The Back Mounted Counterlungs (BMC) are available as an upgrade kit for existing APD rebreathers or as an option specified with any new unit.

Why Back Mounted Counterlungs?

The benefits of the Back Mounted Counterlungs include:

# Clutter-free chest area

# Stream-lined diver profile with reduced drag

# More space available to clip on kit

# Easy location of manual inflators

# Easy to trim

# Unique integral shoulder strap & harness design ensures the counterlung is fixed in the optimum position for best breathing performance

# Excellent breathing characteristics in all typical diving positions

The BMC has been third party tested and is CE Approved.

The Back Mounted Counterlung design is the product of many years experience and development involving extensive manned and unmanned trials and testing. Our primary goal was to optimise the work-of-breathing performance of the lung.

As a result, we believe we have now produced a unique back mounted counterlung – the best available – and comparable to the renowned high performance of our existing over-the-shoulder design.

The BMC consists of 3 main components and 2 optional components.

The oxygen inflator assembly is sold individually and is optional according to the diver’s training level and preferences (for example PADI Rec18 – 30 does not allow an O2 inflator).

Although the ADV is optional, we strongly advise that the BMC performs best with an ADV fitted. The ADV is optional because existing customers may wish to transfer the ADV from their existing unit. If this is the case, obviously, care should be taken to refit correctly and test the loop integrity thoroughly before use. Advice or factory-fitting is available.

The BMC is sold with a redesigned harness which is necessary to accommodate the unique new shoulder strap design in which the strap is integral with the lung and ensures that the counterlung is fixed in the ideal position on the shoulder for optimum breathing performance.

The BMC features regular APD over-pressure valves on the inhale and exhale lung which are designed to maintain lung pressures below 40mbar when in the “dive” setting. Both valves allow manual gas dumping, water drainage and feature dual settings for loop test and dive modes.

[shown with both inflators and an ADV fitted]

Sizing

The Counterlung (2 colour options: yellow or grey) is offered in 1 size only but with two attachment points (high and low) allowing adjustment to cater for different body lengths to ensure the BMC sits in the optimum position on the shoulders.

The Harness is offered in 4 waist sizes which correspond to the existing harness sizes. So if you currently have a Large harness, you will fit a Large in the new harness etc. The exception to this is the current Small and current Medium are both the same size on the waist and therefore have been combined into the new Medium harness.

The Manual Inflators are offered with 3 hose length options (70cm, 76cm and 84cm) on the hose that returns gas from the inflator block to the counterlung. These lengths are designed to match up with your existing low pressure inflator hoses that feed gas from the diluent manifold or the oxygen first stage to the inflator block. These existing hose lengths are determined by rebreather model and the size of your current OTS counterlung. Therefore, to size your inflator hoses correctly we need to know this information.

Pandora’s Box

It was on the Queen’s Birthday weekend in June 2012 that I first experienced The Dark Side of Scuba…..Rebreather Diving!

I was invited to spend the weekend with friends Teri and Fil and some of their (technical diving) friends in Jervis Bay and had the opportunity to go for a leisurely boat dive on the Saturday morning with Dive Jervis Bay.

I met Teri and Fil a couple of years ago in Vanuatu, where they were diving the President Coolidge on their rebreathers, while my friends and I were on ‘normal’ gear (or Open Circuit as the techies call it!). We usually saw them whilst on our way to the deco stops, when they were still exploring the wreck, about half way through their bottom time.

Whilst we hung off the spare tanks on the 5m stop and played Sudoku to kill deco time, they emerged out of the deep and went to the surface with only a few minutes stop – basically just to say ‘hi’ and help with the puzzles.

So, I knew what a Rebreather could do for your bottom time, air consumption and deco time, and that it is the first step in the evolution to grow gills.

We drove down to Jervis bay on the Friday evening, late enough to avoid most of the long weekend traffic, and basically arrived, unloaded our gear & slept!

Jervis Bay presented us with a beautiful sunny day, and over breakfast Jan suddenly asked me if I wanted to try out her Breather? It took me a minute to comprehend – The magic machine that allows you to stay down longer and deeper was offered to me!! I could not believe my luck and did not hesitate to say ‘I’d love to give it a try”!

Over breakfast we completed the necessary paperwork & discussed the basic concepts, and you can imagine my excitement as we headed across the bay to Bowen Island with our operator, Dive Jervis Bay.

Our first dive was to be at ‘Little Egypt’, where I dived on my ‘normal’, recreational dive gear, buddying up with Fil and Jan who were on their Rebreathers. The visibility was better than we expected, given the rain & wind that has hammered NSW over the last week or so, and whilst cruising around at 20-30m, we found plenty of fish life & beautiful triangular rock formations that look somewhat like pyramids (hence the name “little egypt”).

Needless to say, I was close to getting into deco when we started our ascent and came up with a bit more than the standard 50bar, whilst Jan & Fil still had 30 minutes of no-decompression time remaining, and had only used about 20 bar of their gas supply!

We enjoyed hot soup, bread and cheese during the surface interval and decided to do the second dive in the sheltered area of the ‘Nursery’ on the west side of Bowen Island….this was to be the location for my rebreather try dive!!!

I knew I was in good hands as Fil Gray would take me down. He is at the very top of the food chain for Technical Diving, training instructors not only on Rebreathers, but also on all the other ‘Dark Arts’ of Technical Diving like Wreck and Cave Diving.

So, while I got my drysuit zipped up, Jan and her husband Bob started to adjust The Box, Fil calculated the amount of weights I needed and I got more and more excited. Then they strapped me in, adjusting the hoses, cutting off some cable ties to rearrange the straps, and curling a hose with a TV sized display onto my wrist, all while speaking in what seemed to be another language, full of abbreviations and technical terminology. I could not contribute to that conversation at all, so I just sat there and let it all happen, feeling like the astronauts must when they are suited up and strapped into the seats of a rocket.

Jan then explained that I now had an extra set of lungs (cool!!) that I had to control in addition to the air pockets of my drysuit and the BCD (sounds complicated!). She also told me that I needed to switch between ‘OC – open circuit’ and ‘CC – closed circuit’ on the mouth piece, before the descent. Fil would take care of the rest ….

When I finally stood up, I was surprised that The Box on my back was not as heavy as I expected and that I could still walk by myself to the aft exit. Somebody put on my fins, I held on to my mask and the “vacuum cleaner hose” with the mouth piece and … jumped!

While we were bobbing on the surface, Fil got me to switch from open to closed circuit and explained that in order to reduce the amount of air in my new set of counter lungs (cool!!), I had to breathe out through the nose. He helped me get the air out of my drysuit, but in vain, I bounced on the surface like a big black buoy. When he got another 12 pounds of weight and brought my total to about 32 pounds, I realized that I was about to learn how to dive all over again! It would take a few dives on The Box to reduce the weights to a non-embarrassing level.

I finally made it down – duck dive style. The first thing I noticed on my descent was the silence. I missed the familiar noise of air gushing through the regulator with every breath. The breathing was a bit different too, as the air it did not get “pushed” into my mouth like a normal regulator. I did get a bit startled when the serene silence was interrupted by a burst of air being released into my second set of lungs (cool!!), but then it was silent again.

On the bottom, Fil made me switch between Open Circuit, which meant breathing on a normal regulator, and Closed Circuit, which meant breathing through all the hoses, valves and counter lungs of the Breather. Fascinating, that you actually have two different systems in the magic box! Switching between OC and CC seems to be an important skill as Fil made me do it twice, on the surface and on the bottom.
Note to self: Don’t forget to switch to OC before you spit the dummy!

Then the buoyancy game started…….whilst I am really good with buoyancy on my normal gear (note to self: Start using tech-lingo – it’s called ‘Open Circuit’), I now had three air pockets to take care of: my drysuit, the BCD and the counter lungs (cool!!). Pumping air into and releasing it out of the drysuit and BCD is easy, but the counter lungs are a different game altogether. The magic box has a mind of its own and decides itself when to pump air from one of the cylinders into the system.

I later learnt that it is called a ‘diluent’ because it dilutes the oxygen which is released from the second cylinder. And releasing air out of the closed Rebreather cycle is done through blowing air out of the nose, something I do anyway, so not a problem. The issue is to coordinate the three and to find the right mix for good buoyancy. Well, I didn’t find it! And I guess I would spend a lot of time on the quest to find the perfect buoyancy.

It seemed as if I was back to square one with diving, with an exorbitant amount of weights on me and a dive profile in the form of a sine wave. Now I understood how a young Albatross must feel when he bounces off the ground a few times before his first flight! I just hadn’t made it into flight mode yet.

The next 40 minutes or so I spent on The Quest, mostly either shooting to the surface or pounding head first into the sea floor, but enjoying immensely the short intervals when I silently floated through the underwater world of Jervis Bay. I was concentrating so hard on my buoyancy that I almost swam into a huge black ray which rested in the sand, just a few meters in front of us.

At one point I even started to look at the baking tray sized computer on my wrist. Not that I had any idea what it tried to tell me, but Fil seemed to be happy with all the numbers, so I didn’t worry about it. It took me a while to locate the time and depth on the screen as they were shown in the smallest font. I guess time and depth don’t matter anymore when you have a magic box with a seemingly endless supply of gas to breathe, and you take in the least amount of Nitrogen possible throughout the dive, which means you get much longer no-decompression times than diving on Open Circuit.

The other cool bit, is that you can get closer to fish life, as the lack of bubbles means there is less to scare them away from us divers!

When we finally ascended I felt a sense of accomplishment – I did it! I dived on a Rebreather! It was a great and exciting diving day and thanks to Jan, Bob and Fil I started to learn how to dive all over again, just without the bubbles!

Back on land I got a ‘Rebreather for Dummies’ summary and Fil told me that I had done very well for my first time on the box. Did he say that just to lure me to ‘The Dark Side’?

Note to self: Set up a savings account for a Rebreather.

…. and that’s when I realized: Pandora’s Box had been opened!!

Thanks very much to Jan for allowing me to use her “baby”, and of course to Fil Gray & Bob Thompson of Stingray Divers, for keeping a watchful eye over me!

Sotti
Founding member of the Diving Divas

http://www.facebook.com/#!/pages/Diving-Divas/465442483469625

Stingray Divers specialise in Advanced Diver education at all levels, including Instructor Training, Mixed Gas, Rebreather, Cave & Wreck.

They can be contacted on fil@stingraydivers.com.au or 0405 224 618