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Thread: Deco Observations Spawned from the deep stops debate

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    RBW Member atedeschi is an unknown quantity at this point atedeschi's Avatar
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    Deco Observations Spawned from the deep stops debate

    I will the first to admit that am I not a deco expert. When I started my decompression diving I started w/ an air computer and navy tables as a backups breathing air and 80% from 30' to the surface. Then when I took my first set of tec courses I had V-planner which everyone seemed to be using and what was recommended for me.

    At the start I was using VPM-B tables and a bottom timer, then I continued to use VPM-B but started basing my schedules off of the average depth function on the newer bottom timers. This served me well for wreck and cave diving, deep and shallow, OC or CC. Up until last year I was still using this method until I finally got an X1. I have been running my X1 with V-planner live and again no issues for the most part.

    I started reading the Deep Stop threads and tried to follow them but they were growing to fast. I was also busy with work and really not the much interested in the topic from a research aspect (I do appreciate those that do the research). To me decompression is just what I have to do to go diving.

    What I took out of the debate was deep stops may not be as helpful as we thought but the experiment did not show one out weighs the other (Maybe more research will). I also didn't really see much in the way of what gradient factors to use to bump up your first stops during deco, however I did see Bruce's post from Shearwater who said he was going to start trying 40/75.

    For myself like I stated previously I have not had any big or major issues using VPM-B, however on some of my dives where the thermocline is shallow or were there maybe two, the deep stops start to make me cold. For CCR bailout purposes I also would like to get shallower sooner then later.

    So I started playing with gradient factors vs VPM-B to try and see what gradient factors would match similar to my normal runtimes but maybe make my first stops shallower. I was surprised what I saw.

    Depth ---- BT (min) ----VPM ---- 40/xx (Dil:10/50 Setpoint 1.0)
    250' 30 180 150
    240' 35 170 150
    230' 35 160 140
    220' 40 150 140
    210' 45 140 130
    200' 50 130 130

    In the above only the dives in the 240-230 range have any real change in the 1st stop and the others is 1 stop or less.

    Depth ---- BT (min) ----VPM ---- 40/xx (Dil:14/33 Setpoint 1.0)
    200' 40 130 120
    190' 45 120 110
    180' 50 110 110
    170' 55 100 100
    160' 60 90 90
    150' 65 80 90

    Again the above is little to no difference for the first stops.

    Depth ---- BT (min) ----VPM ---- 40/xx (Dil:14/33 Setpoint 1.0)
    150' 45 80 80
    140' 50 70 80
    130' 60 60 70
    120' 75 50 60
    110' 85 40 60
    100' 95 40 50

    On this set of dives listed above the gradient factors are actually deeper then VPM. Also these are shallower dives so maybe the lower number needs to be changed, but to what?

    Depth ---- BT (min) ----VPM ---- 40/xx (Dil:21% Setpoint 1.0)
    110' 90 50 60
    100' 120 40 50
    90' 120 30 40
    80' 120 15 30

    Now with this set of dives the gradient factor 1st stops are all deeper. Yes I know these are shallow dives.

    After playing with the two deco models I'm not sure what the big debate is. Am I missing something? or are people using gradient factors stopping deeper the VPM? When I messed around with GF before I noticed you have to change them for depth ranges. Are people doing this or they just setting there computers and forgetting it?

    Final note if trying to replicate results or comparison purposes I run V Planner conservatism at 0.

  2. #2
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    jj ccr

    Re: Deco Observations Spawned from the deep stops debate

    Vpm+0 is very very aggressive. Even Ross will recommend you a +3 or +2

    Run your exercise again and we'll discuss then.

    Sent from my GT-I9300 using Tapatalk

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    RBW Member atedeschi is an unknown quantity at this point atedeschi's Avatar
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    Deco Observations Spawned from the deep stops debate

    The conservatism does not effect the first stop. Time is just added to shallower stops.

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    jj ccr

    Re: Deco Observations Spawned from the deep stops debate

    Yes it does. You are attempting to control the size of the critical radius of the bubble. There is no magical add time to the shallow stop unless you are performing a GF exit.

    Sent from my GT-I9300 using Tapatalk

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    Deco Observations Spawned from the deep stops debate

    I mean when bumping up VPM conservatism I didn't notice a change in depth to 1st stop. I only tried 2 profiles real quick.

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    jj ccr

    Re: Deco Observations Spawned from the deep stops debate

    It may have something to do with the stop size. Change it to one meter and you should see the change

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    Re: Re: Deco Observations Spawned from the deep stops debate

    Quote Originally Posted by innova  View Original Post
    It may have something to do with the stop size. Change it to one meter and you should see the change

    Sent from my GT-I9300 using Tapatalk
    If you compare two profiles you need to use same stop size and min stop time. Only that way comparision is relevant.

    Sent from my PAP4500DUO using Tapatalk 2

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    jj ccr

    Re: Deco Observations Spawned from the deep stops debate

    Hi Igor, I realise that. The OP couldn't see a difference in the place of the first deep stop by making the model more conservative. It may well be because it's rounding to the nearest 3m. One way of observing this is to make the stop steps smaller. I didn't intend for him to use it in anger or even for comparison purposes.

    Sent from my GT-I9300 using Tapatalk

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    Re: Deco Observations Spawned from the deep stops debate

    Anthony

    People went to a lot of trouble in the last thread to control for runtime. They also considered a more complex set of factors. An added complication is that VPM is controlled by a single parameter whereas GF is controlled by 2.

    Basically, you're comparing a high risk VPM model with a half specified GF model. It's hard to know what to do with that. 40/40 is a very low risk GF model. 40/150 is a very high risk one.

    So... What high GF would give you a total runtime similar to the runtimes in your examples. And what do you think of that GF? BTW my guess is that it's probably higher than 100 which will make finding software able to produce profiles hard to find.
    Last edited by aainslie; 26th February 2014 at 14:37.
    Andrew Ainslie

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  10. #10
    RBW Member atedeschi is an unknown quantity at this point atedeschi's Avatar
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    Deco Observations Spawned from the deep stops debate

    I havnt played much with the high end but what I found more interesting was the low number say 40 is giving the first stop about the same as VPM. Even if I bump the conservatism up to 4 or 5 it seems VPM is only a stop or two deeper then 40/xx.

    I'm not stuck on trying to match runtimes I know there different models. What I found about the 1st stop surprised me. I assumed with all the debate there would be a larger difference.

    When you use GF were your 1st stops a lot deeper then VPM?

    Also to note when I started I was 20-21 yrs old and now 28 so my age is a helping factor. I was planning in the next year or two to maybe bump it up to +1

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