>I hadn't even gotten my hands on a rebreather yet, but I'd been doing a lot of reading. I had studied my training manual for weeks, and on the flight to Grand Cayman I carefully read every page of the owner's manual for the Poseidon MKVI, the rebreather I would be learning to dive during Tek Week 2012. Once I actually started my class I learned that checking my console was a better response to a warning light, but I was still reassured by my heightened awareness.
>I've been diving for 20 years, but I have yet to venture into technical diving. With the growing popularity of recreational rebreathers, though, I saw an opportunity to get a glimpse into that world.
>In addition to relearning buoyancy control, I had to get over my desire to feel the familiar flood of cold, dry air that a second-stage regulator delivers. I've always heard divers talk about breathing normally while open-circuit scuba diving, but breathing with a rebreather is much more like normal topside breathing than open-circuit breathing is. It's so similar to normal breathing, in fact, that it felt very strange to do it underwater.
>Rebreathers combine stunningly complex components with very simple, yet brilliantly implemented ones. On the complex side, the battery of the unit I used can get 30 hours out of a charge, has its own onboard computer (which stores dive-log data and decompression status separate from the unit's main computer) and even houses LEDs and a speaker that broadcast distress signals if the computer detects any problems. On the simple side, rebreathers' mushroom valves are a pair of thin, rubbery discs that sit within the hoses on either side of the diver's mouth. When the diver inhales, the valve on the side of the freshly scrubbed and properly oxygenated gas is pulled open, while the one leading toward the scrubber is pushed closed. When you exhale, the flexible discs blow the other way. These two thin discs are all it takes to keep the air moving through the loop in the right direction.
>A recreational rebreather is so thoroughly automated that I had some initial trepidation about trusting my life to a computer. "You do it every time you fly," pointed out my instructor, Georgia Hausserman, who was a pilot. I also appreciated the perspective offered by another grinning rebreather diver, who said, "Think of it this way — who would you rather have making these calculations: Richard Pyle and Bill Stone or YOU?" Perhaps most reassuring was a comment made by another diver: "Don't think of your rebreather's computer as a PC; think of it as a calculator." That worked for me; I've wanted to throw my laptop out of a window more than a few times, but I've never had a calculator tell me two plus two equals five.
>I've only logged a few rebreather dives so far, but I've had some memorable interactions, too. A big mutton snapper and I watched each other closely as it swam toward me, gazing intently, before veering off mere inches from my face. Early in my training before I had figured out how to maintain the right amount of gas in my loop, I was watching some jawfish dance above their burrows. Every time I had to vent gas from the loop they shied downward into their holes. When I managed to achieve proper loop volume and stopped making bubbles, they danced like no one was watching.
>I heard some unforgettable sounds while diving with the rebreather, too. I watched a parrotfish nibble the reef for minutes on end, and I heard every crunch. Later, I became keenly aware of a rushing roar that seemed to come out of the heavy blueness around me as I hung above a deep pinnacle.
>"So this is what all those tech divers are going on about," I thought.
>© Alert Diver —Winter 2013