Hang around cave diving long enough, and youll run into divers wearing sidemount gear. For the uninitiated, your basic sidemount rig consists of two cylinders, one on each side of your body. Whats on your back? Nothing, and thats the point! Sound weird? Maybe, but in many of the places I cave dive, like the Mexican Yucatan, I dont even take regular backmount gearI dive only sidemount.
Cave divers developed sidemount rigs for crawling into tight spotsplaces too low to squeeze through while wearing the usual double-tank setup. Okay, now youre lower, but youre widerdoes that help? You bet, plus theyre 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 theyre
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 voiláyouve 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 its a pain
in the butt to reach your waist. So, thats where you wear your
cave light and reelson your butt. Theyre 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 youre 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 Ive got a gas leak, I know right away; I know whats leaking and where. And, I can switch a regulator without help if I have to.
Not Just for Tight Caves
If, at this point youre saying, Karl, what does this have to do with me? As far as Im concerned, any diver who scrunches through caves that tight has a screw loose. Let me say this: 1) Youre 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 youre in the water. In truth, you cant 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 youve 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, its easy to get singles (because recreational
divers use them), but you cant get doubles. While Im personally
not comfortable with independent tanks on my back, its 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 arent an
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 its
easier to don and doff tanks in the water because thats 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 doesnt
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, Ill stick with my standard BC jacket, thanks very
But, there will always be plenty of caves where Im happiest, because there, everythings 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.