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Thread: Helium penalty

  1. #11
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    Last edited by graham_hk; 02-12-2020 at 07:03 PM.

  2. #12
    Old but keen Mark Chase's Avatar
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    Quote Originally Posted by graham_hk View Post
    Not strictly true - deep stops are still pretty much de rigueur. Do you know anybody who does 100/100? Interestingly, a recent study by DAN (I think) Italy showed 40m dives in a controlled setting (there's a 40m pool) that used GF50/100 were better than those using 100/100 (bad form I know but I don't have the citation - but will post it if I can find)

    The magnitude of deep stops is certainly working more shallow - but lets be correct in our descriptions

    The above is slightly misleading in so far as 100/100 is defo a no deep stop dive but then 50/50 is also a no deep stop dive. Its just a more conservative dive.

    A dive with ADDED deep stops is one where the GF low and GF High are different

    SO 50/100 = deep stop dive 50/70 =deep stop dive 50/50 is a no deep stop dve


    the 100 part of the profile is VERY aggressive so 100/100 would be a profile for the very young and very fit and even then only for DCI tolerant divers


    I progressed to an 80/80GF no deep stop profile and that's been working fine for me but I only really tested it for about three years (2-3 hours dives in 50 -80m range) as in recent years I hardly do any deco


    Again suggesting a 50/100 is better than a 100/100 is like stabbing your self in the face with a fork instead of a knife.

    Doing aggressive deco ALL the way out as opposed to only doing aggressive deco in the shallow stops surely is an obvious increase in DCI risk

    I look at some of the test comparisons and dispair

    If you want to compare a profile the total run time must be the same


    SO

    using a profile where the difference becomes more apparent, lets say an air dive to 40m for 60mins

    OC running air air deco thats a 169min dive on 100/100gf

    But on 50/100 its a 180min dive?

    SO if you want to compare a deep stop to a no deep stop profile, to match run times you have to compare 50/100 to 95/95 using air for 60mins at 40m


    But the other point is, a 40m Air profile doesn't create a lot of deep stops in the first place


    So lets look at a proper deco dive. 70m 45mins bottom time CCR running 14/60 on a 1.3 set point

    100/100 = 163 mins run

    50/100 = 175mins

    90/90 =177mins

    Again not much in it but still a safer deco profile than 100/100

    But lets not be fooled. 50/100 isnt a deep stop profile like the profiles we used to run in the beleif they were better.

    We ran 20/80 30/90 20/100 and the very dedicated were running stuff like 5/125?????

    THOSE were the proper deep stop profiles of that era

    Things take a more obvious twist when those are used.

    20/80 is a good example as it was a base line used by many.

    Now running 20/80 you have a run time for your 45mins at 70 of 217mins

    Running the same level of max aggression (80GF) you have a run time of 194, so 23mins less deco

    To match that run time you need to get aggressive on the shallow stops and crank it to 20/95 (191mins)


    I offer the 45mins at 70m profile on CCR as its a dive I have done many many times. I'd run 80/80GF with 100% 02 from 6m and up and do the dive in 181mins which was the max run we did on our boat.

    At that time I was an early 50s smoker, 1.78m tall and 105kg so fat but pretty fit for my age.
    Last edited by Mark Chase; 22-11-2020 at 09:51 AM.

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    Last edited by graham_hk; 02-12-2020 at 07:02 PM.

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    Simon Mitchell had some specific comments on the efficacy of the recent Dan study in this thread

    https://www.scubaboard.com/community...-count.601213/

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    Last edited by graham_hk; 02-12-2020 at 07:02 PM.

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    https://youtu.be/nIO9qI5XODw

    Somewhere in this presentation I think he explains why there was some relevance of the Nedu study to tech profiles, also mentions his own preferred GFs 50/75 or 70 IIRC.

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    Quote Originally Posted by graham_hk View Post
    Not strictly true - deep stops are still pretty much de rigueur. Do you know anybody who does 100/100? Interestingly, a recent study by DAN (I think) Italy showed 40m dives in a controlled setting (there's a 40m pool) that used GF50/100 were better than those using 100/100 (bad form I know but I don't have the citation - but here's author talking on DAN SA about studies https://www.youtube.com/watch?v=DjOx...&pbjreload=101)

    The magnitude of deep stops is certainly working more shallow - but lets be correct in our descriptions
    Deep stops such as Pyle stops are out of favour by most.

    Deep stops as in staying deeper by tweaking the GF/low downwards is out of favour by a lot of people (under the principle of why stay down on gassing when you should be getting up and off gassing)

    Gradient Factors seem to be using higher numbers now. Quite a few people have brought their GF/low higher and, as a result of less on-gassing, there's no need to have a high GF/high to get out in time.


    As you said later, it's up to the individual diver to work out what works for them.

    We could extend this discussion to which Gradient Factors would you use for bailing out as opposed to the happy path.

  8. #18
    Gone diving back later Vanny's Avatar
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    I think if we are going to be down with the kids we should look at how we word this stuff. Saying deep stops are in or out isn’t really what the latest research says. Staying too deep has research contradicting that idea. Without quoting prof. Simon Mitchell we can bring our initial stops shallower but where we need to start stops is still up for grabs. So Graham’s take above on finding like minded divers and adopting what works for you / the team , taking latest research into consideration, is , I think , a very pertinent way to go.

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    Last edited by graham_hk; 02-12-2020 at 07:02 PM.

  10. #20
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    Quote Originally Posted by JonG View Post
    https://youtu.be/nIO9qI5XODw

    Somewhere in this presentation I think he explains why there was some relevance of the Nedu study to tech profiles, also mentions his own preferred GFs 50/75 or 70 IIRC.
    The Nedu study used profiles that were approximately... GF 60/77 for the "deep" one. and 105/60 for the shallow one. He pretends these are relevant to tech diving, and falsely imagines they represent bubble models / deep stops - they do not.

    Then his personal recommendation is a 50/75 style GF's, which is very much related to the failed Nedu profile. What a conundrum - to hold the Nedu test up as some bizarre truth, only to then recommend doing the same failed profile style. diagrams


    Then as suggested in his comments in the DAN youtube post above, he belittles the Y-40 test profiles, because one was "too shallow" (100/100). However, this same argument of his should then equally apply to the Nedu study.

    He can't have it both ways.
    Last edited by rossh; 24-11-2020 at 01:52 AM.
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