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Air Integration & NDL Accuracy?

Discussion in 'Shearwater Research' started by CaveSloth, Nov 12, 2019.

  1. rhwestfall

    rhwestfall Solo Diver

    # of Dives: 200 - 499
    Location: "La Grande Ile"
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    Oh, and I have a bridge to sell....
     
  2. Jan_oi

    Jan_oi Angel Fish

    # of Dives: 100 - 199
    Location: Shanghai
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    I'm wondering, and it's a bit related to this topic, the following scenario:
    - Perdix AI in OC REC, Transmitter, Singe Tank Nitrox 32%
    - 40m deep watching a school of hammerhead
    - NDL is reached so deco stop mandatory. GTR is OFF (as deco stop)
    - what data should I monitor to "know" how long more I could reasonably keep enjoying the school at 40m ?
    I was thinking of multiplying TTS by SAC and comparing it with T1.

    (I just got a Perdix AI and didn't use it yet, now in the reading phase to understand it more. Used to dive with a basic Suunto D4i before that).
     
  3. KenGordon

    KenGordon Rebreather Pilot

    2,652
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    Before you get in the water you plan the dive. What the computer tells you in a dive like that is really not important. Using 32% to 40m (don’t do this at home) will mean the deco will not be enormous but on a single your bottom time will be maybe 20 minutes. You will know your SAC beforehand or you can’t plan the dive and so should not be thinking of going to 40m.

    If you don’t know to expect a given profile or not then work through a few examples and figure out a gas pressure as the minimum allowed before ascending from particular depths. Either remember those or write them down. Don’t assume you can ascend at 10m/minute unless you have tried it and know you really can. Absolutely do not assume that you can reach the surface in the TTS time unless you have practiced significant ascents and know you can hit the numbers. Nobody manages that first time.

    Hammerheads school over a range of depths. If some are at 40 some will be above that, probably most of the way to the surface. Pick a depth where you will remember what the experience was like.
     
  4. Jan_oi

    Jan_oi Angel Fish

    # of Dives: 100 - 199
    Location: Shanghai
    7
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    Hi KenGordon,
    what would be your answer to the following statement:
    - Perdix AI in OC REC, Transmitter, Singe Tank Nitrox 32%
    - Dive planned with a stop of 3min at 40m to look at a nice cave entrance
    - NDL is reached after 3min, as planned, so deco stop mandatory. GTR is OFF (as deco stop)
    - my buddy is having an issue with his equipment OR make up another fact that makes me stay longer than 3min at -40m
    - what data should I monitor to "estimate" how long more I could "reasonably" stay at 40m ?

    Nothing sarcastic here, I hope you understand my point and the fact that I want to learn something from experienced divers.
     
  5. Mike1967

    Mike1967 Manta Ray

    # of Dives: 100 - 199
    Location: Victoria, Australia
    915
    382
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    @Jan_oi
    You realise the MOD for 32% is 34m yeah?
     
    Andrei Astra likes this.
  6. Jan_oi

    Jan_oi Angel Fish

    # of Dives: 100 - 199
    Location: Shanghai
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    PpO2 1,6 bar 32% 40m.
    But again, it's not the point... Replace in my statement 32% by 29%, 40m by 32m, 3min by 2min.
     
  7. Mike1967

    Mike1967 Manta Ray

    # of Dives: 100 - 199
    Location: Victoria, Australia
    915
    382
    63
    Good luck to you.
     
  8. Jan_oi

    Jan_oi Angel Fish

    # of Dives: 100 - 199
    Location: Shanghai
    7
    1
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    I'm sorry, maybe my poor English doesn't help. I was reading this website (in French sorry!) La plongée au Nitrox | Plongée Plaisir, site officiel

    But again, even though these data are wrong and I'm super sorry about it, it's not really the point ! Is my question that stupid ?! I'd take a yes (and some explanation) as an answer, no pb, it's good to learn anyway !
     
  9. Mod63

    Mod63 Dive Con

    # of Dives: 1,000 - 2,499
    Location:
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    Besides the fact that this is bad practice, your computer should show you an estimated remaining air time or something like that (my old Uwatec does have a remaining botom time, which is the time that I could theoratically still stay at depth but get to the surface including all stops). I never ever rely on this, as it can change quickly and I have seen far to many divers running out of gas by trying to maximise bottom time.

    And my personal MOD for EAN32 is 39.9m :wink: I'm one of those old farts that grew up with ppO2 of 1.6
     
  10. Mike1967

    Mike1967 Manta Ray

    # of Dives: 100 - 199
    Location: Victoria, Australia
    915
    382
    63
    He keeps saying GTR is off.
     

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