Get Wet, Dive Dry

Understanding the basics of drysuit technology

Drysuits have long been standard dress for many technical divers, underwater photographers, instructors and other professionals who spend a lot of time underwater. It's not surprising then, that with longer dive times arising from the use of nitrox and larger capacity cylinders as well as a greater awareness of the available options, recreational divers are increasingly choosing to dive dry, even in relatively warm water.

Drysuits are based on the idea of an inflatable, watertight shell, which creates a dry envelope around a diver's body, combined with insulating undergarments. This two-part system, invented by British engineer Augustus Siebe in 1837, effectively limits heat loss, which is 25 times greater in water than on land. The insulating benefits of the system are especially useful at deeper depths, where compression of the tiny air pockets in neoprene wetsuits diminishes their insulating ability. Drysuits are easily adapted to a wide range of water temperatures; all you have to do is choose the appropriate thermal undergarments for the water temperature and your anticipated level of exertion.

Another benefit drysuits offer is improved ability to maintain neutral buoyancy throughout the water column. The diver can add gas to the suit using a manual inflator valve, and excess gas is purged through an exhaust value positioned near the top of the suit. In general, a drysuit should not be used as a buoyancy device in place of a BCD, particularly in emergencies; divers should add just enough gas to the suit to avoid suit squeeze and make sure to vent excess gas when ascending. Compared to wetsuits, they generally require more weight to submerge, depending on the undergarments worn. Like other diving technologies, drysuits require both training and practice; most training agencies offer a drysuit course.
The Shell Game

Broadly speaking, there are two types of drysuits: shell suits (also known as membrane suits) and neoprene suits. Shell suits typically consist of one or more layers of durable fabric such as polyurethane-coated nylons, vulcanized rubber or crushed neoprene (neoprene without air cells). Trilaminate shells are a popular option; these consist of three layers of material such as nylon, butyl rubber and another layer of nylon bonded together to form a tough waterproof barrier.

Shell suits, particularly those made with trilaminate, tend to be lightweight and flexible and can therefore be worn all day without physically exhausting the diver. They are easier to don than neoprene suits and dry faster. In addition, because the shell itself offers minimal thermal protection, the suit is ideal for diving over a broad range of water temperatures, from near freezing up to 70 or 75 degrees, depending on the undergarments used. The trilaminate shell suit is probably the most popular among technical divers, though many wreck divers prefer the heavier-duty crushed neoprene.
Foam Neoprene

Constructed of the same material as wetsuits, older-style foam neoprene drysuits are typically cut more snugly to reduce drag. Because the warmth comes primarily from the neoprene itself, these suits usually require fewer or lighter undergarments. This also means they are best suited to diving in colder water. They require more weight than shell suits and, like wetsuits, suffer from diminished insulation at deeper depths. Many commercial divers, who tend to work at fixed depths, prefer these suits because they can take a lot of abuse. They are also used in specific applications like recreational dive instruction and dry caving where sumps must be negotiated. They are usually less expensive than shell suits, making them an attractive choice for some beginning drysuit divers.
Selecting Suitable Options

Because drysuits are typically made of tough fabrics and are roomy, which means less stretching and straining of the material, they can last a long time. They come in a variety of styles including self-donning (with the zipper across the chest from shoulder to hip), telescoping torso, and shoulder entry or back donning (with the zipper across the back). The trend these days is toward self-donning suits, which allow greater range of motion, though many divers still find a buddy's help makes suiting up much easier.

Drysuits' watertight neck and wrist seals come in two varieties: latex and neoprene. Latex, which can stretch up to 400 percent, generally creates a better seal and is easier to put on and take off. They require more careful handling, though, and have a shorter life expectancy, requiring replacement when they wear out. Neoprene seals, which usually include a Lycra lining, expand by only about 100 percent and are harder to get on and off, but they hold up longer and can take more abuse. Latex seems to be the preferred choice for most tech divers. One of the latest innovations in drysuits is Diving Unlimited International's (DUI) patented "zip seals," which snap into place rather than being glued, allowing them to be changed out in the field if necessary.

A feature that makes a nice addition for cold-water diving is a warm neck collar overlay, and some divers wear a silk scarf underneath. Another option for really cold water is dry gloves, which are worn at the cost of some minor dexterity loss. A word to the wise: Warm, dry hands are divine. Several additional features to consider are bellows pockets (with Velcro flaps and enclosed bungee cords for securing items), crotch pads and kneepads.

If you plan to stay hydrated, which is critical for safe diving, you will need a way to relieve yourself while wearing your drysuit. If diapers aren't your style, the P-valve system consists of a balanced dump valve, mounted on the suit near the inside of the thigh, which is attached to a length of rubber tubing. Men attach the tube to a self-adhesive condom catheter, and they're good to go. Women wear a self-adhesive external catheter cup, such as the She-P.

Suitable undergarments are typically made from synthetic fleeces like Polartec or Thinsulate. Be sure to select undergarments designed for the water temperature(s) you plan to dive in. Layering is often a good choice. Also consider choosing materials that maintain their thermal properties when wet in case of a suit flood or serious leak. Drysuits are rarely 100 percent dry. Despite modern materials and advanced designs, they can leak, and moisture and perspiration can accumulate. Sometimes getting wet means getting wet. Ultimately, however, the thermal benefits of drysuits are unmatched. Whether you're trying to extend your dive times or your dive season, diving dry might just be the way to go.

© Alert Diver — Winter 2012
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