Diving Fact

You've always wanted to take the scuba diving plunge, your friends are always talking about it and your best mate keeps raving about his amazing dive trip to the Sipadan. But, how do you start this adventure? Who's out there to baptize you into the sport and who's around to help you side step any aquatic snags?

The skill of being able to dive, survive and actually enjoy the underwater experience can be a life-long learning curve. It can also be incredibly rewarding!

Many aspiring scuba divers switch-on their days of marine adventure by donning mask, snorkel and fins and skimming across acres of water, faces planted downwards and eyes a-goggle at what dwells below. Once hooked and feeling bereaved at their gill-less state, enthusiasts look for the next steps in the diving evolution ladder - the sacrosanct dive course.
 

To allow you a wee taste of the sport, diving agencies have designed the Try Dive, Resort Dive or Discover Scuba Dive. These courses are usually over one or two days and teach you a few diving skills needed to safely introduce you to the underwater world. During these early diving days you will be shackled to your instructor by virtual elastic bungee and kept at a limited depth.

Your first venture below the surface is one you'll never forget. Your body submerges like a submarine on a mission; the water and air bubbles disorientate you as the light intensity decreases. The little gremlin, the dive instructor has planted in your mind, seems to be on automatic replay and all you hear is "breath, slow down, relax". You soon come to realize that these are not easy things to achieve. There is so much to look at! You will be amazed at how the buzz of spotting your first moray eel jutting it's pointed snake-like head out of a rock crevice can over-ride your nervous system ambushing your air intake for a good 30 seconds.

To enjoy your diving experiences and make sure you remain safe, it is strongly recommended you complete a certified diving course. These courses are designed to teach you to survive while breathing underwater, understand and know how to use your dive equipment and protect and respect the marine environment.

The general pecking order of dive training gets going with the 4-5 day Open-water course; Specialties, Advanced Diver, Rescue Diver, Dive Master, Assistant Instructor, Dive Instructor and Master Scuba Trainer courses follow this.

Dive training is organized by a number of international certification agencies, the following are some of the most prominent associations: the British Sub Aqua Club (BSAC), the Confederation Mondiale des Activities Subaquatiques (CMAS), the Professional Association of Diving Instructors (PADI), Scuba Schools International (SSI) and the National Association of Underwater Instructors (NAUI).

These dive courses not only provide you with the skills to survive underwater, but you are also awarded with a certification or C-Card. The C-card is important proof of your qualification and reputable diving centres will need to sight this before signing you up on their dive trips.

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THE HISTORY OF DIVING

For thousands of years man has shown an inborn need to explore, conquer and experience the unknown. Decades before the first weighted boot was stamped upon the moon divers had been delving into the gravity defying depths below the ocean waves.

When did it all start?

Although there is no official record of the first underwater adventure historians guess it's some 5000 years before the three wise men trundled into Bethlehem. Early Persian records tell of a diver being sent into the ocean depths to salvage sunken treasure in the fifth century BC.

To increase stamina and lung capacity many salvaging divers were trained from a young age. The deeper these divers could go the more they got paid, so with the aid of a flat rock and a rope around the waist they could drop down to 30 meters.

Breathing under water

Using reeds to breath while submerged was one of the first primitive air supply systems adopted for warfare. It wasn't until the end of the 16th Century that the open-ended diving bell was produced. This contraption allowed trapped air to be compressed within it when dropped vertically into the water giving divers a small reservoir of air to draw from.

In 1823 inventors revolutionized diving by converting a smoke apparatus used by firemen into the "Deane's Patent Diving Dress" - a heavy suit for protection and leaded helmet with viewing ports and a hose for surface air. As the exhaust air was released through the open bottom of the helmet divers had to remain upright or risk drowning. In 1840 an added exhaust valve made the suit a precursor for today's standard deep-sea surface-air-supplied diving dress.

SCUBA

SCUBA, - Self Contained Underwater Breathing Apparatus, was developed with the increase in technology enabling demand regulators to be invented, air to be compressed, and tanks to be designed light enough to be carried by divers while containing pressurized air. During WW2 French naval officer, Jacques-Yves Cousteau and French engineer, Emile Gagnan, developed the open-circuit SCUBA system and aqualung - the blueprints for the safe and efficient scuba systems of today.

HISTORY

With the massive increase in technology and the modernizing of dive equipment over the past 50 years, diving has become more accessible not only for salvaging and hunting but also as a sport. Every day new marine species, terrain and ecosystems are being discovered and explored. The next decade of diving is shaping up to be another milestone in diving and marine history.

Men and women have practiced breath-hold diving for centuries. Indirect evidence comes from thousand-year-old undersea artifacts found on land (e.g., mother-of-pearl ornaments), and depictions of divers in ancient drawings. In ancient Greece breath-hold divers are known to have hunted for sponges and engaged in military exploits. Of the latter, the story of Scyllis (sometimes spelled Scyllias; about 500 B.C.) is perhaps the most famous. As told by the 5th century B.C. historian Herodotus (and quoted in numerous modern texts),

During a naval campaign the Greek Scyllis was taken aboard ship as prisoner by the Persian King Xerxes I. When Scyllis learned that Xerxes was to attack a Greek flotilla, he seized a knife and jumped overboard. The Persians could not find him in the water and presumed he had drowned. Scyllis surfaced at night and made his way among all the ships in Xerxes's fleet, cutting each ship loose from its moorings; he used a hollow reed as snorkel to remain unobserved. Then he swam nine miles (15 kilometers) to rejoin the Greeks off Cape Artemisium.

The desire to go under water has probably always existed: to hunt for food, uncover artifacts, repair ships (or sink them!), and perhaps just to observe marine life. Until humans found a way to breathe underwater, however, each dive was necessarily short and frantic.

How to stay under water longer? Breathing through a hollow reed allows the body to be submerged, but it must have become apparent right away that reeds more than two feet long do not work well; difficulty inhaling against water pressure effectively limits snorkel length. Breathing from an air-filled bag brought under water was also tried, but it failed due to rebreathing of carbon dioxide.

In the 16th century people began to use diving bells supplied with air from the surface, probably the first effective means of staying under water for any length of time. The bell was held stationary a few feet from the surface, its bottom open to water and its top portion containing air compressed by the water pressure. A diver standing upright would have his head in the air. He could leave the bell for a minute or two to collect sponges or explore the bottom, then return for a short while until air in the bell was no longer breathable.

In 16th century England and France, full diving suits made of leather were used to depths of 60 feet. Air was pumped down from the surface with the aid of manual pumps. Soon helmets were made of metal to withstand even greater water pressure and divers went deeper. By the 1830s the surface-supplied air helmet was perfected well enough to allow extensive salvage work.

Starting in the 19th century, two main avenues of investigation - one scientific, the other technologic - greatly accelerated underwater exploration. Scientific research was advanced by the work of Paul Bert and John Scott Haldane, from France and Scotland, respectively. Their studies helped explain effects of water pressure on the body, and also define safe limits for compressed air diving. At the same time, improvements in technology - compressed air pumps, carbon dioxide scrubbers, regulators, etc., - made it possible for people to stay under water for long periods.

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WHAT IS DIVING?

The word "diving " conjures up a number of different meanings, most of which have the action involving descending.

Diving, for our purposes, basically means spending time underwater.

There are several types of diving. The most common forms of recreation diving are snorkeling or free diving and SCUBA diving.

Snorkeling

Snorkeling, as the name suggests, is when a diver is using a mask, snorkel and fins to swim around, mainly on the surface, looking down to see what is under the water. Occasionally snorkeler dive down for closer investigation of the underwater world.

Free Diving

Snorkeling is sometimes referred to as free diving. Generally this term is used when divers/snorkellers dive down holding their breath and spending quite long periods underwater.

Common free diving activities include spear fishing, photography (with no bubbles it's easier to get closer to your subject) and various competitions.

SCUBA Diving

SCUBA stands for Self Contained Underwater Breathing Apparatus. It is a system originally designed by Jacques Cousteau in which high-pressure air is stored in tanks and reduced to a breathable pressure - that of the surrounding (ambient) water pressure. The main components of SCUBA are:

Tank - stores high pressure air for use underwater.

Regulator - breaks down the air pressure to a breathable level and delivers air from the tank to your mouth.
 

Instruments - indicate your tank pressure, depth, dive time, and sometimes body nitrogen levels, remaining allowable safe dive time, safety or decompression stops required, surface intervals, and the list goes on!
 

Another component usually needed is a BCD - Buoyancy Control Device (funnily enough, used to control your buoyancy).

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SCUBA DIVING EQUIPMENT
 

Scuba Diving is made possible thanks to specialized, state of the art equipment. All Diving comes in a wide variety of colors, having bright colors underwater helps buddy recognition as well as looking cool and stylish..

The Mask

The mask is your window into the underwater world, it allows you to by creating an air space in front of your eyes, which also covers your nose so you can equalize the mask air space. The Mask should make an airtight fit against the face, you can check to see if the mask fits by putting your face up to the mask and gently breathing in through your nose. If it fits the air will be not be able to breach the mask The mask will then be stuck against your face caused by you breathing in through your nose and creating a vacuum.

All faces are different and as a result there are many different shaped masks, if you have trouble finding the right mask, just ask for help at your local dive store, they will be more than pleased to find the mask best suited for you. Unless you know what kind of mask fits, you should go to your nearest shop and try some on before buying online. Diving is largely a visual activity, and the importance of having the proper mask cannot be overemphasized. As a result masks are left out of the beginners Scuba Package, why? Because we wont supply you with something that doesn’t suit your personal needs. We can sort you out with a snorkel though…if you have tried and found the right mask then by all means feel free to buy it from us!

Tips when buying a mask

Tempered-glass lens plate. If broken, tempered glass is less likely to shatter into harmful shards.

Comfortable 100% silicone skirts for a positive feather edge seal

Low volume masks can be more desirable to the beginner as they are easier to clear if it floods, mask clearing is one of the first skills you will learn in the pool on the Open Water Diver Course

An easy to adjust strap

A wide field of vision, such as the Oceanic Trend 3 mask You can buy some masks which have a purge valve, a purge valve is a one-way valve used for clearing masks using the pressure change created by your out breath within the mask air space. The purge valve will be found on the bottom of the mask, if not correctly maintained the salt chrysalises and can cause the valve to leak, as the valve cannot seal itself due to the salt. Most divers prefer not to use the purge valve simply as mask clearing is so easy to learn anyway and becomes effortless very quickly anyway.

Preparing Your New Mask

New masks come with an oily protective coating that must be scrubbed off, I use a toothbrush and toothpaste to lightly rub away the film, don’t forget to scrub both side of the lens. If you don’t remove the film of silicone then the mask will fog up upon use, thus spoiling your valuable dive time, so don’t forget.

The Snorkel

he Snorkel is a standard piece of diving equipment without you to breathe at the surface without having to lift your head from the water, they come in a vast range of colors and styles but all do the same thing.

Fins

Fins allow you to propel yourself through the water with far less effort than just your hands and feet, they become an extension of the diver and allows them to glide through the inner space that can only be found underwater. Fins come in two basic styles (1). Adjustable strap (2). Full foot

Divers more commonly use adjustable fins as they can be worn with thermal protection such as wetsuits, semi-dry suit or dry suits. The Buoyancy Compensator Device (BCD)

The BCD is basically an expandable bladder that can be inflated or deflated to control your buoyancy. The BCD can be orally inflated or mechanically inflated with air from your tank that fixes on to the back of the BCD. Some tanks use integrated weight systems, which eliminates the need for a weight belt. All BCD’s will have pockets and fixing points for your alternate air source and submersible pressure gauge.

Regulators and Submersible Pressure Gauges

The dawn of the new millennium is an exciting time to be a diver if for no other reason than the highly refined state of scuba regulators as a result you don’t need to spend a fortune when you are just starting out to get a high performing budget regulator. A good regulator will deliver sufficient air in a stable manner when at depths that far exceed those of the recreational diver. So why would you want a regulator with high performance when you will never de diving to those depths? Because of in the very unlikely event that there is an emergency situation, there is no such thing as “to much air”. Today’s high performing models will deliver more air more easily, with greater stability at greater depth, with less tank pressure and will stay “in tune” longer than ever before.

A regulator is designed to reduce the high pressure of a scuba tank to a breathable pressure. Modern scuba regulators are very simple and reliable devices with only a few moving parts. They have two stages: the first stage, which attaches onto the cylinder and the second stage has a mouthpiece. The high pressure from the tank is reduced to an intermediate pressure by the first stage. The second stage reduces the air pressure to a comfortable breathing level that is required for scuba diving. The first stage of the regulator will have an extra second stage, called an alternate air source. This is used to simplify sharing air with another diver in the really unlikely event that you have an out of air situation, which of course you all being good, safe divers will never happen. The alternate air source is usually bright yellow so it can be easily identified.

Submersible Pressure Gauges

The submersible pressure gauges allow you to monitor the amount of air in your tank during a dive, this allows you to calculate estimated dive times so you can return safely you exit points without running low on air. The submersible pressure gauge also connects to the regulator first stage. You can also tell your depth in increments of meters by using the depth gauge. A compass to aid navigation is usually included on the SPG’s. Our models also come with temp gauges as if that wasn’t all enough.

Thermal Protection

Most Divers require thermal protection; the basic forms are wetsuit (warm water diving), semi dry suits, and dry suits. There is a wide choice of suits, gloves, and boots to suit every divers need no matter where they are. Technology today means that all divers can enjoy warm comfortable diving.

Dive Computers

Dive computers are just getting better and there's no reason for the improvements to stop. Unlike regulators, which are probably as good as they're going to get until the next design revolution. Dive computer technology has just begun to show its full potential. Dive Computers have many benefits as opposed to the older dive tables, the computer works out how much nitrogen is in your body and then works out your total allowable bottom time which changes throughout your dive (with dive tables you work out your dive based on your greatest depth) after you start to ascend for instance (diving up a reef or wreck) and works out your new nitrogen levels accordingly. The computer also tells you how deep you and your assent rate (most modern computers warn you audibly or on the screen you if you ascend to quickly) The PADI system states that divers can ascend at no faster than 18m a min, the dive computers are usually set to 10m so when you are alerted about a speedy assent you have time to compensate and slow down.

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WOMEN AND DIVING
DOES ONE'S SEX AFFECT SCUBA DIVING?

There are two answers to this important question. The short answer is "no." Much has been written about the difference between men and women divers, and no self respecting dive columnist would stop with such a simple answer. But the fact is, the differences between men and women regarding scuba diving are, with one exception, minor and not significant. The one exception, of course, is pregnancy.

The long answer is that women, on average, have smaller lungs, a lower aerobic capacity, a greater percentage of body fat, and less upper body strength than men, and these differences have some effects on diving. Women tend to use less air/minute than men (because of their smaller lung volume), but in recreational diving that is rarely an important factor. Women may not have the same capacity for extreme physical exertion as men, but that too is of little consequence in recreational diving. Since women have a higher percentage of body fat in men, in theory they should have better tolerance to cold water. Although some think the higher percentage of body fat increases the risk of decompression sickness.

The long answer also recognizes that the menstrual period poses some concern for women, but this is not ordinarily a limitation. The long answer must also include the observation that men as a group seem to take more risks than women, and as a result show up more frequently in mortality statistics associated with cave, deep, and mixed gas diving.

However, except for pregnancy, the anatomic differences between men and women are simply not a big deal when it comes to scuba diving. Either sex can learn to become quite proficient both as a recreational diver or as a scuba diving professional.

SHOULD WOMEN EXPECT SPECIAL TREATMENT WHEN SCUBA DIVING?

Ideally, no. The stereotype of a weak, mechanically disinterested, and/or uncoordinated female is out of date and harmful to both sexes. Any woman who expects manual chores will be done for her (carrying her tank, attaching the regulator, etc.) because she is a woman, loses the opportunity to learn important skills and remain self-sufficient. Any man who abridges a woman's chance for self-sufficiency by insisting on doing things for her not only demeans her but also perpetuates an outdated stereotype. Also, if the woman is his dive buddy, he may weaken skills she may one day need to help him.

Scuba diving is a level playing field; it is no place for machismo behavior or sexism of any sort. Equality certainly reigns at the professional level. Hundreds of women instructors teach open water and advanced courses to men and women. Women run dive shops, operate dive boats and lead diving expeditions. Resorts that carry tanks, attach BC's or perform other dive-related chores for its customers do so for men and women alike. Obviously, scuba diving is no longer "a man's world" as it was perhaps a generation ago. Today, it should be as acceptable for a man to ask a woman for help with equipment or some other problem, as vice versa. When diving, women and men should wan t and expect to be treated as equals.
 

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WATER AND THE PHYSICAL LAWS THAT AFFECT ALL DIVERS
WHAT ARE THE IMPORTANT DIFFERENCES BETWEEN AIR AND WATER?

The laws are particularly important in understanding what happens to air-containing spaces under water, particularly the lungs, sinuses, and middle ears. Before discussing air pressure under water, it will be useful to review important differences between air and water (Table 1).

1) Water is much heavier than air. A cubic foot of air weighs 1/12 pound (lb). A cubic foot of fresh water weighs 62.4 lbs and a cubic foot of sea water weighs 64 lbs.

2) Water molecules are made up of hydrogen and oxygen, chemical symbol H2O. Each water molecule contains two atoms of hydrogen and one atom of oxygen. Salt water contains salt (sodium chloride, chemical symbol NaCl) and other minerals in solution (i.e., dissolved into it, not chemically combined with the water). Salt adds to the weight of water, and for this reason sea water has slightly greater weight - and hence pressure - than fresh water (sea water contains approximately 35 pounds of salt for every 1000 pounds of water). It takes a depth of 34 feet of fresh water to equal one atmosphere of pressure, as opposed to 33 feet of sea water.

3) Air is a mixture of gases, principally oxygen (O2, 21% of the air by volume) and nitrogen (N2, 78% by volume). Each gas exerts its own independent pressure, the sum of which equals the total air pressure (Dalton's law). Unlike water, air (and any other gas or mixture of gases) is compressible; the greater the pressure exerted, the more tightly packed together are the individual gas molecules. Regardless of the air pressure, however, water molecules are much more tightly packed together than air molecules. Compared to air at sea level pressure (1 atm.), water is about 800 times denser.

4) Just as air has weight and exerts pressure on all sides of an object in the atmosphere, water exerts pressure around any object immersed in it. We can push water out of the way because its weight is distributed on all sides and the molecules can be easily moved. The resistance we feel under water reflects the extreme density of water (compared to air), and the fact that it takes time for water molecules to move out of the way.

5) Water pressure, like air pressure, is a function of weight; the deeper one goes the greater the surrounding water pressure. The marked increase in water pressure with depth affects every scuba and non-scuba diver, indeed anyone who goes under water (unless inside a heavy vessel with walls that resist pressure, such as a submarine).

TABLE 1. SOME DIFFERENCES BETWEEN AIR AND WATER
 

                                           Air                            Fresh Water                      Sea Water

Description                          Mixture of gases      Liquid                            Liquid with dissolved Minerals
 

Composition                        21% O2                  H2O                              H2O
                                          78% N2                  molecules                       molecules + dissolved minerals
                                            1% other gases                                            
 

Weight per cu. ft (lbs)          1/12                      62.4                              64
                                          (at sea level)

Maximal weight per volume: depends on             is same at all depths        is same at all depths
                                          pressure
 

Compressible                      Yes                       No                                 No

Freezing Pt.                         -500 ds. F              32 degrees F                   24 degrees F

7) Differences between air and water, in both weight and density, predict a radical difference in pressure with changes in altitude/depth. Sea water pressure changes one whole atmosphere every 33 feet (every 34 feet for fresh water). Provided they are of the same circumference, a column of sea water 33 feet high weighs the same as a column of earth's entire atmosphere.

8) Water freezes, whereas air does not freeze at any temperature occurring in nature. Sea water freezes at a much lower temperature than fresh water because of the dissolved salt, which slows down the formation of water crystals.

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HOW MUCH AIR IS IN A SCUBA TANK?

Eighty cu. ft. is the volume inside a box 5 ft. x 4 ft. x 4 ft., or the volume of a telephone booth 7 ft. x 3.3 ft. x 3.3 ft. (Figure 4). Since a cubic foot of air weighs 1/12 lb, the air in an 80 cu. ft. tank filled to capacity weighs about 6.7 lbs. This weight is in addition to the much heavier weight of the tank itself.

HOW DOES AIR PRESSURE CHANGE FROM THE SCUBA TANK TO THE DIVER'S LUNGS?

Sea level pressure is 14.7 psi. An 80 cu. ft. tank at 3000 psi contains 80 cu. ft. of air that has been compressed 204 times (3000 psi/14.7 psi) higher than sea level pressure. If you tried to breathe air at 3000 psi it would blow you away; you couldn't do it. The scuba diver is able to breathe tank air by virtue of a two-stage regulator system that 1) steps the pressure down to a level slightly above ambient, and then 2) delivers the air at ambient pressure. The first stage regulator brings the pressure down to ambient + a predetermined pressure. The pre-determined pressure is set by the regulator's design, but is generally 120-140 psi. Thus the pressure in the hose between first and second stages is 120 to 140 psi higher than the ambient pressure.

The second stage regulator contains a demand valve that requires only a slight inspiratory effort to open; when the diver inhales on the mouthpiece attached to the second stage, the demand valve opens and air enters the lungs at ambient pressure. Note that the air is at the pre-determined pressure immediately upon leaving the second stage (i.e., 120-140 psi), but it rapidly reaches ambient by the time it is inhaled. The second stage regulator is also designed so that air flow ceases when the diver exhales. (When air flow doesn't cease on exhalation it is said to "free-flow," a problem that can usually be corrected by adjusting the regulator or briefly occluding the mouthpiece.)

Recreational divers use "open circuit" scuba, which means all exhaled air enters the surrounding water; none is re-breathed. The value of 1500 psi for tank pressure in the table, for each depth, is shown as example only. Obviously, as the dive progresses the amount and pressure of air in the tank will decrease. The rate at which the tank's air volume and pressure decrease is a function of the diver's ventilation rate (how much air is breathed per minute), depth, and length of time under water. Note that regardless of the tank's psi, as long as it is above some minimum value the first and second stage regulators will deliver air at the ambient pressure. (Not all regulators work the same at very low tank pressures.)

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WHAT IS BUOYANCY?

Buoyancy refers to the tendency of objects immersed in water to float or sink. Objects that are positively buoyant float on top of water; objects that are negatively buoyant sink; and objects that are neutrally buoyant neither float nor sink, but stay where you place them (Figure 6). This principle was first stated by Archimedes (Greek mathematician and engineer, lived about 287 B.C. to 212 B.C.). He observed that an object immersed in water sinks or floats depending on the weight of water it displaces. If the weight of water displaced is less than the object's weight, it sinks; if the displaced water weighs more, the object floats; and if the displaced water is the same the object is neutrally buoyant.

For example, a cubic foot of solid wood weighing 63 lbs. would float in sea water (cu. ft. = 64 lbs) and sink in fresh water (cu. ft. = 62.4 lbs.). A cubic foot of solid steel weighs much more than 64 lbs., and so will sink in any body of water, whereas a cubic foot of styrofoam will always float. The steel displaces much less than its weight of water, the styrofoam much more.

WHAT IS BUOYANCY CONTROL?

"Buoyancy" also refers to an all important scuba diving skill, perhaps the one most difficult to master. A diver who has learned to control buoyancy has learned: the proper amount of lead weight to carry for each dive; how to use natural breathing to inflate or deflate the lungs to control vertical position; how to position equipment in order to stay horizontal; when (and when not) to put air in the BC; and how to ascend at a slow and steady rate.

Good buoyancy control is perhaps the single skill that most distinguishes experienced from novice divers. For most divers it does not come easily or quickly. Consider the many factors that can affect a diver's buoyancy:

Innate buoyancy differs among individuals, and depends on the amount and distribution of body fat, bone and muscle; as a result, some people naturally float and some sink. Fat tissue has a lower density than bone or muscle, so people with a lot of fat are more likely to float (i.e., displace an amount of water weighing more than their body), whereas lean, muscular folks are more likely to sink (i.e., displace an amount of water weighing less than their body).

The amount of air in the lungs affects buoyancy. If you establish neutral buoyancy during quiet breathing, a full inhalation will make you rise (become positively buoyant), whereas a full exhalation will make you sink (negatively buoyant).

A wet suit will be positively buoyant on the surface but will change to neutrally or negatively buoyant at depth.

A typical 80 cu. ft. aluminum scuba tank filled with air is negatively buoyant by 2-3 lbs., but when near empty the same tank will be 2-3 lbs. positively buoyant. (80 cu. ft. or air weighs about 6 lbs.)

The typical buoyancy compensator is positively buoyant without any air, and becomes more so as it is inflated.

Most ancillary equipment carried on a dive, such as a light, knife, or camera, tends to sink and therefore adds to negative buoyancy.

Some fins are positively buoyant, some negatively buoyant.

Finally, salt water weighs more than fresh water (64 lbs. vs. 62.4 lbs. per cu. ft.), so divers are more buoyant in salt than in fresh water.

Because most people have slight positive buoyancy naturally, and because the BC and wet suit add to positive buoyancy on the surface, it is usually necessary to carry lead weights while diving. Weights tip the scale to negative buoyancy and allow the diver to sink easily below the surface. Depending on body makeup and type of equipment carried or worn, warm water divers need anywhere from 4 to about 12 pounds of lead weight. The single item most affecting the amount of weight required is the wetsuit (the thicker the suit, the more weight needed to establish negative buoyancy).

As the dive progresses buoyancy is constantly changing. Consider:

Pressure compresses air cells in the wet suit, so the positive buoyancy contributed by the suit on the surface decreases significantly at depth.

As air is used up, the tank's buoyancy changes from negative to neutral to positive (steel tanks remain negative buoyant throughout the dive).

Any air in the BC at depth will expand as the diver rises, increasing buoyancy steadily with ascent; the higher the diver ascends the greater the increase in positive buoyancy.

Any change in the breathing pattern during the dive (e.g., a tendency to hyperventilation) may alter the diver's average lung volume, and thus affect buoyancy.

For the novice diver the net result of all the factors affecting buoyancy can be confusion and a bad dive. Consider two typical scenarios.

Novice A goes to 60 feet with a group of other divers. He has trouble emptying his BC of air and kicks hard to stay at depth and with the group; no matter how hard he tries to stay down he keeps rising. He looks in vain for something to hold on to. His depth gauge shows 40 feet...then 30...then 20. He simply cannot dump any air out of his BC and a few seconds later breaks through the surface of the water.

Novice B claims trouble sinking on her dives. She enters the warm Caribbean water with 16 pounds of lead, even though the dive master warns "it is too much." At 50 fsw she has difficulty staying off the bottom and puts some air in her BC. She then starts to rise, so she dumps some air. All the while she notices herself kicking hard to stay level and with her buddy. About 20 minutes into the dive she alerts her buddy that her tank has only 800 psi; her buddy still has 1800 psi. Together they begin an ascent to the safety stop line.

Diver A's problem was a BC with residual air that he could not properly vent. The closer he came to the surface the quicker he rose, as air in his BC expanded further. Fortunately he did not hold his breath and suffered no barotraumas from the rapid ascent.

Diver B's problem was carrying too much weight; this caused her to work extra hard under water just to stay level. As a result, she used up air much faster than her buddy. As with Diver A, she had a less than optimal dive because of poor buoyancy control.

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First, understand that buoyancy is not a static phenomenon, but one that changes constantly in the water, even if you stay at a level depth (because the quantity of tank air is constantly decreasing, and also because breathing affects buoyancy). Appreciating buoyancy as a constantly changing factor during every dive is the first step to mastering it.

Second, understand the role of the BC. As a rule, one should not have to rely on the BC for buoyancy control. For novice divers this piece of advice may seem paradoxical; a BC is, after all, a buoyancy compensator (sometimes also referred to as a buoyancy control device). No matter. Experienced divers learn how to use their lungs to fine tune buoyancy, and reserve the BC for an occasional adjustment, mainly to compensate for the decrease in wet suit buoyancy with depth.

Ideally, inflating the BC should only be necessary on the surface (for flotation), for wet suit compensation, and for emergency ascents. However, because wet suit compression will alter buoyancy at depth, it is often necessary to add a little air to compensate and re-establish neutral buoyancy. From that point of the dive, buoyancy should be controlled mainly by breathing. (It will also be necessary at the end of the dive to dump out any air added to the BC, in order to prevent too rapid an ascent.)

Third, one can take a formal buoyancy control course, offered in many resorts around the world. These courses teach the nuances of buoyancy control, including how to position equipment on your body so weight is evenly distributed.

Finally, gain experience. There is no substitute for experience, which means making many dives. Some divers find that learning good buoyancy control takes perhaps 100 or more dives. It also helps to practice such basic open water skills as the fin pivot. (In this skill the diver establishes neutral buoyancy with only his fins touching the bottom; using his fins as the fulcrum, he can then rise up with each deep inhalation, and fall back toward the bottom with each exhalation.) Only with many dives can one experiment with equipment, weights, wet suits and breathing techniques, and learn to master buoyancy control.

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