The breathing-gas economy has a lot to do with it (think about spending 8 hours underwater with only two 3 liter tanks), and the idea of doing surface intervals underwater is definitely exciting, but it was the lack of bubbles – the complete and utter silence – that really sold me on rebreathers. On our first open-water rebreather dive, we focused on getting comfortable. After doing about four hundred dives in the last four years, I feel very comfortable and confident in the water, but the first time I jumped in with a rebreather I was back to square one. First of all, the buoyancy just felt all wrong. Thanks to the counterlungs which trap our exhalations, the total volume of gas never changes. On open-circuit scuba, I happily make small adjustments to my buoyancy by inhaling or exhaling, increasing or decreasing the total gas volume slightly to make myself either more positive or negative. On a rebreather? No such luck. Your buoyancy has to be absolutely perfect, because once it’s set, it’s not changing that easily. Ascend a foot or two by accident? No problem, I’ll just exhale and sink back down. Oh wait! Before I know it I’m on my way to the surface. By the end of the first dive I had the buoyancy more or less under control, and we spent the second and beginning of the third dives working on bailout procedures, sharing air with a buddy, and some other basic skills.
Once we took a break from our skills on dive number three to explore the depths and get a sense of how efficient rebreathers truly are, I instantly began to appreciate our bubble-free zone. At about one hundred feet we ran into a torpedo ray. I’ve been fortunate enough to have some pretty extraordinary animal encounters, but this was entirely unique. The scene was absolutely surreal. The ray was hovering three feet about the slope, completely motionless, suspended in the water column as though frozen in time. Seven divers were kneeling on the bottom watching this electrified torpedo ray which, as Jeff aptly described, looked like an Imperial Destroyer (I guess he was a Star Wars nerd as well). With a casual flick of its tail, the ray would propel itself gently towards one of these foreign creatures, investigating briefly before heading on to the next one. I resisted the urge to reach out and touch it, wary of the powerful electric shock these rays can deliver. For several minutes we stuck around, not a single bubble escaping our units, no sounds or vibrations to make our new friend nervous. And when it was apparently bored with us, it turned around and made its way slowly towards the depths, in an unstressed, care-free manner that was entirely new to me.
Why do the bubbles make such a difference, you ask? Well, creatures underwater are very different from the animals we encounter every day on land. Sound and vibrations are extremely amplified underwater, and most aquatic animals live lives that are very fine-tuned to vibrations and disturbances in the water column. Fish, for example, have what’s called a lateral line, a line of highly-sensitive nerves along each side of their body that can detect even the slightest movement (vibrations) in the water around them. These lateral lines are what allow fish to evade predators and respond to quick movements happening around them (schooling fish, for example). When a scuba diver swims along a reef, exhaling a flurry of bubbles every few seconds, it’s essentially like a marching band parading through your living room: you wouldn’t stick around either, would you? Some fish are intrigued by bubbles and even attracted to divers as a result (the more musically inclined fish, perhaps), but the bottom line is that natural behavior is significantly altered when bubbles are thrown into the mix. In our bubble-free zone, we were left to observe the oceanic critters going about their daily business as though we weren’t even there, which often occurred in very close proximity to our faces. When we came upon a couple of open-circuit divers, the kelp forest seemed to clear out in front of my eyes.
On our third day of open-water diving, I was feeling comfortable enough in the rebreather unit to grab my camera and take advantage of this new silent tool. We were able to get incredibly close (I’m talking 4-inches-close) to four-foot-long juvenile Black Sea Bass, capturing some incredible shots and becoming more and more addicted to the next generation of diving (see photos).
There are a few limitations to rebreather diving. The first being gas supply, which can last more than 8 hours (not a huge constraint). Then there are the no-decompression limits which, with a constant partial pressure of oxygen and underwater surface-intervals, aren’t a major limitation either. Typically, the constraining factor is the lifetime of the carbon scrubber, which varies from 4 to 6 hours depending on the type of scrubber you’re using, the water temperature and the work load. But in the cold waters off of Catalina, thermal protection was what threatened to get me out of the water fastest. For the first couple of days I was wearing a 7mm wetsuit while getting comfortable with the rebreather’s buoyancy characteristics. After an hour below the thermocline at 95 feet, I was more than ready to get out. Once I was comfortable, though, I appreciatively threw on my DUI drysuit and went for a test run with the new heated undergarments.
In 50-degree water, under my drysuit I was wearing a 1mm-thick Stretchliner, gloves and socks (all electrically-heated, mind you) and wearing the same amount of weight as I had been in my wetsuit. The difference was that I had increased mobility, and could have stayed well past the hour long dive times. On the boat I was staying nice and cool while my fellow dry-dive buddies were sweltering in their thick undergarments. When it was time to get in, all I needed to do was flick a switch and Ta-Da, I could instantly feel the heat radiating into my torso, hands and feet. I was good to go for as long as Jeff was willing to keep us under, my fingers nice and toasty and ready to operate my video camera. They always say that you really notice the benefits of a drysuit when you’re suiting up for your second dive. That is, of course, unless you leave your drysuit on between dives in summertime in California, in which case what you’re noticing is the dehydration and heatstroke creeping in as you burn to death in an air-tight container with an inch of fleece around you. I, on the other hand, had the best of both worlds! My only bad experience with the heated undergarments was sending them back to DUI for their Demo Day tour up the west coast.
