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Wibble's CCR odyssey

Discussion in 'General Scuba Diving' started by Wibble, Jul 5, 2020.

  1. Wibble

    Wibble Fish don't talk
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    Thanks Dave.

    Which other gasses do you bank, say for shallower dives? Or do you use 15/55 for all dives below, say, 30m? Similarly bailouts?
     
  2. barrygoss

    barrygoss Active Member

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    If Dave is anything like me. 15/55 for all dives. Even pool dives.

    It costs nothing, so you do a bit more deco, who cares. You can’t make a gas mistake with only 15/55 and O2 in the garage.

    B
     
  3. Wibble

    Wibble Fish don't talk
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    Banking; have a couple of twinsets which I'm probably going to dispose of one.

    How low do you run your 'banks' before refilling? 150? (Obviously depends if it's a deep dive where more dil's used)

    Pondering getting another couple of 3's for batch filling.
     
  4. Dave Whitlow

    Dave Whitlow Super Moderator
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    My shallow bailout (and scallop transport gas) is an AL40 of 32% and I have a dumpy 12L of 32% for topping that up.
    I only bank 32% because the end of an O2 J isn't worth boosting but pushed through a nitrox stick (thanks @nickb ) it becomes useful.

    As @barrygoss says, there's no point making life complicated so the only diluent I bank is the 15/55 but I'm too lazy to stress about the actual mix I'm diving.

    I don't like narcosis so all that matters is that the EAD is shallow. I often air-top bottles to get the extra gas pressure so I actually dive a range of mixes from 15/55 down to 20/10. I never use air in my CCR.

    Having four diluent bottles I apply a 'least effort' approach to keeping them filled. A strip of masking tape on each bottle is adjusted after each fill so the contents of every bottle is known at all times.

    Before any dive I'll pick a suitable bottle and put the numbers into the OSTC cR when I mount it on the unit.

    For shallow stuff the lower helium bottles will be used, and air-topped if pressures is below 150 bar, and for deeper stuff I'll use a rich mix.
     
    Wibble likes this.
  5. Dave Whitlow

    Dave Whitlow Super Moderator
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    One twinset of trimix is useful and if rich enough can get quite low before refilling. Air tops are your friend!

    For oxygen single 12s are better.

    A couple of air cylinders IS useful for suit bottles and air topping. These are also the only ones that get kept in test. They also get wet when I blow bubbles on Chesil.

    A number of diluent bottles makes life simpler.

    (I have a lot of cylinders in my garage, definitely more than I need)
     
  6. Wibble

    Wibble Fish don't talk
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    Was vainly hoping that my cylinder count would decrease. Alas it was a only a dream as more smaller tins appear.

    Like the idea of a strip of tape for the subsequent dilutions.

    I guess that there is a use for 300 bar cylinders; as banks.
     
  7. Dave Whitlow

    Dave Whitlow Super Moderator
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    Not less cylinders just optimised gas use. The contents of my garage would exceed some dive shops! :eek:

    The huge gain is the infrequency of needing to drive and acquire fresh gas and the reality that the amount of gas actually used is tiny.

    With O2 and diluent banked the only external need is the occasional air fill.

    Forget 300 bar. Cylinders are heavier, fills are rarely delivered, and receiving cylinders won't match.
     
  8. Wibble

    Wibble Fish don't talk
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    Been working on sidemounting the bailout tins. I say tins as, with the exception of a shallow non-deco dive, it's always a good idea to have an optimised bailout decompression gas.

    The first thing that needed to be sorted out was the Revo harness which is rather clip-tastic and doesn't allow a backup torch or additional D-rings to be added to the chest part. Replaced the harness with a one-piece Halcyon harness with a breaking loop (using the DirZone buckle). This enables two D-rings to be threaded on each side; the lower for the cylinder and the upper for clipping 'stuff' off. This works better when using sidemount bungee to pull the cylinders back under one's armpits; i.e. jump in with the cylinders clipped on as 'normal' then pull the bungee around and pull the cylinders back once on the bottom.


    Revo harness 1.jpg
    Revo harness 2.jpg




    This is now modified to use a couple of shoulder pads and is a lot more comfy to carry the unit when wearing a T-shirt. It's also been furkled with to get the positioning exact.

    Revo harness 4.jpg

    Revo harness 5.jpg


    Have settled on adding a small length of stiff webbing attacked with a soldering iron to generate the holes for the sidemount bungees. These are low enough to clear one's armpits, so it's comfy.
    Revo bungee mount 3.jpg


    The point of all of this is to get it sorted such that I can carry the tins dangling from the D-rings, but easily bungee the tins out of the way in the water.

    Just need to add some photos of the whole thing in the water.
     
  9. Wibble

    Wibble Fish don't talk
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    Ran a bailout ascent yesterday. Had done about 75 mins on the bottom, only 30ish metres, so about 30 mins of deco. Was running 28% for bottom gas and 70% for deco gas, both in 7 litre tins. Wanted to check that all was well in the ascent; to use a second small yellow warning SMB up the main SMB line; and to remind myself of how much gas is consumed.

    Was running the deco off of the wrist mounted Petrel controller, but wanted to ensure the NERD was updated too (backup computer and the one I use to log the dives). Becomes quite interesting trying to position the NERD to see it when not on the loop so that I could duplicate the gas switch.

    The ascent was easy, as are all open circuit ascents! Needed to occasionally dump the gas from the loop as the orifice was injecting O2.

    Will run another soon, this time as a mid-water bailout.

    Still delighted with my choice of rebreather. Really appreciate how clean the chest area is.
     
  10. Vanny

    Vanny Well-Known Member

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    Just an observation from my training / experience so may not be relevant to your unit.

    In the bailing out all the way to the surface scenario we’re assuming a catastrophic failure on the unit , would you not shut off the O2 valve , therefore eliminating the orifice , meaning the loop contents have much less effect during ascent/deco. Not a massive inconvenience but in a real poo fan interface one less thing to manage.
     
  11. Wibble

    Wibble Fish don't talk
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    Good point. Did consider shutting down the O2, but thought that was begging bother for the bailout drill preventing a return to the unit.

    Aside from the racket from the bubbles, the 6m stop was almost pleasant as buoyancy control is so easy, so it wasn’t a significant challenge to dump the loop gas every few mins (and is good loop dumping practice).

    When I got home and cleaned the unit I was pleased to see no additional water in the unit, thus managed the drill without flooding it.


    Was also good to be reminded that bottom gas usage is a lot higher than expected — 90 bar (of ali7) in 13 mins. So next time get a wiggle on and get the heck out of Dodge.
     
  12. Vanny

    Vanny Well-Known Member

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    My observation would be that your practicing the resolution not the issue that would bring You to that point. Bailing out and ascending is simple, more so for you now having just come off OC , it should feel like going home.

    From an instructional point of view I would expect you to practice for the issue that brings you to a bailout resolution. E.g high PO2 , you run the drill as you’ve been taught , theoretically come to the conclusion you can’t stay or return to the loop so the resolution is BO and go home.

    I’m trying to think of an OC analogy. I guess I’d liken it to twin set , switch regs. Easy done , but you haven’t run through the diagnosis of why your switching or carried out the valve drill.

    The fact your practicing is good just expand to include the full drill. I’m a little surprised your instructor hasn’t expressed this , running scenarios in your head during the dive / deco , you should have a list of issues and appropriate resolutions to practice from mod1.
     
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  13. Wibble

    Wibble Fish don't talk
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    As you said, the bailout's easy for a recent OC person. Was useful to do a reminder, but no new skills or knowledge gained.

    I do run the unit manually in "parachute" mode; setting the setpoint to 1.2 and running the unit at 1.3 or 1.4 (still shallowish). Am checking both the NERD and the controller agree. Definitely getting a feeling for when to inject O2, and for how long. Interesting watching the O2 'bubble' run over the cells and have definitely reduced the injections to lots of small injections rather than a longer one. This is also good for realising when you're task loaded as to how much more O2 you consume. In essence if the solenoid injects, it's to be considered a reminder slap!

    On every dive I do what I hope is "good practice": on reaching the bottom, settle down and bailout, back on the loop, restow the hose, sort out the sidemount bungees. On the ascents I do full O2 flushes and occasionally check that the cells can read 1.6+.

    Should do some full 'loose lips' dil flushes. Now noted.

    Getting much easier to control this now. Just short of 40 hours thus far.

    There's no question that the hardest thing about CCR is the ascent and deco hangs. The ascent is full of the paranoia of being out of control; think this worry is getting in the way as it's not out of control, but probably a bit slower than it should be especially when swinging under the SMB line (tide takes it off sideways and coming up means swimming under the line and not descending). It's hard holding the stop too, again too much concern of breaking the ceiling.

    More practice required. It's definitely getting better, but it's really telling to see yesterday's bailout curve being flatter than most of my CC hangs.
     
  14. Vanny

    Vanny Well-Known Member

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    Ok, I’m writing this as your reply leaves me concerned. Hopefully unduly but it’s how you’ve expressed that reply. So please take the following the way it’s intended to keep you safe and enjoying ccr Diving.

    In no particular order ; what was the point of the BO , you say nothing learned / new. If we’re going to train/practice let’s have an objective, as I outlined above this should be part of a drill, not just the resolution.

    “Should do more dil flushes” - this should be a core skill you are constantly practicing. Flushing enables you to validate cells and provide a very temporary known safe gas if there’s an issue you can deal with whilst staying on the loop.

    O2 injection on ascent- yes good but whilst I have some appreciation of the way your managing your loop content PPO2 this is something you can do throughout the dive. On initial descent it will show cells are capable, inspo scrubber takes 20 mins or so to warm up , again temperature and humidity can bring cell issues so as the dive progresses checking cells reactivity is good. I guess some of this is mitigated by the manual management of PPO2.
    O2 injection- short bursts are your friend with increasing depth you’ll discover one long bursts will push your ppo2 way past where you want it.

    your reply doesn’t hint at any response procedures to the main issues on ccr - the 3 H’s , hypoxia , hyperoxia & hypercapnia. I sincerely hope you have a set of procedures to deal with both the electronic alarms and physiological symptoms- these I what I would expect you be continually practicing not only now but throughout your time ccr diving.

    you say the stops are hard and your BO ascent profile reflect this. As I’ve said before slow the progression down , get that curve better and away from the ascent paranoia.
    You are wracking up hours pretty quick but I fear this will give you a false sense of achievement, all the skills need hitting home , not just the ability to perform a dive and deco stop.
     
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  15. Dave Whitlow

    Dave Whitlow Super Moderator
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    Interesting thought about switching off the O2 and one I don't like.

    On my mod1 (10 years ago last weekend, said Facebook) I was taught that, after bailout out, the O2 is left on so the loop can later offer a breathable gas. Yes, it means loop volume needs to be controlled on ascent but, apart from catastrophic flood or CO2 issue, it retains the option of returning to the loop as oxygen rebreather at 6m. Switching off the O2 would result in an hypoxic gas in the loop and expose the depressurised O2 system to the risk of water ingress. It sounds a terrible idea.

    Optimal procedure on units with a leaky valve that continues to inject oxygen is something I'd put to someone qualified to teach the unit. Wasn't this covered on mod1?
     
  16. Wibble

    Wibble Fish don't talk
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    Thanks. Much appreciated.

    By "not a lot learned" from the bailout, I meant that the actual bailing out is pretty much old OC skills just with added third bag of buoyancy control. It was a very useful exercise and one I'll periodically repeat.

    Especially appreciate this:
    Not heard of the term "3 H's" before. A very succinct and useful phrase.

    I think I'm implicitly addressing all of these in my diving and dive practices. Hypoxia: am constantly monitoring the PPO2, with the manual injection it does need to be actively monitored (which is why I like manual rather than relying on the controller); at deco I'll flush up the PPO2. Hyperoxia: ditto**. Hypercapnia: "feeling funny, bailout" then work out what's going on.

    ** Am monitoring the PPO2 and adjust O2 levels as oxygen is consumed or depth changes. It's clear that I've been omitting dil flushes, simply because I've not needed to do this. Will explicitly drill that over the next few dives and thereafter.

    The Revo does help in that the pre-breathe process requires the RMS (scrubber monitoring system) to show more than 45 mins before moving. By the time I've waddled over to the jump this will be over 2 hours - and I'm feeling 'right'. I think this is a useful way of ensuring that the scrubber's working.


    I know I'm pushing the hours and it does need time to 'sink in'. I'm mainly doing this as I've the opportunity and we've a really short season this year.

    One of my paranoias is complacency. Am doing all I can to ensure I follow checklists even when I know them; and to keep practising the skills.
     
    #96 Wibble, Sep 7, 2020
    Last edited: Sep 7, 2020
    JimmE and Vanny like this.
  17. Vanny

    Vanny Well-Known Member

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    Understand your concern but looking specifically at the Inspo , ignoring the latest gizmo to shut off the solenoid , which isn’t standard. How , at mod1 level during BO would you control O2 injection with a stuck open solenoid ? You can’t. The response for this both from my TDI mod1 and what’s currently taught on BSAC mod1 is bail , try to resolve , can’t it’s stuck , stay on BO , shut off O2 , computers switched to OC , go home. The latest range of optional mavs has a shut off to the solenoid so in this scenario you could run manually , which I think is great. I was also taught the option of fluttering the O2 valve. I did in fact use this when my solenoid stuck open in February , however this skill isn’t part of the BSAC syllabus.
     
  18. Dave Whitlow

    Dave Whitlow Super Moderator
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    When I did my CCR training (to mod3) with Rich Stevenson a stuck solenoid wasn't a crisis worthy of the madness that is deep OC diving. I've seen nothing to change my view. Feathering the O2 works. It is annoying but it works. Why is bailout better? With independent pp02 monitoring the only reasons to bail out (apart from loss of O2, or a suitably rich OC mixture) are a flooded loop or a CO2 issue. In every other situation staying on the loop is the best survival plan.

    'If in doubt bail out' is mod1 thinking and really doesn't translate to deeper diving and has no place is in any CCR training beyond mod1. The gas requirements for an OC return from a deep CCR dive are terrifying, and should be avoided where possible. If BSAC say otherwise then I'll disagree with them like I did with the hogloop debacle.
     
    #98 Dave Whitlow, Sep 7, 2020
    Last edited: Sep 8, 2020
  19. Vanny

    Vanny Well-Known Member

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    Dave were we’re not talking mod2 or 3 training. We’re talking to Wibble at mod1 and current training procedures and standards for mod1. I never mentioned standards for deeper diving from any agency.
     
  20. Vanny

    Vanny Well-Known Member

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    Also I didn’t criticize feathering the valve , in fact I said I’ve used it. No where did I say bailout is better Simply what is taught now and it’s relevance to wibbles current activities.

    you say , when you've bailed out you leave the O2 valve open , on the inspo you can’t leave a stuck open solenoid with the O2 valve open. Your wrong. It’ll continue to inject , empty the cylinder and completely screw you bouyancy for the ascent. To feather the valve you must have closed it.
     

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