Swimfin

Swimfins, swim fins, fins or flippers are finlike rubber or plastic shoes worn over the foot 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 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.

Swimfins are also known as "flippers", due to the ambiguity of the word "fin"; "fin" can reference the fins on cars and auxiliary airfoils on aircraft. Scuba divers all around the world would generally be familiar with the word "fins".

History

Early inventors, including Leonardo da Vinci, 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.

Louis de Corlieu in France and Owen Churchill in the United States, working independently of each other, were the first to make swimfins a practical reality. Churchill's design caught the attention of the US Navy, issued it to their underwater demolition teams in the early 1940s. Fins of this design can still be found in just about any sporting goods store or surf shop.

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.

Specialized types of swim fins

Different types of fins have evolved to address the unique requirements of each community using them. Scuba divers, in particular, need large, wide fins to enable them 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 allow less awkward walking on the beach. Other, more specific design trends are listed below.

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 a water vent through the blade, opening backwards on the underside and forwards on the upper side, as in the third image. As the hip joint is flexed, a jet of water blows backwards out of the vent in the fin. This type of fin is sometimes called a "jetfin"; but the name Jetfin is a brand name. Other paddle fins have convoluted channels and grooves to improve power and efficiency though it has been show that the desired effect does not occur. Paddle fins are widely believed to be the most versatile and have improved economy in men. Tests in women showed a more flexible fin to be more economical, most likely due to lower leg power.

Split fins

Some swimfins have the end of the blade split. In hydrodynamic principle, split fins operate similarly to a propeller, by creating suction and lift forces to move the swimmer forwards. The theory is that water flowing toward the center of the fin's "paddle" portion also gains speed as it focuses, creating a "scooping" or channeling effect. Split fins are sometimes called "Biofins", although "Biofins" is a tradename.

Force fins

"Force fins" represent a type of fin that is only manufactured by Force Fin. They are radically different from all other fins - they have a wide upturned blade made of polyurethane, with a shallow V-shaped cut into the end like some fishes' tails. Force Fins are valued for their high efficiency and acceleration, but are often chided for their poor maneuvering characteristics. Also, for divers who wear neoprene wetsuit booties in cold waters, the negative buoyancy of the lightweight Force Fins is not sufficient to counter the positive buoyancy of their boots. This leads to a condition colloquially known as "floaty feet".

Delfins

The Mor-Fin Corporation produces "delfins", which are swimfins that have a secondary fin which looks similar to a forked homocercal caudal fin. It is based on a the anatomy of a dolphin's fluke.

Freediving fins

These are very similar to paddle fins, except they are far longer, and designed to work with slow stiff-legged kicks that conserve energy and oxygen. Though primarily intended for high efficiency at variable depths, they can still deliver impressive acceleration if necessary. The vast majority are made in the "full-foot" design with very rigid footpockets, which serves to reduce weight and maximize power. Freediving fins are commonly made of plastic, but are also often made from materials such as fiberglass and carbon fiber.

Monofins

Training

The upper limit of a diver's fin-kick thrust force using a stationary-swimming ergometer was shown to be 64 Newtons. Resistive respiratory muscle training improves and maintains endurance fin swimming performance in divers.

See also

• Swimming
• PowerSwim
• Diving equipment
• Scuba equipment

References