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Find the screw-ups

Discussion in 'Rebreather Diving' started by rjack321, Jul 31, 2019.

  1. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: I'm a Fish!
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    the dil doesn't really bother me, but I'm a cave diver, so there's that. I usually shoot for 1.0 bottom dil ppO2 for cell validation, but close enough given the circumstances, I certainly wouldn't call a dive because of that, though I would probably have asked for a bit more He due to the END.

    Bottom ppO2 is a lot higher than I normally like to run though, even with the rich dil, it comes down but that's personal preference.

    Descent rate looks fine for OW at about 60fpm, nbd there and ppO2 was stable which is what matters.

    The last few mins at low ppO2 is weird to me but you were already fully cleaned out.
    Strange stop depths though but to each his own there, though depth stability looks a little rough, but who's to say what the surge was like.

    your comment on flaw 2 for ascent rate is what it is. 17fpm is a lot better than 70fpm, certainly not what I would call a cockup, especially on a CCR.

    Flaw #3 I would actually call out as no air breaks instead of letting the ppO2 drop. Your sinus's like the air breaks which helps with deco efficiency to boot.

    The 1.6 check I do, and is especially important if you're running a 1.3/4 for setpoint. I usually run a 1.0/1.1 so it isn't really critical on descent since I'm running at the level that I calibrated with. If I'm going to run a high setpoint on deco, at least before 20ft, then I will do it on the way down since I need to know that they aren't limited before I get back to 20ft. If my only plan to use setpoints higher than what the bottom dil would be is on the 20ft stop with O2 then it doesn't really matter. In this dive I would certainly have checked for limiting at 20ft before I got to the bottom and flushed. I try to splash with a loop full of O2 on every dive to not only handle that but there has also been some research done that says it helps the tissues to have that hit of O2 before you start diving.
     
  2. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
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    They already tried "fixing" the original undivable dil so I just let it go. At $2/cf and more "traditional" TDI etc ENDs many Great Lakes divers are using a lot less helium than you & I would choose. The next fill was 12/48 IIRC. I'd have loved diving 12/65 for the 3 dives we did on this wreck (max depth for dive3 was 245ft).

    less than 2 hrs I have no problem running 1.3. Taking 10-15mins off the deco is a bigger deal if you end up having a suit leak, even the 59F thermocline is not that friendly

    They were basically 73-75 IIRC
    62-65
    etc
    Not too surge-y but the line could definitely yank you above the ceiling. Trying to ride the ceiling for an hour in OW is honestly exhausting and doesn't really matter. I was also hovering just above my buddy who was consistently below me a little bit with his GFs. TTS-wise it doesn't matter. Plus - Honestly I was far more focused on him once I realized his 25min deco oops. I wasn't totally sure what the issue was (forgetting to adjust setpoint, shearwater fail, wrong dil, etc) so I wasn't as focused on me as I could have been.

    For 65mins of deco I don't really worry about snot.
    With my TOS CLs I would actually have to dil flush to get the ppO2 down. Or let the ADV fire.

    Not entirely sure what was going through my head on descent. (this dive was 8 days ago)
    Spiking on descent sounds all great but when the dil is too hot, I think I was being paranoid about how much dil I'd need to dilute the O2 back down again.

     
  3. Zef

    Zef Divemaster

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    I find this dsicussion very interesting but much of it is over my head as I do not dive CCR or to tech depths. I would really like to follow the discussion closer, can anyone suggest some online reading that would give me a primer to help better understand what is being discussed?'

    -Z
     
    aviator8 and ChuckP like this.
  4. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
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    Although there are a couple of ok paper books delving into CCRs, I don't know of anything beyond the bare rudiments of CCRs that is online. But just ask, happy to try and elaborate. Maybe one issue/concept at a time.
     
    Zef likes this.
  5. JohnnyC

    JohnnyC Divemaster

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    There isn't much in the way of easily digestible material online that's at a rudimentary level. Even the wiki article on rebreathers gets pretty in depth. Rebreather - Wikipedia

    Many of the specifics are only relevant when viewed within the scope of other concepts. Talking about current limiting without knowledge of the construction and functionality of a galvanic oxygen cell is pretty meaningless. Talking about current limiting without understanding the pitfalls of high PO2 exposure is also fairly meaningless. Talking about spiking O2 to validate cells for current limiting is meaningless if you don't understand the way the partial pressure of gases, specifically oxygen, relates to the function and design of a rebreather, and how various units control loop PO2. Etc., etc., etc. ad infinitum......

    Get ahold of "Rebreathers Simplofied" by Mel Clark. It's a pretty basic primer, and would be an ok start. In the mean time, ask questions.
     
    Zef, Schwob, tbone1004 and 1 other person like this.
  6. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
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    Remembering a bit more especially in the intermediate stops (like 40ft)

    I was up at ~37ft while my buddy was below at 41ft This was around the time I realized how much more deco he had than me. And trying to look over his shoulder more & more. So I was compromising on my stops vs his stops. The profiles came back into alignment up at 20ft. Not my regular buddy and at the time I thought his hardwired shearwater was broken.
     
  7. Schwob

    Schwob Solo Diver

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    Warning, I am wondering a bit from a point of relative ignorance here. Doubly so if that misding item already was covered in following replies but went straight over my head. So here it goes:
    Crack divers like you wouldn't stop at some shallow depth to do a thorough bubble check etc. prior to "abyssing" and might just do it on the plunge down..., ... or would they stop? If the latter, then that seems missing (at least not 30 sec. or more)
     
  8. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
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    we did a bubble check actually. Its so fast on a CCR (bubbles are yes/no when there's no exhalations getting in the way) that you basically don't see that 20second pause

    Earlier in the week I actually did have a weird leak which was not detectable on positive or negative check. It wasn't even detectable in the water unless I was prone. Not sure exactly what cause that (hair?) but getting out, removing, the hose, wiping the relevant O-ring with a finger and reinstalling fixed it.
     
  9. huwporter

    huwporter DIR Practitioner

    # of Dives: 1,000 - 2,499
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    Thanks for putting it out there for discussion, it's good to not pretend we are all perfect. :)
     
    rjack321 likes this.
  10. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
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    Eh but thanks, I never claimed to be perfect. Between my two units (meg and kiss sidewinder) I have roughly 275hrs over 5 years. 75% of my hours are in <50F/10C water which tends to limit hours.

    Overall I am still a baby in the grand scheme of CCR things. I have a cave profile from last month I can throw up later.
     
    JonG1 likes this.

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