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Rock Bottom Information

Discussion in 'Basic Scuba Discussions' started by lamont, Dec 26, 2006.

  1. WesTexDiver

    WesTexDiver Solo Diver

    # of Dives: 50 - 99
    Location: Midland Texas
    221
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    Under Precise Tables for pony bottles section it states that "Pony bottles do not have a second regulator"....My question would be why do you bring a tank with you that you can not breath out of? All my pony bottles have 2 regulators....a 1st stage regulator, AND a 2nd stage regulator.
     
  2. CompuDude

    CompuDude Divemaster

    # of Dives: 200 - 499
    Location: Studio City, CA, USA
    4,238
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    A first stage plus a second stage makes up one complete regulator system for breathing.

    I believe it means you don't add a secondary second stage (octopus) to a pony. Poor wording on their part.
     
  3. TomP

    TomP Solo Diver

    # of Dives: 200 - 499
    Location: Burlington, NJ
    249
    3
    18
    I dunno, it was clear to me. I've also found Lamont's posts to be among the most the most cogent and valuable on the board. For me, it's a bigger stretch to think that he [or any reasonable diver] would suggest non-functional system.
     
  4. CompuDude

    CompuDude Divemaster

    # of Dives: 200 - 499
    Location: Studio City, CA, USA
    4,238
    4
    0
    I agree 100%, and I also understood what he meant quite well, too, so much so that it didn't occur to me to have an issue with it. But once the question was asked, it became clear that it is indeed a somewhat inaccurate sentence subject to mis-interpretation (thus the poster's query). The wording would be made more accurate simply by changing the sentence to read:

    "Pony bottles do not have a [-]second[/-] secondary second-stage (aka Octopus) regulator".

    Perhaps someone else could tweak it further to be more clear, but put this way, at least it is correct on it's face and cannot be mis-interpreted in the same way.
     
  5. lamont

    lamont Photographer

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    Yeah, I can fix it. I'm sure that I'll find more stuff like that which I'm not happy with.

    I changed a lot of examples that I had of Al80s going to 100 fsw, I included tanks cooling and doing turn pressure calcs on that number so that it was more obvious that you don't blindly use the service pressure of the tank, etc. I'm sure there's a lot more bugs.

    This is a 1.99 (2.0-beta) release. When I get up to 2.6.x it'll be a lot more mature...

    I also don't have an editor and you all are my reviewers...

    fixed to:

    "Since pony bottles only have one second stage regulator these values assume a RMV of 1.0 cu ft / min for a single diver."
     
  6. CompuDude

    CompuDude Divemaster

    # of Dives: 200 - 499
    Location: Studio City, CA, USA
    4,238
    4
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    Nice. :) And I wasn't trying to pick nits, just responding to the question WesTexDiver asked... I think you've done a fantastic job. :)
     
  7. ShoalDiverSA

    ShoalDiverSA Manta Ray

    # of Dives: 50 - 99
    Location: Kwazulu Natal, South Africa
    795
    6
    0
    lamont, thanks for the great article, I found it most informative.

    As I think in metric, I plugged the calcs into Excel. I have attached my worksheet for information/comment.

    What was interesting to me was that I came up with some really useful (easy to remember) "rules of thumb" for the common steel cylinders that are used down here, namely:

    [table 0 0 3]Tank Capacity(litres)|Rock Bottom(Bar)
    15|Depth + 25
    12.2|Depth + 35
    10|Depth + 50[/table]​

    The above calculations render good approximations up to 45/50m (although I wouldn't go anywhere near those depths on air). The approximations also fall on the "safe" side of the actual values in all but one data point (1 bar less than actual).

    I was thrashing this out while doing something else, so I would appreciate comments before committing the figures to memory...

    Cheers,

    Andrew
     

    Attached Files:

  8. lamont

    lamont Photographer

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    Interesting, I'll have to play with the numbers and make some additions when i get a little time...
     
  9. divemaster_jim

    divemaster_jim Solo Diver

    # of Dives: 500 - 999
    Location: Central Virginia / Michigan
    287
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    thanks lamont!
    "Simplified Rock Bottom Values" Makes it easier to figure things on the "fly"
     
  10. Blackwood

    Blackwood DIR Practitioner

    # of Dives: None - Not Certified
    Location: Southern California
    5,535
    318
    83
    Nice read.

    I have a table in my wetnotes of RB for my different tank configurations based on GUE-style min deco. I may make some modifications based on some of your rules of thumb.

    Thanks.


    Edit: If anyone is interested, check out the attached PDF. Standard disclaimers such as "don't use this information" and "don't dive to 130' on EAN32" apply.
     

    Attached Files:

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