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  1. #1
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    12 litre steel stage

    I have been keeping an eye out for a 2nd hand ALi 80, but they are seemingly rare. Recently though I acquired a 12 litre steel cylinder as part of a set and have been wondering how bad an idea it would be to use it in place of an 80.

    It's buoyancy empty equates to 1.116kg as opposed to 2.47kg for an ali 80, so less of an issue if you do bailout.

    It's buoyancy full (with air admittedly) is 1.71kg as opposed to 0.4kg for an 80, but does this mean that weight carried to offset the buoyancy of a floaty 80 would not be needed (assuming you arent't jettisoning the empty stage)

    It seems increasingly popular for cave divers in the US to use side mounted steel 12s as bailout on CCR, but this is a different environment to my usual wreck diving.

    As has been demonstrated previously my grasp of physics is poor, happy to be schooled if figures/ideas above don't stack up.

  2. #2
    Established TDF Member OutOfTest's Avatar
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    Sidemounted is a very different world to staging. So let’s just discount that entirely.

    All that said, just try it. It’ll probably be fine. You can dive pretty much anything if you practice.


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  3. #3
    Last of the Mohicans gobfish1's Avatar
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    Jon pm me and I'll sort you a Ali 80
    None diver as of 2018.

  4. #4
    rEvo-lution iamyourgasman's Avatar
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    It will be quite a lump with rich deco mix. If you can try it with something like 15/55 as deep bailout, I recon you wouldn’t even notice it. If you need to use it it could help you to keep your last stop as you empty all the gas from your floatier Ali cylinders. All IMHO!

  5. #5
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    Yeah I only had this in mind for deep mix so would be usually around 45-55% He which would help and may even make it neutral.

  6. #6
    Old but keen Mark Chase's Avatar
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    With trimix it will be fine.

    That daid just how much deep bailout do you need?

    I by choice dive deep mix in a steel 10 at 250bar and use an AL80 for my 50%. They balance nicely on a left right config

    I say by choice because I own a few AL80 and AL40 tanks but prefer mix in steel.


    A steel 10 with 250 bar 18/45 in is about 1.3Kg neg with a valve on and a AL80 with 250 bar 50% in is about 1.6kg neg



    I didn't use physics to work this out, I used fishing scales

  7. #7
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    I only get about 200b at the shop Mark so my 12 will be about the same as your 10 litre for litre.

  8. #8
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    Quote Originally Posted by JonG View Post
    I only get about 200b at the shop Mark so my 12 will be about the same as your 10 litre for litre.
    That will also make it a lot less negative than it could be

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    Quote Originally Posted by OutOfTest View Post
    Sidemounted is a very different world to staging. So let’s just discount that entirely.
    Why so different?

  10. #10
    Established TDF Member OutOfTest's Avatar
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    Quote Originally Posted by WFO View Post
    Why so different?
    Attachment method. Weighting.

    Forgetting sidemounting different sized cylinders (I’ve got a video of me somewhere diving a KISS with a sidemounted 9L composite left, 12L sidemounted steel right, and 3L steel staged left...)

    Sidemounting is even. You’re not just adding weight to one side, you’re evenly adding to both.

    The attachment method is hugely different. There’s no large leash on sidemount cylinders (or shouldn’t be). The rear attachment used for stages is entirely unsuitable for sidemounting.

    The attachment point for sidemounting is further towards the spine when compared to staging (this is a separate point from above).

    The forward attachment point for sidemount brings the cylinders much more in line with the body when compared to a stage.

    In short...sidemounting is different from staging because they’re accomplishing very different things and have different goals.

    Any attempt to use a sidemount technique to justify a stage technique, or vice versa, is a bit like swerving down the road in your car to warm up the tyres cos F1 drivers do it. It’s just not applicable.


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