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Wibble's CCR odyssey

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

  1. Dave Whitlow

    Dave Whitlow Super Moderator
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    I can't comment on current standards but I don't recall any change in valve protocols from mod 1 through to mod 3. If things have changed in 10 years than maybe things have changed. Maybe my instructor diverged from standards. Maybe IANTD differed. Does it matter?
     
  2. Dave Whitlow

    Dave Whitlow Super Moderator
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    I'm pleased to say I've never needed to deal with a stuck solenoid during a dive and the only time I've feathered the valve has been in drills. On both times I did bail out (last was in 2011) I made an ascent to the surface with the O2 on, like I was taught in my mod 1.

    The protocols for the revo would need to be different as a leaky valve is similar to an open solenoid. Therefore, turning off is the only option for wibble after bailing out. On the inspo (the only unit I've ever dived) turning off the O2 is an option that is not required, or desirable, in most bailout situations. Keeping the loop available is definitely a better choice.
     
  3. Vanny

    Vanny Well-Known Member

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    No it doesn’t matter.

    I am not talking about shutting off the O2 in all scenario’s , the only one I’m discussing is stuck open solenoid and in particular on the inspo. Other problems have other solutions , as you say with experience bailing out becomes very much not the preferred option.

    You have reached the same conclusion I made earlier. For Wibble coming off the loop I would expect closing down the O2 to be a benefit. Therefore, the point I’ve been making is that Wibble needs to execute the full drill and resolution (which ever drill & appropriate solution) rather than just practice a bailout ascent. For practice to be effective and promote muscle memory we need to involve the full scenario not pick out the bits we fancy.
     
  4. Wibble

    Wibble Fish don't talk
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    We did feather the valves. But being MOD1, a stuck O2 solenoid would mean it's bailout time.

    Totally agree there's other options to workaround a stuck O2 solenoid: feathering, injecting diluent (SCR), offboard connection to a rich mix (which you'd have if you're diving to any depth or duration).

    Am currently focussing my skills & drills on having "more than" sufficient bailout for all the depths I'm doing (using standard OC gas calculations). When I have enough CCR experience I'll then look at MOD2 and incorporate those skills.

    In some ways it would be nice to have a list of drills & skills to practice outside of the normal dive process. Off the top of my head I can think of:
    * Diluent flush
    * "boom" shutdown drills (if a load of bubbles happened) - shutdown everything then slowly open again
    * Offboard diluent injection (i.e. connecting and using the bailout)
    * Offboard O2 or rich mix injection (connecting and using the bailout rich deco mix)

    Others to practice?
     
  5. Vanny

    Vanny Well-Known Member

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    Whilst your partly manual ccr I’m guessing there’s still a need to have responses to low / high PPO2 with or without alarms?

    cell error response ?

    fluid in loop ?

    probably others , BUT I would refer back to your instructor for a definitive list appropriate to your unit.
     
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  6. Dave Whitlow

    Dave Whitlow Super Moderator
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    Why feather the valve if you are going to bail out? I remember doing a circuit of New England quarry feathering the O2 valve to maintain ppo2 of 0.7 with setpoint at 1.3. Definitely a tedious process though and I can see the appeal of bailing out.
    - dodging overweighted twinset divers plummeting from above the spacial awareness of a brick
    - filling sacks with scallops and using a lift bag to keep them off the seabed
    - doing a drift dive over an undulating seabed without using lots of diluent
    - do your stops with your reel in front of you and not being used to assist buoyancy
    - at the end of your dive do extra stops at metre increment up 1m
     
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  7. barrygoss

    barrygoss Active Member

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    Learning when deco has completed, without a computer.

    And although that sounds an impossible skill, it’s actually very easy.


    B
     
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  8. Wibble

    Wibble Fish don't talk
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    Watching the O2 levels dropping as you expire N2, until you stop off gassing.
     
  9. barrygoss

    barrygoss Active Member

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    And why you can’t hold a stop as easily. Nigel H worked it out to be about 2l.
    That’s why your stops are so much trouble. You went too fast and straight to deco. Stops on no deco dives are easier.

    You’ve started to think. (There’s hope)

    B
     
  10. Wibble

    Wibble Fish don't talk
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    This buoyancy malarkey's interesting, or to me certainly. On a wreck I can do all the faffing from the bubble+bail (bailing out, back on loop, sodding around re-stowing the hose, sorting out the sidemount bungees for the tins...) and all without moving vertically. Same with nosing around inside a wreck, all still and calm. Not a problem outside either. Really enjoying the bottom phase of diving, and particularly the calm, even with the recent crap vis.

    Then comes the ascent and the deco stops. It's still too much of that conscious competence which is hard work, far harder than the simple OC stop which is definitely unconscious competence. Getting better but definitely needs more practice.

    Searching for that nirvana of almost falling asleep with the SMB spool dancing up and down below me. Give it time...
     
  11. barrygoss

    barrygoss Active Member

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    And you stopped thinking......
    On oc every time you breathe out you vent the soda stream to the surface
    On CCR you vent into the loop.

    The CCR stop will never be static. Because you can’t control off gassing.

    B
     
  12. Wibble

    Wibble Fish don't talk
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    I realise that. The main issue with CCR is the missing micro-adjustments which OC facilitates through breath control. With CCR you've got the slow increase of buoyancy as you're off-gassing, but you've also got to be quick to react to vertical movements before they become significant. As the PPO2 drops, some breath out through the nose and a quick squirt of O2 restores the levels.
     
  13. barrygoss

    barrygoss Active Member

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    And there’s the bov need ;) (apart from the bailout scenario;) )
    And the dil flush with setpoint restoration. Tbh that’s deco until the off gassing stops. Just do
    It all without moving vertically

    B
     
  14. Dave Whitlow

    Dave Whitlow Super Moderator
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    The ascent gets easier with time.... but no falling asleep for me as I like to check what I'm breathing and avoid vertical drift.
    However, thank you for the reminder to sort out my deco tunes for tomorrow!
     
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  15. barrygoss

    barrygoss Active Member

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    Any space this weekend? I have the keys to the rib, lacking another boat handler. Pink pass is good so willing to pay 4 times my normal dive day rate for a hard boat this weekend

    B
     
  16. Dave Whitlow

    Dave Whitlow Super Moderator
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    and there's getting deco tunes out of the bag, stuffing headphones into the hood, switching on, and enjoying the music.
    all without moving vertically...
     
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  17. Dave Whitlow

    Dave Whitlow Super Moderator
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    I'm diving off Wey Chieftain tomorrow (Gripfast) and have nothing planned for the weekend (no boats with spaces).
    No idea about that other bunch as I stopped diving with them a few months back. It was my choice and maybe in future I'll return but not this year.

    (I am a BSAC boat handler, albeit a bit rusty with RIBs and could probably find company)
     
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  18. Wibble

    Wibble Fish don't talk
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    Bailout Valves (BOV).

    There seems to be three main arguments for using a BOV: a CO2 hit, the convenience of taking a sanity breath and being able to get on the loop if you've no breath left. There seems to be a consensus that in the extremely unlikely event that there was a CO2 'hit', the BOV could be a lifesaver because it is apparently nigh-on impossible to switch from the rebreather loop to an open circuit regulator when gasping for breath. The convenience of being able to switch from CCR to OC could mean you'd switch more early to get sanity breaths rather than switching from a bailout regulator stored on a stage.

    Getting back on a loop when using a normal DSV (Dive Surface Valve) mouthpiece requires some breath in your lungs in order to expel water in the mouthpiece. If you don't do this, some water will enter the loop when you switch over to CCR. Although it's only a mouthful of water, this is inconvenient with some rebreathers as it could find its way back into the mouthpiece (yes, this is primarily a Revo issue)

    Installing a BOV brings lots of other issues, not least how good the BOV is at normal breathing; it's reliability; the gas source it's connected to; it's additional weight and size for the mouthpiece, cost (circa £1k all in); additional complexity in setting your kit up pre-dive (connecting the bailout to the BOV); management protocols during the dive (particularly connecting the BOV to the correct gas source for the depth, especially if using hypoxic gas).

    I've come to my own conclusion that the exceedingly small risk of a CO2 hit -- it seems that most rebreather divers will never experience this during their whole diving career -- whilst real, doesn't warrant the additional overheads of installing and managing a BOV. Similarly the convenience of switching could arguably make you 'lazy' and doing at least one bailout during every dive will be a better mitigation to train the bailout reflex. Water in the loop of a Revo is annoying, but it can be mitigated (and my loop's getting drier as I do more dives and gain experience).

    Might revisit this later, but for now I'll carry on without a BOV.
     
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  19. Vanny

    Vanny Well-Known Member

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    Barry if you do go to your rib I might ask a if you’d pull the bung out of the transom on our wreck. Apparently we’re filling up with water , my boat handler says he pulled it out but I’m not convinced. No worries if not.
     
  20. barrygoss

    barrygoss Active Member

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    Sorry didn’t go, spent the weekend first and second fixing electrics in the conservatory warm roof conversion, will be back now weekend after next as that trips full (6)

    B
     
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