Sidemount diving
Sidemount is a scuba diving equipment configuration which has scuba sets mounted alongside the diver, below the shoulders and along the hips, instead of on the back of the diver. It originated as a configuration for advanced cave diving, as it facilitates penetration of tight sections of cave, allows easy access to cylinder valves, provides easy and reliable gas redundancy, and tanks can be easily removed when necessary. These benefits for operating in confined spaces were also recognized by divers who conducted technical wreck diving penetrations.
Sidemount diving is now growing in popularity within the technical diving community for general decompression diving, and is becoming an increasingly popular specialty training for recreational diving, with several diver certification agencies offering recreational and technical level sidemount training programs.
Terminology
;Sidemount diving: Sidemount diving is the practice of diving with two or more cylinders secured at the sides of the body in line with the torso and without cylinders on the diver's back. A common characteristic of the sidemount configuration is the use of bungee cords hooked over the cylinder valve to keep it tucked in close to the armpit. These bungees are normally routed from behind the diver's upper back to a chest D-ring. The lower part of the cylinder is secured to the diver's harness near the waist or hips by bolt snaps clipped to a butt-plate or waistband D-rings.;Sidemounting stages: Sidemount stages is the practice of using sidemount configuration as a means for stowing stage/deco cylinders in a streamlined manner against the sides of the torso, when otherwise diving in back-mounted doubles or CCR.
;: Monkey diving is the use of sidemount configuration and procedures with a single cylinder. It is presented as an option on some recreational level sidemount courses and may also be a considered strategy for some overhead-environment penetrations. The use of a single cylinder may require counter-weighting to prevent lateral instability in the water, depending on the buoyancy of the chosen cylinder, and does not provide a redundant gas supply.
;No-mount diving: No-mount diving is a specialized overhead-environment strategy for dealing with particularly tight restrictions. This may involve divers wearing a very basic harness under their existing configuration, or simply hand-carrying cylinders. Upon reaching a restriction through which they could not otherwise pass, they will 'strip down' out of their primary gear, hand-hold or attach a cylinder/s to their 'no-mount' harness and move forwards. A 'no-mount' harness can consist of nothing more than a weight-belt with several D-rings attached. The evolution of sidemount techniques and configurations has largely made this approach unnecessary, as a minimalist sidemount harness/BCD can be worn beneath back-mounted doubles, or even a CCR.
Benefits
Flexibility
Sidemount diving offers some benefits in the flexibility of equipment. Cylinders suitable for sidemount diving are usually freely available for rental, unlike manifolded twin sets for back-mounted use, which allows the traveller to conduct technical or overhead environment dives without having to source twin cylinder sets. When diving in remote locations, the transportation of single diving cylinders, especially by hand, may be less physically taxing. Sidemount harness can be lighter and less bulky than back-mounted alternatives – allowing for easier and cheaper air travel.Accessibility
Unlike back-mounted cylinders, the sidemount diver has immediate access to, and can see, the regulators and tank valves of their cylinders. This enables quicker and more certain problem identification and resolution, without requiring 'behind the head' shut-down drills that require a higher level of joint and suit flexibility and the ability to identify and correctly operate equipment which is out of sight.Low profile
Sidemount diving configuration places the cylinders under the diver's armpits, in line with their body, allowing the diver to pass through smaller restrictions than would be possible with back-mounted cylinders. The ability to remove tanks and push them in front allows the diver to pass through very small passages and holes when penetration diving – being limited only by the bulk of their bodies and diving suits. Streamlining for reduced drag while swimming is not always achieved.Safety
Increased accessibility to regulator first-stages and cylinder valves improves efficiency and speed of critical cylinder shut-down procedures, allows immediate gas-loss identification and provides the diver with quick access to alternative contingency procedures, such as swapping regulators between cylinders, manual operation of a cylinder valve to control gas flow through a regulator which is free-flowing, or to allow breathing directly from the tank valve.Mounting the cylinders at the diver's sides reduces exposure of valves and regulator first-stages to impact and abrasion damage, or accidental shut-down through roll-off against a ceiling. It also significantly reduces the risk of entanglement behind the diver, where it is most difficult to rectify.
Comfort
Some divers will testify that sidemount diving configuration offers greater stability and easier-to-attain trim and control in the water. It is also claimed to be less physically tiring to carry, and get into, sidemount equipment than back-mounted doubles – especially when operating from a small boat or a rough shore entry.The ability to attach, remove and replace cylinders while in the water allows the diver to avoid carrying twinned cylinders. The reduced physical exertion when conducting regulator shut-down procedures is a major benefit to divers who suffer from shoulder or back discomfort or reduced mobility.
Redundancy of gas
Technical divers have generally used a redundant gas supply system, either isolation-manifolded or independent back-mounted cylinders. Recreational divers have traditionally resorted to using buddy supplied gas, or relatively small bailout 'pony cylinders' or 'ascent bottles' for out-of-air emergencies. Whether attached to the primary cylinder, or slung at the chest, these cylinders often present problems with stability and streamlining, whilst not always providing more than a bare minimum supply of air for emergency ascent. Sidemount diving with two equal-sized cylinders helps resolve stability and streamlining issues, and can ensure that an adequate redundant reserve of air is maintained, similar to back-mounted twins.Back-mounted manifolded cylinders provide easy access to the whole gas supply in the event of a regulator failure and shut-down. However, the manifold itself creates additional potential o-ring failure points, and a major leak at the manifold will deprive the diver of at least one-half of the remaining gas supply. Independent cylinders, when sidemounted, provide more reliable gas redundancy, and allow greater access to all remaining gas by switching regulators between cylinders or feather breathing, provided the diver is competent at the additional skills required.)
Convenience
Sidemount does not require complicated hardware. It can be done using the most commonly available rental cylinders, needing only simple rigging. If the diver is also renting the regulators, they can usually be reconfigured for the purpose with a simple wrench and one or two low pressure port plugs. The harness and buoyancy compensator can be light and compact for travel.Problems
Sidemount diving can increase the task loading on the diver, and can cause more drag when swimming, depending on which alternative configuration is compared. The diver's head may be more vulnerable to impact with the overhead, due to lack of the back gas set. This may be mitigated by the use of a helmet.Sidemount for the recreational diver
The benefits for cave diving and wreck diving with tight penetrations are largely accepted, but they are not so obvious for the typical recreational diver.Most recreational divers rely on their buddy for bailout gas, and do not carry a redundant gas supply. The position of the cylinder valve behind the head has proven to be reasonably safe in millions of dives, though some divers do have physical difficulty reaching the valve while wearing the set, particularly if the cylinder is mounted relatively low on the harness. Though sidemount divers may benefit from being easily able to see and manipulate valves, first stages or cylinders, this is rarely required in recreational use. In single cylinder diving there is seldom a reason to shut a cylinder valve while diving, and there is no need for changing cylinders or managing different gases. The recreational diver with a single cylinder is not supposed to enter low overhead spaces, so the single valve behind the diver's head is unlikely to come into contact with objects which might roll it closed.
Divers with back problems often benefit from sidemounting, since the weight is transferred from the spine to the hips and shoulders and the back is kept less rigid. Furthermore, sidemount divers benefit from an increased gas supply, potentially allowing longer dives. Tucking the cylinders under the arms reduces water resistance, potentially increasing kick efficiency.
Sidemount divers using two cylinders will generally benefit from improved stability and balance due to the lowered center of gravity relative to backmount divers and improved trim due to the more adjustable designs of common sidemount harnesses. When using a single cylinder in sidemount some of that benefit is negated since balance is off, though with an aluminium cylinder and proper body tension single cylinder sidemount diving is easier and more comfortable than many divers expect.
Transportation on the surface can be easier either with backmount or with sidemount, depending on requirements. Carrying weight on the back is less stressful on the spine than carrying it to one side when out of the water, so for carrying a single cylinder, a backpack-style backmount BCD can be more comfortable. A heavy twinset can be unwieldy and heavy on the back though. In the case of sidemount, the two cylinders can be carried separately, distributing load and making transport on rough ground easier.
Sidemount divers generally have more options available for donning and doffing than backmount divers, since they can choose to don or doff their single or double cylinders either on the surface or while in the water, depending on preference and conditions. Individual cylinders can be passed to and from a boat crew or a buddy on shore who is not burdened by gear, or lowered and raised by a line. In rougher conditions, cylinders can be prepared for hand-off below the surface and quickly passed to boat crew or attached to a line for later retrieval.