About the cave
Tank Cave is one of my favourite places to be. Miles of tunnel, clear water, great photo opportunities, stairs to the water…and shallow tunnels, narrow spots and lots of small depth changes. Those last three points mean Tank is not generally regarded as a great cave for rebreathers. The counterlung acts as a third source of buoyancy in addition to the wing and the drysuit. As well as managing the oxygen levels in the rebreather, the diver also has to manage the gas volume. So every up and every down means either adding or venting in at least two locations. On an open circuit dive I manage microbuoyancy with my breath. Need to go up slightly? Breath in to slightly more than half full lungs, float up, breath out again and let the expanded air in the wing take care of staying up. Of course on my rEvo, breathing in just shifts the gas from the counterlungs to my lungs, and nothing happens.
About the dive
With years of open circuit cave diving behind me, breathing in and out to control my vertical position in the tunnel is instinctual. So I knew that my first dives in Tank Cave with my new rEvo were going to be a bit challenging. Once in the water I definitely had to think about the level I wanted to swim at, and stop swimming on occasion to see whether I was going to float up or down. With the buoyancy sorted for a particular depth I could swim happily along the tunnel without worrying about it – perfect. Until the next rock pile appeared up ahead and rebalancing started all over again.
I was glad to have a manual unit and be able to manage my ppO2 without a solenoid interfering. For the dives I sidemounted a pair of AL40s, using bungee to bring the tank valves in close to my chest. It worked well and I was happy with my bailout situation. You can see in the photo below that with the exception of one errant hose, the whole configuration is nice and flat across my front. This definitely helped with fitting the unit up the Goat Track and back.
About the photo
The first photo above was taken on the second long dive of the weekend. The three of us had very slowly traversed to the end of the gold line. Past the jumping off points for various side lines are these beautifully untouched silt banks. I love the shapes of the silt piles over the rocks, and having models with excellent buoyancy control helped frame the photo I was looking for. Staying in one place in the less visited regions of Tank is normally a recipe for silt raining down off the roof, but I wasn’t making any bubbles and the water stayed clear. All in all it was a great shake out weekend for my rEvo and I can’t wait to get back in the (fresh) water.