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  1. #11
    Kit Junkie Kermit's Avatar
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    Quote Originally Posted by jturner View Post
    Can't be sure if you're joking or not but assuming you aren't, I'd rather not have to go to such an extremity, especially in a hurry and whilst trying to maintain a stop!
    I've done it before (once). Ascending with a duff unit the CLs can soon max out. It was impossible to maintain buoyancy with full CLs and a less than full bailout tin. Just do it in a controlled manner, not one great big flood in one hit. It seemed quite easy at the time.
    I'll think of something witty some time soon.

  2. #12
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    Quote Originally Posted by Kermit View Post
    I've done it before (once). Ascending with a duff unit the CLs can soon max out. It was impossible to maintain buoyancy with full CLs and a less than full bailout tin. Just do it in a controlled manner, not one great big flood in one hit. It seemed quite easy at the time.
    Apologies for going off topic and asking stupid questions but why didn't you just vent the counterlungs?! I just keep mine emptied on bailing out...

  3. #13
    Kit Junkie Kermit's Avatar
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    Quote Originally Posted by jturner View Post
    Apologies for going off topic and asking stupid questions but why didn't you just vent the counterlungs?! I just keep mine emptied on bailing out...
    That's exactly what I did. Perhaps it's down to differences in which unit you are using and, perhaps, terminology. I can only vent the CLs by opening the mouthpiece (which is, of course, not in my mouth). This introduces some water into the loop. This needs to be done on a regular basis on the ascent as the loop volume increases back up to full CLs. So, by venting the CLs I'm partially flooding the unit.

    In retrospect this actually makes life a little easier as it also reduces the maximum loop volume.

    I dive the unit with just enough weight to keep things under control (just) with a fully inflated loop and a full bailout tin. The rationale being if, in the very unlikely (and never yet needed) event of having to hand the tin off, I can control things as I haven't got a full loop. If I need the bailout gas then I can reduce the volume of the loop by venting/partially flooding.

    Hope that makes sense.
    I'll think of something witty some time soon.

  4. #14
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    Quote Originally Posted by Kermit View Post
    That's exactly what I did. Perhaps it's down to differences in which unit you are using and, perhaps, terminology. I can only vent the CLs by opening the mouthpiece (which is, of course, not in my mouth). This introduces some water into the loop. This needs to be done on a regular basis on the ascent as the loop volume increases back up to full CLs. So, by venting the CLs I'm partially flooding the unit.

    In retrospect this actually makes life a little easier as it also reduces the maximum loop volume.

    I dive the unit with just enough weight to keep things under control (just) with a fully inflated loop and a full bailout tin. The rationale being if, in the very unlikely (and never yet needed) event of having to hand the tin off, I can control things as I haven't got a full loop. If I need the bailout gas then I can reduce the volume of the loop by venting/partially flooding.

    Hope that makes sense.
    Yep! Thanks Kermit!

  5. #15
    TDF Member Paul H's Avatar
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    Quote Originally Posted by gobfish1 View Post
    thanks for your reply .
    i only ask as i used to dive twin12l,s and could not run up the deco to need a ali80,

    most of my time id be on air back gas and deco on o2 and maybe something other ie 57 64 nitrox and id only use 300l or 400l from both cylinder,s of mix, often do two 50m plus dives on one set of 7ls , buddys on ccr so no need for me to look out for them gas wise,

    Id rather have a 3l of o2 , than a ali80 of a low pp2 nitrox , i say low as most stops are 12/m and up , on the diving i was doing . or could do on a set of 12ls

    3l 5l 7l were my mix of cylinders,

    also one deco gas seems to be all your eggs in one place ,

    but if your thinking of topping off and the like then maybe the ali80 will do that for you ,

    best ,
    I also use an Ali 80 and a 7 for deco gases and plan for the increased volume in the 80 to ensure I can get out if either of my deco gases become unavailable for whatever reason I.e. a longer deco on 40% when the 80% is cacked (fortunately not happened yet).

    It also doubles as a bottom stage for those two dive days where fills between dives are not possible.

  6. #16
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    Hi Paul H

    Did you increase your weight when you dive with the stages for when they are empty?

  7. #17
    Established TDF Member Iain Smith's Avatar
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    Quote Originally Posted by Keith Wood View Post
    Did you increase your weight when you dive with the stages for when they are empty?
    Keith,

    An AL80 is 2.65 kg positive when empty. The valve, reg and rigging kit are all negatively buoyant, so you're probably looking at less than 1.5kg positive buoyancy from a completely empty AL80. 50bar of air in twin 12s is 1.5kg.

    So, unless you think you're going to be in a situation where you have completely drained your twinset AND completely drained the AL80, I wouldn't bother changing your weighting. (That would equate to having to use the whole of my back-gas reserve AND all of my deco reserve. If I used the AL80 as a bottom stage, then ended up using all of my back-gas reserve to the point that I was feeling "floaty" I'd send the AL80 up my DSMB line to get rid of it.)

    Iain

  8. #18
    TDF Member Paul H's Avatar
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    Quote Originally Posted by Keith Wood View Post
    Hi Paul H

    Did you increase your weight when you dive with the stages for when they are empty?
    No. Never felt the overall weight inc valves, regs etc pulling me to the surface. Basically, wot Iain said up there ^^^^

  9. #19
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    Cheers guys for your comments. Will give it a go next time i have the Ali 80 low of gas and its a shallow dive.


 
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