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.

WHEN I GOT AN EMAIL FROM ONE BEN A MAZIN telling me that every diver should be equipped with JetBoots, I thought it was a spoof message from Paul Merton with his on-going jet-pack joke, and that Diver had finally made it to be guest-publication on Have I Got News For You!
     But Ben is American, did not think his own name to be anything remarkable (he pronounces it as you would the last two syllables of "magazine") and he certainly was not joking. He arranged to show me his product at our office in Teddington, on his way to a Red Sea diving trip.
     I decided to take the precaution of briefing the blonde not to laugh openly at him, such was my expectation of this preposterous idea.
     Instead, I have to report that I was so impressed by the quality of the construction and the general high level of engineering of the JetBoots that, before Ben left, I was gagging to try them.
     I returned the favour to Ben a few weeks later, when passing through his home town of Los Angeles on my way further south. I had a day to spare and arranged to try his JetBoots in the pool of the Sheraton Four Points Hotel near the airport.
     The management were very accommodating. The pool was large at around 30m, though certainly not Olympic size. We decided to let me loose in it with the JetBoots early in the morning, when there was no danger of collision with any other swimmer.
     The JetBoots came equipped with a big 25V ni-mh 15 amp/hour battery-pack which was mounted onto the steel backplate of the wing BC. This powers the two drive units via a control switch which you wear on a belt around your waist.
     As I wore no more than a lightweight wetsuit top, I needed no lead as ballast, and in fact had to put a lot of air into the BC to counteract the negative buoyancy of the battery pack, which looked very much as if it might have come from Custom Divers.
     The drive units are brushless motors, each fitted with small propellers in cowlings. They are manufactured from anodised aluminium and carbon-fibre. Each one straps to a leg below the knee, and the cables with wet-connections are routed through straps at the thigh to keep everything neat.
     Out of the water, complete with scuba cylinder, I felt fairly loaded up. I dropped into the water and tried finning a length of the pool submerged first before attempting to use the power. So far so good. You need fins either way to steer and it is nice to know that the option of finning home is there in the event of a technical failure, even in a pool.
     Then I tried turning the power on. There is a green light on the power controller, if you can see it past your other equipment. This indicates that the electronics have recognised the command, and the propellers begin slowly to turn. The power switch progressively allows the user to add more revs. It is continuously variable.
     And then I was off.
     ItÕs amazing how small a swimming-pool can become when you are doing three or four knots. I quickly had to learn how to turn, and those turns needed to be tight. I began to think we needed either a bigger pool or a smaller diver.
     I soon improvised and made more use of the space by accomplishing figures of eight. I was grateful for the wetsuit top, which saved me from grazed elbows when I occasionally took the corners too wide.
     I found I needed to keep my legs together and bend my body in an arc to get the fastest turns, and after a few tentative laps sticking out one leg to less effect, I got the hang of it.
     Zoom, zoom, zoom! I shot around that pool, which seemed to get smaller and smaller as I got faster and faster. I never really knew how fast I went but I would have loved to have tried the JetBoots out in the sea with a Pete McCarthy underwater speedometer. In the event, Ben was reluctant to allow me to leave the country with what is a very expensive item of kit.
     The great thing was that there was absolutely no effort involved on my part. No aching wrists, no wake turbulence, no bulk associated with a big diver propulsion vehicle, and no danger of any diver finning past me, as there is with the less expensive DPVs on the market.
     The feeling was the same as going up in a high-speed lift. Our legs are used to taking that sort of strain.
     The advantage for a photographer is obvious, in that both hands are left free. That is a major difference between JetBoots and any DPV. I can imagine all sorts of applications for a pair of JetBoots and a camera in places such as Cocos Island or the passes of French Polynesia.
     How long will the batteries give you before needing a 4-6 hour recharge?
     For a typical 90kg male diver I am told you can expect 35 to 45 minutesÕ hurtling at full speed.
     Remember, at full speed you can go a long way in that time. If you needed more, you would simply buy a second battery pack and change it over as necessary during the dive with the aid of the wet-connections provided.
     The whole outfit weighs 10kg and delivers up to 18kg of thrust. An Apollo AV-1 weighs in at 18kg. I am told a Farallon DPV weighs 36kg and gives only slightly more thrust.
     Not only that but, stripped down and packed, the JetBoots will fit in an overhead locker on any airliner. The only problem I can foresee is that someone, not the user, might stick their fingers into the props while they are spinning. I was glad that no-one ventured into that swimming-pool while I was occupying it.
     Would JetBoots suit the British technical diver? The ni-mh battery technology gives good duration at low temperatures, and much better than the equivalent lead-acid battery. JetBoots do not thrust cold water over any part of the diver. Subject to the battery-pack spec, JetBoots are good for use to 100m of depth, so I would say: "Yes." The cost is comparable to a Farallon DPV.
MST JetBoots cost US $3500 (around (£2100).

MST, www.jetboots.com

+ Lightweight + Bags of thrust + Easy and relaxing to use + Beautifully engineered

- An expensive toy if you don't need it - What about one for your buddy?

Fins for those who work out
I recently spent two weeks on a liveaboard dive boat with a group of divers who included the two equipment-designers from Scubapro. Roberto is from Genoa and Sergio, although also very Italian, has adopted San Diego as his new home and adopted certain Californian character traits.
     The more mature Roberto is very much the confident traditionalist, whereas Sergio is young and thrusting. Inevitably, there is a certain amount of rivalry between them.
     Sergio's baby was the Twin Jet fin design, whereas Roberto was responsible for the Twin Speed fins. Now Sergio has come up with the totally different Scubapro Razor.
     Just when I thought Scubapro was totally committed to the Nature's Wing philosophy of split-fin designs, they come along with a fin that uses the sprung-blade water-flicking system.
     Razor fins get their efficiency from storing up the energy not imparted directly to the water with the upthrust stroke, and releasing it, spring-like, as the fin returns to the downthrust.
     This is achieved by using different thermoplastics, including an infill in the fin blade in the shape of a zigzag. If the blade was not able to supply this whiplash effect, the energy would simply be lost in the turbulence of the water as it slipped off the blade.
     The blades are big and responsive and certainly have the capability to shift some water, provided you have the strength to do it. I was grateful that the foot-pockets of the fins fitted my feet comfortably right up to the heels and made them part of me, because I felt that I was swimming in high gear.
     The effect was as if I had two boards strapped to my feet, but I expected to get some good speeds out of them.
     However, less than 10 years away from a free bus-pass and equipped with long but less-than-muscular legs, I was unable to get anywhere near the speeds indicated on my underwater speedometer that I have achieved with some other fins. The best I could do was just 3kmph, when I would have hoped to get near to 4kmph at least.
     I deduced that I was just not strong enough to do it. I would guess that these fins would fit those of a short stocky build, though I know that equally long and lanky Sergio will tell me I am wrong.
     The Scubapro Razor fin is the antithesis of the floppy Twin Jet design, which allows the user to fin with no effort and what some would describe as to little effect.
     I remember trying some similarly big-bladed fins years ago. The buckles snapped after only a few hours in the water, which then made them useless. I noted the strong metal pin incorporated in the Razor fin's strap-buckle fitting.
     This one has obviously been designed to take the stresses and strain that comes with heavy leverage.
Available in sizes S-M, M-L, and L-XL, Scubapro Razors offer reasonable value at £69 per pair.

Scubapro UK 01256 812636, www.scubapro.co.uk

+ Good fins for divers with strong legs + Good value for money

- Not so good for "gentleman" divers

One for your next five-hour dive
A prototype Prism was the first rebreather I ever used. I took one on an expedition to the Red Sea in 1992. It required a lot of Duck Tape and faith, at that time, on the part of the user.
     It was agreeable to find that its inventor, engineer Peter Readey, is now living in California, and that the production Prism Topaz is now a polished product, honed by the requirements of the US Navy COTS (commercially off-the-shelf) purchasing policy. COTS allows the military to save millions of dollars in development costs Š and the private buyer gets the advantage of all that military testing and development .
     Luke Inman, an instructor at the Cortez Club in La Paz, Baja California, Mexico, is helping the American University Research shark-tagging program. That organisation uses only closed-circuit rebreather (CCR) units tested and approved by the US Navy, including the Prism. So I met Peter 1000 miles south of his home at the Cortez Club, with a view to getting to know the Prism.
     The Cortez Club is now a complete CCR facility that can support both Prism and Inspiration users with 3 litre DIN cylinders, oxygen at high pressure and Sofnolime or Sodasorb, and of course both semi-closed-circuit and CCR training.
     Most readers are by now familiar with the advantages of closed-circuit rebreathers. The user consumes only the O2 actually metabolised; the mix breathed is at a fixed partial pressure of oxygen; and the inert gas is kept to a minimum, conferring great advantages when it comes to decompression. The duration of the unit depends on that of the scrubber that removes exhaled carbon dioxide. With the Prism that is 5 hours at only 4ūC.
     Until now the APD Inspiration has been the only CCR available with CE certification. Peter intends to change that. His Prism Topaz, currently sold in the USA, is second only to the Inspiration in terms of number of units in private hands.
     The Prism is modular, making it easy to transport. It will go as carry-on luggage on a plane Š fully loaded it weighs around 21kg. Inevitably the Prism invites comparison with the Inspiration and it makes for a viable alternative purchase.
     The Prism uses 3 litre cylinders but has been designed to accommodate a variety of sizes. The oxygen valve is a 200 bar DIN connection and the diluent a 300 bar DIN connection, to avoid confusion. Scubapro valves are used.
     A display appears at the bottom of your mask, on a little unit mounted on the mouthpiece. It uses a series of LEDs: blue indicates dropping ppO2, red rising ppO2, and green is good.
     The warning lights flash if level changes become serious. There is also a bi-coloured LED for warnings of cell failure. The green LED pulses to indicate that it is functioning normally and this is what you mainly see during a dive. The brightness of this green light is adjusted automatically according to ambient light levels. It is not blinding or distracting.
     The other colours certainly get your attention, even if they indicate only a momentary spike in ppO2 levels.
     There is also a totally independent secondary display in the form of an analogue ppO2 meter which runs directly from the three analysing cells, no battery needed. This can also be used to check the state of the 9V battery that runs the primary LED display and controls automatic mixing of ppO2 and diluent.
     You also use it to check set-points and cell status, and even to find out if there are higher voltages than normal present anywhere in the electronics, caused by an unwanted ingress of water leaking power from the battery.
     Every time I got a red or blue light (increasing or decreasing ppO2 levels) during a dive, I was able to go to this display to see exactly what was happening. I found this very useful.
     The secondary display allows you to fly the unit manually, even if your electronics suffer a disastrous malfunction, and you can completely over-ride the automatic system at any time.
     Prism training requires trainees to use the system manually, which imparts a good understanding of what is happening to ppO2 levels during a dive. If you leave the automatic system switched on when you do this, you will have to endure the resulting colourful warning light display.
     You set up the unit to your choice of working set-point for ppO2 (usually 1.3 bar) from a range of 1.0 to 1.4 bar, but a pressure transducer changes this to 0.7 bar when you are shallower than 5.5m deep. This is entirely automatic, and there can be no diving at the low set-point by mistake.
     The electronics are plotted in re-enterable urethane (watertight but accessible). The solenoid is outside the breathing loop, so that should it fail it will not dump high levels of O2 into the mix. There is no high-voltage electricity in areas where there are elevated levels of oxygen.
     The gas is analysed after passing through the radial scrubber but is injected into the loop prior to the scrubber, thus ensuring a good mix.
     Water from the exhaled breath condenses on the face of the scrubber bucket so that the three analysing cells stay perfectly dry. The scrubber takes around 2.7kg of scrubber material.
     There is an automatic diluent-addition valve and an adjustable over-pressure valve on the counter-lung. I found that I could simply blow out into the mouthpiece during an ascent to push expanding gas in the counter-lung through this over-pressure valve. It truly is a hands-free operation. There is also a manual oxygen over-ride valve, exactly like that of an Inspiration.
     Nice touches are the drains fitted on the counter-lungs, which allow you to dump any water that might find its way into them during the dive. The absence of any T-junctions means that any flood caused by clumsy dropping of the mouthpiece while open and submerged goes directly into a counter-lung rather than any other part of the loop. The mouthpiece is negatively buoyant.
     I also liked the fact that the mouthpiece was easy to open and shut. It is operated by a large lever, which enabled me to close it during the dive and eject some water that had collected in my mouth through the drain-hole provided in that position. I didn't have to remove the mouthpiece.
     The work of breathing at depth seemed very low. I don't know if it was less than with an Inspiration. I was always very comfortable and our no-stop dives were always of several hours' duration.
     A Scubapro Air II is used as open-circuit bail-out and to control buoyancy by means of a large wing-style BC. Two of my fellow-divers preferred to carry their bail-out in separate sling-tanks.
     Weight-pockets are integrated and it is possible to zip two weights on to each counter-lung to resist any tendency for them to float up.
     The harness has the usual cummerbund and straps and the works, including scrubber and cylinders, are housed inside a black-coloured shell. Peter Readey is a passionate engineer and I can understand that he was reluctant to see his work covered up in this way, but it does make the latest Prisms looked more finished than the uncovered original.
     So what did I not like about the Prism? As it was originally aimed at the military, preparing the unit involves much paperwork. Most of these issues are taken care of with the Inspiration by the interrogating handset display just before diving.
     Preparation of the Prism seemed to take a lot longer. In fact, prescribed pre-dive preparation could take the best part of an hour. But it does make it very safe and, with five hours' duration, you don't have to prepare so often.
     I also found to my cost that it is possible to put the radial scrubber unit into the scrubber bucket upside-down. No-one noticed me make this mistake.
     After preparing my unit with this user-error in place, I entered the water for my second Prism dive to find myself breathing open-circuit. I was pulling in diluent gas through the automatic diluent valve and exhaling it through the over-pressure valve on the counter-lung. It was like breathing through a poor-quality regulator while watching Blackpool illuminations on the display!
     I felt I was getting a dose of CO2 poisoning, such was the breathing effort. My dive was quickly aborted. I suggested to Peter that he write the word "top" on top of the scrubber unit.
     Five of us were diving Prisms at the Cortez Club. We were swimming along at the sea-mount El Bajo, when we saw a new video-housing lying beyond reach of any open-circuit diver.
     We retrieved it, and Luke swam to the only other boat to ask if anyone had lost anything.
     "Yes, but you'll never find it," came the reply. "We've searched everywhere. It'll be too deep."
     "Was it a Top Dawg housing with a Sony digital camera? Did it have a green lanyard?" asked Luke.
     "Yes, but you'll never find it." It was sheer joy to see the owner's delighted double-take when Luke asked him if it had green Radio-Shack batteries in it!
The Prism Topaz costs around £5700 fully loaded.

Steam Machines , www.steammachines.com

+ Very safe when properly prepared + Military safety specification

- Long prep needed

It was staring us in the face
Sometimes the solution to a problem is so simple, so glaringly obvious, that everyone misses it. And what are the design problems on which BC manufacturers seem to have become fixated recently? One: getting rid of the now-thought-to-be-redundant corrugated hose. Two: integrated-weight systems falling out unexpectedly, with dire consequences for both those suddenly heading for the surface and those waiting to be concussed below.
     Dumping air has never really been a problem. All but the most basic BCs have some sort of dump valve operated by a toggle on the end of a cord. Of course, this needs to be positioned at the highest point of the buoyancy bag. The alternative of raising the hose to dump air from the manual inflation valve lets lots of water back in the other way, but people still seem oblivious to that.
     They do it all the time. Why? Because they can!
     So is the corrugated hose necessary? All we need is some form of direct-feed control to put air in.
     The direct-feed control to your drysuit has no corrugated hose. Scubapro has simply fitted the direct-feed control it supplies with its drysuit range directly to the body of the BC buoyancy bag of its Glide 3000 BC.
     So no complex pneumatic controls, no cocky fly-by-wire joystick. It's neat and simple and it rotates so that you can feed it from any angle. It gives the opportunity to run the hose from the regulator either neatly under your arm or over your shoulder. Job done.
     As there is no corrugated hose, neither is there a dump-valve at that side of the BC. This area is now taken up with the oral inflation system, a small hose that feeds to where a dump valve might have been and is tucked away under that shoulder-strap facing, with only its red end-cap revealing its whereabouts. It took quite a puff to inflate the jacket manually at the surface. Heavy smokers need not apply.
     Two dump-valves are provided and both are on the right side of the BC. One is at the shoulder top, operated by a toggle-ended cord fed neatly through to where it falls conveniently to hand. The other is at the lower back, for use during fast head-first descents.
     I was keen to test the efficiency of this manner of dumping air but had no problem with air unwilling to be released from the buoyancy bag.
     So why was the corrugated hose invented in the first place? Because the original ABLJ design had to be inflated by mouth and air dumped by repositioning the inflator/deflator valve. The corrugated hose gave the flexibility to do this before the direct-feed was invented. Does this suggest that divers are prepared to accept new ideas only provided they do not have to let the older ones go?
     Now that we have direct-feeds and reliable dump-valves, the corrugated hose is likely to be consigned to history in the same way as the starting-handle of a car. Time will tell.
     Scubapro is the third manufacturer as far as I am aware to have consigned the corrugated hose to history, and its solution is a simple one, cleverly using components it already has in production. That brings us to simple solution number two.
     All BC manufacturers are racing to find a way of keeping integrated-weight pouches where they belong. Scubapro has simply added large pinch-clips to those of the Glide 3000. It's as neat and simple a solution as any.
     Some will argue that pinch-clips make the weight-pouches more awkward to jettison in an emergency. I would argue that a correctly weighted diver should be able to get positively buoyant in a moment, simply by swimming up a little and letting Boyle's Law do the rest.
     Many divers strap on unnecessary quantities of lead. Few remember to jettison lead in an emergency - we are not well practised at doing it. However, there have been plenty of emergencies caused by lead going into unexpected free-fall.
     Pinch-clips are more useful when passing up lead before climbing into a small boat. However, it does take two hands to do each side, one to hold the attached weight-pouch D-ring, one to release the pinch-clip. This can be a pain if you have to hold onto the boat in rough conditions or if the boat is being blown down on you, but it is not impossible.
     The Glide 3000 is an otherwise conventionally shaped BC. It has two toggle-zipped pockets which are quite small and almost impossible to get to under water, a comfortably cushioned collar area, a hard backpack with a cushion and cummerbund which are separate from the buoyancy chamber, two large stainless-steel D-rings at the shoulders and two at the bottom edges, the usual waist strap closed by a pinch-clip and a very normal sternum strap.
     There are two mini stainless-steel D-rings from which less bulky items can dangle, and I assume the designer intended these items to lodge in the open pockets.
     As with presumably all new Scubapro BCs, the Glide 3000 has the benefit of the recently improved camband buckle, which allows quick swapping of any tanks of identical circumference. Apart from the improved integrated-weight system, there are two very visible trim-weight pockets closed by pinch-clips at the rear.
     Instead of struggling for complexity, Scubapro has come up with two simple solutions. They're so obvious, I can't think why no-one else thought of them!
The Glide 3000 costs £375, including the integrated-weight system.

Scubapro UK 01256 812636, www.scubapro.co.uk

+ Two simple solutions to two modern BC design problems

- Only two dump valves - Almost useless pockets

Long experience brings French polish
It was two Frenchmen who invented the compressed-air aqua-lung as we know it. How they managed to develop such an idea into a viable item of kit during World War two, without the occupying Germans finding out, remains a mystery. However, it does mean that the French have been scuba-diving for longer than anyone else.
     One company, based down in the south of France near the birthplace of open-circuit scuba, has been producing diving equipment for almost as long, yet its name is still relatively unknown in the UK. Its British importer is now Typhoon International, and the name of the company is Beuchat.
     The VX100 and VX80 regulators from Beuchat look beautifully made. They are nicely machined and the chrome work is of the highest quality. Both have a diaphragm-type action and two high-pressure ports together with four mp ports. The VX100 has a turret first stage while the VX80 has a fixed barrel.
     The second stage of the VX100 has both a venturi ± switch and a breathing-resistance adjustment knob, whereas its slightly less expensive sibling has only the venturi ± switch.
     What makes these second stages different from previous Beuchat regulators is their compact dimensions and small exhaust ports.
     The soft front of the second stage with the purge hidden beneath it, the squashy soft material of the exhaust port, the soft hose-protector and the silicone mouthpiece all add up to provide a very diver-friendly effect.
     As I found myself taking the photographs to illustrate this item while diving in very cold fresh water, I took the precaution of pulling the hose-protector back down the mp hose to reveal the big connecting nut, thinking that this might act as a bit of a heat-sink. Suffice to say, I had no problems with free-flow due to icing.
     In fact the only problem I had was with the face-Jacuzzi provided by my own exhaust bubbles once I stopped finning forwards. This proved problematic only when I stopped to take photographs, but it was extremely disconcerting. Other compact regulators do the same.
     I was using the VX100 and found the BRA knob a little hard to get to grips with because of the thick gloves I was wearing, so I chose to leave it fully cranked open and simply inhale less forcefully if I needed less air. The way the inside of the second stage is designed, there is no direct routeing for air to allow it to gush past your tonsils. Instead it comes in a diffuse flood.
     I found that the venturi ± switch made precious little difference, probably for exactly the same reason. The air has time to flood around the inside of the second-stage housing before it pours out through the mouthpiece. The effect is very pleasant.
     Beuchat regulators have not always done so well in our big comparison tests. The new VX100 is not the highest-performance regulator I have used but it certainly could not be faulted at the depths to which I used it, and I have to say that I would be happy to use it as my primary regulator under almost any diving circumstance.
The Beuchat VX100 costs £249 and the simpler VX80 costs £189. Both are available in A-clamp or DIN fitting.

Typhoon International 01642 486104, www.typhoon-int.co.uk

+ Beautifully made + Friendly soft-style second stage

- Exhaust bubbles disrupt vision at times

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