Diver Dave's AKA-60 "Orca" Dive Report
In Early April I braved a cold and rainy day to try a dive on the Russian AKA-60 (nee "Orca") rebreather. This is a constant mass flow semi-closed circuit rig, which I have described fully in the accompanying photo-essay. Prior to diving it, I serviced it with a 45% nitrox mix, ran a quick flow-check (time to fill the counterlung from empty is my rough field check), and filled the cannister with Sofnolime. Then it was off to the local test-site, the Dutch Springs quarry.
The rig was set up with the original Russian harness, modified only by attachment of two D-rings to allow attachment of a 19 cubic foot side-mount bottle for some open circuit gas and for drysuit inflation. The original harness resembles the old US military harness used by generations of divers wearing double 72's. No wings were fitted, as I've been using my drysuit for years as inflation and figured this isn't the time to change. I had no clue how the rig would balance or trim underwater, nor did I have any clue regarding it's buoyancy, so I just decided to treat it like any other set of doubles and dragged along my 20 pound belt, with a set of light ankle weights to keep the feet of the Viking suit down.
Entering the water, I found that my guess as to weighting was dead-on, being just slightly negative when my drysuit was dumped, and neutral with just a squirt of air. So far, so good! Trim was also good, with no tendency to bring me to a heads-up position. This relieved some concern, as the counterlung is fairly large, and is mounted at the top of the inside of the chassis. Unlike a closed-circuit rig, a semi-closed rig must be dived with the counterlung completely filled at each exhalation, due to the constant free-flow of gas. I had worried that this buoyancy would make the trim heads-up, but was pleased to find otherwise. Breathing resistance was negligible, and exhalation resistance against the exhaust valve was just right. The auto addition valve kept up with a fast descent to 70 feet with ease, and the rig swam great.
Once on the bottom I tried the rig in various positions, and found that the rig balanced well and breathed well in every position. The position of the counterlung seems just about ideal, and all systems functioned perfectly. I had made the mistake of not tightening the crotch-strap fully, but quickly fixed that to tie the rig down securely on my back. The rig is dead silent, the flow through the orifice not being audible at all. I was sort of surprised at this, as the flow is fairly high, and to make sure it was flowing right I referred frequently to the Draeger Oxygauge that I had installed earlier. This showed the PP02 to be perfectly stable, so obviously the orifice was working fine. I had not filled the cylinders fully, as I wanted to be able to determine the effectiveness of the audible "whistle" function, warning the diver of a nearly exhausted gas supply. Sure enough, at 30 BAR I began to hear a low volume "Weeeee" noise, which became slightly louder as the gas was used further. Making my ascent, I deliberately positioned myself for a surface swim and monitored the PP02 as I worked up a sweat kicking. The 45% mix never dropped the PP02 below 0.32 BAR, so that's a good sign that I can reduce the mix to perhaps 40% safely for the next set of dives.
Climbing back up to the picnic table behind my truck, the rig drew quite a lot of attention as it was obviously different, and its clean design drew several compliments. A quick inspection showed the scrubber to be dry, the counterlung to be dry, and the rig ready to be refilled with gas and dived again. All in all the rig dove flawlessly, and I enjoyed it immensely.
How does this rig compare to others available on the market? Perhaps it is best compared to a Draeger FGT-1D rather than to the more common Atlantis/Dolphin series. It's lots nicer than an Atlantis, that's for sure. The shell is clean, the rig balances better, and the separate gas-cylinders would allow the diver to carry two mixes for travel/deco and bottom mix. For half the price of a new Draeger, it's a lot of bang for the buck. I'd recommend it without hesitation, and feel that a Draeger SCC course would adequately prepare a diver for employing it, with just a routine lesson in the physical differences between the two rigs. I'll be diving this rig a lot all summer, and have 2 more local guys who will also be diving them. I'll continue to report as the season progresses, but for now it seems great!
Dave Sutton