SWIMFINS

Swimfins, swim fins, fins or flippers are worn on the foot or leg and made from finlike rubber or plastic, to aid movement through the water in water sports activities such as swimming, bodyboarding, bodysurfing, kneeboarding, riverboarding, and various types of underwater diving.

Scuba divers use fins to move through water efficiently, as human feet being very small provide relatively poor thrust, especially when the diver is carrying equipment that increases hydrodynamic drag.  Very long fins and monofins are used by freedivers as a means of underwater propulsion that does not require high frequency leg movement.

History

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; they were two thin pieces of wood, about the shape of an art palette, which allowed him to move faster than he usually did in the water.

Modern swimfins are an invention from the Frenchman Louis de Corlieu, capitaine de corvette (Lieutenant Commander) 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 later in 1926, invented an early model of scuba set. De Corlieu left the French Navy in 1924 to fully devote himself to his invention.  In April 1933 he registered a patent (number 767013, which in addition to two fins for the feet included two spoon-shaped fins for the hands) and called this equipment propulseurs de natation et de sauvetage (which can be translated literally as "swimming and rescue propulsion device").

After floundering for years, even producing his fins in his own flat in Paris, De Corlieu finally started mass production of his invention in France in 1939. The same year he issued a licence to Owen P. Churchill for mass production in the United States. To sell his fins in the USA Owen Churchill changed the French De Corlieu's name (propulseurs) 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 (UDT). American UDT and British COPP frogmen (COPP: Combined Operations Pilotage Parties) 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 (except for home-made attempts such as gluing marine plywood to plimsolls), until Oscar Gugen began importing swimfins and swimming goggles from France.

In 1946 Lillywhites imported about 1100 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.

In 1949 Ivor Howitt or a friend of his mailed to the Dunlop Rubber Company for swimfins; Dunlop answered that they had no plans to make swimfins and saw no use for them in peacetime. Howitt made his own swimfins with innertube rubber stretched across a frame of stiff rubber tube.

Types

Cressi-sub vented paddle fin   Beuchat Closed-heel Jetfins Beuchat Open-heel adjustable Jetfins Long bladed open heel fin with moderately stiff plastic blade A freediver using a monofin

Types of fins have evolved to address the unique requirements of each community using them. Scuba divers, in particular, need large wide fins to overcome the water resistance caused by their diving equipment; snorkelers need lightweight flexible fins; ocean swimmers, bodysurfers, and lifeguards favor smaller designs that stay on their feet when moving through large surf and that make walking on the beach less awkward. In general there are two main groups of fins; full foot and open heel. Full foot fins fit like a shoe, and are designed to be worn over bare feet. If a larger size is chosen, however, full-foot fins can also be worn over socks and thin-soled booties. They are commonly used for surface swimming, and are in non adjustable sizes. Open heel have a foot pocket with an open heel area, and the fin is held to the foot by springs or straps. They can be worn over boots, and are common in diving. Many companies design fins with the same fin architecture but a choice of heel type. Other, more specific design trends are listed below.

Common types

Paddle fins

These are the most basic fins; a pair of simple stiff plastic, composite, or rubber blades that work as extensions of the feet while kicking. Some paddle fins have channels and grooves to improve power and efficiency though it has been shown that the desired effect does not occur. 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.

Vented fins

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. This style of fin is strongly favored by technical divers that use a frog kick allowing a high degree of control but sacrifice speed for low oxygen consumption. 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. There is a risk of objects catching in the vents.

Split fins

Some swimfins have the end of the blade split. 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.

Freediving fins

These are very similar to paddle fins, except they are far longer, and designed to work with slow stiff-legged kicks that claims to conserve 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 fins are commonly made of plastic, but are also often made from materials such as fiberglass and carbon fiber.

Monofins

A monofin is typically used in finswimming and free-diving. It consists of a single surface attached to footpockets for both the free-diver's feet. Monofins can be made of glass fibre or carbon fibre. The diver's muscle power and swimming style, and the type of activity the monofin is used for, determine the choice of size, stiffness, and materials.

Less usual types

Open and closed heel fins are predominant, but there is a range of fins that have specialised blade attachment architecture. These include (these names are tradenames):

Delfins

The Mor-Fin Corporation produces "delfins", which are swimfins that end short and to the end is attached a shape like a fish's forked homocercal caudal fin. The entire fin is based on the anatomy of various marine animals.

Force fins

"Force Fin" is the trademark for fins designed, developed, manufactured and distributed by Bob Evans Designs, Inc. They are distinguished by an open foot pocket, that encloses only the instep, leaving the toes free so the foot can flex.

Shinfins

These fins are attached to the ankle and rest against the (anatomically) upper side of the foot. The manufacturers claim this avoids leg cramps and reduces foot strain.

Flipfins

 

Flipfins in use by frogmen attacking in a harbor, for better mobility on land

Flipfins are an open-heel swimfin designed to allow easy walking on land. Its blade and foot part are separate: the blade hinges onto the foot part at each side, roughly on the level of the metatarsal heads, and when swimming is held in line by a clip on the front of the foot part. On land or when wading the blade can be unclipped and hinged vertically so it does not interfere with walking.

Breast stroke fins

Breast stroke fins are optimized for use with the breaststroke.

 Swim fin strap attacment with simple rubber strap and wire buckle

 Swim fin strap attachment with swivelling plastic buckle and clip

 Aftermarket stainless steel spring fin strap attached with long D-shackles for security

Open heel fin with stainless steel spring strap with rubber padding

Training

Divers are initially taught to fin with legs straight, without excess bending of the knee, the action coming from the hips; a leg action with much knee bending like riding a bicycle is inefficient and is a common fault with divers who have not learned properly how to fin swim. Fins with differing characteristics (e.g. stiffness) may be preferred, depending on the application, and divers may have to learn a modified finning style to match.

The upper limit of a diver's fin-kick thrust force using a stationary-swimming ergometer was shown to be 64 newtons (14 lbf). The maximum thrust averaged over 20 seconds against a strain gauge has been measured as high as 192 newtons (43 lbf). Resistive respiratory muscle training improves and maintains endurance fin swimming performance in divers.

MORE SWIMFINS

Source :

http://en.wikipedia.org/wiki/Swimfin

Swimfins

SNORKEL

A swimmer's snorkel is a tube typically about 30 centimeters long and with an inside diameter of between 1.5 and 2.5 centimeters, usually L- or J-shaped and fitted with a mouthpiece at the lower end, and constructed of rubber or plastic. It is used for breathing air from above the water surface when the wearer's mouth and nose are submerged. The snorkel usually has a piece of rubber that attaches the snorkel to the outside of the strap of the diving mask. An older technique is pushing the snorkel between the mask-strap and the head, but this practice increases the chances the mask will leak.

Swimmers snorkel with splash guard on top, but with no sump valve.

The optimum design length of the snorkel tube is at most 40 centimetres (about 16 inches). A longer tube would not allow breathing when snorkelling deeper, since it would place the lungs in deeper water where the surrounding water pressure is higher. The lungs would then be unable to inflate when the snorkeler inhales, because the muscles that expand the lungs are not strong enough to operate against the higher pressure.

Snorkels also constitute respiratory dead space. When the user takes in a fresh breath, some of the previously exhaled air which remains in the snorkel is recycled into the lungs, reducing breathing efficiency and causing a build up of carbon dioxide in the blood, which can result in hypercapnia. The greater the volume of the tube, and the smaller the tidal volume of breathing, the more this problem is exacerbated. A smaller diameter tube reduces the dead volume, but also increases resistance to airflow and so increases the work of breathing. Occasional exhalation through the nose while snorkeling will reduce the build up of carbon dioxide, as well as helping to keep the mask clear of water.

Flooding and clearing

The most common type of snorkel is a simple tube that is allowed to flood when underwater. The snorkeler expels water from the snorkel either with a sharp exhalation on return to the surface (blast clearing) or by tilting the head back shortly before reaching the surface and exhaling until reaching or breaking the surface (displacement method) and facing forward again before inhaling the next breath. The displacement method expels water by displacing its presence in the snorkel with air; it is technique that takes practice but clears the snorkel with less effort, but only works when surfacing. Clearing splash water while at the surface requires blast clearing.

  

 Snorkeler underwater, with snorkel's sump valve apparent in foreground.

Some snorkels have a sump in the mouthpiece to allow a small volume of water to remain in the snorkel without being inhaled when the snorkeler breathes. Some also have a one-way output valve in the sump, which automatically drains the sump as it fills with water. A few snorkels have float-operated valves attached to the top end of the tube to keep water out when a wave passes, but these cause problems when diving as the snorkel must then be equalised, using part of the diver's inhaled air supply. Some recent designs have a splash deflector on the top end that directs any water that splashes over the open tube to the outside of the tube, thereby keeping the tube relatively free from water.

A common problem with all assistive mechanical clearing mechanisms is their tendency to fail due to infrequent use, long periods of storage, and lack of maintenance, and also to fail due to environmental fouling.

Natural rubber slowly oxidizes and breaks down due to ultraviolet light exposure from the sun. It eventually loses its flexibility, becomes brittle and cracks. This causes one-way clearing valves to stick in the open or closed position, and float valves to leak water due to a failure of the valve seat to seal out water. It is unlikely that natural rubber is still used for any part of a snorkel. Silicone rubber is more resistant to degrading and so tends to have a longer service life. Application of a grease to the valve seats can aid in sealing, but this is mechanically washed away over time, and a heavy grease can cause valves to stick closed and trap grit, which will cause the valve to leak.

Environmental fouling can be caused by beach sand or loose floating plant or animal matter getting lodged in the valves and preventing proper opening or closing.

Although swimming with a snorkel is much easier than without, it is important that a novice swimmer also learns surface breathing and floating without a snorkel, in the event that these assistive clearing mechanisms fail. If either the sump clearing valve sticks open or the top float valve sticks closed, a snorkel is rendered useless as a breathing aid and the swimmer is forced to fall back on alternative surface breathing methods.

Some snorkels used to be made with small "ping pong" balls in a cage mounted to the open end of the tube to prevent water ingress, but these are no longer sold nor recommended to be used since they are considered hazardous to the snorkeler. Similarly, diving masks with a snorkel built into them are considered unsafe and obsolete.

The dive mask

Snorkelers normally wear the same kind of mask as those worn by scuba divers. By creating an airspace, the mask enables the snorkeler to see clearly underwater. All scuba diving masks consist of the lenses also known as a faceplate, a comfortable skirt, which also encloses the nose, and a head strap. There are different styles and shapes. These range from oval shaped models to lower internal volume masks and may be made from different materials; common choices are silicone and rubber.

The practice of snorkeling

 

Snorkeler with mask and snorkel.

Although donning a mask and snorkel and swimming in any body of water would technically constitute "snorkeling," by and large it is generally accepted that a "snorkeler" would don such gear and practice such activity within the vicinity of a reef, wreck, or other submerged objects, either to observe aquatic organisms including fish, algae, etc. or to look at rock formations. Being non-competitive, snorkeling is considered more a leisure activity than a sport.

Snorkeling requires no special training, only the ability to swim and to breathe through the snorkel. However, for safety reasons, instruction and orientation from a fellow "experienced" snorkeler, tour guide, dive shop, or equipment-rental shop is recommended. Instruction generally covers equipment usage, basic safety, what to look for, and what to look out for, and conservation instructions (fragile organisms such as coral are easily damaged by divers and snorkelers). As with scuba-diving it is always recommended that one not snorkel alone, but rather with a "buddy", a guide or a tour group.

Some commercial snorkeling locations require snorkelers to wear an inflatable vest, similar to a personal flotation device. They are usually bright yellow or orange and have a device that allows users to inflate or deflate the device to adjust their buoyancy. However these devices hinder and prevent a snorkeler from free diving to any depth. Especially in cooler water, a wetsuit of appropriate thickness and coverage may be worn; wetsuits do provide some buoyancy without as much resistance to submersion. In the tropics, snorkelers (especially those with pale skin) often wear a rashguard or a shirt and/or board shorts in order to help protect the skin of the back and upper legs against sunburn.

Experienced snorkelers often start to investigate amateur free-diving, which should be preceded by at least some training from a dive instructor or experienced free-diver.

Safety precautions

The greatest danger to snorkelers are inshore and leisure crafts such as jet skis, speed boats and the like. A snorkeler is often submerged in the water with only the tube visible above the surface. Since these crafts can ply the same areas snorkelers visit, the chance for accidental collisions exist. Sailboats and windsurfers are especially worrisome as their quiet propulsion systems indicates that a snorkeler may be unaware of their presence, unlike any motor-driven craft, as sound travels farther underwater. A snorkeler may surface underneath one and/or be struck by such vessels. Few places demarcate small craft areas from snorkelers, unlike for regular bathers who may have areas marked by buoys. Snorkelers may therefore choose to wear bright or highly reflective colors/outfits and/or to employ dive flags to utilize being spotted easily by boaters and others. On the other hand, some snorklers may use camouflage in order to surprise unsuspecting visitors.

Snorkelers' backs can be exposed to the sun for extended periods and can burn badly (even if slightly submerged), without being noticed. Wearing appropriate covering such as a "rash guard" (in warmer waters), a t-shirt, a wetsuit and/or sunblock will mitigate the risk of sunburn.

Dehydration is another concern. Hydrating well before going in the water is recommended, especially if one intends to snorkel for several hours. Proper hydration also prevents cramps.

Snorkelers can experience hyperventilation, which can lead in turn to “shallow water blackout″; snorkeling with a buddy (and being aware of the buddy's condition at all times) can help avoid this situation.

When snorkeling on or near coral reefs, care must be exercised to avoid contact with the delicate (and sometimes sharp and/or stinging) coral and its poisonous inhabitants, usually via protective gloves and by being careful of one's environment. Booties and surf shoes are especially useful as they allow trekking over reefs exposed by low tide, to drop offs or deeper waters of the outer reef.

Also, for ecological reasons, contact with coral always should be avoided because even boulder corals are fragile. A soft touch can cause decades worth of growth to be undone in mere seconds, and the coral may never recover.

Snorkeling locations

 

Snorkelers observing fish in Cozumel, Mexico.

Snorkeling is possible in almost any body of water, but snorkelers are most likely to be found in locations where there are minimal waves, warm water, and something particularly interesting to see near the surface.

Generally shallow reefs ranging from sea level to 1 to 4 meters (3 to 12 feet) are favored by snorkelers. Deeper reefs are also good, but repeated breath holding to dive to those depths limit the number of practitioners and raises the bar on fitness and skill level.

More Snorkel

Source :

http://en.wikipedia.org/wiki/Snorkeling
Snorkel