Tanks
Configurations vary but easy deployment, easy location and identification has to be of paramount importance. Double tanks with isolator manifold are commonly used, however in recreational diving independent tanks are used. A sufficient quantity of gas must be carried by the diver to allow completion of the planned bottom time, utilizing the minimum gas management rule for the type of diving enrolled in. Furthermore, this gas supply must allow for gas matching between divers.
The first item that needs to be addressed in tank selection for a specific dive is the needed gas supply and with it tank size resulting from factors such as body size, gas consumption, planned depth and duration. Experience has taught that the most logical approach to the question of gas supply can be best summed up by the statement in why there is a need for gas supply requirements. The first step in planning a dive involves computing the amount of gas needed for the dive. This includes primary mixes and decompression mixes. Decompression systems should provide a sufficient volume of gas to complete all appropriate stops with a minimum reserve supply. Each decompression gas cylinder must be appropriately marked as to its use, breathing gas and M.O.D. It’s also suggested that regulators be color coded or coded for easy identification. Mouthpieces should be protected to prevent from accidentally being used with the wrong mix during your decompression at the wrong depth.
The choice between tank materials will be dedicated by the environment and thermal considerations. The diver should be balanced in a way that he or she is neutrally buoyant with empty tanks at 10 feet / 3 Meter, comfortable for prolonged periods of time. In order to archive this diver must balance and trim their rig carefully for the environment one is diving in. Ample emergency gas volumes must be carried for the type of diving engaged in plus a redundant buoyancy device such as a dry suit or back up BCD must be worn on deeper dives.
Steel Tanks
While steel tanks are a great choice for cold water, wreck or cave diving due to their larger volume 104 or 121 cft / 15 or 18 ltr where the weight of the tanks is partially offset by the thermal protection due to dry suit sworn by most divers. Helium based breathing gases do affect weight and buoyancy underwater and must be taken into account.
Aluminum Tanks
Warm water, wet suit ocean diving is best done with aluminum 80 cft / 12 ltr tanks due to their lesser weight and with it lesser negative buoyancy at the bottom phase of the dive. If more gas is needed a aluminum stage tank should be added to fulfill breathing gas requirements.
Harness and Backplate / Softpack
While many dive gear manufacturers offering traditional BCD’s for recreational diving most wreck, technical or cave divers prefer the harness and backplate / softpack combination. Most recreational BCD’s can not be adapted for advanced forms of diving such as cave, technical and wreck diving and when a diver is ready to proceed to higher levels of training a new set of gear has to be purchased. Harness and backplate / softpack combinations eliminate that problem since they can be easily adapted for single tank recreational diving or technical and cave diving activities that may lay n the future.
Harness
A harness is used to attach the tanks to the diver sandwiching the wing style BCD between the tanks and the harness. The harness is attached to a backplate or a soft pack, which is then attached to the single or double tanks. A wing style buoyancy compensator has to be worn, attached to it a low pressure power inflator. The webbing attached to the backplate should be of the all through type with no connections, easy clips, rings or fast buckles intersecting the webbing. Such fasteners who make it easier to get into and out of the diving rig are potential failure points with disastrous potential to loose all of the equipment during the dive and in the long run it is more economic to change a basic webbing when it is worn out.
The crotch strap that has to be worn in order to prevent the unit from “riding up” should be without a clip but made from the closed loop type in order to prevent breaking clips during or prior to a dive. Crotch straps can be used as we for gear storage when a d-ring is attached to it at the back, or to attach a scooter to a d-ring in the front. The all one through webbing allows as well the placement of d-rings at any location throughout the harness to accommodate backup lights, stage tanks on the chest d-rings and gauges or reels on the waist d-ring.
Backplate
Backplate’s are made out of ABS plastic, aluminum or stainless steel. The stainless steel backplate is the most popular one since it is a little heavier and compensates for some of the weight a diver may needs to carry when diving with positive tanks or a dry suit.
Soft packs
The softpack harness systems on the market have the advantage of being well adaptable for the type of diving one is involved in ranging from recreational single tank diving to technical, wreck or cave diving to advanced forms of cave diving such as sidemount diving. The potential downside is the fast clips on the chest that could a dive fast out of the rig but could fail before or during a dive and be difficult or impossible to repair.
Buoyancy device
Back mounted wing style wing’s are known for superior trim characteristics in recreational openwater diving and advanced diving while openwater style BCD’s are not recommended due to limited lift capabilities, buoyancy characteristics, tank attachments and d-ring placement specially in advanced forms of diving such as technical, wreck or cave diving. The lift of the wing needed is depending on equipment weight, tank weight full and empty, scooters and stages if worn. Oversized wings and tight bungeed wings do have a tendency to create more drag in the water resulting in more energy spend and potential exhaustion of divers. All wing inflator and dry suit inflators if used should have the same connector to insure interchangeability of hoses and gas supply.
Wing style BCD
Wings are coming in a variety of lift capacities, styles and some sport a choice of features. The chosen wing should have the right amount of lift for the equipment, tanks and environment dived in. The corrugated hoses should be not as long as to touch the floor when diving close to the bottom and stirring up silt, damaging the environment or entangling the diver. Shorter size corrugated hoses are available to change the log size hose. In demanding environments such as inside wrecks or caves it is a good idea to have the inner bladder protected against puncture. Dump valves in the corrugated hose assembly can fail and present a potential problem. Dump valves on the bottom of the wing should be streamlined by cutting of the plastic knob to prevent entanglement.
Back up wings are recommended in deep dive applications or a dry suit can be used as a back up buoyancy device however dual bagged bladders are potentially creating added drag and degrade performance, this will in the end may slightly increase in gas consumption. The advantage of a dual bladder in the event of a BC failure is that the diver may still function normally and make a safe ascent. Diving with a single bagged bladder provides less drag and maximizes performance. Given a choice, most divers would prefer a configuration that reduces drag. But, if there’s a chance the single bladder could fail and this failure could be life threatening, it makes good sense to sacrifice being streamlined by increasing redundancy. By opting for greater redundancy, divers need to recognize this will increase their gas consumption. They must also realize it’s going to slow them down a little. Keep in mind dry suits can be used as a backup buoyancy control device.
Lift
Depending on fresh water or salt water diving, choice of tanks used, including exposure suit selection the amount of weight can vary greatly. Carrying to much weight should be avoided while conducting buoyancy checks before diving activity striving for a balanced rip that can be use with neither to much weight or to much gas in the lifting device. Drop weights can be used in stable depth caves and left close to the entrance when maximum depth is reached. V-weights can be used for double tanks used in-between double tanks and kept in place by the wing and harness while weight belts should be avoided.