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Structuring CCR bailout in OHEs

Discussion in 'Cave Diving' started by JonG1, Sep 29, 2019.

  1. JonG1

    JonG1 Nassau Grouper

    # of Dives: 2,500 - 4,999
    Location: Glossop UK
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    My nearest OHE dives are relatively shallow mines, usually a 10m level and a 20-25m adit, yesterday I was in the 20m level at one of them and took 3x7l as bailout.

    After the dive though I was pondering whether 2x80s would be preferable or in some way more advantageous.

    I am not comfortable with less than 2 bailouts for redundancy, so can stage one of the 7s if preferred, usually the dives don t incur a deco penalty or very minimal so I am purely thinking about return leg gas volumes.

    Obviously 3 bottles is slightly more complex in terms of management, and adds further failure points but adds redundancy and reduces drag if one is dropped.

    Just wasn't sure if someone brighter than me and thought this through.
     
  2. Superlyte27

    Superlyte27 Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Florida
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    2,609
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    Have you taken a course for CCR in overhead? That should answer all of your questions.

    If you did, and it didn't answer all of your questions, then...

    Yes, two bottles for sure imo. The size of those bottles (and the number of those bottles), depend on the penetration, depth and complexity of the dive. Yesterday I took lp50's for 2000' of penetration at 4ata. Sometimes I take LP85's sometimes AL80's.

    I need to know swim speed, depth and consumption.

    If I'm 2000' back at 4ata with a 1cu' sac rate and a swim speed of 50fpm I know that it's going to take 40 minutes at 4 cu'/minute to get out. I need 160cu' of gas to get out if nothing else goes wrong.

    Fortunately, my sac is better than that at double the swim speed. At least in yesterday's cave.
     
  3. JonG1

    JonG1 Nassau Grouper

    # of Dives: 2,500 - 4,999
    Location: Glossop UK
    119
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    Thanks SL, it wasn't so much about calculating the vol required for a given profile, more once you know the volume what decision making influences how many bottles to split it across.
     
  4. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
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    for us still stuck in the imperial system, 7's are steel 45's.

    I personally would take 2x al80's before I took 3x steel bottles any day of the week.

    Whether it is enough or not, whether to stage or not, etc. depends on how far you're going in, whether you only have one way in or out and if that is your planned route *i.e. no traverses*, how fast you plan to move and can move during an incident, etc. and without the information Pete mentioned, there's no way to answer any of that.
     
    Caveeagle likes this.
  5. JonG1

    JonG1 Nassau Grouper

    # of Dives: 2,500 - 4,999
    Location: Glossop UK
    119
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    My 7s are ali and whilst there are multiple route options in the mines I am currently focusing solely on linear dives which share the same entrance/exit.
     
  6. Superlyte27

    Superlyte27 Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Florida
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    2,609
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    If I'm diving thick under garments I have trouble holding a 10' stop in aluminum tanks. Lp50's are the shizzle at 4000psi.
     
    cerich likes this.
  7. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
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    I like my 45s (what you call 7Ls)
    I pump mine to 3800psi / 260bar but they aren't that much gas honestly.

    I would rather bring lp85s (12L) and have all my gas on me instead of bringing 2x lp45s and an al80 stage.
     
  8. Superlyte27

    Superlyte27 Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Florida
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    Depends on the dive. Some places don't fit. Like Sweet Surprise. I can drop the 80, fit through with lp50's. Can't fit through with LP85's. Right tool for the job. And I have all the tools (except the sidewinder, I want that next)
     
  9. JonG1

    JonG1 Nassau Grouper

    # of Dives: 2,500 - 4,999
    Location: Glossop UK
    119
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    I'm newly minted so not going far, not doing complex nav, not wriggling through anything I couldn't drive through etc.

    Just building up so the 7s are ok for now, but will have to haul some 80s in as I improve.

    The shallow section has a main adit at 10m by circa 600m so plenty to go at.
     
    rjack321 likes this.
  10. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
    8,983
    2,833
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    Maybe you need a diet :p
    I fit through sweet surprise with 85s.

    I like the sidewinder despite having pretty much the worst flood tolerance of anything. I have about 75hrs on mine. About half of that with one of Charlie's fathom needle valves. I only have my (comparatively) giant backmounted meg to compare with, plus my friends' prisms, revos, JJs, and SF2s.
     

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