Sidemount diving
[14] 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.
[14] 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.
Recreational divers have traditionally resorted to using buddy supplied gas, or relatively small bailout 'pony cylinders' or 'ascent bottles' for out-of-air emergencies.
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.
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.
However, because they operated in very confined spaces, and most exploration remained primarily 'dry', they began experimenting and improvising with extremely minimalist configurations, minimising bulk, allowing cylinders to be easily removed and replaced, and retaining the capacity to squeeze through the tightest restrictions.
[9] Many of these early sump explorers adopted an approach based upon a sturdy belt, with attached cam-band, that allowed a cylinder to be dropped in and carried alongside the outer thigh.
This allowed them to crawl, or wriggle, through the dry cave sections, whilst presenting a secure method of attachment for passing through submerged areas.
[9] Swimming efficiency, reduced water resistance, trim and buoyancy control were not generally required due to the nature of those caves.
Divers required buoyancy control devices for extended finning and began shifting the location of the cylinders from against the thigh, up to the armpit and against the torso.
Hollis, OMS, UTD developed equipment, while Steve Bogaerts (a UK-born cave pioneer, who lives and dives in Mexico) released the popular minimalist 'Razor' system and began teaching a specific model training program for his rig.
Other agencies, such as ANDI, IANTD, SSI, TDI, UTD and ISE (Innerspace Explorers) also provide sidemount training at varied levels.
This is the evolution from sidemount pioneers who initially used lightweight hydration bladders (i.e. MSR) for their buoyancy requirements, with a basic harness for cylinder and weight attachment.
This is the evolution from sidemount pioneers who initially used home-converted BCDs/wing systems, typically in response to a higher buoyancy requirement from using steel cylinders/higher weighting needed for colder water exposure protection.
[25] Rigid Hogarthian style backplate and wing BCD systems may be modified by adding butt-plates, bungee cords and optional special sidemount buoyancy compensators.
An example of a commercial backplate and wing harness adapter, including integrated butt plate and attachment points for bungee loops, is the OMS Profile.
Examples of dedicated recreational sidemount rigs: A webbing harness with shoulder straps, waist belt and crotch strap, supporting a variety of sliders and D-rings for attachment of cylinders and accessories, with or without integrated weighting or separate weight belts, and with or without a back-mounted buoyancy compensator, which may be attached to the harness, or directly to the diver.
This style of harness may be off the shelf from an original equipment manufacturer or retailer,[40] or home made, as most of the parts are freely available or relatively simple to make.
As penetration distances into caves increased, the basic belt was replaced by a more sturdy harness with shoulder straps and padding on the waist band to distribute the load more comfortably.
Sidemount allows a low profile to penetrate tight restrictions in cave and wreck diving, and is convenient for carrying a bailout rebreather.
Sidemount rebreathers may also be more susceptible to major loop flooding due to lack of a convenient exhalation counterlung position to form a water trap.
Appropriate length and thickness bungees are critical to ensure that the sidemount cylinders remain in trim horizontally alongside the diver's torso with the valves under the armpits.
A higher level of equipment proficiency and diving skill is required; as additional deco cylinders will be added to the rig, enabling mixed-gas and accelerated decompression procedures to be conducted.
These courses are focused on maximizing the benefits of sidemount for passage through restricted and confined areas; and also teach multiple stage (additional tanks of bottom gas) diving techniques.
[citation needed] Access to courses at this level is typically reserved for fully qualified cave or technical wreck sidemount divers, who have significant experience and skill.
[14] The standard arrangement for sidemount is that all cylinders are independent, and each is provided with a single demand valve, an SPG, and on one or two, a low pressure inflator hose for buoyancy compensator and, if used, the drysuit.
This equipment provided a link between cylinders and dispensed with the need to swap regulators and balance tanks at the cost of adding several possible points of failure, and usually placing the valved manifold behind the neck.
Overhead environment divers find this an especially prudent measure when sidemount diving through restrictions in high silt and muddy conditions.
The UTD Z-system provides an approach to emulate back-mounted Hogarthian configuration by quick-connecting two primary gas supply sidemount cylinders to a manifold block mounted behind the shoulders on the Z-system harness, from which long hose primary and necklace secondary demand valves are supplied, reducing the demand valve arrangement to a functional approximation of the standard Hogarthian configuration at the expense of additional complexity of components.
