For technical divers and Buddy Inspiration users, the Dive Rite Nitex3 computer breaks new ground.
John Bantin explains how it works
Recent advances enable divers who are suitably qualified and equipped to reduce decompression times by switching to progressively richer nitrox mixes during their ascent. Typically, a diver might use air for the deepest part of the dive, switch to nitrox 32 at 33m, then change to nitrox 50 at 18m.
A closed-circuit rebreather diver, breathing gas with a fixed oxygen partial pressure (ppO2) of 1.3 bar, has the further advantage of a progressively richer mix being delivered automatically all the way to the surface.
However, in both these cases dives must be carefully planned in advance using PC software such as Abyss or ProPlanner. This means forfeiting much of the in-water flexibility that most of us now take for granted with deco computers. So far, the only alternative has been to use a nitrox computer set to the mix breathed at the deepest point planned for the dive.
The Dive Rite Nitek3 ≠ a new deco computer from the same stable that gave technical divers their favourite Bridge II nitrox model ≠ allows the diver to pre-set three different gas-mix programs for a single dive.
I recently used a Buddy Inspiration closed-circuit rebreather during a liveaboard dive trip to the Red Sea, and was keen to get the full benefits of long duration and shortened deco times. So I took a Nitek3 with me and chose settings for the oxygen percentages that corresponded to three crucial points in my dive profiles.
For my first computer setting I chose 21 per cent O2 (air), which was what I got from the Inspiration at 52m. My second setting was 43 per cent, which was what the Inspiration gave me at 20m. My third setting was 59 per cent, which corresponded to the mix I breathed at 12m.
Now comes the clever bit! It is necessary to re-set the ppO2 of the Inspiration from 1.3 to 0.7 bar at 6m and this gives a weaker oxygen mix of only 43 per cent at that depth. So at 6m I went back to the 43 per cent setting on my Nitek3, so was able to use the computer to break up my dive into four separate sections.
Although this method took no account of the progressively richer mixes breathed once I had ascended past the point at which I changed the setting on the Nitek3, it still meant I was able to spend a long time at depth without having to stick to the punitive deco stops required by a single-mix computer set to nitrox 21.
I always took a standard air computer with me for comparison and to use as a back-up timer and depth gauge; but, of course, I needed to use different air computers on consecutive dives because they would invariably end up "bent".
On one occasion I was seen safely to the surface by the Nitek3 but, according to my fixed-mix back-up computer, would have missed 87 minutes of stops had I been diving on air!
Usefully, the Nitek3 displays the ppO2 at any particular depth according to the oxygen percentage chosen. It is then a simple matter to compare this with the ppO2 figure displayed on the Inspiration of the actual mix being breathed.
The application for open-circuit use with fixed mixes in separate cylinders is obvious.
Setting the Nitek3 is done using two buttons. Hold down button B for five seconds or so until "mix 1" flashes. It allows you to change the mix figure in single percentage points, and button A allows you to set it.
Under water you press button A to get the computer's attention, then press it again to select your required mix, and confirm it using button B.
The Nitek3 will not remember settings between dives. This design feature may have been incorporated for legal reasons as well as for safety≠ but it means you have to re-input your required settings before every dive. If you forget, the computer goes to its worst-case scenario of 100 per cent oxygen. This means that you are greeted with a loud oxygen toxicity warning as you hit 1.6 bar (6m).
The instruction manual says that if this happens you should simply return to the surface with the Nitek3 and re-set it. However, the one time I found myself doing this, it proved difficult. Waves were breaking over my head, and I was soon bothered by a non-English-speaking cover-boat crew trying to rescue me!
Like other full-function deco-stop diving computers, the Nitek3 gives all the in-water information you would expect, including dive-time, current and maximum depths, water temperature, and a variable ascent-rate from 16m/min at 18m or deeper to 8m/min at 5.9m or less.
There is a nitrogen up-take display in graphic form (a collection of bullet points that build up on one side of the display), and a similar graphic display of square pixels that indicate accumulated O2 exposure. At the surface, there are dive-planning and logbook modes. The user can also choose to preset altitude levels, metric or imperial calibrations, how frequently depth data is required, and whether the water is salt or fresh.
The Nitek3 can also double as a watch. In surface mode it displays date and actual time, alongside total surface decompression time, and time-to-fly. It can be set for any mixes of nitrox between 21 per cent and 100 per cent oxygen, but will not allow a setting to be switched to under water at a depth that would give a ppO2 greater than 1.6 bar.
The algorithms used by the Nitek3 are modified Bühlmann 16 with nine theoretical tissue compartments for monitoring nitrogen up-take, combined with an algorithm by Hamilton/Bohrer for monitoring oxygen exposure. Decompression requirements when set to nitrox 21 (air) seem to be broadly in line with other computers such as Aladins and Suuntos.
The unit remembers dives moment-by-moment when in "profile" mode, and can be interfaced with a PC for later down-loading of information.
This computer seems ideal for the technical diver using three different nitrox mixes and goes a long way towards giving the closed-circuit rebreather diver a true picture of his decompression status.
The Dive Rite Nitek3 costs £799.
Sea & Sea Ltd 01803 663012
Quick steps to a tank change
I usually travel long distances between dive locations and tend to use whatever tanks are available locally. This is fine if I am leisure diving with a single. But a problem arises when I want to use twins ≠ or, worse, when I want to use a stage tank.
Buddy Twinning Bands have proved the ideal solution for twinning local tanks. However, until recently I had not cracked the problem of rigging a stage tank with, say, nitrox 50 in it.
The answer has proved to be the Quickstage Tank System from RED (UK).
The kit comes with a 5cm webbing camband complete with stainless steel D-ring, a tank valve strap, a regulator clip, a double-ended clip, some cable ties, and a length of silicone tubing.
The main camband will fit round any cylinder from 3l to 18l. The valve strap lashes round the valve of the tank. (Both are clipped to the appropriate D-rings on the BC harness.) The stage-tank regulator valve has its hose passed through a small loop of 2.5cm webbing which has the female part of a fastex buckle attached. The male buckle end is secured to a loop that passes round the tank valve strap.
The silicone tubing is tied around the body of the tank and knotted so that its effect is that of a big rubber band. There is enough for two such rubber bands on a 3l tank and this is used to stash away a long hose that might well be fitted to the regulator. Use the cable ties where you need to.
I found that it was convenient to stow one 3l cylinder across my abdo-men. but I am assured that many divers will use two as side-mounts. Like many simple ideas, it works.
The Quickstage Tank System costs £30
RED (UK) Ltd 01703 454550
Buddy Explorer fails to probe into uncharted territory
When David Parker started making valves for ABLJs (old-style BCs) in his garage, he did so with his own dive club members in mind. Things took off and his company, AP Valves ≠ still with the philosophy of giving UK divers what it thought they needed ≠ grew and grew.
It now claims to hold 80 per cent of the British buoyancy-control market with its Buddy jackets. But, with the notable exception of Germany, Buddys are not widely distributed abroad.
So is it true to say that the Buddy BC is a uniquely British product, designed largely to satisfy the special require-ments of the typical UK club diver?
It is true that some divers from other parts of the world are not enamoured of certain aspects of the Buddy design. Derogatory terms such as "potato sack" are sometimes applied to the over-engineered double-bag design with its tough, but bulky, 1100 denier outer material.
Foreign divers have also been known to run for cover when Buddy users decant air from their main tank into the Buddy's auxiliary air cylinder (perhaps this is because it is taking more than 200 bar of pressure yet does not bear a test-date stamp). These 400ml cylinders are now sold as optional extras, but they are so enshrined in British dive-club think-ing that they will probably still be demanded as a BC feature for many years to come.
It is a shame that so many club divers have also been taught to dump air on ascent by raising the corrugated hose. This works, but it lets in water. The Parker-designed shoulder dump valve available on all Buddys doesn't do this, and is for me one of the finest features of Buddy jackets.
Many Buddys that have seen a lot of use are now looking pretty worn. They have lasted so long that they have lost almost all vestige of their original day-glo colour. Sadly, however, a scruffy jacket is not a good advertisement for any brand, no matter how long it has lasted.
The Buddy Explorer is the latest in this line of BCs that started with the Commando and was represented most recently by the Profile. It is no surprise that the newcomer is not very different!
The Explorer has the usual Buddy hard back-pack and Buddy buckles at shoulders and waist. There is also a 25mm strap and fastex buckle at the lower chest. The jacket I tried came equipped with the standard Buddy Auto Air ≠ AP Valves' combined alternate air-source and direct-feed inflator.
The main difference between the Explorer and its predecessors seems to be in the design of the pockets, which are zipped so that their contents remain securely inside until needed. They also incorporate pleats, so that they keep a slim profile unless loaded.
The standard purple-and-black Explorer also has a new, large stainless-steel D-ring at each side; while the all-black technical Explorer TD has an additional six D-rings. Both versions have high-intensity light-reflective safety stripes too.
At the surface, the Buddy held me high out of the water when fully inflated (15kg of lift with size M). However, contrary to its publicity, I detected a certain amount of torso squeeze.
Because it fitted so snugly under the arms, there was no danger of my "swimming within the BC" when submerged.
Martin Parker, current MD of AP Valves, urged me to notice how the full jacket design gave me better manoeuvrability under water than a wing. He says that this is because the air is allowed to move around and does not get trapped in any one place. I have to say I remain unconvinced. I would rather use his Buddy Tri-Mix wing-style BC any time!
The Explorer and the Explorer TD are available in sizes S, M, L and XL. They cost from £289.
AP Valves 01326 561040
Light fantastic shows the way
Diving has come a long way since people improvised with oxygen cylinders out of Spitfires and converted Calor gas regulator valves. Divers no longer make their own wetsuits held together with yellow tape, nor do they contrive underwater lamps from car headlights and bell batteries.
People seem happy buying high-quality equipment ≠ owning the right hardware has become an important aspect of diving. Many modern divers enter the water with several thousand pounds-worth of gear.
Not so long ago they would have baulked at paying more than £50 for an underwater lamp. Now even these simple items can be engineered in such a way that they become precision instruments ≠ and bear a price tag to match.
Diver's underwater light review last year featured two beautifully engineered lamps from the Netherlands. They were very desirable, but the would-be owner needed to write a cheque for almost a grand.
A less ambitiously priced yet still desirable bit of kit to own, the Gilan Chrystal dive light also comes from the land of windmills. It is equally well-engineered, but has a simpler design.
The Chrystal battery tank and permanently fixed umbilical light head features a 15W halogen bulb which is slightly over-run to provide the light equivalent of a 22W bulb. The 7.2V ni-cad battery will keep it running for 85 minutes.
You can get to the battery for charging by unscrewing one end of the anodised aluminium head and connecting up either a mains voltage transformer or the car cigarette-lighter adaptor. Charging takes 16 hours with the charger set at 7.5V. Sophisticated electronics prevent the ni-cad being overcharged.
An optional charge processor takes only two and a quarter hours, and this also allows you the freedom to recharge the battery at any state of play without compromising its perform-ance. It is a simple matter to disconnect the battery for transport.
A handle allows you to strap the battery compartment to the camband on the tank. This method at first seems too casual to be safe, but it proved very effective and was ideal when rigged between the two cylinders of a twinset.
The lamp is activated by a revolving magnetic switch. As the power drops on the ni-cad the brightness of the bulb is reduced by half, to make sure you are not suddenly left in the dark!
A choice of reflectors give you different beam angles, and you can vary the power of the bulb.
What did I not like? The absence of a lanyard on the lamphead meant that it had to be stowed in a BC pocket. The on/off switch was effective, but spoilt by having no detent to prevent its accidental operation. I imagine it would soon burn a hole through a BC pocket if left on while out of the water.
Overall, the Gilan Chrystal was enjoyable to use and very bright.
The version tested costs £348, but a cheaper conventional version, which includes the lamp in a single unit with the battery, costs £291.
MarKat 01935 815424
Appeared in DIVER - November 1998