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Thread: Double Vision!

  1. #1
    still learning... gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan's Avatar
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    Mar 2006
    Laleham, Middlesex, England, UK

    Double Vision!

    There have been quite a few threads recently about double rebreathers, streamlining, deep cave bailout, time for sofnolime to be activated etc,
    so I thought I’d post about my attempted solution to some of these issues.

    DISCLAIMER: I’m a rank amateur, this solution has worked well for me over several hundred dives, but there are many alternative solutions / I’m sure there are lots of improvements that could be made. One of my motivations for posting is to get some constructive criticism/feedback/ideas for further refinement, so let the posting(s) being

    What follows is a bit of an unformatted brain dump, from about a year ago, entitled A little bit of double vision, followed by some more recent thoughts...

    A little bit of Double Vision

    One of the biggest issue’s with deep diving is carrying enough bailout.
    A way around this is to place ‘stage cylinders’ at various points along route. The downside is that you then have to deliberately do ‘setup dives’ just to place the gas & on a quick diving weekend it makes for a stressful affair especially it something goes wrong on the setup dive. Also tear down dives \ cost of gasses / time to fill, cost of stages regs, O2 cleaning etc, etc. i.e. LOGISTICS ARE A NIGHTMARE.

    May Bank Holiday was the turning point for me.
    The car was totally full – 2 rebreathers, 1 Bonnex scooter, 26 cylinders, + spares, lights, clothing, etc & it really struggled in a few traffic jams on route – the clutch left a nasty smell that took hours to dissipate.
    I was driving to Ressel (France) for a long weekend Cave diving with Pete Smith (Diving Pete) & the conversation solely consisted of a discussion about building a dual CCR unit & its pro’s & cons.

    Something about:
    building a unit to extend your diving vs one for bailout. Something about
    staging vs carrying. Something about custom making parts vs building out of off the shelf components. Something about using parts/components you’re familiar with.
    Something about minimising single points of failure. Something about keeping it simple. Something about task loading leading to the conclusion unit has to be automatic eccr vs manual.

    Serve’s me right, as I hadn’t a car radio working for the 14 hour road trip. We got most of the fine details sorted on the way back to the UK & then proceeded to investigate what was really required. I’d actually been thinking of the idea for several months, mainly based on the foreign trips where i’d paid a small fortune for bail out gasses that didn’t get used, and practicing with a kiss rebreather dive buddy and realising that although you can carry multiple cylinders, the speed at which you can swim/scooter, combined with delays caused by dropping and picking up tanks means that the distance covered on a dive is less than if you were diving alpine/with minimal equipment. In fact I got to the point of estimating that for every additional stage I carried, I lost 3m a min off my swim speed!

    I was booked on a Deep Caving trip (various sites in the LOT again) in late August which only gave us a few weeks to be able to get the unit working ‘properly’ – nothing like having a deadline to push a project forward…

    The crux (for us) of this was that each unit was to be ‘totally self contained’ & have no single point of failures. This was a design choice based on the idea that the 2nd unit was a replacement/alternative for OC bailout, so have to have the same level of independence/redundancy or greater.

    Now for us the biggest issue we had with a ‘bob’ was that they flood, leading to the requirement to have an ADV – adv ensures pressure is balanced on descent, stops ambient pressure being higher than internal pressure. Also, to ensure unit works, have to periodically switch to it & or are not as capable as the primary unit….
    So that left a dual…
    Now as I dive a Vision, that meant a getting another..

    Now my version of engineering & metalwork is: Give it to Pete & let him sort it out.

    Pete built a slimline chassis for both the ccrs out of Plywood (mockup) that worked so well we used it for a couple of ‘try dives’ @ 6 - 10m in a local puddle. This proved that our initial concept worked so a local fabricator copied the ply box in 3mm alloy to move the testing to the next level. Possibly something about realising the right shape was a rectangle rather than circular. Learnt that an accurate prototype would have saved time/cost, especially with hose routing.

    30m @ Chepstow NDAC.

    1st dive, we managed to get 230% CNS reading on the 2nd handset (30 min dive, max 5min @ 30m) due to the pp02 in the 2nd loop spiking - handset stopped reading @ PPo2 2.55.
    2nd dive was equally ‘fun’ but slow & although we managed to control the 2 loops better with only a ‘mild’ spiking of the cns clock - 110% in 30 minutes. I love the sound of the buzzer beeping at you before you even get in for the 2nd dive

    Not looking great for a sub 100m cave dive & 5hrs + in water time.

    So now it’s all about how do we control the CNS clock from spiking on the unit that’s not breathed from? Thinking of alternative like leave unit off, run 2nd unit at high set point/low set point for the entire dive. Issues with keeping the deco stops and calcs the same as both units use same deco algorithm lead to realising that had to run both units with the same/similar set point. Realisation, that allowing the solenoid to fire when not breathing loop meant spiking the loop because the o2 didn’t move round loop/get diluted by diluent/loop contents.

    Something about fears over dwell time/gas mixing. In practice dwell time not so much issue because drastically affected by breathing rate. Fears over lung volume/WOB, in practice not an issue by using large counterlungs. Talk about researching/dismantling other units to see how they solved counterlung issues. Thinking about bulk/bouyancy/simplicity lead to idea of single lung

    Came as a surprise, generally, building unit was less effort than expected due to some help from friends and using off the shelf components, but learning to dive it took more time than expected, because the unit behaved in slightly unexpected ways.
    e.g. loop spiking, frequency of change of loop etc.

    The next weekend took us back to Chepstow & we had also figured a ‘method’ to try & contain the CNS issue. This managed to keep the units within a couple of minutes of each other & was ‘acceptable’ to use…
    However, we then had the issue of the ADV’s not working very well – the ADV’s were pumping up both lungs (fully) – on ascent…!!! Control buoyancy…dump everything…still too light…hit surface…. Arghhhh !!!!
    Buoyancy hard.

    After the dive, we realised that the placement of the ADV’s in the lungs is critical & as we had mounted these lower in the lung the ADV kept firing as they were bottoming out due the water pressure compressing the counterlungs as I sat upright in the water before the dive. This caused the counterlung based adv to fire continuously, as gas was vented from the OPV, situated directly above. Needed to re position adv. Also discovered that adv placement/angle made a big difference to WOB.
    Mention routing of hoses/replacement of all connectors with AP valves stems, to allow cross connecting of O2 and diluent between units and wing/drysuit. Mention use of O2 for suit inflation, and Tx dil for wing, mention using 3ltrs vs 2 ltr.
    Ok – Pete moved these up the lung, nearer the T-piece to counteract this.

    I’m starting to feel like a Test Dummy…..

    1 week later, now at Vobster with another friend Steve & the next issue to overcome was Counter Lung’s. The unit was quickly put together the evening before, & on dive 1, I managed to use both dill’s (2 x 3 litres x 230 bar) on a 1 hour dive !!!!!…
    What had happened was that when the unit was put together the harness was placed in the ‘lower’ holes. This put the T Pieces slightly down my back, the CL’s higher up than normal so the ADV’s were on my shoulder blades. Every time I moved, the ADV’s fired so used up the dil…. Counterlung placement critical

    Solution – I quick call to Pete who advised setting the unit with T-pieces on the shoulder – (normal AP style) – this actually worked perfectly & I then felt I could go back to Chepstow a week later for deeper testing with Pete.

    Chepstow 50m

    2 x AP Vision Rebreather
    2 x Golumn Gear ADV
    2 x exhale T
    2 x OPV
    2 x 3 litre ‘dil’
    2 x 3 litre ‘O2’
    1 x custom box
    Drysuit & wing inflators changed to the AP type connectors

    We decided that running 4 x lungs was not an option, - too much task loading,
    so we removed the inhale lung & T piece out of each system. We kept the exhale T-piece due to wanting the water trap. This however meant that we could not use the standard ADV, so 2 x Golem ADV’s were bought & 1 each placed into the lungs.
    A little testing / modification of the lungs was required for the correct placement of the ADV - the AP Tear Aid for the bladders works very well.

    We are using only 2 large lungs (1 for each rebreather) mounted OTS (standard position) & each have:

    ADV (Golem), also doubles as manual dill add.
    O2 add

    Total weight: Unit: 60kg
    + LEAD for undersuit/drysuit buoyancy compensation, OUCH!

    Now the biggest part of using a Dual ECCR Rebreather is monitoring ‘both’ & controlling buoyancy on assent, so a few trial dives were required.
    & these were ‘interesting’…..


    I’ve learned quite a bit since then, and have made a few tweaks (removed flowstops, adjusted weighting/cylinder position(s), etc. I now connect the O2 into the ADV @ 6m, and have tested that I can cross connect the diluents / O2 between both units, and I like this additional level of redundancy in the unit.
    One message I took away from diving with KISS divers is keep it simple. I removed all unnecessary manifolds, 1st stages (don’t have separate suit inflate bottle), hoses (use a CO2 DSMB), etc, and that seems to have worked well.
    I only use ONE (exhale) counterlung for each unit, managing 4 counterlungs is too much bulk/task loading. I know this because I’ve recently been experimenting with wearing a 3rd classic inspo on my front...

    The one issue I’m not 100% happy with is the speed I can scooter/swim with the box. This is probably largely down to needing more practice/needing to refine by buoyancy control, but I do genuinely wonder if making a more streamlined cover / top for the scrubbers may make me more hydrodynamic. My initial thought were to minimise surface area / just let the water flow through the box with minimal hindrance, but now I wonder if a semi spherical / elliptical cover on the scrubbers would work better. Any suggestions for who/how to do this gratefully received ...

    This setup has now been tested to 122m DEPTH / a max runtime of 7.5 hours

    Perhaps the most telling thing for me was being comfortable recently doing some 6 hour solo cave penetrations in France, and the unit ran flawlessly for a week.
    Perhaps I got lucky, but its convinced me that carrying bailout as well as the second rebreather is unnecessary. I realise this may be controversial/foolhardy/MUCH wiser/better divers than me have advised against this, but there comes a point when you have to trust your equipment/ability/accept the risks involved, and there IS a strong argument for simplicity/streamlining/simplicity etc.

    I owe some genuine thanks to good friends like Pete Smith and Laurence Gulliver who’ve helped with the project, and been very patient as we’ve bored/frustrated each other as we thrash out the design(s). I also owe a big thanks to Martin Robson / Antii Apunen / Janne Suhonen / Zoltan Varga for putting up with this monstrosity on a previous training course. These guys simply left me behind, they’re the best divers I’ve been in the water with, and it was a humbling experience.
    Attached Images
    Last edited by gallathan; 29th June 2010 at 09:48. Reason: add images

  2. #2
    Christian Rasmussen depth is just really nice depth is just really nice depth is just really nice depth is just really nice depth is just really nice depth is just really nice depth is just really nice depth is just really nice depth is just really nice depth's Avatar
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    Aug 2006

    Re: Double Vision!


    Any pictures of the "monster"?

    Come to the darkside.... we have cookies...

  3. #3
    still learning... gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan is a glorious beacon of light gallathan's Avatar
    Join Date
    Mar 2006
    Laleham, Middlesex, England, UK

    Re: Double Vision!

    More images, including 2 from a 110m cave dive. In one, I've just switched to the 2nd loop to check its working. Primary loop/RB, all black, all on the LHS. Backup RB, all yellow / all RHS
    Attached Images

  4. #4
    RBW Member Diving Pete is on a distinguished road Diving Pete is on a distinguished road Diving Pete's Avatar
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    Sep 2008
    Modified Inspro

    Double Vision

    Re: Double Vision!

    As you may guess this unit is a fair bit wider than normal - BUT it is also slimmer than the standard AP Vision Box.

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