| Dictionary: Div·ing |
That dives or is used or diving.
Diving beetle (Zoöl.), any beetle of the family Dytiscidæ, which habitually lives under water; -- called also water tiger. -- Diving bell, a hollow inverted vessel, sometimes bell-shaped, in which men may descend and work under water, respiration being sustained by the compressed air at the top, by fresh air pumped in through a tube from above. -- Diving dress. See Submarine armor, under
| 5min Related Video: springboard and platform diving |
| Britannica Concise Encyclopedia: diving |
For more information on diving, visit Britannica.com.
| Sci-Tech Encyclopedia: Diving |
Skin diving, scuba diving, saturation diving, and “hard hat” diving are techniques used by scientists to investigate the underwater environment. Skin diving is usually without breathing apparatus and is done with fins and faceplate. The diver's underwater observation is limited to the time that breath can be held (1–2 min). Diving with scuba (self-contained underwater breathing apparatus) and “hard hat” provide the diver with a breathable gas, thus expanding the submerged time and the depth range of underwater observations. This type of diving is limited by human physiology and the diver's reaction to the pressure and nature of the breathing gas. Saturation diving permits almost unlimited time down to depths of 100 ft (30 m).
Scuba diving
Scuba is used by trained personnel as a tool for direct observation in marine research and underwater engineering. This equipment is designed to deliver through a demand-type regulator a breathable gas mixture at the same pressure as that exerted on the diver by the overlying water column. The gas which is breathed is carried in high-pressure cylinders (at starting pressures of 2000–3000 psi or 14–20 megapascals) worn on the back.
Scuba can be divided into three types: closed-circuit, semiclosed-circuit, and open-circuit. In the first two, which use pure oxygen or various combinations of oxygen, helium, and nitrogen, exhaled gas is retained and passed through a canister containing a carbon dioxide absorbent for purification and then recirculated to a bag worn by the diver. During inhalation additional gas is supplied to the bag by various automatic devices from the high-pressure cylinders. These two types of equipment are much more efficient than the open-circuit system, in which the exhaled gas is discharged directly into the water after breathing. Most open-circuit systems use compressed air because it is relatively inexpensive and easy to obtain. Although open-circuit scuba is not as efficient as the other types, it is preferred because of its safety, the ease in learning its use, and its relatively low cost.
For physiological reasons scuba diving is limited to about 165 ft (50 m) of water depth. Below this depth when using compressed air as a breathing gas, the diver is limited, not by equipment, but by the complex temporary changes which take place in the body chemistry while breathing gas (air) under high pressure.
Saturation diving
This type of diving permits long periods of submergence (1–2 weeks). It allows the diver to take advantage of the fact that at a given depth the body will become fully saturated with the breathing gas and then, no matter how long the submergence period, the decompression time needed to return to the surface will not be increased. Using this method, the diver can live on the bottom and make detailed measurements and observations, and work with no ill effects. This type of diving requires longer periods of decompression in specially designed chambers to free the diver's body of the high concentration of breathing gas. Decompression times of days or weeks (the time increases with depth) are common on deep dives of over 200 ft (60 m).
Physiology
Environmental effects on the submerged diver are quite different from those experienced at sea level. Two elements are very evident during the dive. As the depth of surrounding water increases, pressure on the air the diver breathes also increases. In addition, as the pressure increases, the solubility of the gases in the diver's tissues increases. The tissues, therefore, accumulate certain gases which are not metabolized. The increased presence of certain gases causes specific and often dangerous physiological effects.
The total pressure of the atmosphere at sea level is approximately 760 mmHg or 30.4 in. Hg. Pressure increases underwater at the rate of 1 atm (10 kilopascals) for each 33 ft (10 m) that the diver descends. The total pressure applied to the body and to the breathing gas increases proportionately with depth. As pressure of the gas increases, the amount of gas that is absorbed by the body increases. This is particularly evident if the diver is breathing air within a caisson since the percentage of nitrogen in the breathing gas increases proportionately to the amount of oxygen that is removed. Likewise, the amount of carbon dioxide in the body increases during the dive, particularly if the exhaled air is not separated from the inhaled air.
One of the more obvious effects of gases on divers is caused by nitrogen. This gas makes up about 78% of the air that is normally breathed, and its solubility in the tissues increases as atmospheric pressure increases. When nitrogen is dissolved in the body, more than 50% is contained in the fatty tissues; this includes the myelin sheaths which surround many nerve cells. When divers undergo increased pressure, amounts of nitrogen in nerve tissue increase and lead to nitrogen narcosis or “rapture of the deep.” Nitrogen narcosis can occur at 415 ft (130 m) or 5 atm (500 kPa), and increases in severity as the diver descends below this depth. The irrational behavior and euphoria often seen in nitrogen narcosis can result in serious, even deadly mistakes during a dive. The maximum time that divers can remain underwater without showing symptoms decreases with increasing depth.
One of the earlier recognized problems associated with human diving is known as decompression sickness, the bends, or caisson disease. If a diver is allowed to stay beneath the surface for long periods of time, the volume of dissolved gases in the tissues will increase. This is particularly true of nitrogen in the case of air breathing. When nitrogen accumulates in the tissues, it remains in solution as long as the pressure remains constant. However, when pressure decreases during the ascent, bubbles form in the tissues. Nitrogen bubbles can occur in nerves or muscles and cause pain, or they can occur in the spinal cord or brain and result in paralysis, dizziness, blindness, or even unconsciousness. Bubbles forming in the circulatory system result in air embolism. If the embolism occurs in the circulation of the lungs, a condition known as the chokes occurs. See also Decompression illness.
A method of prevention of decompression sickness was suggested by J. S. Haldane in 1907. Haldane introduced the method of stage decompression, in which the diver is allowed to ascend a few feet and then remain at this level until the gases in the tissues have been allowed to reequilibrate at the new pressure. This stepwise ascent is continued until the diver finally reaches the surface. A modern variation of this method consists of placing the diver in a decompression chamber after the surface is reached, to allow for periods of decompression which simulate ocean depths.
| World of the Body: diving |
As divers descend below the surface of the sea, they are affected by the increased pressure on their bodies which occurs because water is heavy (just consider the weight of one bucketful). At the relatively shallow depth of 10 m of seawater the environmental pressure is 200 kPa, twice that at the surface. Because the body is composed predominantly of incompressible fluid, the effects of increased pressure may not be evident to the diver, except as applied to the gas-containing spaces — notably the lungs. As Robert Boyle observed in 1670, when pressure is doubled, gas volume is halved.
The effects of increased environmental pressure upon the body can be considered as: (i) effects on the gas-containing spaces; (ii) effects of the increased partial pressure of the respiratory gases; (iii) direct effects on cells and molecular mechanisms; (iv) consequences of the uptake by the blood and tissues of dissolved respiratory gases. As well as the effects of pressure itself, there are other complications at great depths, such as thermal imbalance. There are also some long term effects of diving, of which the precise causes are less certain.
Early diving
The breath-hold diver was certainly the first to venture below the surface, and divers who have no external source of gas to breathe underwater are at work today around the world, mostly gathering shellfish. During descent they hold their breath and at the same time must equalize the pressure in their middle ears via the eustachian tubes to avoid rupture of the ear-drum.
The compression of the air within the chest means also that, for a diver with full lungs who is just buoyant at the surface, descent reduces chest volume and makes his buoyancy progressively negative: he will not spontaneously float to the surface.
Similar effects are experienced by recreational breath-hold divers; they may also use a snorkel to allow breathing when on the surface. The duration of a breath-hold dive is determined by the rise of carbon dioxide in the lungs and blood, and hence the need and the stimulus to return to the surface for a breath of fresh air. Thus a diver may be tempted to prolong underwater duration by prior hyperventilation in order to wash out as much carbon dioxide as possible. This poses an additional hazard because hyperventilation reduces the carbon dioxide, but does not increase the oxygen, in the blood. The dive is prolonged because the carbon dioxide level remains tolerable for longer, but towards the end the oxygen has diminished significantly. A diminished blood content of oxygen at depth is at increased pressure and so may be sufficient to sustain consciousness but, during the inevitable return to the surface, the partial pressure of that oxygen diminishes and the breath-holder may lapse into unconsciousness — a potentially lethal situation.
The first attempts to remain underwater longer than breath holding allows may have included the use of hollow reeds as breathing tubes for concealment in battle, but many of the early drawings of submerged men breathing through long tubes to the surface are physically impossible because of the compression which would be imposed upon the chest by hydrostatic pressure.
The invention of the diving bell reputedly allowed Alexander the Great to descend to depth, but duration would have been limited by build up of carbon dioxide in the trapped air within. The bell used in the river Thames in 1691 by Edmund Halley, the Astronomer Royal, was replenished by barrels of air lowered down to it. When a reliable force pump was invented in 1788, those who ventured underwater could for the first time get sufficient compressed air, with the result that entirely new medical and physiological problems emerged. These were noticed first among men in new industrial applications: tunnelling below water and working in caissons.
Development of compressed air diving
Simply pumping air down a hose may seem a crude technique, but it is still used today by many native fishermen. They hold the open end of a hose between the teeth and wear simple goggles. Such fisherman have a high incidence of crippling decompression illness (see below), but this is due not so much to the equipment as to lack of knowledge and training, since it occurs even when they are provided with modern underwater breathing apparatus.
A hose leading into a bucket inverted over the head, with a window, provides the simplest example of an early diving helmet and is similar to equipment being used today by attendants in large marine aquaria. One advantage is that gas is supplied for breathing at exactly the pressure of the depth of the helmet. The development in the early nineteenth century of the copper helmet attached to a closed dry suit made this system commercially viable.
Prolonged durations became practical but brought with them a greater risk of bubble formation in the tissues on return to atmospheric pressure. Joint pains after surfacing were considered by compressed air workers to be just routine. During the salvage of the Royal George off Spithead in 1843 the first case of neurological decompression illness in a diver was reported.
Problems associated with the exchange of respiratory gases at depth also became apparent and the work of John Haldane and others in the early twentieth century showed the importance of avoiding a build up of carbon dioxide. The greater the depth, the greater the volume of air that had to be pumped to the diver: at record depths of greater than 90 m, teams of 12 or more attendants were needed to man the pumps.
There was concern that divers at such depths sometimes behaved irresponsibly; it was not until 1934 that Al Behnke showed that this was due to the increased partial pressure of nitrogen. The so-called inert gas was acting like alcohol, an anaesthetic, or any narcotic.
The substitution of oxy-helium for compressed air was first demonstrated to be practical by Max Nohl in 1938, with a dive in the Great Lakes of the US. In the 1960s it was recognized that, due to the direct cellular effects of pressure during rapid compression to depths greater than 100 m, a number of manifestations occurred which became known collectively as the High Pressure Nervous Syndrome (HPNS) (see later).
Breathing apparatus
The design and use of underwater breathing apparatus (uba) presents its own problems. A complex closed-circuit rebreather apparatus was designed by Henry Fleuss in 1878. The diver breathed from a bag of pure oxygen (a ‘counter-lung’), which he topped up with more oxygen ‘as required’. His exhaled air was returned to the bag through a ‘scrubber’ which chemically removed the carbon dioxide. This is a hazardous procedure but nevertheless the apparatus was used successfully for the salvage of the flooded Severn Railway Tunnel. Because no bubbles emerge it was further developed for use in clandestine military operations in World War II — leading to recognition of the problems of acute oxygen neurotoxicity. Within strict depth limits it has also been useful for photographers and biologists.
Semi-closed-circuit uba is similar but uses an oxygen-nitrogen mixture rather than pure oxygen, enabling a greater depth to be achieved than with closed-circuit uba; the gas is supplied at a constant mass flow rate, which means that some bubbles emerge. This type of apparatus was developed as acoustically safe for those highly trained men whose underwater task was the clearance of enemy mines, but has recently been adopted by recreational divers. They require special training to minimize the risks from hazards peculiar to such apparatus: ‘dilution hypoxia’, ‘shallow water blackout’, and ‘soda-lime cocktail’.
Enjoyment of recreational diving depends on a sense of freedom in the water and, in particular, freedom from the encumbrance of helmets and hoses. This was made available to the world in the mid twentieth century by the development by Cousteau and Gagnan of a ‘demand regulator’. This allows just the right volume of gas, at the correct pressure for the diver's depth at that moment, to be delivered to the diver's mouthpiece from a tank of compressed air which he carries. Though not the first demand valve to be invented, it was the first to be adopted almost universally, and it is used widely for air and mixed gas diving by recreational and professional divers. Other types of uba with lower resistance have been developed to reduce the work of breathing at greater depths as gas density increases.
In the 1970s the need to exploit offshore oil and gas reserves led to the adoption of ‘saturation diving’ which had been pioneered by George Bond of the US Navy. The commercial diver avoids daily and prolonged decompressions from great depths by living at the surface in a chamber with an internal pressure similar to that of the worksite, until the task has been completed. Each day he descends by means of a pressurized diving bell to his work and, at the end of an in-water shift of several hours, returns to the deck chamber in the closed bell.
The gas-containing spaces and barotrauma
Aural barotrauma Unless additional gas can be admitted through the eustachian tube into the middle ear cavity during descent, to compensate for the reduction of gas volume there, the developing pressure differential may lead to injury — ‘barotrauma’. At depths as shallow as 3 m transudation and possible haemorrhage into the middle ear cavity, and ultimately an implosion of the ear-drum, can occur. The sudden influx of cold water into the middle ear is an abnormal stimulus to the labyrinth of the inner ear, and can cause total disorientation. Most divers avoid such trouble by learning to ‘clear their ears’ from the moment they leave the surface by using a simple swallowing technique. Even lesser degrees of aural barotrauma, perhaps if only one ear is ‘sticky’, can lead to underwater disorientation; this can become a hazard, especially as immersion also reduces sensations from limbs and joints, and as visibility may be impaired.
There is a risk of infection to a middle ear exposed by barotrauma. Even worse, attempts to ‘clear’ the ears by forcing gas through the eustachian tube too vigorously can raise the cerebrospinal fluid pressure enough to rupture a membrane which separates the middle from the inner ear, causing permanent damage to hearing and balance.
Pulmonary barotrauma In contrast to the middle ear, which is damaged predominantly during the compression phase, the lungs are at risk during ascent: when the diver has inhaled gas at a pressure greater than atmospheric, this gas will expand progressively as he approaches the surface, and failure to breathe out the expanding gases can lead to pulmonary barotrauma — probably the commonest cause of death among sports divers. (The breath-hold diver should not be affected by this, since during ascent his lungs are merely re-expanding to their original volume.) Clearly the risk of lung damage is greatest if the diver holds his breath during ascent — yet lung rupture can occur even when he has exhaled continuously and even when it is known that he has no abnormality in his chest which might impede the venting of gas; rapid expiration may itself tend to collapse the small airways, trapping gas in the lungs.
Rupture allows gas to escape from the lungs into the pleural cavities (pneumothorax) or into the lung blood vessels (gas embolism) — a serious form of ‘decompression illness’.
Barotrauma due to equipment can arise when there is a gas-containing space which becomes rapidly smaller with increasing pressure, if there is no adequate inflow to maintain the volume. An unanticipated rapid fall through the water by a traditional helmeted diver whose helmet pressure is controlled at the surface can lead to a fatal ‘chest squeeze’. A squeeze of the half mask of a scuba diver, if not equalized by small exhalations through the nose during descent, can damage the eyes by conjunctival oedema and haemorrhage. Even a dry suit, worn for thermal protection, can lead to painful pinches of the skin if compression of the air within it is uncompensated.
Increased partial pressure of respiratory gases
When the total pressure is increased, the partial pressure of each component gas in the inspired air (or other mixture) is increased proportionately; these increased pressures in the lungs equilibrate with the blood, resulting in greater ‘tensions’ of the gases in solution in body fluids.
Oxygen neurotoxicity Oxygen can cause an epileptiform fit, but only when breathed at pressures greater than that of pure oxygen at normal atmospheric pressure (∼100 kPa). A partial pressure of 150 kPa in oxy-nitrogen mixtures is an acceptable upper limit for short-term use, but military divers rebreathing pure oxygen for swimming use a limit of 176 kPa which occurs at 7.6 m. The threshold for oxygen toxicity varies greatly between and even within individuals and from day to day, and is influenced by the amount of physical work being done. For a diver at rest, requiring oxygen treatment, up to 280 kPa is commonly used. Intermittent oxygen breathing, with 5 min air breaks every 20 min or so, reduces the risk of oxygen toxicity.
Characteristically the diver has no warning of an impending fit. Occasionally there is an impression of hearing the sound of an engine within the head, but this comes too late for the diver to avoid a convulsion. If this occurs in the water, especially when wearing some kinds of uba, it is likely to be fatal; those using a helmet or with some other guaranteed airway are less likely to drown.
Oxygen pulmonary toxicity In contrast to neurotoxicity the ill-effects of prolonged oxygen breathing on the lung are relatively slow in onset. Characteristic first signs are a dry cough with chest pain; vital capacity shows a progressive impairment which at first is reversible. Later there may be pulmonary oedema which can become irreversible. These effects can usually be avoided by estimating and controlling the cumulative oxygen dose. With more prolonged exposures at lesser partial pressures (~30 kPa), there can be a slow diminution in the ability to transfer oxygen to the blood.
Nitrogen narcosis Like all ‘inert’ gases, nitrogen has actions on nerve cells like those of alcohol and some anaesthetics. At increasing nitrogen partial pressure (proportional to depth when breathing air) the diver becomes incapable of behaving responsibly and this can have disastrous effects upon in-water safety. For this reason amateur divers are recommended to stay shallower than 30 m and commercial divers are restricted to 50 m when breathing compressed air. Some amateur divers practise ‘extreme air diving’ and a number of potential record breakers have achieved 90 m — but not all have returned to the surface. Extreme air diving is really rather stupid.
Carbon dioxide may build up in some types of breathing apparatus and create breathlessness and headaches. A number of divers have been shown to tolerate raised carbon dioxide: they do not respond to it, as normal persons, by increasing their breathing. While one might expect this to be a potentially useful adaptation, in fact the synergism of carbon dioxide with nitrogen and with raised partial pressures of oxygen is thought to be a cause of otherwise unexplained loss of consciousness. ‘Carbon dioxide retainers’ may therefore be at a greater risk of an underwater accident than others.
The direct effects of pressure
The High Pressure Nervous Syndrome (HPNS) begins in the compression phase of deep diving when oxy-helium is used to avoid nitrogen narcosis. It is worse with rapid compression rates and increases with depth. The neurological manifestations include tremors, nausea, and vomiting, and there are changes in the electroencephalogram. Helium itself has no significant narcotic effects at depths to around 600 m and it has been shown that the HPNS is not a gas effect. It is thought to be due to the direct effects of pressure upon transmission of nerve impulses. Paradoxically the HPNS can be ameliorated by the addition of a narcotizing agent, and 5% nitrogen is the one most readily available for oxy-helium divers. Such ‘trimix’ dives have been shown to be an effective solution for very deep diving, but are not used commercially for reasons of expense related to the difficulties of gas recovery and purification; rather, a very slow staged compression rate is used to avoid HPNS in oxy-helium diving, developed over years of experience.
Uptake of gases into solution in the body
Nitrogen accounts for 80% of air breathed into the lungs, so is at 80% of the total gas pressure, but it is relatively insoluble in the blood so that body tissues at sea level contain very little. At depth, breathing air, progressively more nitrogen slowly dissolves in blood and in all body tissues. The amount that accumulates depends on both the depth and the duration of the dive. Then, when rising to the surface, nitrogen is released, and can cause decompression sickness (including ‘the bends’) if the rise is too rapid.
Long-term health effects
The only known long term hazard of diving is aseptic necrosis of bone (dysbaric osteonecrosis), a disintegration in the substance of the head, neck, and shaft of the long bones, where it causes problems very rarely, or under the cartilage in the shoulder and hip joints, where it can be painful and crippling. It can occur even after only a single exposure to raised environmental pressure and has a latency of months or years before symptoms arise. Cases among sports and European commercial divers are rare, but the condition is prevalent in shell-fishing divers who tend to be unaware of safe decompression procedures.
Much has been said about the possible long-term damage to the central nervous system caused by diving, but when sequelae from known episodes of neurological decompression illness are excluded, the evidence is not dramatic. There may be some pathological changes but there is little or no evidence that these are harmful.
In conclusion
Those who dive must be mentally, medically, and physically fit to do so. Some obvious contraindications are epilepsy and cardiac inadequacies, while those who are diabetic or paraplegic should dive only under the careful restrictions of an appropriate organization. Lung and other diseases require assessment of fitness to dive by a doctor experienced in this environment. Assessment is not easy but is justified not only by the subsequent avoidance of unnecessary diving accidents but also for the safety of those who otherwise might suddenly become rescuers.
Those who wish to dive should do so only after rigorous training and each must recognize that the most important feature of every subsequent dive plan is to include the recognition, assessment, and control of risk. Diving is hazardous and the sea is an unforgiving environment.
— David Elliott
Bibliography
See also decompression sickness; gases in the body; hyperbaric chamber; nitrogen; oxygen.
| Columbia Encyclopedia: springboard and platform diving |
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.
Bibliography
See S. Lee and S. Lehrman, Diving (1983); A. J. Bachrach and G. H. Egstrom, Stress and Performance in Diving (1987).
| Word Tutor: diving |
| Wikipedia: Diving |
Diving is the sport of jumping or falling into water from a platform or springboard, sometimes while performing acrobatics. Diving is an internationally-recognized sport that is part of the Olympic Games. In addition, unstructured and non-competitive diving is a recreational pastime.
Diving is one of the most popular Olympic sports with spectators. Competitors possess many of the same characteristics as gymnasts and dancers, including strength, flexibility, kinaesthetic judgment and air awareness.
China came to prominence several decades ago when the sport was revolutionized by national coach Liang Boxi and after intense study of the dominant Louganis. China has lost few world titles since. The success of Greg Louganis has led to American strength in diving internationally. Other noted countries in the sport include Italy, Australia and Canada.
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Most diving competitions consist of three disciplines: 1m and 3m springboards, and the platform. Competitive athletes are divided by gender, and often by age group. In platform events, competitors are allowed to perform their dives on either the five, seven and a half (generally just called seven) or ten meter towers. In major diving meets, including the Olympic Games and the World Championships, platform diving is from the 10 meter height.
Divers have to perform a set number of dives according to established requirements, including somersaults and twists. Divers are judged on whether and how well they completed all aspects of the dive, the conformance of their body to the requirements of the dive, and the amount of splash created by their entry to the water. A possible score out of ten is broken down into three points for the takeoff, three for the flight, and three for the entry, with one more available to give the judges flexibility.
The raw score is multiplied by a difficulty factor, derived from the number and combination of movements attempted. The diver with the highest total score after a sequence of dives is declared the winner.
Synchronized diving was adopted as an Olympic sport in 2000. Two divers form a team and perform dives simultaneously. The dives are usually identical; however, sometimes the dives may be opposites, in what is called a pinwheel. In these events, the diving is judged both on the quality of execution and the synchronicity - in timing of take-off and entry, height and forward travel.
There are rules governing the scoring of a dive. Usually a score considers three elements of the dive: the approach, the flight, and the entry. The primary factors affecting the scoring are:
To reduce the subjectivity of scoring in major meets, panels of five or seven judges are assembled. If five judges then the highest and lowest scores are discarded and the middle three are summed and multiplied by the DD (Degree of Difficulty—determined from a combination of the moves undertaken, in which position and from what height). In major international events, there are seven judges in which case the highest and lowest scores are again discarded and the middle five are summed, then ratioed by 3/5, and multiplied by the DD, so as to provide consistent comparison with 5-judge events. Accordingly, it is extremely difficult for one judge to manipulate scores.
There is a general misconception about scoring and judging. In serious meets, the absolute score is somewhat meaningless. It is the relative score, not the absolute score that wins meets. Accordingly, good judging implies consistent scoring across the dives. Specifically, if a judge consistently gives low scores for all divers, or consistently gives high scores for the same divers, the judging will yield fair relative results and will cause divers to place in the correct order. However, absolute scores have significance to the individual divers. Besides the obvious instances of setting records, absolute scores are also used for rankings and qualifications for higher level meets.
In synchronised diving events, there is a panel of seven or nine judges; two to mark the execution of one diver, two to mark the execution of the other, and three or five to judge the synchronisation.
To win dive meets, divers create a dive list in advance of the meet. To win the meet the diver must accumulate more points than other divers. Often, simple dives with low DDs will look good to spectators but will not win meets. The competitive diver will attempt the highest DD dives possible with which they can achieve consistent, high scores. If divers are scoring 8 or 9 on most dives, it may be a sign of their extreme skill, or it may be a sign that their dive list is not competitive, and they may lose the meet to a diver with higher DDs and lower scores.
In competition, divers must submit their lists beforehand, and once past a deadline (usually when the event is announced or shortly before it begins) they cannot change their dives. If they fail to perform the dive announced, even if they physically cannot execute the dive announced or if they perform a more difficult dive, they will receive a score of zero. Under exceptional circumstances, a redive may be granted, but these are exceedingly rare (usually for very young divers just learning how to compete, or if some event outside the diver's control has caused them to be unable to perform).
In the Olympics or other highly competitive meets, many divers will have nearly the same list of dives as their competitors. The importance for divers competing at this level is not so much the DD, but how they arrange their list. Once the more difficult rounds of dives begin it is important to lead off with a confident dive to build momentum. They also tend to put a very confident dive in front of a very difficult dive to ensure that they will have a good mentality for the difficult dive. Most divers have pre-dive and post-dive rituals that help them either maintain or regain focus. Coaches also play a role in this aspect of the sport. Many divers rely on their coaches to help keep their composure during the meet. In a large meet coaches are rarely allowed on the deck to talk to their athlete so it is common to see coaches using hand gestures to communicate.
There are some American meets which will allow changes of the position of the dive even after the dive has been announced immediately before execution, but these are an exception to the rules generally observed internationally.
Generally, NCAA rules allow for dives to be changed while the diver is on the board, but the diver must request the change directly after the dive is announced. This applies especially in cases where the wrong dive is announced. If the diver pauses during his or her hurdle to ask for a change of dive, it will be declared a balk and the change of dive will not be permitted.
Under FINA law, no dive may be changed after the deadline for the dive-sheet to be submitted (generally a period ranging from one hour to 24 hours, depending on the rulings made by the event organiser.
It is the diver's responsibility to ensure that the dive-sheet is filled in correctly, and also to correct the referee or announcer before the dive if they describe it incorrectly. If a dive is performed which is as submitted but not as (incorrectly) announced, it is declared failed and scores zero according to a strict reading of the FINA law. But in practice, a re-dive would usually be granted in these circumstances.
Divers do not consider themselves swimmers. While each sport shares a pool, and may compete side by side when doing so for their schools, the two sports are very different. Swimming is a full body exercise with emphasis on speed, whereas diving is a full body exercise with emphasis on technical acrobatic execution; swimmers most frequently suffer overuse injuries, whereas divers most frequently suffer impact injuries or strains.
The sister sport of diving is gymnastics. Many divers begin their training as gymnasts, and switch sports. Two of the most common are that they simply prefer diving, or that they develop a chronic injury that makes continuing gymnastics impossible. Gymnastics provides young divers with skills that help them perform complex and risky dives, but there are downsides; some habits developed in gymnastics can interfere with the correct technique of diving. Twisting is the major habit that is different in diving and gymnastics. Gymnasts are commonly taught to twist with the arms crossed on the chest while divers are taught to wrap the arms at head level. Another difficulty for a gymnast entering the world of diving is learning to land on the hands.
The global governing body of diving is FINA, which also governs swimming, synchronized swimming, water polo and open water swimming. Almost invariably, at national level, diving shares a governing body with the other aquatic sports.
This is frequently a source of political friction as the committees are naturally dominated by swimming officials who do not necessarily share or understand the concerns of the diving community. Divers often feel, for example, that they do not get adequate support over issues like the provision of facilities. Other areas of concern are the selection of personnel for the specialised Diving committees and for coaching and officiating at events, and the team selection for international competitions.
There are sometimes attempts to separate the governing body as a means to resolve these frustrations, but they are rarely successful. For example, in the UK the Great Britain Diving Federation was formed in 1992 with the intention of taking over the governance of Diving from the ASA (Amateur Swimming Association). Although it initially received widespread support from the diving community, the FINA requirement that international competitors had to be registered with their National Governing Body was a major factor in the abandonment of this ambition a few years later.
Since FINA refused to rescind recognition of the ASA as the British governing body for all aquatic sports including diving, this meant that the elite divers had to belong to ASA affiliated clubs in order to be eligible for selection to international competition.
In the United States scholastic diving is almost always part of the school’s swim team. Diving is a separate sport in Olympic and Club Diving. The NCAA will separate diving from swimming in special diving competitions after the swim season is completed.
Despite the apparent risk, the statistical incidence of injury in supervised training and competition is extremely low.[citation needed]
The majority of accidents that are classified as 'diving-related' are incidents caused by individuals jumping from structures such as bridges or piers into water of inadequate depth. Because of this many beaches and pools prohibit diving in shallow waters or when a lifeguard is not on duty.
After an incident in Washington state in 1993, most US and other pool builders are reluctant to equip a residential swimming pool with a diving springboard, so home diving pools are much less common these days. In the incident, 14-year-old Shawn Meneely made a "suicide dive" (his hands at his sides - so his head hit the bottom first) in a private swimming pool and was seriously injured (quadriplegic). Family lawyer Fred Zeder successfully sued the diving board manufacturer, the pool builder, and the National Spa and Pool Institute over the inappropriate depth of the pool.[1] The NSPI had specified a minimum depth of 7 ft 6 in (2.55m) which proved to be insufficient in the above case. The pool into which Meneelly dived was not constructed to the published standards. The standards had changed after the diving board was installed on the non-compliant pool by the homeowner. But the courts held that the pool "was close enough" to the standards to hold NSPI liable. The multi-million dollar lawsuit was eventually settled in 2001 for $6,600,000USD ($US8,000,000 after interest was added) in favor of the plaintiff. [2] The NSPI was held to be liable, and was financially strained by the case. It filed twice for Chapter 11 bankruptcy protection and was successfully reorganized into a new swimming pool industry association.[1]
Within competitive diving, FINA takes regulatory steps to ensure that athletes are protected from the inherent dangers of the sport. For example, they impose restrictions according to age on the heights of platforms which divers may compete on.
Group D divers have only recently been allowed to compete tower. In the past, the age group could compete only springboard, in order to discourage children from taking on the greater risks of tower diving. Group D tower was introduced to counteract the phenomenon of coaches pushing young divers to compete in higher age categories, thus putting them at even greater risk.
However, some divers may safely dive in higher age categories in order to dive on higher platforms. Usually this occurs when advanced Group C divers wish to compete on the 10m.
Points on pool depths in connection with safety:
There are six "groups" into which dives are classified: Forward, Back, Inward, Reverse, Twist, and Armstand. The latter applies only to Platform competitions, whereas the other five apply to both Springboard and Platform.
During the flight of the dive, one of the four positions may be specified:
These positions are referred to by the letters A, B,C and D respectively.
Difficulty is rated according to the Degree of Difficulty of the dives. Some divers may find pike easier in a flip than tuck, and most find straight the easiest in a front/back dive, although it is still rated the most difficult because of the risk of overrotation.
In competition, the dives are referred to by a schematic system of three- or four-digit numbers. The letter to indicate the position is appended to the end of the number.
The first digit of the number indicates the dive group as defined above.
For groups 1 to 4, the number consists of three digits and a letter of the alphabet. The third digit represents the number of half-somersaults. The second digit is either 0 or 1, with 0 representing a normal somersault, and 1 signifying a "flying" variation of the basic movement (i.e. the first half somersault is performed in the straight position, and then the pike or tuck shape is assumed). No flying dive has been competed at a high level competition for many years.
For example:
For Group 5, the dive number has 4 digits. The second digit indicates the group (1-4) of the underlying movement; the third digit indicates the number of half-somersaults, and the fourth indicates the number of half-twists.
For example:
For Group 6 - Armstand - the dive number has either three, four or five digits: Three digits for dives without twist and four for dives with twists.
In non-twisting armstand dives, the second digit indicates the direction of rotation (0 = no rotation, 1 = forward, 2 = backward, 3 = reverse, 4 = inward) and the third digit indicates the number of half-somersaults. Inward-rotating armstand dives have never been performed, and are generally regarded as physically impossible.
For example:
For twisting Armstand dives, the dive number again has 4 digits, but rather than beginning with the number 5, the number 6 remains as the first digit, indicating that the "twister" will be performed from an Armstand. The second digit indicates the direction of rotation - as above, the third is the number of half-somersaults, and the fourth is the number of half-twists:
e.g. 6243D - armstand back double-somersault with one and a half twists in the free position
All of these dives come with DD (degree of difficulty) this is an indication of how difficult/complex a dive is. The score that the dive receives is multiplied by the DD (also known as tariff) to give the dive a final score. Before a diver competes they must decide on a "list" this is a number of optional dives and compulsory dives. The optionals come with a DD limit. this means that a diver must select X number of dives and the combined DD limit must be no more than the limit set by the competition/organisation etc.
Until the mid 1990s the tariff was decided by the FINA diving committee, and divers could only select from the range of dives in the published tariff table. Since then, the tariff is calculated by a formula based on various factors such as the number of twist and somersaults, the height, the group etc., and divers are free to submit new combinations. This change was implemented due to the fact that new dives were being invented too frequently for an annual meeting to accommodate the progress of the sport.
At the moment of take-off, two critical aspects of the dive are determined, and cannot subsequently be altered during the execution. One is the trajectory of the dive, and the other is the magnitude of the angular momentum.
The speed of rotation - and therefore the total amount of rotation - may be varied from moment to moment by changing the shape of the body, in accordance with the law of conservation of angular momentum.
The center of mass of the diver follows a parabolic path in free-fall under the influence of gravity (ignoring the effects of air resistance, which are negligible at the speeds involved).
Since the parabola is symmetrical, the travel away from the board as the diver passes it is twice the amount of the forward travel at the peak of the flight. Excessive forward distance to the entry point is penalized when scoring a dive, but obviously an adequate clearance from the diving board is essential on safety grounds.
The greatest possible height that can be achieved is desirable for several reasons:
The magnitude of angular momentum remains constant throughout the dive, but since
and the moment of inertia is larger when the body has an increased radius, the speed of rotation may be increased by moving the body into a compact shape, and reduced by opening out into a straight position.
Since the tucked shape is the most compact, it gives the most control over rotational speed, and dives in this position are easier to perform. Dives in the straight position are hardest, since there is almost no scope for altering the speed, so the angular momentum must be created at take-off with a very high degree of accuracy. (A small amount of control is available by moving the position of the arms and by a slight hollowing of the back).
The opening of the body for the entry does not stop the rotation, but merely slows it down. The vertical entry achieved by expert divers is largely an illusion created by starting the entry slightly short of vertical, so that the legs are vertical as they disappear beneath the surface. A small amount of additional tuning is available by 'entry save' techniques, whereby underwater movements of the upper body and arms against the viscosity of the water affect the position of the legs.
Dives with multiple twists and somersaults are some of the most spectacular movements, as well as the most challenging to perform.
The rules state that twisting 'must not be generated manifestly on take-off'. Consequently, divers must use some of the somersaulting angular momentum to generate twisting movements. The physics of twisting can be explained by looking at the components of the angular momentum vector.
As the diver leaves the board, the total angular momentum vector is horizontal, pointing directly to the left for a forward dive for example. For twisting rotation to exist, it is necessary to tilt the body sideways after takeoff, so that there is now a small component of this horizontal angular momentum vector along the body's long axis. The tilt can be seen in the photo.
The tilting is done by the arms, which are outstretched to the sides just before the twist. When one arm is moved up and the other is moved down (like turning a big steering wheel), the body reacts by tilting to the side, which then begins the twisting rotation. At the completion of the required number of twist rotations, the arm motion is reversed (the steering wheel is turned back), which removes the body's tilt and stops the twisting rotation.
An alternative explanation is that the moving arms have precession torque on them which set the body into twisting rotation. Moving the arms back produces opposite torque which stop the twisting rotation.
The rules state that the body should be vertical, or nearly so, for entry. The arms must be beside the body for feet-first dives, which are typically competed only on the 1m springboard and only at fairly low levels of competition, and extended forwards in line for "head-first" dives, which are much more common competitively. It used to be common for the hands to be interlocked with the fingers extended towards the water, but a different technique has become favoured during the last few decades. Now the usual practice is for one hand to grasp the other with palms down to strike the water with a flat surface. This creates a vacuum between the hands, arms and head which, with a vertical entry, will pull down and under any splash until deep enough to have minimal effect on the surface of the water (the so-called "rip entry"). Once a diver is completely under the water they may choose to roll or scoop in the same direction their dive was rotating to pull the splash away from the channel which they have just created.
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The examples and perspective in this article deal primarily with English-speaking territories and do not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page. |
In the United States, summer diving is usually limited to one meter diving at community or country club pools. Some pools organize to form intra-pool competitions. These competitions are usually designed to accommodate all school-age children. One of the largest and oldest summer leagues in the United States is found in the Northern Virginia area where teams from 47 pools compete against each other every summer. NVSL-Dive hosts annually holds the Wally Martin 3-Meter Championship and concludes the season with its Individual All Stars Championship. In addition, NVSL-Dive annually hosts the largest one-day dive meet in the world, with over 350 developmental divers in NVSL's "Cracker Jack" Invitational! Champions from each of these events have gone on to compete at the collegiate and olympic levels.
In the United States scholastic diving at the high school level is usually limited to one meter diving (but some schools use three meter springboards.). Scores from those one meter dives contribute to the swim team's overall score. High school diving and swimming both conclude their seasons with a state competition. Depending on the state and the amount of athletes competing in the state there are qualifications that must be achieved before competing in the state’s championship meet. There are often regional championships and district championships which are necessary to compete in before reaching the state meet to narrow the field to only the most competitive athletes. Most state championship meets consist of eleven dives. Those eleven dives are usually split up between two categories. There are five required dives and six optional dives.
In the United States, pre-college divers interested in three meter or tower diving should consider a club sanctioned by USA Diving or AAU Diving. There is a group called Future Championship. Top club divers are usually called "junior Olympic", or JO divers. JO divers compete for spots on national teams. Divers over the age of 19 years of age cannot compete in these events as a JO diver.
USA Diving sanctions one East-West one and three meter event in the winter time with an Eastern champion and Western champion determined. In the summer USA Diving sanctions a national event with tower competitions offered.
AAU Diving sanctions one national event per year in the summer. AAU competes on the one, three, and tower to determine the All-American team.
In the United States scholastic diving at the college level requires one and three meter diving. Scores from the one and three meter competition contribute to the swim team's overall meet score. College divers interested in tower diving may compete in the NCAA separate from swim team events. NCAA Divisions II and III do not usually compete platform; if a diver wishes to compete platform in college, he or she must attend a Division I school.
Each divisions also has rules on the number of dives in each competition. Division II schools compete with 10 dives in competition whereas Division III schools compete with 11. Division I schools only compete with 6 dives in competition. These 6 dives consist of either 5 optionals and 1 voluntary, or 6 optionals. If the meet is a 5 optional meet, then the divers will perform 1 optional from each category (Front, Back, Inward, Reverse, and Twister) and then 1 voluntary from the category of their choice. The voluntary in this type of meet is always worth a DD (Degree of Difficulty) of 2.0 even if the real DD is worth more or less on a DD sheet. In a 6 optional meet, the divers will yet again perform one dive from each category, but this time they will perform a 6th optional from the category of their choosing, which is worth its actual DD from the DD sheet.
The highest level of collegiate competition is the NCAA Division 1 Swimming and Diving Championship. Events at the championship include 1 meter springboard, 3 meter springboard, and platform, as well as various swimming individual and relay events. The points scored by swimmers and divers are combined to determine a team swimming & diving champion. To qualify for a diving event at the NCAA championships, a competitor must first finish in the top three at one of five zone championships, which are held after the various conference championship meets. A diver who scores at least 310 points on the 3 meter springboard and 300 points on the 1 meter springboard in a 6 optional meet can participate in the particular zone championship corresponding to the geographic region within which his or her school lies.
A number of colleges and universities offer scholarships to men and women who have competitive diving skills. These scholarships are usually offered to divers with age-group or club diving experience.
The NCAA limits the number of years a college student can represent any school in competitions. The limit is four years, but could be less under certain circumstances.
In the United States divers who continue diving past their college years can compete in Master Diving programs. Master diving programs are frequently offered by college or club programs.
Masters' Diving events are normally conducted in age-groups of 5 or 10 years, and attract competitors of a wide range of ages and experience (many, indeed, are newcomers to the sport); the oldest competitor in a Masters' Diving Championship was Viola Krahn, who at the age of 101 was the first person in any sport, male or female, anywhere in the world, to compete in an age-group of 100+ years in a nationally organized competition.
In Britain, diving competitions on all boards run throughout the year. National Masters' Championships are held two or three times per year.
In the Republic of Ireland facilities are limited to one pool at the National Aquatic Centre in Dublin. Dublin Diving Club, headed by the Mexican High Diver Ricardo Gutierrez, runs out of this facility.
National Championships take place late in the year, usually during November. The 2009 competition will be held at the National Aquatic Centre on the 14th and 15th of November and will consist of four different events:
In Canada, elite competitive diving is regulated by DPC (Diving Plongeon Canada), although the individual provinces also have organizational bodies. The main competitive season runs from February to July, although some competitions may be held in January or December, and many divers (particularly international level athletes) will train and compete year round.
Most provincial level competitions consist of events for 6 different age groups (Groups A, B, C, D, E, and Open) for both genders on each of the three board levels. These age groups roughly correspond to those standardized by FINA, with the addition of a youngest age group for divers 9 and younger, Group E, which does not compete nationally and does not have a tower event (although divers of this age may choose to compete in Group D). The age group Open is so called because divers of any age, including those over 18, may compete in these events, so long as their dives meet a minimum standard of difficulty.
Although Canada is internationally a fairly strong country in diving, the vast majority of Canadian high schools and universities do not have diving teams, and many Canadian divers accept athletic scholarships from American colleges.
Adult divers who are not competitive at an elite level may compete in masters diving. Typically, masters are either adults who never practiced the sport as children or teenagers, or former elite athletes who have retired but still seek a way to be involved in the sport. Many diving clubs have masters teams in addition to their primary competitive ones, and while some masters dive only for fun and fitness, there are also masters competitions, which range from the local to world championship level.
Divers can qualify to compete at the age group national championships, or junior national championships, in their age groups as assigned by FINA up to the age of 18. This competition is held annually in July. Qualification is based on achieving minimum scores at earlier competitions in the season, although athletes who place very highly at a national championships will be automatically qualified to compete at the next. Divers must qualify at two different competitions, at least one of which must be a level 1 competition, i.e. a competition with fairly strict judging patterns. Such competitions include the Polar Bear Invitational in Winnipeg, the Sting in Victoria, and the Alberta Provincial Championships in Edmonton or Calgary. The qualifying scores are determined by DPC according to the results of the preceding year's national competition, and typically do not have much variation from year to year.
Divers older than 18, or advanced divers of younger ages, can qualify for the senior national championships, which are held twice each year, once roughly in March and once in June or July. Once again, qualification is based on achieving minimum scores at earlier competitions (in this case, within the 12 months preceding the national championships, and in an Open age group event), or high placements in previous national championships or international competitions. It is no longer the case that divers may use results from age group events to qualify for senior nationals, or results from Open events to qualify for age group nationals.
Diving is also popular as a non-competitive activity. Such diving usually emphasizes the airborne experience, and the height of the dive, but does not emphasize what goes on once the diver enters the water. The ability to dive underwater can be a useful emergency skill, and is an important part of watersport and navy safety training. Entering water from a height is an enjoyable leisure activity, as is underwater swimming.
Such non-competitive diving can occur indoors and outdoors. Outdoor diving typically takes place from cliffs or other rock formations either into fresh or salt water. However, man-made diving platforms are sometimes constructed in popular swimming destinations. Outdoor diving requires knowledge of the water depth and currents as conditions can be dangerous.
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