Equipment Configuration

DIR Equipment Configuration

A good SCUBA equipment configuration should allow for the addition of items necessary to perform a specific dive without interfering with or changing the existing configuration. Diving with the same configuration not only helps solve problems, it prevents them.

Following is a list of equipment as that is of prime consideration:

  1. Mask: Low Volume mask reduces drag and requires less effort to clear it of water.
  2. Primary Regulator: Quality regulator that will be passed to an out-of-air diver.
  3. Short Hose: Should be long enough to breathe comfortably, but not long enough to bow and create drag.
  4. Back-Up Regulator: Quality regulator that a diver will use as a reserve either in the event of a failure or in an air-sharing episode.
  5. Long Hose: Optional in shallow, open water diving, but mandatory in deeper or overhead diving; the long hose simplifies air sharing. When used, the long hose, along with the primary regulator, should ALWAYS be placed on the diver's right post.
  6. Back-Up Lights: Tucked away to reduce drag but still allow for easy one-hand removal.
  7. Goodman Handle Light Head: Allows for hands-free diving while allowing the diver to easily direct the focused light beam.
  8. Thermal Suit: Appropriate to keep diver alert and comfortable.
  9. Crotch Strap: Allows for custom fit, and supports two D-rings: one works as a scooter attachment point; (divers should not hang equipment here as it would hang too low); and one further up, closer to the back plate, which works for towing additional gear. The crotch strap also holds the BC in position and prevents the BC from floating up away from the body.
  10. Hood: Where necessary to keep diver alert and comfortable.
  11. Mask Strap: Strong strap that will resist breaking.
  12. Necklace: Designed to hold the back-up regulator within easy access.
  13. Corrugated Hose: Should be just long enough to allow for ear clearing and potential dry suit inflation while actuating inflator, but not so long that it drags or entangles easily.
  14. Power Inflation Hose: Should be long enough for a diver to easily use his/her corrugated hose, but not long enough for it to bow or otherwise create excess drag.
  15. D-rings: No more than two on the chest, positioned to reduce the drag of attached items; one hip D-ring to hold the pressure gauge.
  16. Pressure Gauge Hose: Custom hose allows a diver to easily read the gauge after unclipping, but does not bow or dangle, thus avoiding excess drag.
  17. Pressure Gauge: Quality brass gauge should be easy to read and reliable.
  18. Knife: Waist-mounted in front, near the center of the diver's body, for easy access.
  19. Pockets: Hip-mounted to reduce drag; these pockets are ideal for storing slates, decompression tables, small guideline spools or other necessary equipment.
The following additional configuration items appear on the next two pages:
  1. Knobs: Soft knobs (to limit risk of breakage) should be opened completely.
  2. Valve: Contingent on environment and diving activity. Dual orifice valves (H or Manifold) are an excellent way to increase safety and redundancy.
  3. Burst Disks: Use of double disks prevents accidental burst failure.
  4. Buoyancy Compensator: Adjusted based upon needed lift whether one is diving single or double tanks. Buoyancy should be sufficient to float equipment by itself while at the surface.
  5. Cylinders: Contingent on environment and diving activity.
  6. Harness and Backplate: Designed to hold the diver snugly to their rig while reducing drag and increasing control.
  7. Primary Light: Hip-mounted, canister-style light; this is optional in some environments, but valuable in nearly all.
  8. Alternate Lift Device: Lift bag, diver alert marker, or surface life raft, for open water diving. Halcyon's MC system allows for storage in backplate pack for increased streamlining.
  9. Overboard Discharge: Also known as a P-Valve; used with a condom catheter by male divers to allow for urination during long dives with a dry suit.
  10. Bottom Timer / depth gauge: Wrist mounted to eliminate drag and entanglement.
  11. Watch: Wrist-mounted, with a functional stopwatch to allow for timing safety or decompression stops.
  12. Compass: Wrist mounted to eliminate drag and entanglement.
  13. Fins: These should have no attachment buckles that can break. Replace with a more robust connection.
  14. Guideline Reel: Use is contingent on the diving environment; it is usually mounted on the rear crotch strap D-ring for streamlining and to reduce clutter. Spools and other guideline devices are usually kept in the diver's hip-mounted pocket.

DIR Details

DIR equipment configurations are almost identical across a wide range of diving environments. To adjust for specific environments, DIR divers merely add appropriate safety equipment to their DIR foundation.

The primary regulator is breathed during normal diving and passed to a diver in the event of an air-sharing emergency. When used, this regulator is usually affixed to a long hose, which in an air-sharing emergency allows the out-of-air diver additional length and comfort.

In the event of a primary regulator failure or out-of-air emergency, the backup regulator must be instantly accessible; consequently DIR divers hang this regulator around the neck. This regulator is held in place by a necklace made from elastic tubing or cord. Having this regulator placed close to the neck means that it is less likely to be affected by surrounding water turbulence (causing a free flow).

Wearing a SCUBA Tank

Historically, divers believed that diving with a harness and a back-mounted wing was only suitable for double tank technical diving. However, divers have come to realize that a back-mounted “wing-style” BC is a better overall choice for a diver, providing him/her with an array of advantages not possible with conventional jacket-style units. This is because a classic style open water BC is not only bulky and loose fitting, it also tends to force a diver's feet into a downward angle, a terrible swimming position, thereby increasing drag and effort.

Most technical divers recognize the inferiority of a jacket-style BC for use with double tanks; nonetheless, they often do not fully appreciate how many of these same problems plague open water divers. For example, conventional jacket-style BCs try to fit a wide range of divers with only a handful of stock sizes. In contrast to sloppy-fitting jacket-style BCs, harness systems fit all divers snugly and with great precision, and are infinitely adjustable. When fitted with an appropriately sized wing-style compensator, these systems provide the absolute best combination of streamlining and comfort.

The Harness and Backplate

A diver's harness should be rigged from one piece of webbing and should have no quick-release buckles or other failure points. Though plastic quick-release buckles seem to simplify the process of getting into and out of one's dive gear, these “savings” are illusory, putting a diver at greater risk that s/he would be without it. In many cases this could prove fatal as the diver clings to tanks whose negative tendency stands in stark contrast to his/her own positive tendency. In cases where the loosened or dislodged quick release does not cause a diver to lose their tanks it can easily cause a dangerously significant shift in weight, throwing the diver off balance.

The crotch strap is also one piece, and has a loop in the front through which the waist belt is threaded. The crotch strap is needed to hold the diving system in place and to prevent it from sliding up toward the head when entering the water or when inverting; later it will also be necessary for any diving involving a diver propulsion vehicle (DPV). Once threaded through the crotch strap, the belt buckle should be placed to the right of center so as not to get accidentally opened by the crotch strap.2

Furthermore, the area below the tanks is an excellent area for storing equipment. A D-ring attached high on the crotch strap provides ample room for storing items. In addition, this D-ring also provides a diver experiencing a DPV failure with a handhold, enabling them to be towed out quickly and efficiently by another DPV diver.

Commonly, manufacturers adorn their harnesses with several poorly placed D-rings, often incorrectly shaped and of poor design. In contrast, the DIR harness is the model of simplicity. To avoid the unnecessary clutter of multiple attachments, the DIR harness only supports one D-ring on each side of the chest, one D-ring on the diver's left hip and two D-rings on the crotch strap. The chest D-rings should be bent slightly so that only one hand is needed to clip bottles to them. The hip D-ring is used for pressure gauges, stage bottles, and other gear, while the crotch strap D-rings are used for DPV attachment (front) and towing (see above). Individuals should not clip equipment to the front D-ring, because it will hang too low and will create entanglements and drag; divers should clip off any additional gear that is being towed to the rear crotch strap D-ring.

The knife is placed in an open sheath on the waist belt where either hand can quickly deploy it; it should be located to the left of the crotch strap. The knife is small and is designed as a line-cutting tool

Two back-up lights are attached to each of the two chest D-rings, one light per side. Each is held to the strap by an elastic band. This puts them beneath a diver's shoulders, where they are completely accessible but out of the way. Divers can always reach these lights and turn them on without unclipping them from their D-rings. Turning on a back-up light before unclipping it is very important; divers could easily drop their back-up light while trying to get it unclipped before turning it on.

When diving a single tank, this harness system can be mounted to the cylinder using a single tank adaptor; the BC would then sit between the plate and the single tank.4 When diving double cylinders, the back-plate is bolted to the cylinders with a buoyancy wing sandwiched in-between the two. In either case, the amount of wing-lift (i.e., size of wing) each diver chooses will largely depend on the kind of diving they are doing.

Backplates are generally constructed of aluminum or stainless steel. Steel backplates should be used when additional weight is required to offset the positive buoyancy of a particular exposure suit/tank combination, such as a drysuit and positive tanks.

Buoyancy Compensators

Many divers mistakenly believe that they must have large buoyancy compensators to support their diving needs. Actually, divers do not need excessive amounts of lift; large wings, because of the additional material they require, only serve to increase drag. However, if a diver does need more than 65 pounds of lift for diving doubles, or more than 30 pounds for diving singles, then they do not have a balanced rig. The diver should be able to drop unnecessary weight and swim up without a functioning BC. As with all diving, the key component to proper buoyancy is diving with a properly balanced rig.

Divers using dual BCs have experienced an array of problems including increased drag, additional task loading and uncontrolled inflation. There is never a need for “redundant buoyancy” in a properly balanced rig. The DIR approach avoids the use of dual BCs, and instead stresses proper balance between BC, cylinders, weighting and exposure suit.

Some BC's have become known as “bondage wings” because they support a series of elastic bands that restrict the size of the wings. This design introduces a whole new range of problems for the diver who selects to use them. These include: uneven inflation, off-kilter trim, the potential exacerbation of small BC punctures, increased drag, and resistance to manual inflation. In short, bondage style wings have no place in DIR diving configurations. Historically, divers have had to make a number of changes to their BC in order to increase its reliability. The DIR diver can make some fairly simple changes to these wings to increase their ease of operation and to extend their longevity. First, if the wing is not constructed with internal protection for the bladder, then the inner bladder can be covered with inner tube material to protect it against being punctured. Second, the corrugated hose on nearly all BCs is far too long and therefore, because of its length, often impossible to streamline. By refitting the BC with a shorter corrugated hose, and coupling it with a custom inflator hose, the diver can significantly improve the cleanliness of his/her system. Finally, all BC fittings should be checked to ensure that they are secure. Alternatively, divers can avoid all these modifications, and purchase a BC that is specifically designed for DIR, namely, the Halcyon BC.

Regulators

Scuba diving can be taken up in a variety of environments and conditions. Though this is one of diving's most fascinating features, it is also what places great demands on equipment. This means that divers should consider how and where a regulator will be used.

Regulators may be divided by use as follows:

  • Primary regulator: worn on the diver's back and breathed during normal diving
  • Back up regulator: worn on a diver's back but not breathed (backup)
  • Decompression regulator: used on a decompression bottle
  • Stage regulator: used on stages typically at depth and to extend bottom time
  • Argon regulator: used for suit inflation

Many divers prefer a high-performance, balanced, second stage as their primary regulator, and a slightly lower performance, unbalanced, second stage as their backup.6 This proven configuration gives a diver the best of both worlds. Stage bottle regulators are used to extend bottom time; so many divers prefer to use a similar regulator to that used as a primary. However, stage and deco first stages are more likely to be flooded with water, making piston-style regulators a common favorite.7 Argon bottle regulators should be robust in design and function well at a low intermediate pressure.

Two areas that tend to generate confusion are a regulator's breathing performance and its first stage intermediate pressure. The intermediate pressure (INP) is the internal pressure in the regulator's first stage. Generally speaking, the higher this pressure is, the more force is available to deliver air to the diver. However, elevated INP also increases wear on internal components, most notably on the high pressure seat which regulates air flow as it rests against or moves away from the orifice. Most regulators have an INP of approximately 140 psi. However, some regulators are designed to run at a higher internal pressure (e.g., some regulators from the Poseidon line); these are not recommended. Most regulators deliver enough air to exceed the demand of most divers. At depths below 100' (30m), where the density of air would introduce breathing resistance problems, divers switch to Helium based mixes, which at 300' (90m) are similar to breathing air at the surface. There are two basic types of regulator first stages: piston and diaphragm. A piston regulator is available either balanced or unbalanced. Unbalanced or “standard” piston first stages should only be considered for shallow low-demand applications. The balanced-piston first stage allows massive quantities of air to flow through a large piston, and is considered an extremely high performer. A balanced-diaphragm regulator, can respond quickly to inhalation demands, and so may be perceived by the diver as more sensitive.

Another important consideration in choosing a regulator is the water temperature in which the regulator will be used. Not all regulators are adequate for the extremes of ice and arctic diving. Generally, diaphragm regulators are more reliable in water that is colder than 40° F (4° C) because their sealed mechanisms resist freezing. Nonetheless, several manufacturers offer cold-water kits for their piston regulators.

Second Stage

Regulator second stages are also available in balanced and unbalanced forms. Practically, what differentiates a balanced from unbalanced second stage is that the former is a better performer while the latter is more reliable. Total failure is uncommon with any regulator. Though the unbalanced second stage does not give optimal performance, its simple design increases the likelihood of trouble-free operation.

Some second stages have an adjustment knob that, by moving the regulator seat closer to the orifice (see picture/diagram), allows the diver to increase or decrease regulator sensitivity. This should never be completely turned down because it will indent the seating surface. Many second stages also have a switch, called a venturi adjustment, which facilitates air delivery by adjusting a flow vane in the second stage body. This flow vane can either impede the flow of breathing gas to the diver's mouth or direct greater volumes to it. Lastly, several companies have second stages with storage mechanisms that are designed to hold the seating surface away from the orifice.

Hoses

Divers should use high quality hoses to reduce the risk of hose rupture, and hoses should be replaced every several years or when they begin to show wear. All hoses should be fitted with strain relief to reduce the risk of kinking and failure. While under pressure, divers should periodically pull the protector aside to ensure that there are no leaks or impending failures. Long hoses typically range from 5 to 7' (1.5-2m). Shallow open water divers who do not use a long hose commonly use a standard 32” (81.3 cm) hose. Overhead divers should use a 7' hose. Open water divers who use a long hose often use a 5 or 6' hose, depending on their size and the use of a hip-mounted canister.10

Restrictive areas, like caves, often require that divers travel single file. This means that unless divers are equipped with a long hose second stage, in the event of a failure, they will be unable to effectively share air in such an environment. The use of the long hose was primarily designed to manage air-sharing problems in restrictive areas, and has been a standard feature of cave diving for many years. Anytime divers are forced to travel while air sharing, using the long hose is mandatory. Furthermore, divers facing decompression will use a long hose. Today, many open water divers also choose the long hose because of the comfort it provides during air-sharing situations. Properly trained and equipped divers often dive with a long hose; this allows them greater flexibility while diving. The backup regulator hose should come across the diver's shoulder, allowing the regulator to sit below the chin without the hose bulging to the side.

Diving in a shallow, open water environment allows a diver direct ascent to the surface, thereby reducing air-sharing complications. In this case, divers will sometimes use shorter primary regulator hoses, an acceptable practice in this environment. Obviously, such an event is only for emergencies. Divers ascending from SCUBA on a breath-hold must exhale during the ascent to prevent embolism. This technique should be practiced and discussed during open water training.

Power inflator hoses should run over the diver's left shoulder and be long enough to comfortably supply the power inflator, while not so long that they bulge out to either side. In turn, the inflator itself should be long enough that, with one hand controlling all maneuvers, a diver is able to easily reach his/her mouth, his/her dry suit inflation valve, and his/her nose; it should also be long enough that, if necessary, one could breathe out of it by simultaneously holding down both buttons.13 The inflator from the wings runs over the shoulder and through a small bungie attached with the left chest D-ring. This keeps the inflator where it can be located instantly. To provide additional redundancy when using two first stages, the inflator hose should always be run from the right post. This requirement is illustrated in the case of a diver's left post rolling off or breaking. If the inflator is run from the left post, the diver will simultaneously lose not only the use of the backup regulator around the neck but also the ability to inflate the BC. These two problems together could be inordinately compounded by an out-of-air situation in which a diver would not only be without the means of controlling his/her buoyancy but would also be deprived of the use of a third regulator (cf. note 7). In addition, the inflator mechanism itself should not be designed to fill rapidly; this allows one to manage a runaway inflation more effectively, should an inflator failure cause a continual addition of air. The pressure gauge hose should run from the diver's left post to the left hip D-ring, where it is attached by a stainless steel clip wire-tied to the pressure gauge. This pressure gauge does not need a protective boot, nor does it need to be in a console or in any other device that increases its size and/or entanglement potential. The hose should be short enough to stay out of the slipstream and long enough to allow for viewing of the gauge once it is unclipped from the D-ring.

Regulator Configuration

Diving With One First Stage
Shallow, open water divers often use one first stage attached to a single tank. With a single regulator, the two-second stages come over the diver's right shoulder while the pressure gauge and power inflator run to the left.

Diving With Two First Stages
Divers use double tanks for technical diving not only because they seek to increase their available air supply, but also because they understand the safety margin provided by redundancy. Therefore, the use of double tanks usually indicates deeper or overhead diving. Both single tank diver and double tank diver systems require the following configuration. Open water divers using a single tank should assume that all necessary hoses run from one first stage. In a doubles configuration, the primary second stage regulator is attached via a long hose to a first stage that is affixed to the diver's right post (right shoulder). This configuration not only ensures redundancy, but also facilitates gas sharing. The long hose runs straight down behind the wing, under the light canister (if one is worn, if not it is routed around the knife, or tucked into the belt), back up the left side, and around the neck; the attached second stage is then placed in one's mouth and breathed. During an emergency air-sharing episode, divers will have to unclip this regulator to pass it to an out-of-air diver. While using stage or deco bottles, donors should pass the regulator in their mouth (stage or deco) and then deploy the long hose. Should the out-of-air diver need additional decompression gas, the divers will likely take turns using the bottle (such as five minutes each) or buddy-breathe. Out-of-air divers should also be practiced in going directly to the long hose, and be able to breathe from it while it is still clipped off, deploying it later without assistance. Divers must also practice quickly deploying the long hose in a variety of situations.

Divers should NEVER put their primary regulator on the left post because they risk a post roll off during contact with an overhead. Furthermore, severe contact might cause this knob to be severed in the off position, leaving the diver without a long hose in case of an emergency. Placing the long hose on the diver's right post means that the post can only be rolled open, and, in the case of a broken knob, will still be usable (both knobs turn clockwise but are on opposing sides). As with any new technique, divers may notice an early learning curve. However, a couple of dives should be sufficient for them to become proficient in managing a long hose. Whenever it is not in use divers should become habituated to clipping off their long hose to their right D-ring. While diving, hoses generally float and sit comfortably against one's body. Since, for purposes of gas exchange and general good form a diver should always be in a supine position, this long hose will usually be held in place against the body.16

Does the Long Hose Decrease Regulator Performance?

Regulators can easily supply air through a long hose without registering any notable drop in breathing performance. If there is any reduction in regulator performance when using the long hose, it is negligible, and in all but the lowest performance regulators, not even a noteworthy concern. If being attached to a long hose diminishes a regulator's performance, then the regulator itself is not suitable for normal diving use.

Gauges

Historically, divers have been led to believe that consolidating an array of gauges into one bulky console and then dragging that console along behind them was somehow a sensible and responsible practice. Not true. By dragging a bulky console behind them, divers not only kill whatever coral they come in contact with, they also risk entanglement. Instead, divers should wear their depth gauge and compass on their wrist or forearm. In the ocean, a compass is of paramount importance, and, without interfering with other activities, needs to be viewable and held in its correct orientation on the left hand. The bottom timer/depth gauge needs to be viewable at all times and should be placed on the right hand.

Mask

The mask should fit comfortably, be low volume, and be of durable construction. The lenses should not remove too easily. The strap must be secure and resilient. After-market straps that substitute a neoprene-style attachment for the original may be more comfortable and are nearly unbreakable.

Technical divers are often in the water for hours and sometimes carry a spare mask. A spare mask should be as small as possible while still providing a comfortable seal; stored in a pocket on the side of one's leg; and regularly checked to determine whether it is still functional. Also, to prevent the mask from fogging it should be cleaned regularly and pre-treated with a concentrated de-fogging agent before the dive.

Snorkel

Snorkels are useful only while divers are at the surface; during a dive they are typically in the way and pose an entanglement threat. If snorkeling, divers should choose a snorkel with a good size tube that mounts comfortably and does not offer breathing resistance. Rather than choosing from the array of gimmicky snorkels common to the dive industry, divers should learn proper skin diving techniques.

Fins

Stiff blade fins are popular among divers who need to swim quickly, move against strong currents, or push large amounts of equipment through water. Less rigid fins will work when pushing less equipment or when less power is desired. The best practice for divers is to use the same gear all the time. Divers should remove all plastic buckles from their new fins and substitute for them stronger attachment springs.

Valves

The benefits of bargain valves are questionable; therefore, divers should purchase valves of long lasting quality. Common favorites are Sherwood, Beauchat, Halcyon, and Scubapro valves.

Burst ports on valves and manifolds can cause serious problems if they fail. Should these release unexpectedly underwater, a diver would rapidly lose their available air supply. Technical divers typically replace these disks with higher-pressure plugs, which should be changed yearly along with the visual inspection of the cylinder.

DIN vs. Yoke

Yoke valves have been around since the advent of SCUBA diving. Deutsche Industrie Norm (DIN) valves were intended to replace Yoke valves by offering a threaded design that was able to handle higher pressures. DIN valves also reduce problems by employing orifice o-rings. But, the DIN connection tube could come loose if a diver mistakenly twists the first stage to loosen the regulator-to-tank connection. For this reason, divers should only turn the hand wheel to remove the regulator.

Knobs

Knobs should be spring-loaded and soft, with a metal insert that prevents them from being stripped. Divers should not use metal knobs. Rubber knobs are durable, shock absorbent, shatterproof and easy to turn. Divers should be aware that, if rubbed along an overhead, rubber knobs could turn inadvertently. Plastic knobs do slightly reduce the chance of a “roll off” but can be dangerous if, on impact, they shatter. Rubber knobs—like those found on the Halcyon manifold—are very robust, while softer plastic knobs—such as those found on the Scubapro manifold—also seem to resist breaking. However, hard plastic knobs break very easily and should be replaced at once.

Manifolds

Manifolds are designed to connect two cylinders together to allow divers access to either or both cylinder. As divers continued to explore deep and overhead environments, it became necessary to maximize access to their gas supply, which was accomplished by attaching two first stages to one manifold. Should the regulator, o-ring, or hose fail, the diver merely shuts down the supply to that regulator, thereby preventing any further loss of gas. Because the valve knob nearest the regulator only controls flow to that first stage, the diver, through the manifold, still has access to the gas in both cylinders.

In the very unlikely event of a catastrophic failure of the tank neck o-ring or the burst disk, the diver can close the isolator valve and interrupt the airflow to that side of the manifold, thereby protecting the gas supply in the other cylinder. Manifolds should have barrel-style o-rings, no face seals, and should be adjustable. The 300 bar manifold provides more threaded depth and a more secure attachment. Valves should face straight, with no angles. Manifolds that place regulators at an angle increase their exposure and elevate the risk of breaking DIN connections.

Special Note About Isolator Valves on Manifolds

One must always guard against accidentally turning off an isolator valve during a fill or a safety drill; a closed isolator can create problems. The isolator should always be left completely open. Symptoms of a closed isolator depend upon which tank the diver is breathing. If the gauge and “isolated” regulator are on the same tank, the diver should notice an unusually quick depletion of his/her gas supply. Divers might mistakenly believe that they are out of gas. This is unlikely (in the DIR configuration) unless the diver has had cause to breathe from the backup regulator. If the gauge and regulator in use are on opposite sides of the isolator, the gauge will continue to read the same pressure as the other tank is depleted. In this case, divers will have breathed the one tank dry and mistakenly believed that they were out of air. Realistically, this only happens to divers that are paying almost no attention to their gas supply. Unusually rapid or nonexistent depletion of gas supply is cause for evaluation and rectification.

Cylinders

The type of cylinder that a diver should choose depends on his/her diving environment and his/her other equipment.

Improper weighting, i.e., being too positive or too negative, can be very dangerous for divers. In the ocean, an over-weighted diver with buoyancy problems could find it difficult to reach the boat, and sink ever deeper in the ocean. While in a cave, the loss of buoyancy is not as risky; nonetheless, divers could be overcome by problems associated with negative weighting. Being too positive is also very dangerous. For example, ocean divers that are too positive could not stay submerged, and would risk dangerous ascents, missed decompression, or buddy separation. In an overhead environment, positive buoyancy could make it nearly impossible for divers to stay off the ceiling and swim out of an overhead area.

The goal of any SCUBA configuration is to create a system that, when empty, is as near to neutral as possible and that, when completely full, is not excessively heavy. It stands to reason, then, that at the outset of a dive, one's cylinders will be much heavier because they will be full. How heavy they will be, though, depends on the type of cylinder and the gas mixture.

Proper weighting involves balancing a number of factors; these include: increased surface buoyancy, the weight of one's breathing supply, and the need to remain neutral at 10' (3m) assuming an empty set of cylinders. Furthermore, this diver must also wear enough weight to counteract an empty set of tanks near the surface where the neoprene suit will again begin to exert additional lift. The additional weight necessary to accomplish these goals could easily leave a diver nearly 40 pounds negative at depth, making a buoyancy failure a potentially serious problem.

    Diver Wearing 80cf Cylinders In Full Wet Suit
    Weight of Tanks with Air In Double 80's ~6 pounds
    Weight Worn to Offset Neoprene Suit ~25 pounds
    Total Negative Weight ~31 pounds

As a worst-case scenario, imagine a failure occurring early in the dive that would cause the diver to have no control over buoyancy. Here the diver would be weighted down by both the weight required to offset surface buoyancy and the weight of the gas in the cylinders. In this situation, the diver should be able to remove enough weight (in the form of a weight belt or a canister light) to enable him/her to swim to the surface.

There are several ways to weight a diving rig; these include weight belts, canister lights, v-weights (placed beneath the back plate on doubles), and Keel™ weights (placed on the back of a single tank).18 Removable weight that allows divers to remove some of their weight allows greater control over a buoyant ascent. It is important not to overweight the diving rig with too much fixed weight, because it will prevent one from “ditching” the weight and swimming to the surface in the event of an emergency.

Too many people assume that an easy solution to the weighting problem is to wear a lot of additional weight and then counteract that weight with oversized double wings. This “solution” will leave a diver carrying far too much weight, and it will cause him/her to struggle with increased resistance caused by the unnecessary drag of an oversized BC filled with too much air. As we mentioned earlier, trying to solve the weighting problem by resorting to a double BC system creates more problems than it solves.

The ideal configuration for a diver is one that, while being as light as possible, allows him/her to remain neutral at 10' (3m) with a nearly empty set of tanks (to allow for decompression/safety stops). Quite often the only way to ensure this is to incorporate removable weights. Most divers carry this weight in the form of a belt that, in the event of an emergency, can be dropped. The bottom line here, however, is that divers should be certain that, without any air in their buoyancy compensators, they are capable of swimming against the weight of their configuration with full tanks and all weight in place. This would allow them to verify that they are able to manage their SCUBA configuration in the event of a buoyancy failure.

Choosing A Cylinder

Choosing the appropriate cylinder depends on several factors; e.g., body size, breathing rate, dive profile and diving environment. Selecting the wrong cylinder contributes to buoyancy control problems, environmental damage and diver risk. Failure to match the appropriate cylinders with the right exposure suit and buoyancy control system can also prove fatal. Most people find that Pressed Steel 104cf steel tanks are great for cave or cold water diving, where heavy thermal insulation and dry suits offset negative weighting. For longer dives or larger divers, 120's are also a popular choice.

For ocean diving in a wet suit, twin aluminum 80's are the cylinders of choice. If one needs more gas, then they should take an aluminum stage. The buoyancy characteristics of aluminum, especially when filled with helium, are such that an added weight belt and/or canister light provides the necessary ballast that allows the rig to be only reasonably negative when full, neutral when empty, and capable of being swum if the weight is dropped. In cave diving, steel tanks are commonly used with a dry suit, because they must be negative enough to allow the diver to stay down in a low-on-gas emergency. For this reason, prior to use, a rig must be balanced and weighted to accommodate a no-gas situation.

Aggressive dives require ample reserve breathing supplies. Therefore, individuals often prefer larger volume, lower pressure, steel cylinders made by manufacturers like Pressed Steel and Faber. Lower pressure tanks allow for higher volumes when necessary. This is especially useful for partial pressure Nitrox and Trimix fills. Divers using steel tanks should use additional buoyancy in the form of a dry suit to protect them from BC failures.

Dive Lights

Primary Lights
The basic DIR configuration uses a single primary light canister attached to the diver's hip, and two reserve lights clipped to the diver's chest D-rings where they are held to the harness by two elastic bands. The size and weight of the canister light usually depends on the particular diver's needs. Lights are optional for shallow open water diving; however, most experienced divers prefer the versatility offered by the above configuration, even for open water diving. Divers should use primary lights with a beam that can be focused for better visual reference, and a better means of communication with other team members.

The primary light canister is worn on the right side of the waist belt, adjacent to the backplate, and is held securely there beneath the shoulder by either the waist belt buckle or by a second buckle that is slid up behind it. The light is part of a diver's weight and balance, and should be placed under the shoulder where it is protected and out of the flow, and can be conveniently operated or removed if necessary. This location not only keeps the light canister from interfering with a diver's kicking movement, but also places it in the same water column as the one broken by the diver's shoulder as s/he moves through the water. This insures that the light is streamlined and does not impede a diver's progress through the water. When the light is in use, the light head should be held in the left hand. When the light is not in use or when one's hands are needed to switch to a stage bottle or to a decompression bottle, the light head should be clipped off to the right chest D-ring.

Some people believe that divers with hip-mounted lights cannot efficiently wear multiple stage bottles. A glance at the configuration of today's most active explorers will suffice to put these concerns to rest. In such a configuration, a multiple stage dive is conducted with all stage bottles located on the left side of the body, opposite the light canister.

Reserve Lights
Reserve or back-up lights are key components of the DIR gear configuration. These lights must be reliable, streamlined and conveniently stowed. Following a primary light failure in an overhead environment, the diver must switch to the reserve light and initiate an exit. Reserve lights whose burn times equal a diver's total bottom time would be excellent choices.22 While primary lights should contain rechargeable batteries, reserve lights should contain disposable batteries (more reliable, consistent and predictable). Reserve lights should be stored on the harness below the arms, where they tuck neatly out of the way and are essentially snag-free. A diver with a primary light failure can easily turn on the reserve light before removing it. The benefits of this are clear; if the light has been turned on before it is unclipped and dropped it can be easily found. Also, another advantage of positioning the reserve light in this manner is that it can be activated and left clipped off while one is managing other equipment.

Stage/Decompression Bottles

A stage bottle is a bottle used to extend bottom time, whereas a decompression bottle is a bottle used during the ascent portion of the dive to promote efficient decompression by reducing inert gases (e.g., N2 and He) while elevating oxygen percentages. Stage and decompression bottles are almost exclusively used in technical diving, where longer bottom times and/or multiple gas mixes are the standard. These bottles usually rely on the same or similar equipment and are filled with appropriate gases for a given dive.

While ocean diving, stage and decompression bottles should be made of aluminum so as to not overweight the diver. Cylinders as small as 40cf are usually perfectly adequate for most ocean decompressions, with 80cf cylinders being the permissible upper limit.

In cave diving, where decompression bottles are left behind in the spring basin, steel bottles are appropriate. Cave divers usually prefer steel bottles' lower working pressure providing them with a better volume of oxygen for the given pressure (i.e., a steel 95cf bottle contains 95cf of oxygen at 2,640psi, whereas at 2640psi a 80cf cylinder will only hold 72cf of oxygen). In cave diving, the decompression cylinders of choice are steel 72's or steel 95's for oxygen, and aluminum 80's for Nitrox mixes. All stage and decompression bottles should be rigged with stainless steel bolt snaps; what size these will be is determined by whether or not one's diving requires gloves. Steel bolt snaps are attached by a piece of 1/4” line run under a hose clamp placed halfway down the tank. The upper bolt snap should be placed slightly above the break of the neck and sit snugly against the tank. The lower bolt snap should be affixed to the 1/4” line that will extend beyond the hose clamp. This tie point for the snap should be near the middle of the bottle (roughly 16 inches between clip attachments). To prevent drag, the bottle needs to be held close in the front and relatively loose in the back. If the bottom clip is placed too low or is affixed too tightly, then the bottom of the bottle will be pulled higher, and will form a wedge with the front of the bottle. Cylinders should float horizontally and sit parallel to a prone diver. There should NEVER be any metal-to-metal connections of any part of one's equipment. Stage bottle clips MUST be able to be cut free should the clip jam or the bottle become entangled.

All bottles should be permanently marked to reflect their maximum operating depth (MOD), using three-inch high letters placed horizontally in the orientation of the tank. Furthermore, tanks should be marked on both sides to allow both the diver and his/her buddy to take note of the depth, regardless of tank position. A decompression or stage bottle regulator is fitted with a short pressure gauge bent back on itself to face the diver, and is held in place, at the first stage, by bungie cord. Its regulator hose must be "octopus length", or 38” (96cm). When not in use, regulators are always tucked away in an elastic band on the bottle, and the bottle turned off.

To facilitate streamlining and one-hand valve management, decompression/stage bottles are generally worn on the left side. Wearing bottles on both sides forces a diver's arms into a bulky “muscle man” posture and greatly limits flexibility. In addition to limiting diver flexibility, stages on a diver's right side interfere with efficient DPV piloting.

To deploy a bottle, divers should carefully adhere to the following procedure:

  1. Divers should operate as a team, verifying proper mixture and depth.
  2. Arrive at the desired switching depth, retrieve and attach the cylinder if required.
  3. Locate the properly marked cylinder and deploy its second stage. Open the valve completely.
  4. Each diver should double-check their buddy's cylinder depth and the second stage used.
  5. Remove regulator from the mouth and replace with stage regulator.
  6. Grab the second stage hose and retrace it back to the stage cylinder.
  7. Double-check cylinder marking.
  8. If beginning decompression, start decompression time.

Scooter Diving

Underwater propulsion vehicles can be remarkable assets to a variety of diving activities. By allowing divers to cover great distances while reducing effort and air consumption, scooters offer divers incredible tools to work with underwater. The most versatile form of propulsion vehicle is the “tow behind” scooter and should be preferred to the ride-on, torpedo-style scooter. The latter presents special problems: 1) it can “eat” gear, 2) both scooter and diver need to break the water, and any added gear must also break water, 3) it must be maneuvered by “body English,” which results in higher gas consumption, and 4) it makes towing a diver or additional gear difficult. On the other hand, tow behinds entail none of these problems: 1) they break the water in front of the diver, 2) the props are in front of the diver where he can be seen, 3) they are very maneuverable, and 4) they facilitate equipment.

When scooter diving, one must reconcile a scooter's speed and power with one's ability to return to safety without it, should it fail. In fact, not only can too much speed sabotage one's gas planning, it also cannot be accurately estimated when planning for a towing emergency.

Scooters need to be easy to work on and easy to clear of hydrogen gas from batteries. The best scooters these days have removable lids and o-rings, and can be repaired in the field. Components of the scooter must be in proper working order. First, one should test the batteries' “burn time.” Second, the motor seal and the seals between the battery and motor compartments should be checked for integrity by a vacuum test.

A scooter's propeller assembly must incorporate a clutch assembly that will allow the blades to slip should the assembly become entangled. A slip clutch allows the scooter to still be used if the motor sticks on; when one needs to stop, the blades can be stopped and adjusted to zero pitch, and then reset to run. The best method of attaching a scooter is by a tow cord that runs from the scooter handles to the front D-ring on the diver's crotch strap. This configuration allows the diver to be pulled by the D-ring attachment and not by the arms. The best position for the scooter is where the propeller wash will not hit the diver at all. The best handle position is riding with the scooter out in front, the arm extended but relaxed, the hand lying on the handle.

The protocol for towing a diver with a disabled scooter is to first stow the disabled scooter. This is done by threading the disabled scooter's tow cord through its forward lifting handle and using the excess loop with the attached bolt snap to clip off onto the diver's rear D-ring. Thus, the diver tows his own scooter while holding onto his buddy's D-ring, and being towed himself. Divers in overhead environments, e.g., a cave, might encounter areas that do not allow for continued use of a DPV. This dictates that scooters be left behind. Protocol for leaving scooters in the water includes first pinning the trigger, and then turning the blades back to no pitch. Gas “rules” for scooter diving in caves can be replaced with a review of objectives: 1) maintain sufficient gas reserves that would allow a diver to swim out of a cave in the event of a scooter failure; 2) carry a backup scooter (and a buddy) in order to get out in the event a scooter fails, 3) place safeties, or 4) and the best method, is to have twice the scooter burn time and twice the gas needed. Safety scooters should be placed at stage drops and should only be burned for about 33% of their capacity in one direction before they are switched. The reasoning here is that, in light of this, barring a catastrophe, divers will never be without a scooter; any scooter will then get them back to one of their last scooters. Even if one breaks, the scooter a diver will be riding will have a 33% reserve to get them to the next one; all of the scooters have power left.

Computer Diving

Divers have three primary methods by which to calculate dive and/or decompression time, namely, tables, wrist-mounted computers, and personal computer decompression programs. There is a great deal of debate surrounding the use of wrist-mounted decompression computers; divers wear these to calculate dive time limitations and decompression obligations during the dive. All divers should learn the proper use of decompression tables in order to learn the actual process of decompression diving. Divers that choose to use computers should do so after becoming well-versed in diving limits and then using the computer primarily as an educational tool. To see a list of problems with computer diving, consult Doing It Right: The Fundamentals of Better Diving, Chapter six.

A Baker's Dozen: Problems With Computer Diving

  1. Dive computers tend to induce significant levels of diver dependence, and undermine the awareness essential to all diving, but particularly essential to divers just beginning decompression diving.
  2. Dive computers prohibit proper planning; they discourage divers from “studying” the impact of various mixtures and decompression choices.
  3. Dive computers are of little educational benefit because they promote neither questioning nor proper planning discussions.
  4. Dive computers often use algorithms that heavily pad decompression time; this sometimes results in odd and ridiculous levels of conservatism.
  5. Dive computers are expensive, and prevent divers with limited resources from purchasing truly useful equipment.
  6. Dive computers significantly limit the likelihood that divers will track their residual nitrogen groups, leaving them less informed in the event of computer failure.
  7. Dive computers do not allow for diving helium in any format but the bulkiest and most questionable. It is very likely that new helium-based decompression computers will be inordinately conservative and suffer from all the limitations of air and Nitrox dive computers.
  8. Dive computers often generate longer decompressions than an astute, well-educated, experienced diver generates.
  9. Dive computers often confuse matters by providing the diver with too much useless information, sometimes even obscuring depth and time in favor of blinking CNS and/or decompression limitations.
  10. Some dive computers become very difficult to use if a decompression stop has been violated. Some computers will lock up completely, while others will just beep or generate erroneous and distracting information.
  11. Dive computers do not allow the educated diver to properly modify his/her decompression profile to account for advances in knowledge, e.g., the use of deeper stops in a decompression profile.
  12. Dive computers do not offer divers much flexibility to generate profiles with varying conservatism. For example, the right mix would allow 100 minutes at 60 ft rather than 60 minutes at 60 ft, but a diver might prefer to do one or the other or a hybrid of the two. Computers confuse this issue by not providing divers with the proper information.
  13. Dive computer users often ignore table proficiency and therefore do not learn to read tables properly. When faced with a situation where they can't dive a computer (e.g., failure or loss) these divers are seriously handicapped.

The Body

Many debates have revolved around the necessity of fitness in diving, and no doubt these debates will continue for years to come. It seems that the most reasonable course is to evaluate the type of diving to be done and adjust the fitness level accordingly. The average diver should be seeking good cardiovascular fitness with aerobic activity AT LEAST three days a week for a minimum of 30 minutes. However, good fitness can serve a diver in life as well as diving, and a thorough fitness routine will leave one more prepared for the rigors of diving.


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