment such as 4 km and 6 km.
It is reported that BF was introduced in 2006 to provide the opportunity for competition by swimmers who cannot afford to purchase a set of monofins. Swimmers must remain on the surface of the water at all times for the duration of the race except when starting or make a turns at the end of a swimming pool where an immersion of a distance of 15m is permitted. Finswimming, compared to sports swimming differs from that sport in the use of masks, fins and underwater breathing apparatus; this reflects the sport’s origins in the underwater diving techniques of snorkelling, breath-hold diving and open circuit scuba diving. Apart from requiring the use of a mask for protection of the eyes and for the ability to see underwater, the international rules have no requirements regarding selection. Centre-mounted snorkels are the only type approved for use subject to meeting minimum and maximum requirements in tube length and internal diameter. Fins are regulated by the international rules. Monofins have a maximum size which can be checked by the use of a template while bi-fins must be one of the brands certified by CMAS.
Underwater breathing apparatus is restricted to open circuit scuba using compressed atmospheric air as the breathing gas. The use of oxygen enriched. Cylinders are limited by maximum cylinder pressure rating of 200 bar and a minimum cylinder capacity of 0.4 litres. While there are no requirements for regulators, swimmers appear to be free to modify these to remove any unnecessary parts. Garments such as swimsuits, swim caps and wetsuits, the use of logos printed on these garments and the equipment are subject to the requirements of the international rules; the following age groupings and associated restrictions for both men and women are mandated by the International Rules. The sport developed in Europe following the ready availability of the first rubber fins during the 1930s. Luigi Ferraro, Italian diving pioneer, is reported as organising the first fin-swimming competition in the sea during 1951 followed by a 100 kilometres ocean swim in 1955; the first competition in the Soviet Union was held during 1958.
The first European Championship, a multi sport event involving both finswimming and underwater orienteering was held under the title
You Only Live Twice (novel)
You Only Live Twice is the eleventh novel in Ian Fleming's James Bond series of stories. It was first sold out quickly; the book holds the distinction of being the last novel by Fleming to be published in his lifetime, with subsequent works being published posthumously. You Only Live Twice is the concluding chapter in what is known as the "Blofeld Trilogy"; the story starts eight months after the murder of Tracy Bond, which occurred at the end of the previous novel, On Her Majesty's Secret Service. James Bond is drinking and gambling and making mistakes on his assignments when, as a last resort, he is sent to Japan on a semi-diplomatic mission. Whilst there he is challenged by the Head of the Japanese Secret Service to kill Dr. Guntram Shatterhand. Bond realises that Shatterhand is Ernst Stavro Blofeld and sets out on a revenge mission to kill him and his wife, Irma Bunt; the novel deals on a personal level with the change in Bond from a depressed man in mourning, to a man of action bent on revenge, to an amnesiac living as a Japanese fisherman.
Through the mouths of his characters, Fleming examines the decline of post-World War II British power and influence, notably in relation to the United States. The book was popular with the public, with pre-orders in the UK totalling 62,000. Indeed this was something; the story was serialised in the Daily Express newspaper and Playboy magazine, adapted for comic strip format in the Daily Express. In 1967, it was released as the fifth entry in the Eon Productions James Bond film series, starring Sean Connery as Bond; the novel has been adapted as a radio play and broadcast on the BBC. After the wedding-day murder of his wife, Bond begins to let his life slide and gambling making mistakes and turning up late for work, his superior in the Secret Service, M, had been planning to dismiss Bond, but decides to give him a last-chance opportunity to redeem himself by assigning him to the diplomatic branch of the organisation. Bond is subsequently re-numbered 7777 and handed an "impossible" mission: convincing the head of Japan's secret intelligence service, Tiger Tanaka, to provide Britain with information from radio transmissions captured from the Soviet Union, codenamed Magic 44.
In exchange, the Secret Service will allow the Japanese access to one of their own information sources. Bond is introduced to Tanaka—and to the Japanese lifestyle—by an Australian intelligence officer, Dikko Henderson; when Bond raises the purpose of his mission with Tanaka, it transpires that the Japanese have penetrated the British information source and Bond has nothing left to bargain with. Instead, Tanaka asks Bond to kill Dr. Guntram Shatterhand, who operates a politically embarrassing "Garden of Death" in a rebuilt ancient castle on the island of Kyushu. After examining photos of Shatterhand and his wife, Bond discovers that "Shatterhand" and his wife are Tracy's murderers, Ernst Stavro Blofeld and Irma Bunt. Bond gladly takes the mission, keeping his knowledge of Blofeld's identity a secret so that he can exact revenge for his wife's death. Made up and trained by Tanaka, aided by former Japanese film star Kissy Suzuki, Bond attempts to live and think as a mute Japanese coal miner in order to penetrate Shatterhand's castle.
Tanaka renames Bond "Taro Todoroki" for the mission. After infiltrating the Garden of Death and the castle where Blofeld spends his time dressed in the costume of a Samurai warrior, Bond is captured and Bunt identifies him as a British secret agent and not a Japanese coal miner. After surviving a near execution, Bond exacts revenge on Blofeld in a duel, Blofeld armed with a sword and Bond with a wooden staff. Bond kills Blofeld by strangling him with his bare hands in a fit of violent rage blows up the castle. Upon escaping, he suffers a head injury, leaving him an amnesiac living as a Japanese fisherman with Kissy, while the rest of the world believes him dead. While Bond's health improves, Kissy conceals his true identity to keep him forever to herself. Kissy sleeps with Bond and becomes pregnant, hopes that Bond will propose marriage after she finds the right time to tell him about her pregnancy. Bond reads scraps of newspaper and fixates on a reference to Vladivostok, making him wonder if the far-off city is the key to his missing memory.
The central character in the novel is James Bond himself and the book's penultimate chapter contains his obituary, purportedly written for The Times by M. The obituary provides a number of biographical details of Bond's early life, including his parents' names and nationalities. Bond begins You Only Live Twice in a disturbed state, described by M as "going to pieces", following the death of his wife Tracy eight months previously. Academic Jeremy Black points out that it was a different Bond to the character who lost Vesper Lynd at the end of Casino Royale. Given a final chance by M to redeem himself with a difficult mission, Bond's character changes under the ministrations of Dikko Henderson, Tiger Tanaka and Kissy Suzuki; the result, according to Benson, is a Bond with a purpose in life. Benson finds the transformation of Bond's character to be the most important theme in the novel: that of rebirth; this is suggested in Bond's attempt at a Haiku, written in the style of Japanese poet Matsuo Bashō: The rebirth in q
Katsushika Hokusai was a Japanese artist, ukiyo-e painter and printmaker of the Edo period. Born in Edo, Hokusai is best known as author of the woodblock print series Thirty-six Views of Mount Fuji which includes the internationally iconic print, The Great Wave off Kanagawa. Hokusai created the Thirty-Six Views both as a response to a domestic travel boom and as part of a personal obsession with Mount Fuji, it was this series The Great Wave print and Fine Wind, Clear Morning, that secured Hokusai’s fame both in Japan and overseas. As historian Richard Lane concludes, "Indeed, if there is one work that made Hokusai's name, both in Japan and abroad, it must be this monumental print-series". While Hokusai's work prior to this series is important, it was not until this series that he gained broad recognition. Hokusai's date of birth is unclear, but is stated as the 23rd day of the 9th month of the 10th year of the Hōreki era to an artisan family, in the Katsushika district of Edo, Japan, his childhood name was Tokitarō.
It is believed. His father never made Hokusai an heir, so it is possible that his mother was a concubine. Hokusai began painting around the age of six learning from his father, whose work on mirrors included a painting of designs around mirrors. Hokusai was known by at least thirty names during his lifetime. While the use of multiple names was a common practice of Japanese artists of the time, his number of pseudonyms exceeds that of any other major Japanese artist. Hokusai's name changes are so frequent, so related to changes in his artistic production and style, that they are used for breaking his life up into periods. At the age of 12, his father sent him to work in a bookshop and lending library, a popular institution in Japanese cities, where reading books made from wood-cut blocks was a popular entertainment of the middle and upper classes. At 14, he worked as an apprentice to a wood-carver, until the age of 18, when he entered the studio of Katsukawa Shunshō. Shunshō was an artist of ukiyo-e, a style of woodblock prints and paintings that Hokusai would master, head of the so-called Katsukawa school.
Ukiyo-e, as practised by artists like Shunshō, focused on images of the courtesans and Kabuki actors who were popular in Japan's cities at the time. After a year, Hokusai's name changed for the first time, it was under this name that he published his first prints, a series of pictures of Kabuki actors published in 1779. During the decade he worked in Shunshō's studio, Hokusai was married to his first wife, about whom little is known except that she died in the early 1790s, he married again in 1797, although this second wife died after a short time. He fathered two sons and three daughters with these two wives, his youngest daughter Ei known as Ōi became an artist. Upon the death of Shunshō in 1793, Hokusai began exploring other styles of art, including European styles he was exposed to through French and Dutch copper engravings he was able to acquire, he was soon expelled from the Katsukawa school by Shunkō, the chief disciple of Shunshō due to studies at the rival Kanō school. This event was, in his own words, inspirational: "What motivated the development of my artistic style was the embarrassment I suffered at Shunkō's hands."Hokusai changed the subjects of his works, moving away from the images of courtesans and actors that were the traditional subjects of ukiyo-e.
Instead, his work became focused on landscapes and images of the daily life of Japanese people from a variety of social levels. This change of subject was a breakthrough in Hokusai's career. Fireworks in the Cool of Evening at Ryogoku Bridge in Edo dates from this period of Hokusai's life; the next period saw Hokusai's association with the Tawaraya School and the adoption of the name "Tawaraya Sōri". He produced many brush paintings, called surimono, illustrations for kyōka ehon during this time. In 1798, Hokusai passed his name on to a pupil and set out as an independent artist, free from ties to a school for the first time, adopting the name Hokusai Tomisa. By 1800, Hokusai was further developing his use of ukiyo-e for purposes other than portraiture, he had adopted the name he would most be known by, Katsushika Hokusai, the former name referring to the part of Edo where he was born and the latter meaning,'north studio'. That year, he published two collections of landscapes, Famous Sights of the Eastern Capital and Eight Views of Edo.
He began to attract students of his own teaching 50 pupils over the course of his life. He became famous over the next decade, both due to his artwork and his talent for self-promotion. During a Tokyo festival in 1804, he created a portrait of the Buddhist priest Daruma said to be 600 feet long using a broom and buckets full of ink. Another story places him in the court of the Shōgun Ienari, invited there to compete with another artist who practised more traditional brush stroke painting. Hokusai's painting, created in front of the Shōgun, consisted of painting a blue curve on paper chasing across it a chicken whose feet had been dipped in red paint, he described the painting to the Shōgun as a landscape showing the Tatsuta River with red maple leaves floating in it, winning the competition.1807 saw Hokusai collaborate with the popular novelist Takizawa Bakin on a series of illustrated books. The two did not get along due to artistic differences, their collaboration ended during work on t
Vertical Blue is a freediving competition, held annually in The Bahamas at Dean's Blue Hole since April 2008 by freediving world record holder William Trubridge. It is an AIDA International judged competition and has been the venue for multiple world and national records for athletes coming from countries all over the world. On November 17, 2013, American freediver Nicholas Mevoli died after attempting to set an American record during a Vertical Blue competition at Dean's Blue Hole. Vertical Blue is the name of the freediving school operated by William Trubridge at Dean's Blue Hole. Vertical Blue is a depth competition which consists of the freediving depth disciplines of free immersion, Constant weight without fins and Constant weight; the event is held at Dean’s Blue Hole on Long Island in the Bahamas and is organized by William Trubridge with AIDA International providing judges. Vertical Blue 2008 was held from 1 to 11 April in the same year, it was attended by competitors from the following countries - Brazil, Columbia, Japan, New Zealand, the Russian Federation and the United States.
A total of 23 national and 3 world records were achieved. Vertical Blue 2009 was held from 1 to 9 April 2009 and was attended by competitors from Austria, Brazil, Columbia, France, Japan, New Zealand, the United Kingdom and the United States. Vertical Blue official webpage Deeper Blue Article about Vertical Blue 2008
Swimfins, swim fins, fins or flippers are finlike accessories worn on the feet, legs or hands and made from rubber, plastic or combinations of these materials, to aid movement through the water in water sports activities such as swimming, bodysurfing, riverboarding, float-tube fishing, 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 when the wearer is carrying equipment that increases hydrodynamic drag. Long fins and monofins used by freedivers as a means of underwater propulsion do not require high-frequency leg movement; this helps to minimize oxygen consumption. Short, stiff-bladed fins are effective for short bursts of acceleration and maneuvering, are useful for bodysurfing. Early inventors, including Leonardo da Vinci and Giovanni Alfonso Borelli, toyed with the concept of swimfins. Benjamin Franklin made a pair of early swimfins when he was a young boy living in Boston, Massachusetts near the Charles River.
Modern swimfins are an invention by the Frenchman Louis de Corlieu, capitaine de corvette in the French Navy. In 1914 De Corlieu made a practical demonstration of his first prototype for a group of navy officers, Yves le Prieur among them who, years in 1926, invented an early model of scuba set. De Corlieu left the French Navy in 1924 to 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 producing his fins in his own flat in Paris, De Corlieu 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 USA Owen Churchill changed the French De Corlieu's name to "swimfins", 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, 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. 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. In 1949 Ivor Howitt or a friend of his mailed to the Dunlop Rubber Company for swimfins. Howitt made his own swimfins with innertube rubber stretched across a frame of stiff rubber tube.
Six military and international standards relating to swimfins are known to exist: US military standard MIL-S-82258:1965. Types of fins have evolved to address the requirements of each community using them. Recreational snorkellers use lightweight flexible fins. Free divers favour long fins for efficiency of energy use. Scuba divers need large wide fins to overcome the water resistance caused by their diving equipment, short enough to allow acceptable maneuvering. Ocean swimmers 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, the chosen fin style is 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.
The structure of a swimfin comprises a blade for propulsion and a means of attaching the blade to the foot of the wearer. The vast majority of fins come as a pair, one fin is worn on each foot; this arrangement is called bifins, to distinguish it from monofins. A monofin is 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 carbon fibre composites; the diver's muscle power and swimming style, the type of activity the fins are used for, determine the choice of size and materials. Full-foot fins fit like a shoe and are designed to