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View Poll Results: What Deco Algorithm Do You Use?

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  • Bubble Model

    3 3.03%
  • Varying Permeability Model

    10 10.10%
  • Gradient Factors – Even – Like 30/70 or 20/80

    49 49.49%
  • Gradient Factors – Favor Deep Stops – Like 20/70

    4 4.04%
  • Gradient Factors – Favor Shallow Stops – Like 40/80

    33 33.33%
  • Ratio Deco

    9 9.09%
  • Tables – Like Navy

    2 2.02%
  • Other - please explain

    4 4.04%
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  1. #1
    Memberator
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    Question What Deco Algorithm do you use? (Poll)

    DECOMPRESSION CONTROVERSIES - Dr Simon Mitchell Briefing (Video)

    Wondering what algorithms you use, and why?

    All opinions are my own and do not reflect the view of the board.

    "If a small thing has the power to make you angry, does that not indicate something about your size?" ~Sydney J. Harris

  2. #2

    Default

    not quite 40/80, but certainly favor shallow stops. With a controlled ascent profile, I don't think there is any reason to be concerned about deep stops


  3. #3
    Memberator
    Join Date
    Jul 2010
    Location
    SE Coast of Arizona
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    Default

    I suffered from fatigue when diving, and found "Pyle stops" on research. That made huge difference for me.

    I'm not willing to give up my 2-minute midway . . .

    But I let the Petrel's 40/80 rule . . .

    All opinions are my own and do not reflect the view of the board.

    "If a small thing has the power to make you angry, does that not indicate something about your size?" ~Sydney J. Harris

  4. #4

    Default

    I started cave/deco training with vpm, and I see no reason for me to change to anything else. I haven't done any really long hangs yet, but on +2 or 3 for conservatism I've never felt even slightly fatigued after several dives in the same day. Most of my dives do seem to end up with a profile that causes a quasi deep stop though (front section of devil's, top of the superstructure on a wreck, etc).

    Dive Safe,
    Frank

  5. #5

    Default

    I dive a 40/85 or 40/80. I skip deepstops as I feel better after deep dives.

    Maybe interesting, but in German: https://techdiving-network.de/wp-con...deco_et_al.pdf
    It is about when ratio deco becomes aggressive.


    JRT EDIT: Completed the link to make it clickable.

    Last edited by Jax; 06-06-2016 at 09:21 AM. Reason: Link completion

  6. #6

    Default

    I wish you had added another category, which is self created algorithm. That is the person who dives any algorithm, but will "pad" stops by adding extra time. If I understand the research correctly, this practice from what I read is fairly common,does have a tendency to introduce other ongassing issues of certain compartments.

    "Not all change is improvement...but all improvement is change" Donald Berwick

  7. #7

    Default

    I would be interested in finding information that could be titled "Gradient Factors for Dummies." Something that would help generate enough knowledge to lead into deeper level materials. Any suggestions?

    Thanks,
    Greg


  8. #8

    Default

    Quote Originally Posted by GregO View Post
    I would be interested in finding information that could be titled "Gradient Factors for Dummies." Something that would help generate enough knowledge to lead into deeper level materials. Any suggestions?

    Thanks,
    Greg
    http://www.rebreatherworld.com/showt...rs-for-Dummies


    http://www.diverite.com/articles/gradient-factors/
    https://decodoppler.wordpress.com/20...lified-primer/
    http://www.alertdiver.com/Gradient_Factors
    There's a great article written by the GUE folks on it, too... but I can't find it and I'm at work and should be doing... you know... work.

    Edited to add: I found the GUE article I was thinking of. It had nothing to do with gradient factors at all. (Unsurprising, really. I don't know why I thought GUE would be writing anything about GFs.) It was about hyperbaric oxygen.


  9. #9

    Default

    Quote Originally Posted by GregO View Post
    I would be interested in finding information that could be titled "Gradient Factors for Dummies." Something that would help generate enough knowledge to lead into deeper level materials. Any suggestions?

    Thanks,
    Greg


    Here you go:
    "Gradient Factors for Dummies
    Gradient Factors for Dummies
    By Kevin Watts




    This article attempts to provide a user's view of gradient factors, an Erik Baker derived method of calculating decompression schedules. The title is not meant to be derisive, but simply an indicator that this article is meant to be a primer.


    Back to Buhlmann

    Everything in the gradient factor decompression algorithm revolves around Buhlmann’s tissue model. Currently this means 16 hypothetical tissue compartments (TCs) that are constantly tracked during a dive in order to determine each TC's inert gas pressure.

    As you ascend all those TCs start to release pressure ("off- gas"). The question is "How fast can you let those TCs off-gas?"

    Buhlmann answered that question by coming up with an “M-value”. Basically, an M-value is a maximum pressure value (different for each depth and tissue compartment) that tells you, if you exceed that value, Buhlmann thinks you’re crazy and believes you're about to get bent.

    A natural ascent strategy, then, would be to move up in the water column until the pressure in your TCs just reaches Buhlmann’s M-value and then let your TCs off-gas a bit, rise to the next level, etc. In this strategy, you would keep going up in such a way that you never let your TCs exceed Buhlmann’s M-value.

    Unfortunately, decompression illness does not exactly track Buhlmann's M-values. More sickness occurs at and above the pressures represented by M-values and less sickness occurs when divers never reach Buhlmann’s M-values.


    Enter Gradient Factors

    Gradient factors (GFs) were invented to let the diver choose how fast, and how close, their TCs get to Buhlmann’s M-values.

    Gradient factors are calculated as follows:



    What does this formula tell us?


    First, the gradient factor formula tells us that at a GF=1.0, you are at Buhlmann’s M-value. Therefore, staying at or below GF=1.0 seems important. Second, it tells us that when our tissue compartment pressure just reaches ambient pressure, then the GF=0.0.

    Another ascent strategy, then, might be to shoot up to a GF=0.8 and ascend in such a way as not to exceed that value. In this way you know that your tissue compartments are never over 80% of the distance between ambient pressure and Buhlmann’s M-value. In essence, you have a 20% safety margin on Buhlmann's M-values. Dive computers implementing GFs usually let you set two GF parameters. Moving straight to GF=0.8 and ascending in such a way that you always keep your TCs at GF=0.8 would be equivalent to setting your dive computer to 80/80.


    Erik Baker's Strategy

    Erik Baker didn't like the idea of ascending directly to a GF close to Buhlmann's M-Value. Instead he said, “Let’s all ascend first to a lower GF, then slowly move to higher GFs.” So, let’s say you want to first ascend to a GF=0.30 and then slowly move to reach GF=0.85 as you surface. This setting on your gradient factor computer is 30/85. In fact, my Shearwater computer uses 30/85 as it's default setting.


    So what is happening when you use a GF setting of 30/85?

    First your dive computer allows you to ascend until the pressure in your TCs first reaches a GF=0.3. This means your TC pressure is 30% of the way between ambient pressure and Buhlmann’s M-value. Then you sit there until your TCs drop enough pressure so that you can ascend to your next stop.


    How much pressure must leave your TCs before you can ascend?

    Assume you hit your first stop (GF=0.3) at 110 ft. Well, then, we now have two known points. Point 1 is (110,0.3), that is, at 110ft we are at a GF of 0.3. Point 2 is (0, 0.85), that is, at the surface we want to be at a GF=0.85. A natural way to ascend (and this is what Baker did) is to create a line from those two known points and ascend in such a way that you never exceed the GF generated by that line.

    Once you've determined your two points, the formula for the maximum GF at any depth is:



    But, since the high gradient factor is reached at the surface, HiGFDepth=0. So,



    Therefore, if you hit your first GF=0.3 at 110ft, then your LowGFDepth=110. Before you can ascend to 100ft you must let off enough TC pressure so that when you arrive at 100ft the GF of your TCs does not exceed 0.35 calculated as



    You can ascend to 90ft when your TCs let off enough pressure at your 100ft stop so that when you reach 90ft your TC's GF does not exceed 0.40 calculated as



    The GF method allows you to ascend by walking that line all the way to the surface.


    Summary

    If you understood the above explanation, then you see why divers on RebreatherWorld say that setting your GF parameters to 10/90, or 10/80, etc. helps generate deep stops. The low GF of 10 means a stop must be generated when your TCs are only 10% of the way between ambient pressure and Buhlmann’s M-value, rather than 30% if you were to set the low GF to 30. Simply, the GF line just starts deeper.

    The gradient factor method is a natural extension of Buhlmann's tissue compartment model. Diver's using computers implementing the gradient factor method should understand how modifying their GF parameters will alter their decompression profiles. My understanding is that it may be wise to consider altering your GF parameters based on dive characteristics, your physical condition, and your general attitude toward the risk of decompression illness. The gradient factor method provides the diver substantial flexibility in controlling their decompression profiles. Your responsibility is to choose the factors appropriate for you."






  10. #10

    Default

    In regards to the poll. I opted for GF, favor shallow stops given the latest and greatest feedback in research and as a result positive results from divers changing their approaches.
    I used to do the exact opposite though when I started, I chose my strategy favouring deeper stops and I even added Pyle stops on top of that in between..


    I think the poll is a bit misleading as there is no such thing like "even GF".. I am not sure Jax how you chose the examples, but the even seem to match 100 overall when you actually add the numbers..
    The favour shallow stops seems to exceed 100 while the favour deep stops seems to stay below 100..
    Might be complete coincidence, might be a system..


    Just a few comments to that.. when I alter/shift my stops from one side towards the other from a proven concept, then I try maintain the same overall decompression time a my overall concept..
    So when I want to move my stops shallower I start moving up the low GF and then I resolve the hi GF to a value where I am close to the overall decompression time..
    Doing it anyway different like just pushing up the Low GF and keeping the high GF at the old number etc.. will not only cause your depth of the stops being moved but you ARE EFFECTIVLEY changing the overall conservatisim of your decompression!
    So one needs to be aware of that playing around with theses values..


    Also apart from the choice of Lo GF + high GFs one needs to make up their mind on ascent speed before the first stop and between stops..
    Here is something I have adapted from the (proven by the many dives conducted in the community as also succesful) Bubble model approach.. Rather than doing deep stops I am doing a consciously slow ascent until the first stop.. With Trimix there is the not faster than 10m/min recommendation anyways and that is what I do on Trimix but also on air I am not going faster..


    Ascend speeds to your first stop will impact your feeling after decompression as well.. and maybe doing a slower overall ascent to first stop can eliminate the "need" for deepstops for you as well..



 

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