Drysuits in Cave Diving

By Natalie Gibb

I read an uniformed and rather prejudiced opinion on Facebook the other day. Actually, I read quite a few such opinions, but this one had to do with the use of drysuits by cavern diving and cave diving guides in Mexico. “If you use a drysuit in the cenotes, you are an idiot!” The opinion read, “Anyone who uses a drysuit in Mexico is just trying to show off.” As the owner of a custom, royal blue DUI Flex Extreme drysuit I admit I do enjoy prancing about in the suit—it’s quite handsome. However, the decision to dive dry, even in Mexico’s warm waters, has nothing to do with showing off. In my opinion, for most divers drysuits are better for cave diving.

The cold diver

Maintaining a comfortable temperature is a safety factor in diving. While some divers do try to ‘tough it out’ with the cold, this is dangerous and places both the diver and his teammates at risk. During a dive, the body’s physiological response to being cold is typically twofold: a combination of shivering and an increase in breathing rate. An increased breathing rate quickly leads to hyperventilation, which is truly dangerous in cave diving. It may cause a diver to breath through his exit gas more quickly, sometimes to the point that he eats into his reserve gas, which should be available for his buddy if needed. Furthermore, hyperventilation leads to carbon dioxide build up, which causes a diver to feel starved for gas and increases stress. Divers who become truly cold on a cave dive are unfocused for these reasons, and more likely to make mistakes that may affect their team’s ability to safely exit. 

Clearly, this is a major concern in cold and in temperate waters. But what about where I dive? In Mexico’s cenotes the water temperature is usually 78˚F (26˚C). The truth is that any water temperature lower than a diver’s body temperature will eventually chill him; colder water does so quickly and warmer water takes some time. As a cave instructor and cave diving guide, my average time in the water on a given day of guiding is around four hours; longer if I am teaching! 

Over the period of a week of diving, I usually see wetsuit divers go from proclaiming how warm the cenotes are at the start of the week, to shivering by the end of the week. Cold is cumulative over successive dives and days. As a dive professional, I got to the point that even during the summer in Mexico, I was sleeping with a heating blanket because my body could simply not recover its warmth. Of course, for most divers this will not be as extreme, but cold is a major consideration for anyone who will spend a great deal of time in the water, even in ‘warm’ conditions. 

Drysuits provide a second safety benefit for cave diving, unrelated to thermal regulation—they may be used as a back-up buoyancy device in the event of a wing failure. In areas with deep caves, or in areas where divers typically dive with steel tanks, redundant buoyancy is a requirement, as a wing failure could make it impossible for a diver to exit a cave. Drysuits are typically the standard choice for redundant buoyancy, but redundant wings also exist. However, with the exception of the Razor Sidemout System, every redundant wing I have tried has been too bulky for me, with additional corrugated hoses making it complex and uncomfortable. Drysuits solve the problem.

In Mexico, where the caves are shallow and aluminum tanks are the standard, redundant buoyancy is often considered optional, and it is not uncommon to see cave divers in wetsuits without a redundant wing. To this I say, really? Perhaps it is possible to drag yourself out of a shallow cave with aluminum tanks, but do you ever want to face that situation? It’s not as easy as it sounds! How do I know? I have done it. It wasn’t fun, and I started using redundant buoyancy after that experience. 

For deeper cave diving with multiple tanks, drysuits have the advantage that they do not compress in the same way as wetsuits do. Consider that diver must weight himself so that he is neutrally buoyant with nearly empty tanks, including any stage tanks he may use. When using a wetsuit for deeper cave divers, the wetsuit will compress, and the diver will often find that he is heavy with an uncomfortably full wing at the deepest part of the dive. With drysuits, compression is not an issue, as the diver adds gas to the drysuit to offset the compression of the suit at depth. 

Once mastered, drysuits can actually make certain aspects of cave diving easier, such as maintaining trim. Trim refers to a diver’s body position, which should be parallel to the floor. When using aluminum tanks, the bottom of the tanks become ‘floaty’ as they are emptied. This can make maintaining a perfectly trimmed body position difficult in a wetsuit. In a drysuit, a diver just puts a bit of air in his arms to counteract the lightness of the tanks. Similarly, when diving with a stage cylinder, a diver may feel that it tips him to one side (this is mainly just an issue in sidemount). With a drysuit, its’s easy to roll air around to counteract the sideways tilt. 

Do you need one?

This all sounds wonderful. Should you run out and buy a drysuit before starting cave training? I would say it depends on several factors. The first is time—it would be foolhardy to start cave training in a drysuit if you have never used one before. There’s a steep learning curve with drysuits, and I would suggest getting comfortable and logging at least 20 hours in a drysuit before using it for technical or cave diving. The second factor is your personal temperature tolerance. If you are one of those superior specimens of humanity that literally never gets cold, maybe you don’t need a drysuit. You should, however, have redundant buoyancy, so be sure to select a wing or configuration that provides this. 

The way drysuit diving is taught for open water usually does not prepare divers for using a drysuit in the cave. Nearly every open water drysuit course I have observed teaches divers to use the drysuit for buoyancy and the wing as a back up. This probably comes from two considerations: first that the additional air in the drysuit when it is used as the primary buoyancy control device helps to insulate a diver from the cold, and second, that it’s task loading to use two buoyancy devices. Teaching divers to keep their wings empty and only use the drysuit for buoyancy reduces task loading. However, this doesn’t work for cave diving. 

In cave diving, the purpose of a drysuit is to keep a diver warm and dry. The wing is still the primary buoyancy device, and cave divers add just enough air to the drysuit to offset the compression of the suit. Without an excess of gas in the drysuit, cave divers can dive properly for the environment, which often requires going head down through holes or head up along a slope. Orienting the body head down or head up with a very inflated drysuit can cause the diver to lose trim and even buoyancy control as the air in the suit moves around. If you are planning to use a drysuit in cave diving, it’s best to learn to dive your suit with minimal inflation, and to practice going head down and head up in a safe environment with an instructor before starting training. 

Kitting it out

When you are ready to purchase a drysuit for cave diving, there are a few considerations for the suit and the environment. If you plan to travel with your drysuit, you will want to order your suit with user-replaceable wrist and neck seals. DUI zip seals and the Si Tech ring system are both good examples of seals that may be replaced in a few minutes at a dive site. You will tear a seal at some point, and having the ability to replace the seal yourself can save a dive or even a whole trip. Similarly, Gorilla Tape can be used to seal most suit holes for a dive or two in a pinch, and Aquaseal can be used to permanently repair small holes in a suit. Have these on hand! 

Finally, I would strongly encourage cave divers to install a pee valve on their drysuits. For men, the pee valve is used with disposable condom catheters, and for women, pee valves are used with the She-P, a reusable female catheter that is worth Googling. Not only will a pee valve allow divers to properly hydrate before long dives, but it helps to reduce drysuit zipper wear… Fewer zips per day extends the life of a zipper! For divers who need to pee on every dive (most of us), I do feel that routing urine outside of the suit is vastly more hygienic than swimming in a pool your own pee during a wetsuit dive. For many divers, particularly women, pee valves reduce the chance of urinary tract infections. 

Practice your technique

Remember that using a drysuit takes practice, and that the technique for using a drysuit in technical and cave diving may be different than the techniques taught in most open water drysuit courses. Get practice with a new suit in the open water before taking it into a new environment. There is a steep learning curve at the beginning but the benefits of diving dry far outweigh the initial suffering! 

Natalie Gibb Is a full cave instructor, explorer, and researcher based in Mexico’s Riviera Maya. She is a published author, international speaker, and cave conservationist. Visit: www.underthejungle.com