John Bantin has been a full-time professional diving writer and underwater photographer since 1990. He makes around 300 dives each year testing diving equipment.

"Don't give this to any inexperienced diver. It might kill him!"
     So said Chris Parrett from Abysmal Diving Inc when I mentioned that I would like to try out the Abyss Explorer.
     It's the sort of honesty I don't get as often as I would like from equipment manufacturers and their agents.
     Chris is an American technical diver who first came into the industry with his Abyss deep-diving mixed-gas decompression software. The Abyss Explorer is a regulator commissioned by him to satisfy what he sees as the needs of those who go deeper than most.
     A high flow-rate and interstage pressure is supplied by the standard Poseidon diaphragm-type first stage. It's a very familiar item to those of you who know the Cyklon and Jetstream.
     The only difference is that it has been modified with a lower interstage pressure and internal O-rings that can work in a high O2 environment, as would be the case with rich mixes of nitrox.
     The second stage has been designed by Kirby-Morgan, manufacturer of the professionals-only bandmask that has become a commercial industry standard. Like Chris himself, this regulator is big and brash.
     There is no concession to trendy compactness, but then there is no problem with the routeing of exhaust bubbles either, because the exhaust-T is large, wide and made of a rubber compound. The breathing-resistance adjustment knob is chunky enough to be able to use easily, even when wearing a thick glove. It has a range that includes 11 complete rotations.
     At the surface, with the second-stage spring screwed right down, you can get a tolerable breathe with your inhalation still sufficient to pull the valve open. Open it up and it will blow your socks off.
     "This is a positive-pressure regulator," Chris enlarged on his opening salvo. "It will give you a good breathe at any depth but you have to adjust it just right. You have to know what you're doing."
     I suspect that many recently certified divers think they know what they're doing. As I get older, I realise that I know less and less.
     I took advantage of the hospitality of the Diver's Lodge TDI technical diving centre in Hurghada to try out the Abyss properly. Entering the water with a sense of trepidation, I was agreeably surprised. In the shallows, with the BRA knob screwed down, the breathe was pleasant and came in a broad flood into my mouth. There was no hint of that "Captain Scott opening the tent-flap" effect.
     As I went deeper, I simply opened the knob accordingly so that it performed exactly as I wanted. I could, if I liked, shut it down or open it up so that it gushed air at me. The choice was mine. As I came back up, I shut it back down to suit. At no time did I suffer any uncontrollable tonsil-blasting. In fact it proved to be the most comfortable-to-use regulator I had with me on that particular dive-trip. I'd say it proved to be excellent all round but, as promised, I had to take control.
     My days of "doing the deepies" are long over. Sixty metres of sea water is now more than enough for me. In fact it's more than enough for most of us but it is not for the average diver that this regulator has been conceived.
     The Abyss Explorer is intended for that small minority of divers who want to go beyond that, who feel that they need big gas flows, and who take sufficiently large reservoirs of gas to last them. I think it will suit most such divers.
     Air really thickens up when you get deep, so that is the gas which tests a regulator's performance to the limit. Ironically, as helium is less dense, many lesser regulators perform well with trimix at depth.
     Then again, if you are the sort of person who drives to Sainsburys in an American pick-up with an enormous pushrod V8 engine, wear steel-capped wellies to weed the garden, or think Vinnie Jones played graceful football, you might well appreciate the robustness of the Explorer and use it for routine dips off Chesil Beach.
     It costs around £350. There is also a version available at £420 with a metal second stage that is more suited to use in cold fresh water.

Dutch set a shining example
It seems a long time since I used a Dutch-made Gilan light during a series of deep dives on the Bianca C in Grenada. I liked it a lot, but it proved too expensive to appeal to British divers and the importer reluctantly abandoned his plans.
     Gilan is a small manufacturer staffed primarily by keen divers, so it was not going to go away. With the changing economic climate and current trading conditions enabled by the EU, Gilan has decided to offer its products again, this time direct, to British divers.
     The Gilan Traveller Plus HID gives you nearly everything you could want in a lamp. It is beautifully crafted in aluminium and offers the best of everything.
     It uses HID technology to produce an exceedingly bright light that penetrates further through warm-light-absorbing water than conventional tungsten bulbs. Though using only 12.5 watts, it gives the equivalent light to 35W of tungsten-halogen. It burns at 6000ûK, a lot nearer in colour to daylight than the 3200ûK of a conventional bulb.
     It has a charge-at-any-time, memory-free, ni-mh battery in a 46cm battery canister that attaches easily to your tank. It is simply clamped under the BC camband and connected to the lamp by a fixed umbilical cable with good reinforced protectors at each end. This adds about 0.5kg of in-water weight to your rig.
     Burntime is said to be nearly three hours, which should suit even a rebreather diver intent on getting the most use out of his scrubber unit! Charging is by means of an "intelligent" any-voltage charger unit and it takes five hours to replenish a fully discharged unit.
     The charger unit may be intelligent but often we divers are not. HID lamps need to be turned on, left to warm up to full brightness, and then kept turned on. They should not be switched on and off.
     If you should turn the Traveller Plus HID off and on again without pause, the switch knows to wait for the 5 seconds or so that will save wear on the expensive end of the lamp. It is a magnetic device worked by rotating a simple collar.
     Divers don't want to stumble around in the dark before or after a dive, either, but you can use this lamp safely in air as well as under the water.
     The Traveller Plus HID may weigh in at only 3.5kg, but what happens if you are overweighted for your journey and have to leave something behind? Or if you used the unit during the day on, for example, a liveaboard, and never got round to charging it for a night dive? The designer has thought of that, too.
     Disconnect the lamp from its umbilical and screw in a blank end-piece instead. It's on a long screw thread and protected by double O-rings. You can then use the lamp as a simple torch with eight AA-size ni-mh batteries in the chassis provided for the job. This enables you to charge the batteries while you're using the larger battery canister.
     You get only 75 minutes' burntime per charge in this case, but I have never done a longer night dive than that!
     You also need to connect the charger via the O-rings. Disconnect the lamp-head and plug the charger in its place. If you are concerned about build-up of gases during charging you can also unscrew one end of the battery canister. There seemed to be space for a longer battery pack than the one provided, but I guess a 2 hour 45 minute burntime is enough.
     The lamp is sexily shaped to sit comfortably in the hand and is slightly negatively buoyant (by about 300gm).
     The cone of light it gives out is quite tight if a little patchy, but has a wide peripheral halo. I liked this because it didn't turn a night dive into a day dive, yet I could detect interesting animals that had not yet been woken by the hot part of its beam. I did note that it flickered occasionally.
     The switching collar was easy to operate and never in danger of being turned off accidentally, though there is no protection to avoid unwanted switching-on during transit. I disconnected the battery pack instead.
     Of course, the normal set-up proved far too patchy to use as a video light, but Gilan has even thought of that, and can provide a diffused front end that does the job admirably.
     Criticisms? When used as a simple torch, the end of the unit is provided with a perfect place to attach a lanyard. When used with the umbilical, the flimsy clip provided for this purpose seems to be an afterthought.
     Also, some other good underwater lamp manufacturers have concluded that we divers can't be trusted to keep O-rings clean and re-grease them properly, so they provide for recharging without breaking into the unit. This lamp requires you to be slightly more intelligent than normal Ð only you can decide whether you are!
     You can buy the Traveller Plus HID direct from the Netherlands by going to the Gilan website, or by e-mail. It costs £425 with umbilical battery pack, AA battery chassis and ni-mh batteries, hand-torch converter and charger. The company will throw in an extra AA battery chassis, diffuser front-end and plastic carrying case during its introductory period.

Fit for survival
Many people think that Charles Darwin conceived the notion of "evolution". Not so.
     His scientific masterpiece, snappily entitled The Origin of the Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life, concentrated on the theory that the survival of any life-forms was due to their being most fitted to the prevailing circumstances and conditions. So it was not really "evolution" so much as "survival of the fittest".
     He was equally interested in the fact that some animals were unable to adapt, hence the modern habit of alluding to Darwinism at work when someone is witnessed doing something extremely foolish and fatal.
     Putting aside the joke that this computer works on a Darwinian principle, let's assume that the good people at Dacor were thinking along the lines of its design surviving because it was the fittest for the purpose and was able to adapt to changing circumstances.
     First glance at the Dacor Darwin gives away its family connection to the Mares M1. No surprise here. They come from the same factory, so comparisons are inevitable.
     I have to say that the Darwin is better-looking. By some simple changes to the moulding and colour scheme of the outer case, the manufacturer has lost the somewhat brutish appearance of its older brother. However, it isn't one of the smallest computers currently on the market.
     The layout of the LCD display has been reorganised too, but without any obvious advantages added.
     It's a nitrox computer. You can set it to give the deco requirements for the mix of nitrox you are going to breathe, from air all the way to 50% O2, and for those not yet familiar with the use of devil-gas, you can simply keep it set for air.
     You can also set the level at which a warning for the maximum ppO2 operates, and that varies from 1.2 to 1.6 bar. As expected, it also monitors any oxygen toxicity that might build up within the diver.
     If you are using a bottom gas other than nitrox, it will double as a depth-gauge and bottom-timer. Audible alarms can be switched on or off to order.
     Once you run out of no-stop time, when using it as a computer, it sounds off in an alarming way and displays the deepest stop depth and the stop time. I found the way it alternated between your actual depth and your maximum depth (and water temperature) slightly disconcerting but I liked the fact that it always gives an additional safety stop of 3 minutes once you are clear of deco-stop time and between 3 and 5m deep.
     The Darwin uses a variable ascent-rate and monitors this by displaying a bold graphic which represents a percentage of the ascent-rate according to depth, and the display has its own integral illumination.
     Once you are at the surface it starts counting and displaying surface interval. Time to fly is always 12 hours in the case of no-stop dives or 24 hours for deco-stop dives, or the total desaturation time if that is the longer. The unit is said to be good for use down to 150m, although I didn't bother to check this.
     The manufacturer has always been a little coy in the past about the algorithm it uses but this one is said to be a deterministic-exponential 11- tissue algorithm with M-values derived from Rogers and Powell studies.
     The important figures it throws up seem to be broadly in line with other European manufactured computers. Some peripheral information is so small on the LCD that only those with 20/20 vision need look.
     At the surface, you'll find all the usual modern functions including logbook, dive-planning no-stop limits, calendar and clock, and simulation modes.
     Simulation allows you to get to know your computer before you find yourself in deep water. All settings are achieved by operating two buttons while at the surface, and you can use a button to turn it onto dive mode, although the whole unit is activated automatically after less than 30 seconds once it makes contact with water.
     PC integration for downloading your dives later is done using an optical connection. The computer logs data with a point profile of 20 seconds during the dive.
     The two-button system of manipulating the unit to provide the setting changes I wanted took a little more understanding than the instruction manual could provide. The frustration I went through in simply setting a nitrox percentage and a ppO2 level took me back to the bad old days of wet-finger contacts and profanity. It's certainly not as simple as they like to portray.
     The whole thing runs on a couple of easily obtainable AAA batteries housed in their own integral watertight section. Follow the instructions and you can change these easily without losing any computed information. If you were to foul up on replacing the sealing O-ring, only the battery compartment itself would be flooded, not the computer.
     Something I spotted in the instruction manual that should interest most people diving in British waters is this: "Never use the Darwin or any other dive computer for repetitive square-profile dives deeper than 18m." Not a lot of people know that!
     The Dacor Darwin costs £235 wrist-mounted or £250 in a console.

Classic mask for classic divers
Certain items of diving equipment have been available for so long that they have become classics. In a world in which the never-ending supply of products from the mask mines of Taiwan and Italy keep on coming in all their endless variety, the TUSA Liberator appears to be an example of constancy.
     The TUSA Liberator name has applied to a number of masks in that range, but I am talking about the original Liberator, the TM5000.
     There are divers who have been around so long that they too deserve to be called classics. Alas, that is not a term I often hear applied to me, but one thing we "classics" have in common is failing faculties.
     Reduced fitness is disguised by long-practised technique. Increasing deafness is not a problem Ð we've heard so many dive briefings in the past that we can usually guess what the dive guide is saying. But when it comes to seeing our instruments, we need prescription lenses in our masks. This brings me to the advantage of using a "classic" mask.
     I once travelled across the world to a small and remote island to go diving, and to my horror found that my mask had been broken in transit. Luckily for me, a group of German diving opticians were staying on the island for a tax-deductible conference. They were not averse to doing a bit of quantitative research underwater (or diving, as tax-payers call it!).
     These gentlemen had so many masks with them that they were certain to have one like mine. I was able to replace my broken mask with a good one, for the cost of a bottle of wine, and swap my lenses over. It was a Liberator. That lesson learnt, I now always carry a spare optically corrected mask.
     The TUSA TM5000 Liberator is available with lenses in minus-dioptre powers to suit young people who might be short-sighted, but this mask is also available with plus-dioptre strengths for those of us classics whose arms are no longer long enough for us to read anything but the headlines in our newspapers comfortably.
     It is one of those items that simply works superbly. I was sent an example and put it on after many years of using other masks. It was totally familiar, like an old friend. I was able to forget about it completely.
     How often are you able to say that about a new piece of diving equipment?
     The TUSA Liberator TM5000 costs £29. Lenses in minus strengths cost £20 each and plus strengths £48 each. Bi-focal lenses can be supplied at £46.