Giant Steps

Cricket - match formats

A cricket match is contested between two teams of (normally) 11 players and is divided into sessions referred to as innings. During each innings one team bats in pairs with the intention of accumulating as many runs as possible, while the other team takes to the field with the purpose of both restricting the scoring of runs and dismissing the opposition batters. A side is bowled out when ten batters have been dismissed. The remaining ‘Not Out’ batter is not permitted to continue batting alone and� the innings is closed. An innings is concluded when a side is bowled out, declares or if the allotted overs have been exhausted. During timed games, the captain of the batting side may declare their innings as concluded when they feel they have enough runs to win and be rewarded for doing so by having more time in which to bowl out the opposition side. Declarations do not occur in limited over cricket.

Each innings is divided into overs. An over is complete when a bowler has delivered six fair deliveries from one end of the pitch. A different bowler then starts a new over from the other end of the pitch- with the umpires swapping positions. At the end of each over the fielding team will be repositioned by their captain to accommodate the change of ends and the change of bowler. The two batters do not swap their respective positions at the end of each over.

In a ‘limited overs’ cricket match, each team bats once and each innings is limited to usually 40 or 50 overs. The number of overs in a limited overs cricket match is designated by the league or cup competition in which the fixture is played or by the agreement of both captains prior to a friendly fixture. In limited overs cricket the side with the most runs wins and when the runs scored are equal, the side with the fewest batters dismissed wins. In the unlikely event that both sides’ runs and wickets are the same then the match is deemed to be tied. A draw is not one of the potential results in limited overs cricket. Limited overs matches place a limit to the number of overs that may be bowled by each bowler and often include restrictions on how many fielders may be placed in the outfield. Fielding restrictions ensure the fielding captain cannot become over-defensive and cannot attempt to restrict the batters from scoring by placing all the side’s fielders on the boundary.

The duration of a ‘timed match’ is based on a set period of time rather than a set number of overs. To win a timed match either the side batting first must bowl out the side batting second for fewer runs than they totalled or the side batting second must total more runs that the side batting first. Timed matches are drawn if the team batting second does not get bowled out but does not reach the total achieved by the team batting first.

‘Twenty20′ is a single innings cricket match in which each team bats for a maximum of 20 overs. This new and explosive format of the professional game has quickly become very popular as a spectacle of the world’s finest cricketers in slog mode. The Laws of Cricket largely apply to Twenty20 with the following revisions:

� A front foot No Ball costs two runs and the next delivery is designated as a free-hit from which the batter can only be dismissed through a run out.
� Bowlers can bowl a maximum of four overs per innings.

The following fielding restrictions apply:

� No more than five fielders can be on the leg side at any time.
� During the first six overs a maximum of two fielders can be positioned outside the infield circle.
� After the first six overs, a maximum of five fielders can be positioned outside the infield circle.

If a Twenty20 match ends with the scores tied then the tie is broken with a bowl-out. Five bowlers from each side bowl two deliveries in turn at an unguarded wicket. If the number of wickets is equal after the first ten deliveries per side, the bowl-out continues and the match is decided by ’sudden death’, i.e. when one bowler hits and the other misses the stumps.

‘Kwik cricket’ is a high speed version of cricket aimed mainly at encouraging children to participate. Many of the rules are adapted from cricket, but for safety and physical reasons Kwik cricket is played with a plastic bat and ball. Plastic cones mark the maximum width of a fair ball. The rules can be easily altered so that any number of children can play in the time available. The game can be made easier or more difficult to suit differing age groups by changing the physical dimensions of the pitch and field.

First class cricket and test matches are the formats of timed matches played by the professionals with each side batting twice and the totals for each team’s innings added together. First class matches are played over three or four days and test matches are played over five days.

Cricket - the field of play

Though not defined in The Laws, a cricket field usually has a diameter of between 120-150 metres but the size, shape and layout of cricket fields will vary from ground to ground and, in some instances, The Laws are locally modified to incorporate unusual layouts and obstacles inside the boundary. For example, for decades the Kent County ground had an enormous lime tree growing in the outfield and four runs were awarded to any batter striking the ball into it.

Around each ground a painted white line or a rope known as the boundary clearly marks the extent of the playing area.

At each end of the ground moveable sightscreens are sited just beyond this boundary. Sightscreens are white (or black when using a white cricket ball) to provide a contrast to the ball and should be positioned directly behind the bowler to assist the batter in seeing the ball as it is released from the bowler’s hand.

The �infield� is the area within approximately 30 metres of the batters and for certain formats of cricket a minimum number of fielders must be positioned within this area. When fielding restrictions are in force, the, perimeter of the infield will be marked with white discs placed 30 yards (27.4 metres) from the stumps. The infield is commonly referred to as ‘the circle’ or ‘the ring’.

In some matches there may also be a requirement for a designated number of fielders to be positioned as catchers within the ‘close infield’ . When this is the case two circles are marked with white discs 15 yards (13.7 metres) from the batters to indicate the perimeter of the close infield.

The �outfield� is the area of the field between the infield and the boundary and is commonly referred to as �the deep�.

Physics of Diving. The Diving Environment - Water & Gases

HYDROSTATIC PRESSURE

Water is a dense medium and, therefore, exerts a noticeable pressure upon anything which is immersed in it. Water pressure increases rapidly with depth and a cubic metre of water (1000 litres) has a mass of 1000 kilograms or one tonne. Some fairly simple arithmetic will reveal that, if our cubic metre is divided up into one metre high columns, each of one square centimetre cross section, that the mass of water in each column is 0�1 kg. If each 1 cm2 column were extended to 10 m in length, the mass would be 1 kg and the pressure exerted by the column would be 1 kgf/cm2.

But 1 kgf/cm2 = 1 bar (approx). So, at 10 m beneath the surface the water pressure or hydrostatic pressure is equal to the atmospheric pressure at the surface. 10 m of water is equal to 1 bar gauge pressure or 2 bar absolute, and for every further descent of 10 m beneath the surface, the hydrostatic pressure increases by another bar. Thus at 30 m the absolute pressure is 4 bar.

In a fluid, pressure has the particular property of acting in all directions: thus, 30 m down the body is subjected evenly to 4 bar absolute all over and in all directions. The reader will recognise that this is so when he considers the pressure of the water inside an underwater cave: although it may be largely covered with rock, not water, the pressure inside will exactly equal that of the open sea at the same depth, the pressure being transmitted horizontally.

As the human body consists largely of liquid, it takes up the ambient hydrostatic pressure without any decrease in volume, but the spaces that contain air (for example the lungs) will be compressed unless they are artificially filled with air of pressure equal to that of the surrounding water. The aqualung demand valve will supply the diver with air at ambient pressure, but this subject should be studied further because it affects the body in many ways. The behaviour of gases under pressure needs to be considered.

PRESSURE/VOLUME CHANGES

When a gas is compressed, its volume varies in inverse proportion to the absolute pressure. This is the basis of BOYLE’S LAW-a relationship first recorded by the early physicist of that name.

Thus, an inverted bucket which is full of air at the surface where the pressure is 1 bar will be only half full at a depth of 10 m, where the total pressure is 2 bar, and only a quarter full at 30 m (4 bar absolute). Here we see that the fractional change in the gas volume for a given change of depth decreases with depth. Thus, a change of 10 m near the surface halves the volume, while the same 10 m drop at 40 m only reduces the volume by a factor of one-sixth.

Divers will encounter the effects of this relationship during training, and several times - and in several ways - on every dive, whether snorkelling or aqualung diving. Ear clearing, mask squeeze, loss of buoyancy, function of a demand valve, ascent risks, air consumption, decompression - ALL are governed and affected by Boyle’s Law. Any compressible air space, be it in the diver’s body or in his equipment, will change its volume during descent and ascent, and if not equalised or controlled, damage of some sort can occur. The term barotrauma is used to describe injuries which result from sudden changes in air pressure: in other words, from failure to allow Boyle’s Law to happen safely.

PARTIAL PRESSURES

It was explained earlier that nitrogen makes up approximately four-fifths of the atmosphere and oxygen the other fifth. If the atmospheric pressure is 1 bar, is it not reasonable to assume that nitrogen is responsible for 0.8 bar and. oxygen for 0.2 bar? Correct, and these are known as the Partial Pressures. DALTON’S LAW of Partial Pressures states that the total pressure of a gas is equal to the sum of the partial pressures which each member gas has and would alone have if the others were absent. Thus, while at sea level the partial pressure of oxygen is approximately one-fifth bar and nitrogen is approximately four-fifths bar, the air breathed by a diver 40 m (5 bar absolute) below the surface contains nitrogen at 4 bar and oxygen at 1 bar, the total pressure being 5 bar. The importance of this Law lies in the fact that the physiological effect of a gas depends upon its pressure or, when in a mixture such as air, upon the partial pressure.

Dalton’s Law reveals itself in such conditions as oxygen poisoning, carbon dioxide and carbon monoxide poisoning, and nitrogen narcosis. An understanding of partial pressures also helps in the study of circulation, respiration, hypoxia and decompression.

SOLUBILITY OF GASES

When a gas is brought into contact with a liquid (e.g. when the air in the lungs comes into contact with the blood) then some of the gas will dissolve in the liquid. The amount that will dissolve and the rate at which this takes place is dependent upon several factors-the pressure of the gas, the contact area between gas and liquid, the temperature, the maximum solubility of the gas in the liquid. As the gas nears saturation level, so the rate of solution decreases. If gas has dissolved in a liquid, and if the prevailing conditions are varied, then the amount of dissolved gas may also vary.

This relationship was established by yet another learned scientist of old, and is known as HENRY’S LAW. The fact that gas will dissolve into the bloodstream and be released again when the ambient pressure is reduced, gives rise to the problems of decompression sickness.

TEMPERATURE OF GASES

Temperature affects both Boyle’s and Henry’s Law, but since temperature variations encountered in diving are very limited, for simplicity, these effects have been ignored. One other gas law which is of interest and which involves temperature is CHARLES’ LAW. The volume of a gas varies directly as its absolute temperature if the pressure remains constant. Usually, it is the volume which is constrained to remain constant, while the pressure goes up! For example, an inflatable boat, left in the hot sun, could suffer from expansion of the contained air to the point of explosion. Keep in the shade or the boat partly deflated when not in use.

Water has several other properties: buoyancy: conduction of heat: and transmission of sound. These will now be considered.

Over the last forty-five years, Doctor Who has been at our screens. With 10 incarnations of The Doctor, it has the world record for the longest Sci-Fi series. When the show started in nineteen sixty three, the first episode that was shown had very few viewers. This is because it was aired on the day President Kennedy was assassinated. (November 23rd) Now, most of the episodes are shot in Cardiff. Interesting? So, step into the TARDIS (Time and Relative Dimension in Space) and read on, learn more about the exciting world of Doctor Who.

The Ten Doctors

Since 1963, there have been ten incarnations of the anonymous time-travelling hero, the list follows-:

William Hartnell - 1963 to 1966
Patrick Troughton - 1966 to 1969
Jon Pertwee - 1970 to 1974
Tom Baker - 1974 to 1981
Peter Davison - 1982 to 1984
Colin Baker - 1984 to 1986
Sylvester McCoy - 1987 to 1996 (TV Movie)
Paul McGann - 1996 (TV Movie)
Christopher Eccleston - 2005
David Tennant - 2005 to 2009

As you can see, Tom Baker played The Doctor for the longest amount of time � eight years! David Tennant is still our present Doctor, but he will be leaving after three specials in two thousand and nine. It is rumored that David Morrissey will play the eleventh Doctor. There was also an actor that did two films - he was Peter Cushing. He was not listed as one of the official Doctors as the films he did were copies of an original episode. It is said the Doctor has thirteen lives, but personally I think he will go on forever!

Enemies

Everyone knows that the Daleks are the supreme race of the universe, but the third Doctor always used to say his best enemy was the evil Master. The Cybermen are also very popular with the Doctor however, there are lots more than these. Here is an A-Z list of some of the monsters that have ever appeared:

Abzorbaloff
Ambassadors of Death
Autons
Axons
Carrionites
Celestial Toymaker
Clockwork Robots
Cybermen
Daemons
Daleks
Davros
Destroyer
Empress of the Racnoss
Empty Child
Gelth
Giant Maggots
Haemovores
Ice Warriors
Isolus
Jagrafess of the Holy Hadrojassic Maxarodenfoe
Judoon
Krillitanes
Krynoid
Macra
Magnus Greel
Master
Morbius
Omega
Rani
Sycorax
Tereptiles
Weed Creature
Zarbi
Zygons

The list could be longer, but I can’t write all of it. The hardest one to say is Jagrafess of the Holy Hadrojassic Maxarodenfoe - which is as big as the monster actually is!

Gadgets

The main gadget in Doctor Who is probably the TARDIS - as I said at the beginning it stands for Time And Relative Dimension In Space. This is the Doctor’s spaceship, which is very special as it can travel not only through space - but in time as well. It is bigger on the inside than it is on the outside, the doors are extremely tough as we know from the ninth Doctor when he said, ‘Genghis Khan couldn’t get through those doors!’

The Doctor’s other gadget is the Sonic Screwdriver. Without this he would be locked out of anywhere! It has been used in a variety of ways - scanning, sealing, and unlocking. It can crack any lock- except a deadlock. Many Doctors have used it but the styling has changed.

Music

Murray Gold � the composer of the Doctor Who music is known to be a genius. The pieces he produces are an essential part of the episodes, they wouldn’t be as scary without it. He writes the music, then records it with help from the BBC National Orchestra of Wales, who also play a big part in the role. Ben Foster conducts them. Currently there are three CDs released, which are the Original Television Soundtrack to Doctor Who, I recommend them if you are a Doctor Who fan!

Quiz

1. What is the Doctor’s spaceship called?
2. How many Doctors have there been?
3. Who played the Doctor longest?
4. Who is the supreme race?
5. Who creates the Doctor Who music?
6. In which year did Doctor Who start?
7. In which city is Doctor Who filmed?

(Answers at end of report)

Writers

The head writer of Doctor Who now is Russell T Davies, although at the end of two thousand and nine - he will leave. Then the head writer will be Steven Moffat who has written some of the best Doctor Who episodes ever; Such as the ‘The Empty Child’, ‘The Doctor Dances’, ‘The Girl in the Fireplace’ and many, many more. Other writers include Tom MacRae, Mark Gatiss, Matt Jones and Matthew Graham.

Merchandise

There are thousands of different Doctor Who products out there on the market, some VERY expensive, but some are reasonably cheap and definitely worth the money. From toothbrushes to TARDISes, you can find the perfect gift for a Doctor Who fanatic - here are some of the best: Voice Interactive Dalek, Voice Changers, Flight Control TARDIS, Encyclopedia, Bedsheets, Box Set DVDs. WOW!

Now you’ve learned a bit more about the best show in the world, do you think you’ll watch it? Certainly hope you do! Next episode is on Christmas Day - 6:00pm!

Answers to Quiz

1. TARDIS

2. 11

3. Tom Baker

4. The Daleks

5. Murray Gold

6. 1963

7. Cardiff

Physics of Diving. The Diving Environment - Water. Conduction & Sound.

Conduction

Water has a colossal capacity for conducting heat away from the body. The high heat capacity and rate of conductivity of water are such that thermal protection is needed in all but the warmest tropical waters. An unclad diver in waters of less than about 21C will lose heat faster than his body can replace it, and he will become chilled. In extreme cases, hypothermia will follow. Protective clothing is necessary to avoid chilling.

Sound

Because water is such a dense medium, sound travels more than four times faster in water than in air. It is anything but a silent world. Since sound travels so quickly it is difficult to determine the exact sound source. However, sound signals made by rapping a stone or knife handle against an aqualung cylinder in a distinct code is a popular way of attracting a dive partner’s attention.

Sounds made above water will not penetrate the surface, and neither will underwater sounds pass through into the air.

Physics of Diving. The Diving Environment - Water & Buoyancy

ARCHIMEDES’ LAW states that any object immersed in a fluid suffers an upthrust equal to the weight of fluid it displaces, i.e., whose volume it occupies. If the immersed body is that of a diver, he has the facility to vary the volume he displaces by breathing. With full lungs he will displace more water than his body weight and he would be positively buoyant. When he breathes out, he may displace less water than his body weight and will sink, being negatively buoyant. Somewhere between the two is the desired state of neutral buoyancy.

A diver seeks to adjust his buoyancy to suit the varying requirements of his diving. In the vast majority of situations he will try to attain neutral buoyancy, i.e. a precise equality between his total weight and the upthrust due to the displaced water. This is achieved in a simple way. The diver, kitted up as the dive demands, launches himself into the water and exhales hard. By emptying his lungs he is reducing his body buoyancy and he should sink. He inhales from his aqualung, increases his buoyancy and floats upwards. He adds or subtracts weights from his weightbelt until the normal span of breathing bridges the gap between sinking (negatively buoyant) and floating upwards (positively buoyant). He is now neutrally buoyant.

However, there are other factors which will affect his state of neutral buoyancy while he dives. These are dominated by two effects, which act quite differently from each other:

CHANGE OF WEIGHT

A 1700 litre compressed air bottle contains about 2 kg of air when full and much less than 1% of this figure when empty. Thus, a diver starting with 1700 litres of air will end his dive some 2 kg lighter. This excess buoyancy can be a considerable embarrassment at the end of a dive, especially if decompressing or returning along the bottom to avoid heavy waves on the surface.

CHANGE OF VOLUME

A rubber diving suit, whether it is a foam wet suit or a dry suit covering woollens, reduces heat loss from the body by interposing an insulating layer of air between skin and water. The volume of this trapped air varies in inverse proportion to the hydrostatic pressure acting on it (see Hydrostatic Pressure and Boyle’s Law) so that at a depth of 30 m the air will occupy only one quarter of its volume at the surface. The average 5 mm thick neoprene suit contains about 6 litres of nitrogen bubbles which makes the diver considerably buoyant on the surface. At a depth of 20 m these bubbles will have been compressed to about 2 litres with a corresponding reduction in buoyancy which will, however, be regained on ascent.

The free diver has a variety of methods of countering these inevitable changes in buoyancy. By swimming downwards if too light, or upwards if too heavy, he can overcome an imbalance of several kilogrammes, but this is extremely tiring and is to be strongly discouraged. A less tiring method of balancing changes of buoyancy is provided by controlling one’s breathing. The human lungs contain on average about 6litres when fully extended and a residual volume of about 1.5 litres after complete exhalation. Thus, the diver can vary his volume by as much as 4.5litres simply by forcibly breathing in and out; this is equivalent to a change of 4.5 kg of displaced water. The range of normal breathing covers only the middle 20% of this range, so that a neutrally balanced diver breathing normally will experience a regular change of buoyancy from about 0.5 kg too light, when he breathes in, to 0.5 kg too heavy when he breathes out. But by controlled breathing he can maintain an average change in his buoyancy of up to 1.5 kilogrammes.

Really deep breaths retained for all but brief periods of exhalation followed by immediate inhalation will make the diver about 1 kg more buoyant than when he breathes naturally. The converse, short shallow breaths designed to reduce one’s buoyancy is less easy and may lead to panting, which for a diver is a very inefficient and possibly hazardous way of breathing.

The simplest means of adjusting buoyancy while diving is to use an ABLJ or other buoyancy aid, which can be inflated - by direct feed, cylinder or mouth- to restore neutral buoyancy at will. On ascent, the air can be vented as it expands, thereby avoiding the dangers of a rapid ascent. The use of buoyancy aids for maintaining neutral buoyancy during a dive should be looked upon as a sensible practice. However, it requires a full appreciation of the possible dangers and good technique in handling your equipment. It should NOT be used as an excuse for not being correctly weighted at the start of a dive.

So far, we have considered methods for adjusting buoyancy continually during a dive. Now we must consider how much constant ballast should be carried in the form of lead weights on a quick-release belt. While the basic technique of achieving neutral buoyancy has been explained above, there are occasions when it is desirable to be slightly otherwise than neutrally buoyant. This is really a matter of philosophy based on physics: in general, it is more convenient to be slightly overweight during the early stages of a dive (both to assist the initial descent and to help keep on the bottom once there) than to be too light at the end of a dive, which will probably be in shallow water. So one carries sufficient ballast to ensure neutral buoyancy at a depth of, say, 5 m with empty cylinders. To achieve this, the diver with a 2000 litre cylinder should aim to be about 1.5 kg heavy when on the surface at the start of his dive. Carry out a normal buoyancy check at the surface, then add an extra 1.5 kg to the weightbelt.

THE USE OF BUOYANCY FOR LIFTING

One of the most convenient ways to lift a heavy object from the seabed is to fill one or more plastic drums with the exhaled air from one’s aqualung. This system has the particular merit of affording a constant-buoyancy system at low cost. An air-filled 12.5 litre drum displaces 12.5 kg of water, so if its mass is 2 kg, the net buoyancy will be 10.5 kg. As the object rises, the air in the drum will expand and the excess will flow freely from underneath, leaving the displacement, and hence the buoyancy, constant. In general, it is best to use slightly too little buoyancy when raising a heavy object by this method, the remainder being supplied by pulling on a rope from the surface. Otherwise, if the buoyancy exceeds the object’s weight, it will rise up with increasing speed until the drums break surface, overturn and fill with water, with perhaps disastrous results.

If, on the other hand, it is decided to use closed bags or balloons, they must be provided with an exhaust valve to allow the expanding air to escape as the object rises. These bags should always be blown up taut on the bottom; if an oversize, partially filled bag is used, its buoyancy will increase as it approaches the surface, giving a spectacular, but quite uncontrolled ascent.

Physics of Diving. Our Normal Environment - Air

The diver is affected by increasing water pressure as he descends and this manifests itself in several ways. Some will be noticed quickly: others will take longer to become apparent. Both the diver’s body and his equipment will be affected. Divers should have a clear understanding of how the laws of physics apply to them and to their equipment. Without this knowledge they put themselves at risk.

Before considering the diving environment, it is necessary to look at the atmosphere in which we normally live and the gases which make up the air we breathe.

ATMOSPHERIC PRESSURE. The earth is surrounded by an envelope of air which we call the atmosphere. Air is a mixture of gases, and like all matter, it has mass. A mass exerts a force on those things which lie beneath it, and at sea level the atmosphere presses down with a force of approximately 1 kilogram for every square centimetre of the earth’s surface. Gas pressure is commonly measured in units of bar and our own atmosphere exerts a pressure at sea level of approximately 1 bar.

Atmospheric Pressure = 1.02 bar (1 bar approx.)

Atmospheric pressure varies slightly with changes in weather and diminishes with altitude until it reaches zero at the extreme limit of the atmosphere. At about 5000 m above sea level, for example, the atmospheric pressure is about 0.5 bar.

Our bodies do not suffer in any way from this pressure which is applied to every square centimetre of their surface-we are born to it!

GAUGE PRESSURE. When a pressure is to be measured, it is normal practice to relate it to ambient pressure. Thus a simple gauge would read zero at an atmospheric pressure of 1 bar. An aqualung contents gauge would perhaps read 200 bar, but this really means 200 bar above the normal atmospheric pressure of 1 bar. Such a recording would be known as a Gauge Pressure.

ABSOLUTE PRESSURE. If the above gauge were related to true zero as found in a vacuum it would read 201 bar - the extra 1 bar being atmospheric pressure.
Such a gauge reading would be termed an Absolute Pressure.

Absolute Pressure = Gauge Pressure + Atmospheric Pressure

In diving physics, it is normal to work in absolute terms, and the reasons for doing so will be soon apparent.

COMPOSITION OF AIR. The air we breathe is a mixture of gases comprising:

Nitrogen (N2) approx. 79% (say, 4/5)
Oxygen (02) approx. 21% (say, 1/5)

There are traces of Carbon Dioxide (C02) and other rare or inert gases, but in such small quantities that they can be ignored. All gases are compressible, having neither shape nor volume.

On the other hand, liquids have a definite volume and mass and may be considered to be incompressible at the pressures we are to consider.

Basic Ability Required to Start Diving

Whatever the reason they decide to start diving, many will come to the sport with an initial sense of apprehension for water presents a strange and, to some, hostile environment that is not fully understood. In any event, it is certain that most newcomers ask either of themselves or of their instructor, ‘Do I have the ability to become a successful diver?’

What might then form an answer to this question? The recent very rapid expansion of professional diving has made necessary research into criteria which might be used to select diving personnel, but so far no positive guide-lines have been published. Nevertheless it is obvious that for the sports diver, for whom the training can be less hurried and the ultimate task less dangerous than that of professional diving, the initial demands on his abilities will be less rigorous. It follows therefore that selection for sport diving begins with the individual himself, for the fact that he has presented himself for training proves that an initial interest exists. However, success depends on more than just an initial interest, no matter how strong; there must also be a sense of motivation, an ability to stick at the task once begun, and to see it through to the end.

Although fins have been designed to increase swimming efficiency, a diver should be capable of swimming confidently and without excessive effort over distances of 2~OO m and should be able to support himself by floating or treading water, without their aid. To determine the trainee’s ease and composure in the water therefore, tests of minimum swimming ability without the aid of equipment are taken early in the training programme, and although speed is not important, the trainee diver should have mastered the rudiments of swimming. Unfortunately it is rare that a diving club, engrossed in the detail of its diver training programme, has sufficient instructors to spare for teaching swimming, but those who wish to take up diving and are of moderate swimming ability may improve their personal standards through practice. If truly motivated, with regular attendance at the swimming pool and practice in swimming with a light - then gradually heavier -weightbelt, the swimming standard necessary for diving can be attained.
Although the basic techniques of diving may soon be mastered, safe diving in open waters depends on a period of organised and progressive training. Such a training programme necessitates regular attendance at both the pool and lecture sessions so that the trainee’s skills and knowledge can develop together. The trainee diver who lacks enthusiasm and attends the courses irregularly will inevitably find that instruction is disjointed and the resultant erratic progress is unsatisfying.

As with all sports, diving makes physical demands upon the body’s resources, and it is therefore essential that the diver be sufficiently fit to meet these demands. It should be remembered that whilst he is underwater the diver is subjected to pressure and that movement under pressure calls for greater exertion than he may at first realise.
He must therefore choose his diving activities to match his physical capability; an inability to recognise one’s physical limitations is potentially dangerous and may well culminate in an accident.
Diving equipment can be very heavy, and difficult access to some diving sites may necessitate carrying this for some distance, but fitness is a relative term and it is certainly not necessary to be a superman in order to become a good diver, in fact many disabled are able to enjoy the sport. Careful selection of equipment to suit the diver’s requirements and physique can keep the weight to an acceptable level, and diving covers a wide range of activities-from the less physically demanding diving in shallow, sheltered waters, to long expeditions and deep dives in tidal waters that can tax the strength of the fittest-so it is possible to find exciting and interesting diving that is within the scope of all ages and physiques.

Basic ability to undertake a particular physical activity can be readily tested, and a person’s physical condition can be ascertained by medical examination. Less easy to define and recognise are those basic mental attributes that contribute to the making of a successful diver, yet these are extremely important. Many of the difficulties that arise as a diver adjusts to the new environment in which he finds himself are frequently a result of temperament. Inevitably it will be necessary to overcome the apprehension that is present when any new activity is undertaken, and this may be even more pronounced in the trainee diver who is also entering a completely strange environment. Frequently enthusiasm and a natural curiosity will overcome this, but far more important in allaying doubts is sound basic training. Under good instruction the learner takes progressive steps, and initial nervousness disappears as success follows success. However, even with the help and careful guidance of an instructor an ability to relax and to adapt to new sensations and changed perceptions is essential: the face mask, whilst permitting underwater vision~ which is one of the most exciting experiences in diving-also restricts the total field of vision to a much narrower field; first the snorkel and then the demand valve requires the technique of mouth breathing (which does not always come naturally); correctly weighted, the diver neither floats towards the surface nor sinks to the bottom, but remains in mid-water apparently suspended, and gone are the clues for personal orientation that are available when on dry land. In such conditions the diver must be able to learn to interpret new signals: the way in which pressure builds up in his ears, or the changed feel of his equipment, in order to orientate himself in his environment. Such adaptation does not always come quickly or easily, and a diver needs patience coupled with a placid and imperturbable temperament, for he is not undertaking a sport in which the training can be rushed with safety.

Whilst the ability to remain calm in the face of a crisis is a very necessary part of a diver’s make-up, he must also have a developed sense of adventure. Without this there would be no urge to explore a new environment. Diving is not for the unsure or the timid, but rather for those whose sense of adventure expresses itself through a confidence in their ability to face and overcome problems when they arise. Personal confidence grows with experience but must always allow a place for reason, for the diver who is over-confident, who tends to make rash decisions and who takes reckless action out of sheer bravado, will soon place himself and his diving companions at risk.

It must be accepted that in all diving there is an element of risk, and it is often this which, consciously or unconsciously, brings a touch of spice to the activity. However, there is a level of risk acceptance that is permissible in a particular situation and this will depend upon many factors: the skill and experience of the divers, the equipment available and the purpose of the dive. A diver’s temperament must be such that he has the ability to exercise a reasoned judgement that is not easily swayed by external pressures, for overconfidence could result in making dives with an unacceptable risk.

In many people a feeling for adventure and excitement is often matched with an independence of spirit and a strong desire to go one’s own way. Such a singleness of purpose is a valuable trait, but in diving this must be balanced by a willingness to accept the disciplines that the sport demands. For instance, sport divers should always dive in pairs, each having a conscious awareness of the partner’s position and actions, and ready to provide support at all times. This demands an ability to behave unselfishly and to be completely reliable. The individualist who continually wanders off is a danger both to himself and his partner.

Although it may not appear so at first sight, diving is very much a team sport in that it relies upon groups of people working together for the good of the group. A diving expedition is supported by a considerable back-up organisation which involves such activities as site planning. transport, equipment checking, and marshalling and organizing at the dive site. Each and every person should be willing to play his part and to make his contribution to the total effort. The ultimate -; responsibility for safety on an expedition lies with the Expedition Leader, and each member of the diving group must accept his authority and decisions unselfishly. Although initially the diver in training will rely heavily upon the more experienced members of his club, the time will come when he in turn will be ready to step into a position of responsibility. In the first instance this may be as an assistant Marshal or as a Dive Leader-as part of the progressive training programme. Eventually he may find that he has risen to the position of Diving Officer. Any prospective diver should be willing to accept the responsibility of leadership as his experience grows.

Finally, those who wish to take up diving must realise that it is an activity that relies upon more than just a sound physique and an ability to undertake certain skills. To be efficient and safe, diving must be supported by a body of knowledge that forms the basis for many important decisions. A diver must be able to understand sufficient physiology to realise the limitations of his own physique; enough physics to appreciate the effects of a hyperbaric environment, and be sufficiently practical to understand the workings of his equipment.

The Lure of Diving

Some people take up diving for a specific purpose such as scientific investigation, underwater photography or salvage. But for the majority of persons taking up the sport, it is simply the thrill of exploring a new, alien and-from what they have been led to believe -fascinating world that lures them to take up diving. They will not be disappointed.

Almost two-thirds of the world’s surface is covered with water. While the abyssal depths account for the greater part of this, there are many millions of square miles of sea-bed which are within reach of the trained sports diver. Most of this is as yet unexplored. Even around the coasts of the densely populated British Isles, there are thousands of square miles of sea-bed which have yet to be visited by the diver. Surely the sea must be the earth’s last frontier and any di ver who is well-trained and suitably qualified can see a new and exciting realm that can never be adequately described, only experienced.

The pleasure of diving is many-sided and as diverse as the feelings of those taking part, but since it depends upon entry into a new en�vironment, it must first be anticipated, assimilated and understood before it can be enjoyed to the full.

Some aspects of enjoyment spring from the untypical experiences of the human senses underwater. Each time a diver sinks below the surface his whole world changes: the light dims and colours fade as the sun’s rays are rapidly absorbed by the water; normal hearing ceases, to be replaced by a vague awareness of slight sounds that cannot be located-sounds of sea creatures, stones rattling in the waves’ thrust and surge, the gurgle of a demand valve. Taste and smell are virtually non-existent, and the feel of the water is all� encompassing. The surrounding water imposes its presence in many ways: its coldness and wetness in direct contact with the skin, the increasing pressure as thee diver descends and the weightlessness when one is neutrally buoyant.

The experienced diver who is at home in the water has learned to understand these previously unaccustomed and frightening perversions of his senses. He has come to recognise the features of being underwater: the silence, the calm, the caress of the water as it supports his weight-laden body. No longer are his senses distressed. They have re-awakened in a new world with a new set of values and expressions, and they have engendered a self-reliance, an awareness of things and of their significance. The diver has become one with the underwater world and has learned to love it.

On every dive, whether in the sea, rivers or quarries, whether the visibility be good or bad, the current fast or slack, the experienced diver makes renewed contact with a world that he has made-in -his own. But there is one thing that stands out above all others: sublime joy that the diver experiences at the instant of breaking surface. The shades of the underwater world are gone, light b in on the senses, hearing returns and the wonder, perhaps awe, compelled creatures to emerge from the seas millions of years a experienced.

The aims of diving are, therefore, two-fold: to explore and uncover the unknown, and then to return to the familiar with an ad appreciation of its beauties. So that a diver may immerse himself in this new environment, and for a time become part of it, he must rid himself of cares and worries about the functioning of his diving equipment and of his ability to use it. Of course, the problems diving, and the fundamental necessity of returning to the surface’ breathe when the air supply is exhausted can never be forgotten, b the diver should acquire a complete self-assurance in the use of diving equipment so that any actions underwater become instinctive. Thought, time and energy spent on the technicalities of diving then reduced to a minimum, and the diver can devote his energies and interest to other ends.

Such familiarity and confidence in diving equipment can only come after an adequate programme of training and no-one should attempt to explore the seas without first receiving proper instruction and training. The sea frowns on the foolish intruder and although professional divers may undertake deep or dangerous dives under controlled conditions for the sake of their livelihood or the needs of the job in hand, the sports diver has no cause to put his life unnecessarily in jeopardy, and even when fully-experienced with his diving equipment, it should always be used sensibly.