Get Off My Back!

By Karl Shreeves

Hang around cave diving long enough, and you’ll run into divers wearing sidemount gear. For the uninitiated, your basic sidemount rig consists of two cylinders, one on each side of your body. What’s on your back? Nothing, and that’s the point! Sound weird? Maybe, but in many of the places I cave dive, like the Mexican Yucatan, I don’t even take regular backmount gear—I dive only sidemount.

Cave divers developed sidemount rigs for crawling into tight spots—places too low to squeeze through while wearing the usual double-tank setup. Okay, now you’re lower, but you’re wider—does that help? You bet, plus they’re independent cylinders that you can swing up or down or be removed, so you can fit through whatever shape the cave throws at you. And, when you get stuck (dive this kind of cave long enough and you will), the setup ensures that you can dismount one tank (or both) for space and scrunch your way back out.

A typical sidemount rig consists of a harness and BC, but they’re modified to meet the unique demands you have when slithering through tiny caves. On a typical setup, the cylinders mount at your hips and in the neighborhood of your armpits (some personal preference here). Heavy duty bungees or bicycle inner-tubing, affixed across your back, stretches around under your arms and clips into your harness to hold the BC down and the tanks close. If need be, you can snap the strap free, unclip the waist and voilá—you’ve slipped the cylinder loose so you can push it ahead of you into the really tight stuff, or back out of a jam.

The first thing you discover about sidemount is that it’s a pain in the butt to reach your waist. So, that’s where you wear your cave light and reels—on your butt. They’re really simple to reach, and you can get rid of them easily when you go through the extra tight spaces. You can use an exposure suit thigh pocket for the small stuff (line arrows, survey slate, tables, etc.), but I prefer using a purse that I clip backside. I reach back, unclip and bring it in front, so that I can see when I get something out or put it away.

Each cylinder has its own regulator and SPG, so you’re constantly switching during the dive (obviously, gas management is a bit more complex than when diving doubles). When you stack stages on top of your mains (four cylinders total), it gets really interesting, but surprisingly intuitive after you do it a bit. From an air management point of view, one benefit I love is that the first stages and valves are right in front, where I can see them. If I’ve got a gas leak, I know right away; I know what’s leaking and where. And, I can switch a regulator without help if I have to.

Not Just for Tight Caves
If, at this point you’re saying, “Karl, what does this have to do with me? As far as I’m concerned, any diver who scrunches through caves that tight has a screw loose.” Let me say this: 1) You’re probably right; and 2) Sidemount rigs have advantages other than the ability to go where most sane people (including quite a few cave divers) have no desire to go. Sidemount works well in many big caves, and even in some special open water situations.

When you dive sidemount, with only a few exceptions, you put your tanks on after you’re in the water. In truth, you can’t walk with cylinders on with most sidemount setups. Hence advantage one: instead of schlepping heavy doubles to the dive site, you can take two singles in two trips. The more difficult the access to a cave entrance, like when diving in newly discovered cenotes in the middle of the Mexican jungle, the more advantageous this is. If you’ve ever climbed through about 100 feet of vertical relief in a dry cave too small to stand up in to reach the water (I have), you really appreciate the difference between hauling single cylinders versus a set of doubles.

Another advantage of sidemount is that, in many remote areas where cave divers go, it’s easy to get singles (because recreational divers use them), but you can’t get doubles. While I’m personally not comfortable with independent tanks on my back, it’s another story when independents ride valve-in-front in sidemount configuration. So, for me, sometimes sidemount is the way to go for open water tek diving when I need two tanks, but manifolded doubles aren’t an option.

Sidemount is also an attractive alternative for people with lower back problems and those with disabilities (permanent or temporary) who find it difficult or impossible to wear a cylinder out of the water. Sidemount puts less stress on the back than conventional doubles, and it’s easier to don and doff tanks in the water because that’s what the rig is set up for. The primary drawback for this use is that you really need two tanks in order to keep yourself properly trimmed and balanced as you swim. This means dragging an extra tank along even in circumstances where you only need one tank.

Even among the most ardent sidemounters, though, sidemount doesn’t completely replace backmount. When I make deep, mixed gas dives in big caves, the sheer number of cylinders involved for gas switches makes having them on your side awkward. For routine, single tank, open water, no stop diving, I’ll stick with my standard BC jacket, thanks very much.

But, there will always be plenty of caves where I’m happiest, because there, everything’s off my back for awhile. In more ways than one.

Karl Shreeves is VP, technical development for DSAT and PADI, and an avid cave diver.