1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

So I bought this pile of plumbing parts...

Discussion in 'Rebreathers Closed and Semi Closed Circuit' started by Doomanic, Feb 28, 2016.

  1. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    4,515
    Likes Received:
    989
    Buoyancy question.

    Say you're at 30 metres and need to ascend by one metre. With open circuit, you'll just take a deeper breath, ascend a little then exhale. Will probably not need to adjust your wing. On closed circuit, you don't have this option. So how do you do that?

    Same for descending a metre?
     
  2. Doomanic

    Doomanic Dinosaur Wrangler
    Staff Member

    Joined:
    Feb 4, 2009
    Messages:
    5,494
    Likes Received:
    1,955
    Some would swim round, some would swim up/down.

    It's not as easy as OC but it is possible.
     
  3. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    4,515
    Likes Received:
    989
    It's a serious and honest question. For example that container 'maze' in NDAC, or in the Stanegarth in Stoney. With OC, it's mostly breath control for your Y axis and fin control for the X & Z.

    So on a box it's learning delicate control of the wing / drysuit / counter lungs ?
     
  4. becky9

    becky9 Diving bore!

    Joined:
    May 5, 2012
    Messages:
    2,159
    Likes Received:
    724

    Tbh you should not be relying on your lungs for those type of manouvers, lungs fine tune, wing for changes in depth. Its buoyancy 101 x

    Edit: Did you never play the rock game? x
     
  5. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    4,515
    Likes Received:
    989
    Isn't it fine tuning though? Thinking of that container in NDAC where you need to descend by a metre at around 25 metres (I think it's that deep), then turn, ascend by a metre, then descend by a metre. All of that's well within lung control if you're properly weighted.

    Agreed for bigger adjustments one would need to dump/inject gas into the wing/BCD, although the initial movement is frequently made with a large inhale / exhale.

    I'm interested in how box divers make these fine adjustments, particularly in confined spaces. I suspect that for open water changes, they'd fin up/down. I guess it's a bit of a knack to get the buoyancy right when needing to go up a gnats crotchet when essentially motionless.

    We often play the little (heavy) dog game in NDAC - usually handed over by surprise and much hilarity as the victim plummets into the bottom -- and double points if the donor shoots upwards. Not familiar with the rock game.
     
  6. Doomanic

    Doomanic Dinosaur Wrangler
    Staff Member

    Joined:
    Feb 4, 2009
    Messages:
    5,494
    Likes Received:
    1,955
    Sorry for the over-simplified response, it was past my bedtime.

    I've gone through the container maze and it's a bit of a pain with so many changes in such a short time. I didn't do it particularly neatly as it's not worth the waste of gas. For a very small change, like a meter up or down, (and lets face it, that's inside the neutral window for a lot of divers) and I wanted it to remain neat I'd use the suit as it doesn't waste dil and O2.
     
  7. nickb

    nickb Active Member

    Joined:
    Oct 13, 2009
    Messages:
    361
    Likes Received:
    138
    I wouldn't piss about with anything fancy doing that container thing, just swim through it. I've done it with a scooter and that makes it much easier on a CCR ;)

    If I'm going up, I add a squirt of O2 as the PO2 will drop anyway. If I want to descend, I'd sooner use brute force rather than dump some loop gas only to add it back again when I get down. You learn these little tricks when you want to save another couple of pennies worth of trimix
     
  8. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    4,515
    Likes Received:
    989
    I've seen a G-Box on a boat that had 4 cylinders. Would it be possible (and cheaper) to use a larger suit inflation cylinder and connect it to both suit and wing? Is this common?
     
  9. Doomanic

    Doomanic Dinosaur Wrangler
    Staff Member

    Joined:
    Feb 4, 2009
    Messages:
    5,494
    Likes Received:
    1,955
    Possible but inadvisable as you potentially lose both sources of buoyancy.
     
  10. nickb

    nickb Active Member

    Joined:
    Oct 13, 2009
    Messages:
    361
    Likes Received:
    138
    It's not common, in fact I've never seen it.

    Maybe I have but not noticed as it's likely that anyone doing this would keep it quiet for fear of being discovered as a prize twat.

    Someone came on CCRx a while back asking a similar question and was instantly rounded upon.

    This is a very bad idea. It would only be very marginally less stupid than doing it with an open circuit setup.
     
  11. becky9

    becky9 Diving bore!

    Joined:
    May 5, 2012
    Messages:
    2,159
    Likes Received:
    724
    The aim is to keep your breathing cycle in the middle, not to avoid using your wing. Artificially changing your breathing cycle is fine for very short periods, but you really should be putting gas in. Doing it improves your control, and prevents the shit hitting the fan when something untoward happens and you get distracted (ring any bells? ;) )


    Yes initial movement is often made with the lungs, but equally you should be happy doing it with the wing. It will almost certainly help you in time to come. x



    The Rock game is a much less intense version of the dog game, the point in some ways is more subtle, but it comes down to - use your wing!!! x
     
  12. Dave Whitlow

    Dave Whitlow Well-Known Member

    Joined:
    Oct 27, 2010
    Messages:
    783
    Likes Received:
    296
    I have a G-box and sometimes dive it with 4 cylinders. As Nick tactfully put it a single failure taking all buoyancy is a very bad idea.

    Cheaper is not a consideration as it all about options and redundancy and 4 cylinders gives lots of options if when things go amiss.

    1: Trimix diluent connected to wing, BOV and ADV and diluent MAV
    2. Oxgen connected to solenoid and O2 MAV
    3. Air (32% when I can be bothered) connected to suit and with 2nd stage bungied on side
    4. Oxygen with LP hose that can be connected to O2 MAV and with 2nd stage bungied on side

    For me this is in addition to bailout bottles, although this is also the ideal configuration for scootering on CCR, without bailout bottles, this being the original requirements met by the design of the G-box.
     
  13. becky9

    becky9 Diving bore!

    Joined:
    May 5, 2012
    Messages:
    2,159
    Likes Received:
    724
    Are we talking about the same container? x

    Edit: Trying to visualise how the scooter would anything other than luggage in those confines x
     
  14. nickb

    nickb Active Member

    Joined:
    Oct 13, 2009
    Messages:
    361
    Likes Received:
    138
    Is there more than one? Big box thing with square holes dotted about.

    My scooter has a smaller cross-sectional profile than me. I can go through that box without touching the sides.
     
  15. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    4,515
    Likes Received:
    989
    I had no idea that you could use a scooter in such a confined environment. It's hard enough to get oneself through without touching anything. Must be very fine control.

    Must "have a go" on a proper scooter...
     
  16. Doomanic

    Doomanic Dinosaur Wrangler
    Staff Member

    Joined:
    Feb 4, 2009
    Messages:
    5,494
    Likes Received:
    1,955
    It's in 18ish meters, under the pontoon, where the commy divers train. It's got a load of scaffolding on and around it, one half of the door is closed, there is a round hole in one side and dividers inside to make you change depth. I can't see how you could scooter straight through it.
     
  17. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    4,515
    Likes Received:
    989
    Rebreather question... One breathes in O2 (and other inert gas). This is metabolised and exhaled as CO2. The CO2 is removed by the soda lime in the scrubber.

    Does the soda lime convert the CO2 into another gas (if so, what), or does it "absorb" the CO2, thus the volume of gas in "the loop" will reduce?
     
  18. clique

    clique Active Member

    Joined:
    Apr 29, 2015
    Messages:
    288
    Likes Received:
    116
    CO2 + Ca(OH)2 → CaCO3 + H2O + heat (in the presence of water)

    So I suppose yep it does? I'm sure someone will be along shortly to call me stupid :)
     
  19. nickb

    nickb Active Member

    Joined:
    Oct 13, 2009
    Messages:
    361
    Likes Received:
    138
    You can't go straight through it. You need to put some turns in.

    The point I was trying to make is that a scooter makes fine-tuning ones buoyancy on a CCR redundant. Going up and down over obstacles is trivial.
     
  20. nickb

    nickb Active Member

    Joined:
    Oct 13, 2009
    Messages:
    361
    Likes Received:
    138
    The CO2 is 'absorbed', as described above. The replacement of the metabolised oxygen maintains the loop volume
     

Share This Page

  • About Us

    Our UKDivers community has been around for many years and prides itself on offering unbiased, helpful discussion among people of all disciplines and abilities. We are working every day to make sure our community is one of the best and friendliest around.
  • Support us!

    The management works very hard to make sure the community continues to run reliably. Care to support us? All donations go to the running costs of the forum: hosting charges, software maintenance, etc. We'd really appreciate it!

    Choose option:  

    UKD Username: