Table of Contents
- 1 Sidemount Diving Course Notes
- 1.1 1. What is, and isn’t, Sidemount Diving?
- 1.2 2. Why choose Sidemount?
- 1.3 3. A brief history of Sidemount Diving Development
- 1.4 4. Sidemount Training
- 1.5 5. Sidemount Diving in the Overhead Environment
- 1.6 6. Primary Commercial Sidemount Diving Systems Currently Available
- 1.7 7. Configuring a Sidemount Diving System
- 1.7.1 Harness
- 1.7.2 Cylinders
- 1.7.3 Regulators
- 1.7.4 Bungees
- 1.7.5 Cylinder Bands/Cam-bands
- 1.7.6 D-Rings
- 1.8 8. Gas Management
- 1.9 9. Stage/Deco Cylinders
- 1.10 10. Critical Sidemount Diving Skills
Sidemount Diving Course Notes
By Andy Davis, ANDI & PADI Sidemount / Tec Sidemount Diving Instructor
See also ‘Sidemount Course Powerpoint Presentation‘
See what courses I have to offer – Andy Davis Sidemount Training, Subic Bay
1. What is, and isn’t, Sidemount Diving?
Sidemount diving is the, now increasingly formalized, approach towards conducting dives with 2 or more primary cylinders secured at the side of the body and in line with the torso – with no cylinders on the diver’s back. A common feature that defines sidemount configuration is the use of bungee cords to provide an upper attachment on the cylinder valve, normally routed from behind the diver’s upper back, whilst the lower cylinder is secured to the diver’s lower harness (butt-plate or waist D-rings) via bolt-snaps.
Sidemount staging is the practice of using sidemount configuration (bungee loops and/or buttplate rails) 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.
Stage-only diving refers to the use of standard deco/stage cylinder configuration, without back-mounted cylinders, on an otherwise standard, or partially modified tec/rec BCD. The lower cylinder is attached to waist D-Rings and the upper cylinder to shoulder D-Rings, both via direct bolt-snap. Some divers (untrained in specific sidemount diving techniques) often incorrectly assume this approach to be sidemount diving. No bungee cord is utilised in the upper attachment, causing the cylinders to hang low beneath the diver and not in line (parallel) with their torso beneath their armpits. Without modification of the BCD design, the lack of back-mounted cylinders also causes taco’ing of wing designs and considerable instability.
Monkey diving is the term used to describe the use of sidemount configuration/procedures, whilst only carrying a single cylinder. It is presented as an option on some recreational level sidemount courses (dependant on agency) and may also be a considered strategy for certain overhead-environment (cave/wreck) penetrations. The use of a single cylinder requires a strategy of counter-weighting to prevent diver instability in the water.
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 couldn’t 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.
2. Why choose Sidemount?
The sidemount diving approach offers divers significant benefits to the flexibility of their approach. Unlike back-mounted doubles, acquiring and transporting sidemount suitable cylinders is often much more convenient and accessible. Sidemount diving configuration allows the travelling diver to conduct technical and/or overhead environment dives without having to source traditional back-mounted cylinders. When diving in remote locations, the transportation of diving logistics, especially by hand, is considerably less physically taxing.
Sidemount diving equipment is also considerably lighter, and less bulky than back-mounted alternatives – allowing for easier and cheaper (considering the rate of many airline’s excess baggage costs) travel.
Unlike back-mounted cylinders, the sidemount diver has immediate access to, and observation of, the regulators and tank valves of their cylinders. This enables immediate problem identification and allows swifter resolution, without recourse to ‘behind the head’ shut-down drills that require a higher level of mobility, flexibility and freedom to operate.
Sidemount diving configuration places the cylinders under the diver’s armpits, in line with their body. This decreases water resistance (improving air consumption and reducing fatigue) whilst also allowing the diver to pass through smaller restrictions than would otherwise be possible in back-mounted cylinders. The flexibility to remove tanks, and propel them in front, allows the diver to pass through very small passages and holes – being limited only by the size of their bodies and exposure protection.
Increased accessibility to life-supporting regulators, first-stages and 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 safety procedures; such as regulator swapping (between cylinders), valve-‘feathering’ to access gas within a cylinder whose regulator is malfunctioned/free-flowing… or even breathing directly from a tank valve.
In addition, stowage of the cylinders next to the diver’s torso, and beneath his armpits, serves to protect vulnerable valves and regulator first-stages from collision, impact and abrasion damage, or accidental shut-down through contact with a ceiling. It also significantly reduces the risk of entanglement behind the diver, where it is least easy to rectify.
Many divers will testify that sidemount diving configuration offers greater stability and easier-to-attain trim and control in the water. It is also less physically tiring to carry, and get into, sidemount equipment than with traditional back-mounted doubles – especially when operating from a small boat or a rough shore entry.
The ability to attach, remove and replace cylinders whilst in the water allows the diver to avoid ever having to carry heavy-weight back-mounted cylinders. This is combined with reduced physical exertion when conducting regulator shut-down procedures, which is a major benefit to technical divers who suffer from shoulder or back discomfort or reduced mobility from old injuries.
Redundancy of Gas
Whilst technical divers have always utilized a redundant gas system, either isolated-manifold or independent back-mounted cylinders, recreational divers have traditionally resorted to using ‘pony cylinders’ or ‘ascent bottles’ as contingencies against out-of-air emergencies. Whether attached to the primary cylinder, or slung at the chest, these cylinders often presented problems with stability and streamlining, whilst simultaneously only providing a bare minimum supply of air for emergency ascent.
Sidemount diving with two cylinders helps resolve stability and streamlining issues, and ensures that a truly capable redundant supply of air is maintained.
Technical divers debate the pros and cons of independent cylinders versus isolated-manifold doubles. Back-mounted manifold cylinders provide easy access to complete gas supplies, in the event of a regulator failure and shut-down. However, the manifold itself creates additional o-ring failure points and a failure in that component will deprive the technical diver of, at least, ½ of his remaining gas supply. Independent cylinders, when sidemounted, provide true gas redundancy, whilst offering access (via regulator switching or valve breathing) of all remaining gas.
3. A brief history of Sidemount Diving Development
The 1960′s – UK Sump Diving
The concept of sidemounting cylinders originated from cave diving in the UK, during the 1960’. During ‘dry’ explorations of Wookey Hole, the River Axe and other underground systems, divers occasionally encountered submerged passages that blocked further exploration. These cavers began incorporating SCUBA equipment specifically to progress beyond underwater areas. 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/replaced and retaining the capacity to squeeze through the tightest restrictions.
The nature of these ‘dives’ in cramped sumps did not prioritize the need for buoyancy control or underwater propulsion – so the bare minimum needed was a mask, a cylinder, a regulator, a method of attachment to the body and, only on rare occasions, a set of fins.
The ‘English System’
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. Swimming efficiency, reduced water resistance, trim and buoyancy control were not generally required due to the nature of those caves. At the time, this approach to ‘wet’ cave exploration was generally called the ‘English System’.
The 1970′s – Florida
During the 1970’s the ‘English system’ began to be incorporated by American cave diver, operating in Florida. Those cave systems were predominantly ‘wet’ and involved prolonged swimming with SCUBA…thus, more emphasis was paid towards developing the diving performance of the system, in particular buoyancy and trim. Divers required buoyancy control devices for extended fining and began shifting the location of the cylinders from against the thigh, up to the armpit/against the torso.
These exploratory level cave divers began by making their own systems, using and adapting ‘off-the-shelf’ SCUBA equipment for their needs or creating configurations ‘from scratch’, based upon webbing harnesses and improvised bladders for buoyancy. One popular approach to improvised bladders was the MSR Dromedary hydration system (like a ‘Camelbak’), which would be sewn/bolted to the rear of the harness and operated by orally inflating and deflating through the adapted ‘drinking tube’.
The 1990′s – Release of First Commercial Rig
In the mid-1990’s, Dive Rite produced the first commercial sidemount diving system, focused on the newly released ‘Transpac’ harness. Other cave divers continued to manufacture their own D.I.Y. configurations.
At this time, the use of sidemounted configuration was primarily restricted to a small number of exploration-grade cave pioneers.
The widespread popularity of sidemount diving systems did not emerge until the mid-2010’s, when the growing popularity of technical and cave diving became exposed to sidemount proponents on the internet – who were offering an alternative approach that matched the minimalism and functionality of the popular ‘DIR/Hogarthian’ back-mounted systems, whilst offering advantages in flexibility, comfort, accessibility and, highly debated online, .. safety.
The 2000′s – Cave Diving Popularity and Sidemount Evolution
The increasing interest in sidemount diving configurations prompted several manufacturers, and individuals, over the last few years to design and sell their own designs of a sidemount system. Hollis, OMS, UTD developed equipment, whilst Steve Bogaerts (a UK born cave pioneer, who lives and cave-dives in Mexico) released the very popular ‘Razor’ system and began teaching a specific to model training program for his rig.
At this time, several technical scuba agencies developed formal sidemount training programs and incorporated sidemount diving configuration as an equipment option within existing technical diving programs.
The late 2000′s – Sidemount Goes Mainstream
When PADI instructor, Jeff Loflin, devised a distinctive sidemount diving speciality course, it proved extremely popular, being replicated by many PADI technical-level instructors. This soon led to PADI devising standardised sidemount diving programs at both recreational and technical levels – truly cementing sidemount as an increasingly attractive and mainstream option for both recreational and technical divers alike.
4. Sidemount Training
Level 1 – Recreational (Rec or Basic Sidemount)
Basic sidemount training is offered by most agencies, and aims to develop initial equipment familiarity and operation. At this level, students are taught to adjust, fit and operate the sidemount rig, whilst diving with 1 or 2 cylinders maximum.
These training courses then develop core diving skills that are specifically relevant to sidemount – namely; trim, buoyancy, alternative propulsion techniques and cylinder handling in the water. Many basic courses also teach supplementary diving skills, such as DSMB deployment and variations on open water skills, such as inverted (upside-down) fining and inverted mask-clearing. Knowledge development covers topics like; gas management, dive planning and equipment considerations/options.
Level 2 – Technical (Tec or Advanced Sidemount)
Technical, or advanced, sidemount courses develop basic sidemount skills with a focus on technical diving activities. A higher level of equipment proficiency and diving skill is required, as additional stage/deco cylinders will be added to the rig, enabling mixed-gas and accelerated decompression procedures to be conducted. Technical sidemount courses often develop utilisation of the sidemount rig for increasingly demanding penetration skills – teaching students how to manipulate cylinders in order to pass through restrictions.
Some agencies/instructors also provide environment specific sidemount courses at this level, focusing on sidemount diving within the cave or wreck overhead environments. These courses might incorporate the respective knowledge, skills and procedures from the cave or wreck syllabus, but adapted and focused only on performance in sidemount configuration.
Level 3 – Expedition
Expeditionary level sidemount courses represent the highest level of training and are targeted at experienced technical divers, who would choose to use sidemount configuration for more demanding and complex diving projects. Exploratory level training is most commonly linked with a specific environment, such as cave.
5. Sidemount Diving in the Overhead Environment
Sidemount diving originated as a solution for cave divers, who needed a compact, streamlined configuration capable of allowing access through the smallest of restrictions underwater. When considering dives within an overhead-environment, such as cave or wreck, the ability to quickly and easily remove and replace cylinders on-the-go is extremely beneficial.
Not only does this permit passage into areas previously inaccessible to back-mounted divers, it increases the potential speed of movement through a passage. When diving emergencies happen in caves or wrecks, speed of exit can be a life-saving factor.
Sidemount configuration is ideally suited to penetration diving in the cave and wreck environments. A well designed sidemount rig will minimise the risk of entanglement, whilst also reducing the risk of entrapment in tight spaces. It provides access through smaller spaces, allowing greater exploration and discovery. It also helps prevent catastrophic impact damage to otherwise vulnerable (when back-mounted) regulators/valves, reducing the risk of lost gas.
6. Primary Commercial Sidemount Diving Systems Currently Available
Designed by Steve Bogaerts, the Razor system offers a distinctly minimalist approach, which makes the enables the diver to make best use of the advantages of sidemount diving. It is based on a ‘Hogarthian’ principled harness, with a small capacity bladder (evolved from the MSR Hydromedary) on the diver’s back. It has a single-piece bungee, which routes across the diver’s back to provide attachments on both sides. It has a bottom/side-mounted inflator and OPV.
UTD – Z System
The Z-System shares many attributes with the Razor, whilst also incorporating elements that allows it to adhere to UTD principles and retain ‘DIR compatibility’. Most noticeable of these is the optional (Z-)manifold system that allows sidemount cylinders to be linked (along with LPI and drysuit inflator), replicating the benefits of isolated manifold back-mount systems and ensuring procedural compatibility in mixed back-mount/sidemount/CCR teams.
It also has a number of optional trim weighting solutions, as well as different bladder options that enhance suitability for technical doubles, recreational sidemount and redundant bladder demands.
Golem Gear Armadillo A2 and S
The Armadillo is a sidemount specific rig, with integral buoyancy compensator and limited adjustment harness. It has an inter-changeable inflator/OPV, allowing divers to decide how they want it to be configured. The harness can be re-configured to allow incorporation of a climbing harness (rather than standard waist belt). A short fitting model (S) has also been released.
The OMS system is a hybrid, allowing inter-changeability between back-mounted and sidemount configurations. The ‘Profile’ adapter fits over the rear of the backplate/wing, to prevent taco’ing and provide attachment points for the bungees and ancillary equipment.
The ‘Tesseract’ wing is similar to other OMS double-tank wings, but was adapted for maximum compatibility with the ‘Profile’ adapter; for instance, the inflator is off-set at the top, to allow the adapter cover/protector to fit over the top of the wing, whilst there are also dedicated attachment points at the top and bottom to ensure maximum fit between the wing and the adapter.
When used with other wing systems, considerable user adaptation and initiative are required to make the ‘Profile’ adapter fit. It will, however, fit any wing/backplate that has standard 11” hole spacing. It is available in double/redundant bladder.
Dive Rite Nomad ESP / JT / XT
The Nomad is available in 3 models, suitable for different uses and diver preferences:
The JT is the most minimalist version (but not ‘hogarthian’ in approach) utilising a ‘modified’ deluxe transpac-like harness, with a 50lb donut wing, an off-set inflator and three OPVs (top and both sides). It utilises a unique ‘daisy chain’ attachment at the diver’s back for attachment of sidemount bungees – preventing a hernia effect on the bladder. It is supplied with ‘ring type’ bungees, which can add security for water entries and in-water fitting of the cylinders, but can also be used with standard sidemount bungees.
The ESP is aimed at the open-water/recreational market. It is hybrid – allowing single back-mounted cylinder or sidemount use, with adjustable buoyancy capacity and dual/single bladder options. It can also be used with back-mounted doubles, if extra ‘stability plates’ are purchased.
The XT is based around the transpac harness and is modular. The wing has up to 50lb buoyancy capacity and is available in single or redundant bladder options.
The Hollis SMS (Side Mount System) 100 is an integrated, hybrid sidemount system, which allows use of sidemount, back-mounted doubles and single tank configurations. It features an adjustable (rather than single-piece) harness, more akin to jacket BCD, or ‘comfort/deluxe’ harness design and is available with a single or double bladder.
Hollis SMS 50
The Hollis SMS 50 is a recent release at the time of writing. It is a dedicated sidemount rig, which features a lower capacity bladder than the SMS100 and a much more minimalist and ‘Hogarthian’ inspired harness system. It also has dedicated trim pockets on the upper and lower harness.
7. Configuring a Sidemount Diving System
The correct fit of the sidemount harness is critical to the stability and function of the rig. Harness designs tend to follow either the single-piece (Hogarthian type) or adjustable (Comfort/Deluxe type) patterns. For adjustable harnesses, the initial selection of suitable size is obviously important; it can then be tightened to fit snugly once worn.
Single-piece harnesses require more care and attention in the initial set-up, but once correctly sized, should fit like a glove. The single-piece harness needs to be sized and adjusted as one of the first steps in equipment set-up. As with preparing a back-mount/hogarthian harness, it is well worth devoting some time to getting this right in the first instance.
Whilst every diver will have a personal preference on harness style, it should be noted that hogarthian-type/ minimalist / single-piece harnesses are generally regarded as being more streamlined, less inclined to entanglement and less likely to cause task loading/stress on the diver. The principle of K.I.S.S. (Keep It Simple ____) is highly valued within the cave and technical wreck communities.
Aluminium cylinders are generally preferred for sidemount diving, as their buoyancy properties enable far better trim and streamlining of the cylinders next to the divers’ body. There is also less of a drastic buoyancy change should the cylinder be removed. 200 Bar DIN valves are normally recommended by sidemount divers.
Sidemount cylinders need to have balanced buoyancy characteristics, if effective trim is to be achieved. This obviously entails selecting matching (brand and capacity) cylinders. However, the actual buoyancy performance of both cylinders should be assessed, as sometimes even matching brand/capacity cylinders can have mis-matched buoyancy; for instance changes in manufacturing process over time.
The size of selected cylinders is also important. Needless to say, the cylinders must supply sufficient gas for the dive/s to be conducted. However, many experienced sidemount divers will state that unnecessarily large cylinders should be avoided as they add bulk and reduce streamlining. These factors can degrade the ability of the diver to penetrate restrictions and can also increase air consumption – thus eliminating the benefit of having more gas in the first place.
When selecting cylinders, it is wise to arrange some trial sessions, so that you can investigate how well a specific brand/model/capacity of cylinder operates in sidemount configuration. Differences in length, design and thickness can have a notable impact on how well the cylinders hang from the diver. Ideally, the cylinders should be equipped with left and right sided valves, enabling a ‘mirror’ configuration on both cylinders – with the valve handle pointing outwards and the regulator upwards/inwards towards the diver.
Some sidemount divers prefer cylinder valves that are designed for back-mount doubles. The extra protrusion of the valve (where the isolator manifold would otherwise be screwed) assists with securing the bungee placement around the tank neck/valve.
Long Hose / Short Hose
Most agencies teach sidemount regulator configuration in a pattern that reflects hogarthian/back-mounted set-ups, particularly in respect of including a long (5’-7’) hose for air-sharing in over-head environments and through restrictions. Some courses don’t demand this at Level 1 training, but all do at Level 2 and above.
A suggestion for regulator configuration might be:
- SPG on a 6” hose
- LPI hose, sized to fit the particular sidemount design (upper or lower mounted inflator)
- Short-hose regulator with necklace bungee (28-36” hose)
- SPG on a 6” HP hose
- LPI hose (if using redundant bladder design) or dry-suit hose.
- Long-hose regulator (5’-7’), with bolt-snap for securing.
The use of a right-angle adaptor may be considered on the left-side regulator, or both, of hose routing creates a pull on the regulator and strains the diver’s jaw.
The choice of regulator brand should reflect some consideration of hose routing requirements; with sufficient and well located ports to enable a clean, streamlined configuration. Hoses should route close to the diver’s body, without protrusion beyond the diver’s outline.
In general, a regulator design that is preferable for back-mounted doubles will also be suitable for sidemounting.
As mentioned earlier, many sidemount divers prefer a 200Bar DIN regulator. A-Clamp type regulators should definitely be avoided, as the protruding handles present an entanglement risk, whilst any impact can more easily dislodge the regulator and cause o-ring failure.
The short-hose regulator (left-side) runs behind the diver’s neck from the left, and is located in the bungee necklace worn around the diver’s neck. The long-hose regulator (right-side) routes similarly to back-mounted doubles in a ‘hog loop’ across the torso and around the diver’s neck from the left side. Any surplus long-hose length is retained by rubber loops against the left-side cylinder.
Miflex/Nylon-braided hoses may be considered for the short-hose regulator and LPI hose/s. Many technical divers are disinclined to use nylon-braided long hoses, as they are less negatively buoyant (“floaty”) and have less friction – making them harder to ‘hog loop’. In addition, some divers note that they are more inclined to be abrasive against the back of their neck. Miflex HP (SPG) hoses have encountered reliability issues and are not recommended at this time.
Both cylinders/regulators are fitted with SPGs. The use of 6” HP hose (not tied back on the reg) enables the diver to manipulate the gauges for reading, whilst maintaining a streamlined configuration with less risk of snagging.
Both cylinders should feature 1-2 rubber loops (1” wide, cut from a car inner-tube, or specifically bought for purpose) to retain hoses whenever they are not in use.
Most commercial available sidemount diving systems are provided with an appropriate bungee system. However, the diver may need to re-size those bungees, or alter their positioning, in order to achieve a comfortable fit and create good cylinder trim. If adjustment is necessary, spending some time in shallow water, with near-empty tanks, will allow the diver to ascertain an optimum length and positioning of their bungees.
Divers may opt to create their own bungees, as replacements or reserves. It is recommended to get ‘marine grade’ bungee (from a boating/chandlery shop).
For separate bungees, start each bungee at approx 2’ length or for a continuous bungee (runs across the back), start at approx 5’ length; then experiment, adjust and shorten until an optimum length is achieved. A bungee may be continuous length, routed behind the diver’s back or two lengths, each secured behind the diver’s back to an appropriate attachment point. Separate bungees need a quick-link for attachment at the rear, and a bolt-snap for attachment to the chest D-rings.
Whilst adjusting the length, use zip-ties to secure the bungees to the quick-link and bolt snap (thread through and zip-tie bungee against itself). Once an optimum length is achieved, more permanent bungee staples can be used to secure the snaps/quick-links. Some divers recommend using some wide diameter heat shrink tube to neaten the bungee attachment.
Some form of secure band is required on each cylinder to allow attachment of a bolt-snap or butterfly snap. Butterfly snaps may be preferred by divers who suffer reduced dexterity due wearing thick gloves. However, the cave/technical wreck communities in general do prefer bolt-snaps as there is less risk of accidentally trapping a line.
The snap is used to clip the cylinder to either butt-mounted rails, or D-rings on the side of the diver’s waist strap. It is attached to a short length of rope, knotted at the other end, which is then ‘trapped’ by the band. There are two approaches to band selection:
Using conventional BCD cam-bands allows individual cylinders to be quickly set-up and disassembled. This is a benefit when using regular rental tanks from a dive centre – and consequently appeals to travelling sidemount divers.
The cam-bands should be configured with the buckle inner-most (towards the diver) and with the release mechanism pointed backwards/upwards (when worn). This offers the most protection against entanglement/ entrapment and accidental opening if snagged. It is best practice to secure the entire cam-band with a loop of rubber bungee (cut a 2” loop/section from a car tire) to hold it in place and reduce risk of snagging.
If the diver possesses their own tanks, or if the tanks will be used as dedicated sidemount diving cylinders, then a more permanent, and streamlined, solution is to use adequately sized hose clamps. These are fitted onto the cylinder and tightened with worm screws. Any excess material should be cut-off the band, beyond the worm-screw.
The screw itself can be protected from snagging by wrapping it in a short (1-2”) length of hose pipe.
Positioning of the Cylinder Bands
The positioning of the cylinder band/bolt-snap plays a direct role in the trim of the sidemount cylinders. Lowering or raising the position of the band will have two effects; it will pull the cylinder up or down alongside the diver’s torso (allowing correct positioning of the valves under the armpits) and it can help control the tendency of aluminium cylinders to float ‘butt-high’ above the diver as gas is consumed.
The ideal positioning of bands on the cylinder will be determined by factors such as the diver’s height and the design of the sidemount harness worn. Spending some time in shallow water, with near-empty tanks, will allow the diver to ascertain an optimum position for their cylinder bands.
On hogarthian type harnesses, or where you can otherwise decide/adjust/modify your configuration, most sidemount divers will recommend low-profile D-Rings for cylinder/bungee attachment. Not only do these reduce the risk of snagging, but also hold the cylinder more tightly and securely against the body – increasing stability and aiding trim management.
Some sidemount divers opt to fit sliding D-rings, or an extra pair of D-Rings, on the waist belt of the harness – as this permits the cylinders to be progressively lowered during the dive, allowing the maintenance of correct tank cylinder as the tanks become more buoyant.
8. Gas Management
Unless utilising a manifold system (i.e. the UTD ‘Z-Manifold), the sidemount diver is operating two independent tanks during their dive.
This requires consideration in gas management in order to maintain balance between the cylinder buoyancy during the dive and also, most importantly, to ensure that sufficient gas is reserved in each cylinder to permit an air-sharing exit/ascent from the dive.
Rule of Thirds and Reserves
Most technical and overhead-environment divers will maintain the ‘rule of thirds’ as the least conservative option when diving sidemount. Because air-sharing will always remain a possibility, it is essential that both cylinders maintain an independent reserve of, at least, 1/3 capacity.
It is not sufficient to drain one cylinder, retaining your reserve in the other.
Balancing Cylinders – Regulator Switching
To maintain balance (approximately matched buoyancy characteristics) between cylinders, there is a requirement for switching regulators during the dive.
One method of maintaining cylinder balance is to swap regulators for every 1/6th cylinder gas consumption. This would mean each regulator was breathed from twice, before reaching the gas turn-point (2/3rd) and a further two switches on each regulator until the reserve (1/3rd) was reached.
An alternative method (simpler, but less refined cylinder balancing) would be to switch regulators with every 1/3rd gas consumed (on each cylinder). This would mean each regulator was used once, before reaching the gas turn-point (2/3rd) and once more, per regulator, before reaching reserve level (1/3rd).
Draining a Tank to Reserve, then switching
It is not possible to breath from a single cylinder until the turn-point, and then switching. This would leave insufficient gas remaining in that cylinder for an air-sharing exit/ascent – as the diver would only have 1/3rd of a cylinder, not 1/3rd total supply for that exit.
Another Benefit of Frequent Regulator Switches
Regular regulator switching also helps ensure that neither regulator becomes unworkable – an especially prudent measure when sidemount diving through restrictions in high silt/mud conditions.
9. Stage/Deco Cylinders
For technical/decompression diving, there are numerous options stage/deco cylinder stowage.
Cylinders are typically configured in the ‘standard’ manner, with bolt-clips/band at the bottom and a loop around the cylinder neck with another bolt clip. The primary decision for a technical sidemount diver is whether to store the stage cylinders above, or below, the sidemounted primary cylinders.
Securing them below the primary sidemount diving cylinders, in a traditional manner attached to waist/butt D-rings and chest harness D-rings, provides easier access for removal, should they be staged along the way, but causes them to hang lower below the body. Some sidemount divers seek to rectify this by adding further bungee options to tighten the tank valve into their body.
The alternative method is to stow the stage/deco cylinders above the primary sidemounts. This has distinct advantages in respect of cylinder trim and overall streamlining, although it can pose further complications in attachment, depending on the harness system used.
Sorenson/Hires – Bungee Staging
One solution for upper stage bottle attachment was popularized by Edd Sorenson and Lamar Hires. This involves rigging the bottom clip higher than usual (for a stage tank) and using further loop of bungee cord around the tank neck to connect the top bolt-snap. The additional flexibility offered by the bungee permits easier attachment/ disengagement of the stage, whilst keeping it more snugly against the diver’s torso. The raised position of bottom clip serves to pull the stage cylinder lower on the diver, below the armpits.
The added advantage of mounting stages about primary sidemounts is that the (full) stages will rest upon the sidemounts, helping to prevent them rising as air is consumed.
10. Critical Sidemount Diving Skills
The following represents a summary of the critical skills taught by a spectrum of agencies at various sidemount diving levels. Please note that this is a very generalized list, covering the sidemount diving syllabus of multiple agencies – there are differences between agencies:
Level 1 – Recreational (Rec / Basic Sidemount)
- Equipment Configuration and Assembly
- Pre-Dive Safety Checks
- Attaching tanks on land and at the surface (shallow and deep water)
- Descent Procedures
- Trim and buoyancy
- Propulsion Techniques – Frog Kick, Modified Flutter Kick, Back Kick, Helicopter Turn
- Gas Planning and Management (Independent Cylinders)
- Regulator switching
- Air sharing – Donor and Receiver
- Tank positioning and Adjustment for continual good trim
- Removal of single tank while swimming
- Removal of two tanks while swimming
- Inverted and/or vertical mask clearing
- DSMB deployment Ascent Procedures
Level 2 – Technical (Tec / Advanced Sidemount)
- Equipment configuration and assembly
- Stage bottle configuration and assembly
- Descent procedures
- Trim and buoyancy
- Propulsion techniques – Frog Kick, Modified Frog and Flutter Kick, Back Kick, Helicopter Turn
- Propulsion techniques (cont)- Finger walking, Pull and Glide.
- Sidemount diving mobility – inverted propulsion, rolls, loops etc
- Gas planning and management, inc decompression gasses.
- Team drills and development
- Guideline/penetration contingency drills
- Sidemount regulator shut-downs
- Feather breathing from a regulator
- In-water stage bottle attachment, removal and replacement
- Sidemount decompression procedures
- Practice of all sidemount skills (L1 &L2) within specific over-head environment (cave/wreck)