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Anyone got a NOAA Diving Manual Handy? Table Question...

Discussion in 'Basic Scuba Discussions' started by Crazy Fingers, Feb 18, 2007.

  1. Crazy Fingers

    Crazy Fingers Barracuda

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    On a discussion on another board, we are trying to determine if bouncing 300 feet is even possible on an AL-80 with air. (Yes, we all realize that this is completely stupid, people have died doing it, you will get oxtox, you will get insanely narced etc. etc. It's just an academic argument. Basically, does an 80 have the gas in it to even let you come close?)

    If we hauled *** down at 100 fpm, touched the bottom, and started coming back up, this would be a dive to 300 feet for 3 minutes on air. What are the required stops and times?

    I think the NOAA Diving Manual goes to 300 feet. I can't find any tables that go this deep online.

    Thanks.
     
  2. Gene_Hobbs

    Gene_Hobbs Instructor, Scuba

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    US Navy chapter nine will cover dives to 300 fsw.
     
  3. SparticleBrane

    SparticleBrane DIR Practitioner

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    NOAA standard air tables go to 130fsw.
    Navy tables go to 300fsw for air. According to the table, for a 300fsw dive with a bottom time of 5 minutes or less, you have a 3 minute stop at 20fsw and a 3 minute stop at 10fsw.

    I'll assume a SAC rate of 0.5cf/min. If you drop down at 100fpm, it'll take 3 minutes to hit the bottom. If you ascend at 30ft/min you're looking at 10 minutes surfacing, plus the 3 minute stop at 20fsw and the 3 minute stop at 10fsw.
    For the purposes of easy calculations, we'll assume 13 minutes (3 for descent and 10 for ascent) at 150fsw (average depth), then add in the stops.
    The ascent and descent would use 36cf of air. The stops would add in ~4.4cf so you're looking at just over 40cf.

    Someone check my calculations.
     
  4. Crazy Fingers

    Crazy Fingers Barracuda

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    Thank you sir, that's exactly what I needed.
     
  5. dsteding

    dsteding DIR Practitioner

    # of Dives: 200 - 499
    Location: Seattle, downtown
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    Maybe it is because I am a hoover, but I'd probably use an RMV of .75 for that. 150 is six ATAs, so you are using 4.5 cf/min average, or ~60 cf without stops . . . of course, at 300 fsw you are using gas at about 8 cf/min, make it 10-12 if you are stressed (easily) so you screw it up or stop to smell the roses and you are dead.
     
  6. SparticleBrane

    SparticleBrane DIR Practitioner

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    Just trying to do an absolutely optimal scenario and give a huge benefit of a doubt. :)
     
  7. Crazy Fingers

    Crazy Fingers Barracuda

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    Here are the numbers I ran:

    On descent, since the depth changes so much I made a formula and integrated it.
    _______________________________________________________________
    Constants:
    volumetric gas rate = 0.5 cuft/min (let's assume a diver with good air consumption)
    descent rate = 100 fpm

    Equations:
    rate of gas usage at any depth = (0.5 cuft/min)([Depth/33] + 1)
    Depth = 100 ft/min x time (min)

    Therefore:
    Rate of gas usage at any point in time = (0.5cuft/min)((100ft/min x time)/33) + 1)

    Integrate over time:
    Limits: T=0 minutes to T=3 minutes
    3
    (
    | (.5cuft/min)((100ft/min x T)/33) + 1) dT
    )
    0

    And I get 9.75 scft of gas used on the descent.
    __________________________________________________________

    For ascent from 300 to 20 feet, I did the same thing except now
    Depth = 300 - 30T
    Air consumption at any time = 0.5*((300-30T/33) + 1)
    Ascent Time = 9.33 minutes

    Integral is much more of a PITA than the other, but I got 27.27 cuft required on ascent. Roughly 3 times what we needed on the way down, which seems right.

    ___________________________________

    On the stops, I got 2.41 scft used on the first stop, and 1.95 scft used on the last stop. I'm ignoring the usage between the stops since it is very small in comparison.
    ____________________________________

    That gives us 9.75 + 27.27 + 2.41 + 1.95 = 41.4 scft.


    We got the gas, but do we got the cohones? :wink:
     
  8. SparticleBrane

    SparticleBrane DIR Practitioner

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    While integrating it would be fine (and I'm sure it gets the ladies :wink:), personally I believe it's easier to say that since you're dropping at a constant rate, you can just choose the middle point as your average depth and use that in your air consumption calculations.
    Either way will work fine. :)
     
  9. Crazy Fingers

    Crazy Fingers Barracuda

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    Hah, yeah... I went overboard. Sometimes though, my gf loves it when I talk math to her. :wink: It's the engineer in me. Actually I am glad I did it because I haven't done even a simple calculus problem like that in years and it took me a good 10 minutes of screwing around with it to even get it going. If I hadn't done it, I'd have forgotten forever!!

    You're right though, average is easier. MUCH easier. :(
     
  10. dsteding

    dsteding DIR Practitioner

    # of Dives: 200 - 499
    Location: Seattle, downtown
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    Understood . . . but the optimal scenario may be to not breathe for the first 10 minutes of the dive . . . sometimes I feel like that is the only way I can match the consumption of Lynne or Bob :wink:
     

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