skin diving, act of swimming freely underwater. It is done with the aid of a face mask, swimming fins for the feet, and either a snorkel breathing tube or scuba [acronym for self-contained underwater breathing apparatus] gear. The fins increase the propulsion and agility of the swimmer. Skin diving is used in scientific, commercial, and military activities and in recent years has gained enormous popularity as a beach sport. Free underwater swimming is not new, and as long ago as the 8th cent. B.C. Greek divers, unconnected to the surface by air hoses or lines, collected sponges and mollusks in depths as great as 100 ft (30 m). The Greeks and Romans employed underwater warriors, trained to hold their breath for long periods of time, to sabotage enemy fleets. In the Pacific islands natives have long practiced skin diving and spear fishing. Many improvements in skin-diving equipment were made during World War II, and the so-called frogmen of the U.S. and British navies played a vital role in operations. An important development of this period was scuba diving with an Aqua-lung (see diving, deep-sea). The scuba diver, with his greater mobility, has replaced in many areas of underwater activity the conventional sea diver who is encumbered by heavy equipment and limited by a lifeline and air hose. However, it is dangerous for a scuba diver to work below a 130-ft (40-m) depth, and although free dives have been made to more than 300 ft (91 m), conventional dress and equipment are generally used for deep descents.

diving, springboard and platform, sport of entering the water from a raised position, often while executing tumbles, twists, and other acrobatic maneuvers. In most dives the upper part of the body enters the water first, and the arms are extended straight over the head. The earliest recorded major diving competition took place in 1871 off the London Bridge. Since then diving has become part of most aquatic meets and is a U.S. intercollegiate event. Men's diving became part of the Olympic games in 1904, when it was called fancy diving. Women's diving joined the program in 1912; synchronized diving became a medal event in 2000.

Springboard diving is done from a flexible plank made of aluminum or steel and measuring 16 ft (4.9 m) long by 20 in. (51 cm) wide. It extends horizontally over the water at a height of 1 m (about 3 ft 3 in.) or 3 m (about 9 ft 10 in.). The flexibility of the board allows the diver to jump high into the air to execute various maneuvers before entering the water. Platform diving (also called high diving) is usually done from a tower 10 m (32 ft 10 in.) high that is not flexible and that projects nearly five feet (1.5 m) over the water. The height of the tower permits more involved acrobatics during descent; it also poses considerable danger as divers enter the water at speeds of 40 mi (60 km) per hr or more.

Both types of diving are done from standing and walking starts, and in competition judges score on the basis of form, execution, and degree of difficulty. There are six groups of dives (forward, backward, reverse, inward, twisting, and armstand) and four basic midair body positions: tuck (bending at both the knees and the hips so that the body assumes a ball shape), pike (bending at the hips but not at the knees), straight (body rigidly extended at all times), and free (combination of two or more of above body positions). On springboard, divers usually perform five dives with degree-of-difficulty limits—one dive from each group except armstand—and five dives (six for men) with no limits. On platform, divers perform four dives with difficulty limits from the six groups. Women then perform four dives, men six, without limits. In all dives the final entry position should be rigid and vertical—the less splash the better.

diving, deep-sea, act of descending into deep water, generally with some form of breathing apparatus, and remaining there for an extended period. It is used in fishing for sponges, coral, and pearls; in work on the underwater parts of bridges, docks, and other structures; in examining and repairing the underwater parts of ships; in recovering valuables from sunken ships; in raising sunken ships to the surface; and in certain military operations, including reconnaissance and sabotage.

Modern Deep-Sea Diving

Helmet Diving Suits

Modern helmet diving suits usually consist of a waterproof one-piece suit made of canvas and rubber that entirely covers the wearer except for the head and hands. Heavy rubber bands seal the suit at the wrists, leaving the hands free. On the feet the diver wears leaded boots weighing about 40 lb (18 kg), and lead weights are fastened to the chest to maintain equilibrium. A metal helmet with side and front windows covers the head. A noncollapsible pipe connects the helmet to an air supply. An attached lifeline hauls the diver to the surface. Too rapid an ascent from great depths causes the diver to suffer decompression sickness. To prevent this, deep-sea divers either use an all-steel, armored diving suit or breathe a special mixture of nine gases developed by the Swiss mathematician Hannes Keller.

Scuba Diving

Helmet diving has the disadvantage of restricting the diver's lateral movement because of the connection to the surface. This fact led to the development of scuba (an acronym for self-contained underwater breathing apparatus). Scuba delivers air to the diver (from tanks of compressed air) at the same pressure as that exerted by the surrounding water. In this way the diver is able to descend to great depths without feeling the ill effects of high pressure (see skin diving). A skilled scuba diver with good equipment can descend as deeply as a helmet suit diver.

Record-setting dives of over 300 ft (91 m) have been made with scuba gear, although careful scuba divers do not go below about 130 ft (40 m). Beyond this depth a condition known as nitrogen narcosis (popularly called "raptures of the deep") tends to set in. Caused by the narcotic effects of the air's nitrogen at high pressure, the condition is marked by a loss of judgment that often causes the diver to discard equipment or engage in other dangerously foolish behavior. Nitrogen narcosis also affects helmet suit divers, but not until a depth of about 200 ft (61 m).

History

Early Diving

The ancient Greeks practiced commercial and military diving, usually with little or no equipment. In the Iliad, Homer describes the use of divers in the Trojan Wars; Greek laws regulating those who dived for sunken treasure are found as early as the 3d cent. B.C. Before the introduction of modern apparatus, divers submerged with the aid of a rope and a stone weight; using the rope as a guide for position, the naked diver quickly scooped up whatever commodity was being sought.

The Development of Diving Equipment

Inventors as early as the 17th cent. sought means whereby divers could stay underwater for extended periods. At that time, various types of diving dress and underwater armor attempted to supply fresh air through a surface pipe kept above the water by a float. Augustus Siebe devised the first practical diving equipment early in the 19th cent. in England. His first suit was of the open type, consisting of a helmet attached to a jacket made of waterproof material. Air was pumped to the helmet through a pipe from the surface—air pressure serving to keep the water level below the diver's head and the air finally escaping through open vents at the bottom of the jacket. The diver had to maintain a generally upright position; a fall could result in drowning because the air in the suit was likely to rush out through the vents. To correct this difficulty, Siebe later developed the closed type of diving suit that, with improvements, is still in general use. Instead of the earlier open vents, the closed type of suit had valves that let air out without letting water in, regardless of the diver's position. The limitations imposed on the helmet diver's lateral movement (because of the connection to the surface) led to early interest in alternative equipment that would permit freer movement, but the scuba apparatus was not developed by Jacques Yves Cousteau and Emil Gagnan until well into the 20th cent. In 1943 successful tests were made of the new compressed-air breathing apparatus, and it has been widely used since.

Development of Diving Vessels

Several types of large metallic structures have been used as underwater diving vessels since early times. Aristotle, as early as 360 B.C., mentions sponge divers using primitive vessels. Otis Barton's bathysphere—a hollow, globular steel structure built to withstand tremendous pressure—was used in undersea exploration in the 1930s, but an attached steel cable and winch limited its mobility. The first free and self-contained diving craft was Auguste Piccard's bathyscaphe. His craft, the Trieste, descended (1960) to 35,000 ft (10,668 m), the deepest known point in the ocean.

See also submarine, submersible.

diving beetle: see water beetle.

Sport of jumping from an airplane at a moderate altitude (e.g., 6,000 ft [1,800 m]) and executing various body maneuvers before pulling the rip cord of a parachute. Competitive events include jumping for style, landing with accuracy, and performing in teams (e.g., making free-fall formations). The sport parachute is designed to be more maneuverable than the safety parachute.

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Any duck that obtains its food by diving to the bottom in deep water rather than by dabbling in shallows (see dabbling duck). Diving ducks prefer marine environments and are popularly called either bay ducks or sea ducks. Bay ducks (tribe Aythyini, family Anatidae), including canvasback, redhead, scaup, and allied species, are found more frequently in estuaries and tidal lagoons than on the open sea. Sea ducks (20 species in tribes Mergini and Somateriini) include the bufflehead, eiders, goldeneye, mergansers, oldsquaw, and scoters; some are also or mainly found on inland waters.

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Sport of plunging into water, usually headfirst and often following the execution of one or more acrobatic maneuvers. It emerged as a competitive sport in the late 19th century and became part of the Olympic Games in 1904. Dives are performed from a firm platform 5 or 10 m (16.4 or 32.8 ft) above the water, or from a springboard 1 or 3 m (3.3 or 9.8 ft) above the water. In Olympic contests, only the 10-m platform and 3-m springboard are used. Contestants are required to do certain dives, as well as dives of their own choice, each rated according to its degree of difficulty. Judges score each dive, and the total score is multiplied by the degree of difficulty.

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