Managing the Additional Air Space
Much of learning to dive dry is about learning how to properly add gas to your suit while descending and dump gas from it while ascending. It can be trickier than it sounds. Too much gas will throw off your buoyancy. It can also create a bubble inside your suit which can travel around as you shift positions. This is something you want to avoid!
If you have too much gas inside your suit and the extra gas makes its way towards your feet, it can cause a dangerous situation where you become inverted in your suit. Because there are no dump valves near your feet you may begin to ascend uncontrollably towards the surface feet first.
This is why you may want to consider a drysuit course or at the very least learning to dive dry from an experienced and qualified instructor.
Another thing that’s different about drysuits is that you have to consider the possibility of a it flooding. If one of the seals become compromised or your suit tears during the dive it may become flooded with water. In very cold waters this can be dangerous. It’s also why drysuit undergarments need to be made from a material which will keep you warm even when wet. This means you can’t just throw on a cotton sweater and jogging pants underneath your suit.
Drysuit Buoyancy Considerations
Drysuits are generally more buoyant than wetsuits. How much more will depend on the suit material and the undergarments being used.
You’ll need to account for this difference in buoyancy by either adding more weight to your SCUBA diving rig, using a stainless steel backplate to add weight to your rig, or using a SCUBA tank that is more negative than the one you use while diving wet.
In order to determine the correct amount of ballast, you should perform a buoyancy check in the drysuit using the undergarments you intend to dive with. Note, changing your undergarments may change your buoyancy requirements in a drysuit.
Drysuits and your BCD
Because drysuits hold an additional air space some people wonder if they can replace a BCD? The answer is NO! The airspace is the suit is not as easy to control as the one in your BCD. It’s also not designed to balance you out in the water. You should never rely on your drysuit alone for buoyancy. Some divers consider a them a redundant form of buoyancy control should your BCD wing fail. While in an emergency this may be possible it is less than ideal.
Drysuits come in several different materials. Neoprene, crushed neoprene, vulcanized rubber, and trilaminate are some of the most common. The most popular of these is trilaminate and neoprene.