The Two Schools of Sidemount Diving Heritage
by Andy Davis
Over recent years, a plethora of new sidemount BCDs has been released onto the diving market. To the casual observer, the range appears wildly diverse. However, there are actually two primary ‘schools’ of sidemount design heritage. These schools were shaped and refined by the environmental conditions and needs of the first pioneers of sidemount diving.
The origins of sidemount diving come from Sump exploration in the UK. However, most of this exploration was dry caving, with only small submerged passages (sumps) that required scuba equipment. The UK sump divers typically carried small scuba cylinders, only of sufficient volume for very short passages, often hung at the waist from their existing cave harnesses.
The sidemount concept migrated to the cave diving communities in Florida and Mexico. These communities developed into two distinct schools of sidemount design; based on their buoyancy requirements, cylinder characteristics (steel versus aluminium) and regional diving preferences.
These two ‘schools of design’, Mexico Cave and Florida Cave, are very evident in the sidemount manufacturing market today. When selecting a suitable sidemount BCD for purchase, you should bear in mind that the history and development of sidemount designs are quite specific for cold or warm water demands; especially in regards to cylinder material and buoyancy requirement.
(above) An early Sump diving rig from the UK… the predecessor of modern sidemount diving.
Click here to read more about Sidemount Diving History
1) British / Mexico Cave Style
A typically minimalist and lightweight approach; generally used with aluminium cylinders which are ubiquitous in warm-water/tropical environments. Most popular with warm-water/wetsuit and travelling divers. Most often seen in Mexican cave systems and SE Asia.
Harness: A ‘Hogarthian’ inspired, bare webbing harness, using separate shoulder and lumbar plates connected via an adjustable length spine webbing strap. The adjustable spine length is necessary as the waist belt must be positioned low on the hips, to enable a suitable cylinder attachment point for aluminium cylinder trim.
Lower cylinder attachment: D-rings on the rear and front waist-belt (or sliding D-rings), necessary to shift the attachment point of aluminium cylinders as they transition from negative to positive buoyancy.
Upper cylinder attachment: Continuous, Loop, Sliding/Floating Loop or Independent bungees.
Wing shape: Triangle, diamond or rectangular/horizontal bladders (lift focused over the hips, less up the torso)
Example rigs: Razor 2.0, XDeep Stealth Tec/Rec/Classic, Apeks WSX-25/45, UTD Z-Trim, Aquamundo.
Influential Proponents: Steve Bogearts, HP Hartmann, Steve Martin, Gary Dallas
This is the evolution of sidemount pioneers who initially used lightweight hydration bladders (i.e. MSR) and converted truck or car inner tubes for their buoyancy requirements. These bladders were fixed onto a basic harness system for cylinder and weight attachment.
The evolution of lightweight sidemount rigs using a converted bladder and minimalist harness
Mexican Cave/English style is defined through the common use of aluminium cylinders and thinner wetsuits for warmer/tropical water diving. This diving required less buoyancy and weighting requirement. It favoured smaller, lighter rigs that could be used to penetrate through very small restrictions.
- These systems are usually the most lightweight and low bulk.
- They are designed to handle aluminium cylinders well.
- Minimalist design suits ‘DIR’ philosophy divers.
- Very modular and easy to modify or customize.
- Lower overall buoyancy provision
- Tendency for the wing to ‘beach ball’ (aka ‘turtle shell’) when fully inflated (if carrying multiple cylinders)
Aquamundo BCD – a modern example of the British / Mexico Cave sidemount school heritage
Mexican cave style BCDs historically struggled to supply a large buoyancy capacity without the bladder expanding too high (aka ‘turtle-shell’ or ‘beach ball’ effect) above the diver. More recent evolutions, such as the XDeep Stealth Tec, are now solving that problem through better design of the bladder to prevent or minimize the ‘beach ball’ effect at full inflation.
American / Florida Cave Style
These are the robust ‘big rigs’, generally used with higher capacity steel cylinders. They are popular with cold/temperate-water sidemount divers in the USA and Europe. Most often seen in Florida cave systems.
Harness: Typically an in-built harness to the BCD, with a hard or soft backplate, along with quick-release buckles and adjustments. No capacity to adjust the length of the harness – you can only lengthen the shoulder straps and let the backplate ‘hang’ lower if you want the wing further down the back.
Lower cylinder attachment: Butt-plate with rails, which is suitable for steel cylinders that will remain negatively buoyant for the duration of the dive. Not ideal for aluminium cylinders that should need re-positioning. A common, but ungainly, solution for aluminium cylinders on butt-plates is to add weights to aluminium cylinders to overcome the positive buoyancy as gas is consumed.
Upper cylinder attachment: ‘Old-school’ Loop, Independent w/Bolt-Snaps and Ring (DiveRite style) bungees,
Wing shape: Donut and horseshoe bladders (lift distributed evenly up the torso), sometimes with bungee restraints.
Example rigs: Armadillo, DiveRite Nomad, Hollis SMS100, SMS75, Halcyon Contour
Influential Proponents: Lamar Hires, Edd Sorensen, Rob Neto, Steve Lewis
This is the evolution from sidemount pioneers who initially used home-converted scuba BCDs/wing systems, typically in response to a higher buoyancy requirement from using steel cylinders/higher weighting needed for temperate/colder water exposure protection and thicker wetsuits.
An early Florida style sidemount conversion of a regular BCD (above)
and a more modern equivalent (below), the SMS100.
The Hollis SMS100 – a modern example of the American / Florida Cave school sidemount heritage
The history and heritage of these two distinct schools do not preclude one style being used effectively under different diving conditions. Indeed, one of the leading ‘British / Mexico Cave’ style sidemount manufacturers, XDeep, originates in Poland and their systems are regularly used for cold-water cave and mine diving. Likewise, ‘American / Florida Cave’ based manufacturers, such as Hollis and DiveRite are also very popular in tropical vacation destinations.
However, there is some debate that each school does offer some distinct optimization, according to the environments where it originated. If a school of design originated through the demands and needs of a particular environment, then it stands to reason that it will be the most optimal choice to be used in that environment.
Lastly, but not least, there is the ‘Confused School’ of sidemount BCD design. These are sidemount BCDs that either stems from one school but is impotently ‘tweaked’ to resemble the other, or they are sidemount BCDs designed by manufacturers that do not understand the heritage of either school and produce something that had no coherent design strategy.
An example of this is the Hollis SMS50; which is a tropical (aluminum cylinder) capacity BCD, but which uses a butt-plate / rails lower cylinder attachment that’s only suitable for steel cylinders; and comes supplied with over-powerful bungees that are meant to tolerate the weight of high capacity steel cylinders (and are totally over-kill for aluminum tanks).
Needless to say, warm-water divers using ‘confused school’ rigs will encounter a myriad of problems and barriers when trying to get their system optimized and keeping their cylinders in trim throughout the dive.
About the Author
Andy Davis is a RAID, PADI TecRec, ANDI, BSAC and SSI qualified independent technical diving instructor who specializes in teaching advanced sidemount, trimix and wreck exploration diving courses across South East Asia. Currently residing in ‘wreck diving heaven’ at Subic Bay, Philippines, he has amassed more than 9000 open circuit and CCR dives over 27 years of diving across the globe.
Andy has published many magazine articles on technical diving, has written course materials for dive training agency syllabus, tests and reviews diving gear for major manufacturers and consults with the Philippines Underwater Archaeology Society.
He is currently writing a series of books to be published on advanced diving topics. Prior to becoming a professional technical diving educator in 2006, Andy was a commissioned officer in the Royal Air Force and has served in Iraq, Afghanistan, Belize and Cyprus.
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