By Jill Heinerth
The philosophy behind sidemount diving is simple. Rather than wearing a tank or tanks on the back, they’re slung on the side of the body, tightly streamlined so that the valves rest just below the armpits. Borrowing from technical dive procedures, gas supply is carefully managed by swapping from tank to tank every 300 to 500 psi. Over the years, tech divers have developed a gas management strategy called the ‘rule of thirds’, wherein a diver uses one-third of each tank for the inbound portion of a dive, and reserves the second third for the return to base. The final third of each tank is left in reserve for the unlikely event of an emergency. By balancing tanks in this manner, a gas supply emergency can be managed independently, without assistance from another diver.
Of course divers still rehearse gas-sharing drills, but in most cases self-rescue can be achieved by switching to the unaffected cylinder or by carefully throttling the valve of the impaired tank on and off to minimize gas loss from a damaged regulator. In sidemount, tank valves are effortless to reach, less likely to become damaged by impact and easy to monitor if there is a failure.
The first noted departure from back mounted dive gear was conceived by British cave diver Mike Boon in the 1960s. Having recently ditched his old double hose regulator, he decided to use an unconventional tactic to explore a small cave called Hardrawkin Pot in Yorkshire. Slinging a tank on his side with a bandolier of webbing, he was able to squeeze through tiny spaces that were previously thought to be impassable. The British took notice and perfected the system to conquer sump systems all across the United Kingdom.
The introduction of the technique in the United States arrived during a much darker episode in diving. In the late 70s, an untrained recreational diver fatally forced himself into an impossibly narrow crevice in Royal Spring in North Florida. Sheck Exley and Wes Skiles, two of the most experienced cave divers in the area, were tasked with the recovery of the wedged diver. After several unsuccessful attempts using back-mounted cylinders, Exley fabricated a single cylinder rig with an old hose clamp and a belt. Holding the cylinder at his side, he slid into the crack beside the lifeless diver, breaking him loose from the cave’s grasp. Seeing this configuration in action, Skiles quickly realized the possibilities of a similar setup for exploration of smaller passages: sidemount cave exploration began to expand through North America.
Pioneering explorers Forrest Wilson, Woody Jasper and Rory Dickens continued to push small caves with their own versions of highly modified scuba equipment, but it was not until 1995, when Dive Rite released their Trans Pac system that the commercial viability of this style of diving became evident.
Store Bought the Best
Today, the sidemount style offers a distinct advantage for traveling divers. Leading designs such as the Razor harness or Hollis SMS50 are among the lightest diving systems available. They pack small and weigh very little; when every ounce equates to airline fees that can pay off! With minor adjustments to sidemount system tank bands and hardware, the harness supports all common diving configurations using one or two tanks. Sidemount rigs accommodate any size tank and offer the advantage of supporting multiple stage tanks for tech divers who know that manifolded back-mounted doubles are scarce or nonexistent in many destinations around the world.
I made my first sidemount rig with an old BCD and several bicycle inner tubes. It worked, but I soon discovered that units available for sale incorporated many hard to duplicate features that grew out of years of developmental testing. The specially shaped air cell concentrates lift around the diver’s hips to compensate for the lower center of gravity of the tanks as compared to back mounted systems. The bottom attachment point of the tank clips to the harness on a rail on the diver’s butt. This clip creates a pivot point or center of balance on the diver’s body. The pivot point can be moved up or down to change the diver’s attitude in the water. If a diver is foot-heavy, the clip can be lowered on the tank to bring the feet up. If the diver is head-heavy and foot-light, the clip may be shifted upward on the tank to recover the horizontal trim. Once the system is properly balanced tanks ride parallel to the diver’s body with the valve tucked underneath the armpit.
Proper placement of cylinders is the most important aspect of the sidemount system. If cylinders are out of trim, the diver will be faced with poor buoyancy and inefficient movement through the water. Poor configuration can lead to entanglement hazards and additional workload for the diver.
The tank valve is held in place by a safety clip and a bungee system that runs from behind the diver’s back to a point under the arms. Each tank is independent with its own regulator and short-hose pressure gauge. The left side regulator is equipped with a short low- pressure inflator hose. Dry suit divers will place an inflator hose on the right regulator as well. The hoses are carefully sized to fit the diver and the hose port locations. There is no secret formula for the perfect hose length since each diver’s body morphology and first stage port configuration present different challenges. Many divers equip their second stages with swivels that assist with hose routing and jaw comfort.
Even though the majority of problems are self-managed, it is very likely that a sidemounter will dive in mixed teams that include other diving configurations. For that reason, most divers choose to install a seven-foot (2m) second stage hose on one tank to make air sharing uncomplicated.
Get Formal Training
With the availability of commercial rigs such as the Hollis SMS series and Dive Rite Nomad line, training agencies saw that sidemount classes could be offered to a wider audience, not just cave divers. Now, most agencies from PADI to IANTD, offer a wide variety of training opportunities. Recreational, technical, specialty and exploration sidemount classes are available at a growing number of facilities around the world. Although some divers choose to adopt the new configuration without assistance, it is highly advisable to get formal training from an experienced instructor. It takes a trained set of eyes to comfortably fit, modify and optimize new equipment for a diver. Sidemount harnesses are extremely versatile for many body types, but it’s important to customize the fit and configure regulators in a way that maximizes streamlining while trimming the diver in the ideal horizontal plane.
Sidemount configuration has transformed the way many technical divers approach their craft. But it’s not just for explorers any more. Sidemount technique is a safe and logical alternative to back mounted doubles in diving environments from caves to open water to wrecks. Configured with small, lightweight cylinders, a sidemount rig also can add a measure of safety serving as a redundant system to a conventional back-mounted tank. Sidemounting allows you to take your buoyancy and trim skills to the next level and for some to the world of technical diving.
In their newly released DVD, dive pros Jill Heinerth and Jeff Loflin lead you through the fundamentals of sidemount diving. Equipment selection, gear setup, techniques and skills are covered in this comprehensive 65-minute video guide. Suitable for all skill level divers from beginner to professional, and for scuba enthusiasts with interest in every day recreational diving, caving and wreck diving. This presentation is designed to help you improve your diving. Filmed in underwater locations around the world, it features leading sidemount divers including Nick Hollis, Brian Kakuk, Jakub Rehacek and more. Available at: www.SidemountVideo.com
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