­ Q: How are wet and dry scuba suits different? A: A wet suit traps a thin layer of water between the insulating rubber of the suit and your body. Your body heat warms the water, which then keeps you warm. Dry suits are made of a double-walled material with an insulating air space between the layers. They keep you warm because air is a better insulator than water and because you can wear undergarments with them.

In 1943, the famed oceanographer Jacques­ Cousteau, along with Emile Gagnan, invented the aqualung, more commonly referred to as scuba (self-contained underwater breathing apparatus). Scuba made divers more mobile and revolutionized exploration of the oceans. Since then, many advances in scuba technology have made the equipment easier to use, safer and more affordable, allowing many people to enjoy this fascinating adventure. The Professional Association of Diving Instructors (PADI) says that each year, almost 1-million people get certified for recreational scuba diving. You can undertake weekend outings to explore offshore shipwrecks and coral reefs or go on longer dive vacations to exotic locations, perhaps meeting such creatures as sharks, dolphins and whales.
­
In this article, we will look at the underwater world, examine the scuba equipment and explore how your body reacts to the underwater environment. You'll also find out what you need to do to take part in this sport.

The underwater environment is hostile to humans and offers unique challenges to the scuba diver with respect to breathing, temperature control, visibility and buoyancy. The basic equipment that you need for scuba diving allows you to cope with the underwater environment. In total, you carry 60 to 75 pounds (27 to 34 kg) of equipment with you into and out of the water.

Let's take a closer look at the equipment. First we'll find out what it takes to control temperature and buoyancy.

Photo courtesy NOAA/Dept. of Commerce To become a scuba diver, ­you must be at least ten years old and take a open water certification course. See more scuba pictures.

­

Thermal Protection
To keep warm underwater, divers wear insulating suits, either wet suits or dry suits. The wet suit traps a thin layer of water between the insulating rubber of the suit and your body. Your body heat warms the water, which then keeps you warm. Wet suits should fit snugly (a loose wet suit will constantly leak in cold water). Wet suits come in short (covers only the arms and torso) or full-body lengths.

In contrast to wet suits, dry suits are made of a double-walled material with an insulating air space between the layers. They have tight fitting necks, wrists and ankles to prevent water from leaking in. They keep you warm because air is a better insulator than water and because you can wear undergarments with them.

The choice of wet versus dry suits depends on the water temperatures encountered during the dive:

• Bare skin or nylon wet suit - 82 to 90 degrees Fahrenheit (28 to 32 Celsius)
• Shorty wet suit - 78 to 90 F (25 to 28 C)
• Full-body wet suit - 68 to 85 F (20 to 29 C)
• Dry suit - below 72 F (22 C)

Wet suits and dry suits also have accessories including gloves, boots, vests and hoods.

Buoyancy Control
Underwater, it is important to control your depth at pre-determined levels set in your dive plan. To do so, you must be able to control your buoyancy, the upward force of the water on you. Buoyancy is caused by a difference in pressure between the upper part and lower part of an object. It is related to the object's weight and density, which determines the weight of water displaced by that object.

Buoyancy control device, showing front (left) and back (right)

To control buoyancy, divers use a buoyancy control device (BCD), which is also called a buoyancy compensator (BC), and lead weights. The BCD is a vest consisting of a coated rubber bladder that can be inflated or deflated with low-pressure air, either directly from the regulator's first stage or by mouth through an inflation tube. BCDs usually have a backpack type harness for holding the air cylinders and come in front-collar, vest and back-mounted styles. BCDs contain several pockets for equipment.

Special thanks to Aaron Harmon, Susan Kaliski and Scott Powell of Down Under Surf & Scuba for their technical assistance with this article.

­ Because the wet suit itself is buoyant, you must add additional weights to counter this buoyancy. The weights can be attached to separate belts that the diver wears. Weights can also be inserted into the pockets of BCDs, and some newer BCDs have weight belts integrated into them.

Scuba enthusiasts often find that cliff diving is right up their alley. Check out this great cliff diving article and stunning video from Discovery Channel’s Fearless Planet for more information about this daring and exciting adventure sport.

Now, let's take a look at breathing underwater.