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  1. #21
    Grumpy Git, Not Old Yet...
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    Balls. Typo plus hypo-caffeination = Edit time

    18l/min SAC. Which is 3/4 bar/min.
    Last edited by Ian_6301; 28-09-2015 at 09:22 AM.
    DISCLAIMER: If you don't understand this shit, ask a grown up, preferably someone with deep pockets, who your widow/kids can sue. Don't trust people on the internet with your life, your credit card details or your naked selfies! This advice may contain, or indeed be written by someone who is (clinically), nuts.

  2. #22
    Grumpy Git, Not Old Yet...
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    Quote Originally Posted by londonsean69 View Post
    Your maths is way out.

    5bar (depth) x 30mins (time) x 28l/min (SAC) = 4200 litres of gas, which in your twin 12s is 175 bar.

    PS - to be using 2/3rs of a bar per minute in twin 12s, your SAC would need to be 16
    and THAT is why you don't try to learn this shit on the interwebz...
    DISCLAIMER: If you don't understand this shit, ask a grown up, preferably someone with deep pockets, who your widow/kids can sue. Don't trust people on the internet with your life, your credit card details or your naked selfies! This advice may contain, or indeed be written by someone who is (clinically), nuts.

  3. #23
    Nicotine, valium, vicodin... notdeadyet's Avatar
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    Quote Originally Posted by Ian_6301 View Post
    and THAT is why you don't try to learn this shit on the interwebz...
    Yep. It was much more fun when you just bought a twinset and taught yourself in the water. Even better is buying a rebreather and teaching yourself

    Sent from my GT-I9300 using Tapatalk
    Caliph Hamish Aw-Michty Ay-Ya-Bastard, Spiritual leader of Scottish State in England

  4. #24
    Established TDF Member Iain Smith's Avatar
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    Quote Originally Posted by Ian_6301 View Post
    1. How much gas do I need on the bottom?

    Gas required (in bar) = Avg Depth (in Bar) x Consumption rate at Surface (in Bar/min) x Minutes of Bottom Time.

    eg, in a 24L twinset, with an SAC of 18L/min, I chew through 3/4 of a bar per minute, so a 30 min bottom time at 40m looks like this:

    Gar Required (in Bar) = 5bar x 3/4 x 30 = 5x22.5 = 112.5 bar.
    Or, to keep the numbers even simpler, 18L/min ≈ 4 bar per 5 minute "block". 30 min = 6 "blocks"

    5ata x 4 x 6 = 120 bar.

  5. #25
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    Quote Originally Posted by Ian_6301 View Post
    and THAT is why you don't try to learn this shit on the interwebz...
    Isn't that quite similar to calculating it in your head underwater?

    I find that I get about 30% more stupid underwater. And I am pretty stupid on the surface already.

    Digs.

  6. #26
    Bacon fiend londonsean69's Avatar
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    Quote Originally Posted by notdeadyet View Post
    Yep. It was much more fun when you just bought a twinset and taught yourself in the water. Even better is buying a rebreather and teaching yourself
    I've never been as cautious when diving as when I had the EDO-04. No monitoring, and only a vague idea of what I was doing.
    The vagueness remains, but the SCR is long gone
    Sean

    A few more pics - www.arrowpix.com

  7. #27
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    Quote Originally Posted by notdeadyet View Post
    Yep. It was much more fun when you just bought a twinset and taught yourself in the water. Even better is buying a rebreather and teaching yourself
    I went the first option. Well, it was independent twins for a bit.

    Never did the second option. I have been on boats over the years with rebreather divers carrying quite a lot of bailout but still probably not enough to get them out of the water if they had to come off the loop. And for those who bought a rebreather because they were gas pigs, not a hope. I doubt they'd last long enough to get up to 21m for the drop tank.
    See http://www.scuba-addict.co.uk/ for trip reports including Grand Cayman, Tulum and the Philippines

  8. #28
    Established TDF Member matt's Avatar
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    Quote Originally Posted by Ian_6301 View Post
    erm, yeah... 8/10
    I use DDPlan for gas-calculations ;-)

    Matt.

  9. #29
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    Quote Originally Posted by matt View Post
    I use DDPlan for gas-calculations ;-)
    Or Multideco software, runs on Windows 10 unlike DDPlan (unless you've found away?)

  10. #30
    Grumpy Git, Not Old Yet...
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    Quote Originally Posted by JPTaylor View Post
    Or Multideco software, runs on Windows 10 unlike DDPlan (unless you've found away?)
    Spin up a W7 VM...?
    DISCLAIMER: If you don't understand this shit, ask a grown up, preferably someone with deep pockets, who your widow/kids can sue. Don't trust people on the internet with your life, your credit card details or your naked selfies! This advice may contain, or indeed be written by someone who is (clinically), nuts.


 
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