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Thread: Choosing GF factors

  1. #11
    RBW Member ChristianM is an unknown quantity at this point ChristianM's Avatar
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    Thumbs up Re: Choosing GF factors

    Thanks to all so far.

    I warmly welcome all the input you gave.
    What I forgot to mention was that we are using 50/75 currently. But we didn't come up with different factors for special conditions.

    Cheers,
    Christian

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    Cognitive surrender TopLeft is an unknown quantity at this point TopLeft's Avatar
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    Re: Choosing GF factors

    Quote Originally Posted by Nitrogenius  View Original Post
    Shit hit the fan BO plan CC and OC: 90/90
    Similar, I use 80/90 on Shearwater.

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    RBW Member tbone1004 is an unknown quantity at this point tbone1004's Avatar
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    Re: Choosing GF factors

    @nitrogenius, dropping the gf-lo pads the total deco time because you are still ongassing in the slow tissues. It still spits you out of the water with the leading compartment having the same theoretical amount of inert gas in it, you just have more total inert gas in your body because the slow tissues were ongassing during the start of the ascent

  4. #14
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    Re: Choosing GF factors

    Quote Originally Posted by tbone1004  View Original Post
    @nitrogenius, dropping the gf-lo pads the total deco time because you are still ongassing in the slow tissues. It still spits you out of the water with the leading compartment having the same theoretical amount of inert gas in it, you just have more total inert gas in your body because the slow tissues were ongassing during the start of the ascent
    I am fully aware that the leading compartment will have the same relative "tissue load status" in regards to gradient..
    however, the individual tissue load shifts with having deeper stops so also the affected tissue might change when you reduce GF lo and start deeper resulting in a different overall decompression stress..
    You will also stay longer shallower and with that further reduce load in the faster compartments than with a higher GFlo keeping the GF hi constant..


    The statement that you will have more total inert gas in your body when keeping GF hi constant and reducing GF load is likely wrong.. Some get more gas due to that different profile but other compartments have less. The overall total should somewhat correlate to overall decompression time why it is likely that your total load over all compartments should be lower if you lower the GF lo only..




    After all the overall decompression stress is relevant as well..
    Of course it is a simplification and a true comparison could only happen looking at each compartments individual saturation status..


    Due to the "NEDU study discussion" we have learned though that the best comparison factor of decompression approaches (deeper vs shallower) is the overall decompression time with the idea that as "general" conservatism your overall decompression time would give the idea and the profile then would only act as relative parameters..


    This is what my comment is based on


    or as I said even when you (which is a somewhat "odd" approach) like Dsix keep your GF hi constant and for more challenging dives decrease the GF lo and therefore start to decompress earlier you are in fact for sure also achieving a less aggressive decompression profile even when the leading compartment at surfacing will still have 90% of the max allowable supersaturation..




    and all fiddling with the GFs due to "latest" evolvelment in deco strategies.. if you increase your GF lo and keep your GF hi the same you are palnning a more aggressive overall decompression. If you want to have a similar overall stress but go shallower earlier (which likely makes sense from what we know today) then you also want to reduce your GF hi!
    Always compare overall decompression times !
    Last edited by Nitrogenius; 25th January 2018 at 12:18.

  5. #15
    RBW Member tbone1004 is an unknown quantity at this point tbone1004's Avatar
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    Re: Choosing GF factors

    having to run OC gas plan, but same would apply on a rebreather as it is the concept

    300ft, 60min on 12/70, with 21/35, 35/25, EAN50 and 100% deco
    70/80 is 300 min deco time
    40/80 is 322 min deco time

    Not a whole lot of difference in the total deco time, but a big difference in the loading of various slow compartments.
    Last edited by tbone1004; 25th January 2018 at 18:28.

  6. #16
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    Re: Choosing GF factors

    Quote Originally Posted by tbone1004  View Original Post
    having to run OC gas plan, but same would apply on a rebreather as it is the concept

    300ft, 600min on 12/70, with 21/35, 35/25, EAN50 and 100% deco
    70/80 is 300 min deco time
    40/80 is 322 min deco time

    Not a whole lot of difference in the total deco time, but a big difference in the loading of various slow compartments.
    Not sure what you are calculating here..


    300ft and 600min for sure isn't what you meant
    300 ft and 60 min with 40/80 get me 332 min overall deco time but generally same ballpark (I use 2 min stop as minimum that might be the difference or ZHL B vs C)


    Never the less I would object to the statement "not a lot of difference in overall deco time) it is app 10% longer, that is relevant.. and yes sure the slowest compartments will be loaded more but your fast to medium compartments will be less saturated ..
    question is what is of a bigger issue?


    But also don't get me wrong.. I am not saying: choose deeper profiles..
    I go more shallow but pad on overall deco time as well,, so I raise GF lo and lower GF hi..
    Before "NEDU" I used to dive 10-25/75-90 ish..
    what I dove now I explained earlier..


    I would also not keep my GF hi constant and lower my GF lo like Dsix.. my point is though I can understand what he is trying to achieve and it is not like "he got it all wrong" like it sounded a bit from Peter..


    BTW 40/80 and 70/80 are still quite substantial similar approaches..
    compare the deepest stops of the profiles..


    BTW with this long BTs at such depths the difference gets quite small in any case


    More interesting to look at same depth but 20 min BT and 10/80 vs 50/80


    10/80 staring at 66m there and overall deco time of 138 min vs 50/80 starting at 45 m and 93 min overall deco time.. so the 10/80 almost doing 50% more overall deco and of such 50% more time at 6m pure oxy stop..


    of course though if for such a dive you are willing to do a 138 min decompression, then you have a poor choice of profile.. and a 50/60 will likely serve you better.. giving you similar deco time with the comfort of having your "most stressed" compartment only at 60% max stress allowed..

  7. #17
    RBW Member tbone1004 is an unknown quantity at this point tbone1004's Avatar
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    Re: Choosing GF factors

    in that profile, compartments 1-9 I think were all negative in their tissue loading in both instances, so they are ongasing as soon as you hit the surface.

    I pulled that bottom time because Don is also a cave diver so a 20min bottom time isn't going to happen in a cave.

  8. #18
    RBW Member JonG is an unknown quantity at this point JonG's Avatar
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    Re: Choosing GF factors

    This might be worth a read, SM chimed in at one point:

    https://www.thediveforum.com/showthr...291-Deep-Stops

  9. #19
    Supporting Member Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36's Avatar
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    Re: Choosing GF factors

    Quote Originally Posted by Nitrogenius  View Original Post
    ...snip...


    I would also not keep my GF hi constant and lower my GF lo like Dsix.. my point is though I can understand what he is trying to achieve and it is not like "he got it all wrong" like it sounded a bit from Peter..


    ...snip...
    On my first 9hr dive, I thought that I began feeling shoulder pain at 40' and it obvious as hell at 30'. I made the decision to try and slow my ascent by adjusting the deco curve by lowering the lo GF. Subsequent dives were pain free. I only felt the need to pad the shallow stops once due to my heated vest not working good enough with a seriously leaking neck seal. Obviously this is all Voodoo to me and Nothing but a WAG.

    Looking at various profiles, the same thing could be accomplished by lowering the hi GF, but for some reason the curve did not appeal to me as much.
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  10. #20
    RBW Member ChristianM is an unknown quantity at this point ChristianM's Avatar
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    Thumbs up Re: Choosing GF factors

    Hi all,


    a bit late but thanks to all the valuable information. I see I still have to learn about that topic


    Cheers,
    Christian

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