Freediving is the sport of breath-hold diving, it has been around for hundreds of years. People have used its techniques as a method of providing themselves with sustenance from the ocean. In recent years the sport of Freediving has developed as men and women challenge their abilities in time, depth and distance on one breath of air. There are many disciplines in freediving: Constant Ballast, Variable Ballast, No Limits, Static Apnea, Dynamic Apnea (with fins), Dynamic Apnea (without fins), Free Immersion, and more. There are many world records currently held in freediving

Constant Ballast
The freediver descends and ascends using flippers and/or using his arms, without pulling on the rope and without any variation of his ballast; only allowed is the holding of the rope in one single hold (one hand or two) to stop the descent and start the ascent.

Variable Ballast
The freediver descends with the help of a sled and ascends using his/her own muscular strength arms and/or legs (either pulling or not on the rope).

No Limits
The freediver descends with the help of a ballast weight (often a sled) and ascends via a method of his own choice (balloons, etc.).

Static Apnea
The freediver makes the longest possible free dive, the body either in or on top of the water with the face in the water.

Dynamic Apnea
The freediver moves along in a horizontal position under the water, his/her goal being the greatest distance thus covered. This discipline is practiced both with and without fins

Free Immersion
The freediver dives to a depth, without propelling equipment, his/her goal being the depth reached (pulling or not on the rope for both the descent and the ascent).

This is a basic explanation of free diving. If you have a better WU, then please post it and I'll be happy to step aside.

Summary

Free diving is quite simply diving underwater while holding ones breath. Free diving is different to SCUBA diving because SCUBA divers use an air tank. Almost everyone who has been swimming has "free dived" by simply diving to the bottom of the pool, or the beach, etc.

Many would think that free diving is an inferior form of diving compared to SCUBA diving, after all, what can a free diver do that a SCUBA diver can't? Actually, quiet a lot, a free diver can dive unencumbered, any time, time after time, and experience being underwater in a more natural manner. As a SCUBA diver myself, I can't say I particularly enjoy the experience, but many find it great.

Technique

Everyone who has held their breath knows that after a short period of time, your lungs begin to feel like they are on fire. This is not caused by the lack of oxygen, but the build up of carbon dioxide. Generally when you experience this sensation you still have plenty of oxygen in your lungs, which is were hyperventilating comes in. By hyperventilating you purge your lungs of most of the carbon dioxide that is always in them. Thus allowing you to fill your lungs with more oxygen and preventing the breath reflex from coming in too soon.

Warning: Over hyperventilating can have the opposite effect and can even cause you to loose consciousness and can lead to drowning and death.

Competition free diving

There are two main categories of competition free diving; variable ballast and constant ballast.

Constant ballast

In this category there are 3 subcategories. Unassisted, line assisted, and equipment assisted.

Unassisted refers to the free diver diving while under his/her own power without using an guide lines or propulsion devices.

Line assisted refers to the free diver diving using a static vertical line to pull him/herself down to the target depth and up to the surface. No other propulsion device is allowed.

Equipment assisted refers to the free diver using self powered propulsion device (eg fins).

Variable ballast

This category is broken up into 2 subcategories: Limited and Unlimited.

Limited refers to the diver using one a guided ballast device for the decent. The diver may use a propulsion device (eg fins).

Unlimited refers to the diver using a guided ballast device for the decent and a guided flotation device for the accent.

Dangers

I won't even begin to go into the numerous dangers there are with free-diving. If you attempt to override your bodies natural defences against suffocating by hyperventilating or using other special techniques, you run into dangers. Much like with SCUBA diving, you should consult a trained professional before attempting free diving.

Records

These change over time, and by the time you read this, these are probably wrong.

No limits: 1999: 150m (492ft) Umberto Pelizzari

Variable weight: 1998: 121m (397ft) Gianluca Genoni

Constant weight: 1999: 80m (262ft) Umberto Pelizzari

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References:

Limited personal experience

http://www.divingfree.com/

http://library.thinkquest.org/28170/45.html

http://www.freediving.net/historia.htm

http://www.geocities.com/~freediver/freedivingpage.htm

The U.S. Navy Sea-Air-Land (SEAL) program grew out of Navy Underwater Demolition Team (UDT) experience in World War II. SEALs began as a secret military program in the 1960s, first created by President John F. Kennedy. The first set of trainers and commanders, old UDT frogmen, still remembered experiences of sharks picking off UDT members in and around Pacific Ocean islands in World War II. The great loss of men experienced by the sunk carrier U.S.S. Indianapolis due to shark attacks was very much on the minds of early UDT instructors.

The U.S. Navy SEALs are expert swimmers. They train in high surf, bad weather, and cold water. Sharks are just another problem to overcome.

Some SEALs hate sharks with a passion. One such SEAL, Scott Slaughter, was described in a book on early SEAL team members (a book that I unfortunately gave away). If he worked or trained in waters with sharks, he would free dive 100 feet down with a bang stick and kill sharks just for fun. A bang stick is a long stick with a quarter stick of dynamite at the tip, that could be set off by sharply striking a shark. The percussive force would kill even fairly large sharks. He'd dive, find a shark, kill it, drag it to the surface, and boil it down for its jaws, which he kept as a trophy. One less shark in the water.