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Ocean's Window, a dive shop in Plano TX, celebrated their birthday today. As part of the festivities, they somehow persuaded Cochran to bring their Prism prototypes and let a bunch of us old bubble-blowers get a taste of the future. The program was conducted by Peter and Sharon Readey. Peter is the engineer who has been working on this project for years; Sharon is his wife (and presumably principal dive buddy). You will go a very long way to find two nicer people. You will also go a long way to find two people more knowledgeable about rebreathers and diving. They clearly knew their stuff; they clearly enjoyed showing it to everyone else; they clearly enjoyed answering questions about it from all of us. This is OBVIOUSLY not just a job for them. We start off with a two-hour classroom lecture on rebreather theory, and where all this came from. It starts with basic closed-circuit oxygen rebreathers, makes a necessary diversion into nitrox theory, then goes into semiclosed-circuit nitrox and eventually into closed-circuit mixed gas. This was not anything like a full course, just an overview to give us some idea of what we were working with. During the discussion, Peter pointed out a number of design features of the Prism, comparing it with his CCR-155 which he had also brought along, and occasionally with the Draeger Atlantis. Peter is an outstanding lecturer, and he has the dry British sense of humor that made it even that much easier. Much of this discussion was review for me, either of things that have been hashed over on techdiver or cavers, or in the magazine articles. Some of it was new, and it was all extremely well-organized and extremely well-presented. I did take notes; I did learn some things; I did get a much better grounding and perspective on rebreather technology. About the Prism, my opinion: They got it RIGHT. Everything on that rig that is not absolutely specifically custom rebreather hardware is standard off-the-shelf parts that any dive shop would have in stock at any given instant. This was not accidental; Peter and Sharon have considerable experience hauling CCR-155s around the world, and are painfully aware of the need to carry spare parts for anything that might break which can't be replaced locally. The unit is SPECIFICALLY designed to use STANDARD SCUBA tanks and regulator first stages; if you want to rig one out with dual 100s, you can. (You won't want to. The time limiter on any rebreather is the scrubber; you won't use NEARLY that much gas before the scrubber is exhausted. The one we dove had a 7-hour scrubber on it.) Some of the ideas were not nearly as obvious as you might think at first glance. (Example: they use two counterlung bags coming over the shoulders, to minimize location sensitivity. The counterlung bags come almost to your waist, the hoses join them at the shoulders, leaving a long "finger" of bag that doubles as a water trap. If you do screw up and flood it, it isn't the catastrophe that it is on some other machines, because most of the water lands in the trap. And they put water dump valves at the bottom of the fingers, to make it easy to flush the water out afterwards.) We broke for lunch, then after lunch met back at the pool. First impression: this thing feels big. You put it on like donning a large-format backpacking pack, with two shoulder strap adjustments, a small chest strap to take some of the side-load off your shoulders, and a waist belt. Adjust the straps for comfortable snug fit. There was a crotch strap, but I didn't use it. There were two readouts, one wired, with some LEDs to give basic functionality reassurance, and a wireless unit that gives all the dive time, depth, gas fraction, decompression, and you-name-it. Final briefing in the water with Peter, stern reminder to NOT take the mouthpiece out without first closing it (there is a valve on the mouthpiece to keep you from flooding the breathing loop, but you have to remember to use it; the guy before me forgot.) and it is time to dive. The first thing you notice is the absolute lack of regulator noise. This thing is SILENT. The second thing you notice is the ease of breathing, much easier than conventional open-circuit. It felt like it took just a little bit more effort to inhale that it does above water, but that may very well have been partially due to the chest strap being snug. Exhalation resistance is zero. It turns out that I apparently subconsciously rely on the regulator noise to remind me to breathe and clear my ears frequently; I was having to remind myself to do things that have been automatic on open-circuit for years. The third thing you notice is the absolute lack of up-and-down with your breathing, because of the constant volume in your lungs and the loop. Peter told us this was coming, but hearing it in class and feeling it in the water are two very different things. In-water drag was considerably higher than my At-Pac with a single 80. This is to be expected; this thing has a LOT more cross-section to make drag than my At-Pac. Swim up, swim down, look around, no orientation sensitivity that I could feel. I didn't try actually standing on my head, although I was headed pretty near straight down into the deep part of the pool. I had a bit of occasional trouble with buoyancy, but that is because the counterlungs were not tuned to my lungs; the safety diver was on top of it. All too soon, the safety diver is motioning me up and back to the shallow end of the pool; time to go home. Stand up, close mouthpiece and remove it, back over to the side of the pool, and Sharon is lifting the rig while I am unfastening the straps, and then handing her the wireless computer. Overall impression: this thing is real, and it is a nice piece of equipment. I don't have a requirement for the kind of diving a closed-circuit trimix-capable rebreather would let me do; for me it is overkill. This year. Some of the other denizens here do have such a requirement; some of y'all should give this puppy a good look. (Rich, you already have your MkIV, you might want to at least look at the Prism. George, you might want to take a look, too. It has the depth capability, and it looks to have the dive time you need. One of Peter's slides was from Ginnie Springs.) Summary: I had FUN today. I would very much like to do it again.
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