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Thread: Ascent rates on Deep Trimix dives

  1. #1
    RBW Member heland707 is an unknown quantity at this point heland707's Avatar
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    Question Ascent rates on Deep Trimix dives

    Hi All,

    I'd like to canvass opinion and would welcome comments on how this particular dive should have been executed, especially in terms of ascent rates.

    Last Friday, my buddy and I dived Dorothea quarry in the UK to the 104m pit. The dive was to 101m (profile attached), my buddy insisted on a slow (what turned out to be a 3.3m per minute to the first deco stop) and beyond. In light of Simon Mitchell’s https://www.youtube.com/watch?v=UY61E49lyos and the USN latest research deep stop ‘bubble’ models have been brought under the spotlight in that although they reduce risk of bubble formation through fast tissues they significantly increase DCI risk due to further saturation of the slow tissues. For these reasons, I dive Buhlmann GF’s 40/75 on my Inspiration.

    The problem in my mind is that although I have GF’s of 40/75, the very slow ascent rate actual has the same effect of carrying out deep stops in that slow tissues continue to be saturated (after all ‘Stops’ are artificial – you simply have a deco ceiling), additionally, I cannot see any logic in a 3.3m per min ascent from 101m to the point of off-gassing around 80m.

    The net effect of the slow ascent was that after reaching 101m 11 minutes into the dive, my total Run time was 135 minutes. I ran the same dive through Multideco with my preferred:
    · 9m/min to point of fast tissue off-gassing
    · 6m/min to 6m
    · 3m/min 6m to surface
    And had a simulated run time of only 61 minutes. This to me proves too slow ascent can be as bad a too fast ascent.

    Profile.jpg

    Andy%27s optimal ascent rate.pdf

    Our dive with actual ascent rate.pdf

    Having looked at many agencies, I cannot get a sense of what ideal/optimal ascent rates should be (no common approach) for Ascent to the off-gassing point, ascent rates between Deco stops etc. Views appreciated.

    Andy
    Last edited by heland707; 28th July 2016 at 12:12.

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    RBW Member Valery is on a distinguished road Valery is on a distinguished road Valery's Avatar
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    Re: Ascent rates on Deep Trimix dives

    9m/min.

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    Re: Ascent rates on Deep Trimix dives

    It would be good to get Andrew Ainslie's opinion on this one. He did some 500+ foot dives and wrote about the deep ascent rates. I cannot remember the conclusion but I believe they used scooters to get up to 10 ATAs as quickly as possible. The thought being you are just loading gas at that depth. I won't even try to explain it but hopefully he can come on and give his rationale. Seemed to work for him.

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    RBW Member heland707 is an unknown quantity at this point heland707's Avatar
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    Re: Ascent rates on Deep Trimix dives

    Quote Originally Posted by Garibaldi  View Original Post
    It would be good to get Andrew Ainslie's opinion on this one. He did some 500+ foot dives and wrote about the deep ascent rates. I cannot remember the conclusion but I believe they used scooters to get up to 10 ATAs as quickly as possible. The thought being you are just loading gas at that depth. I won't even try to explain it but hopefully he can come on and give his rationale. Seemed to work for him.
    Thanks for the tip. I've sent Andrew a PM

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    Re: Ascent rates on Deep Trimix dives

    On anything deeper than 300', I ascend at an almost uncontrollable rate until my first stop or 200' which ever is first. I have no real science to back me up and it may well kill me one day. My dive logs show it at an average of 125 fpm.

    I doubt that many others will do this and even less will admit to it.
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    Re: Ascent rates on Deep Trimix dives

    Quote Originally Posted by Dsix36  View Original Post
    On anything deeper than 300', I ascend at an almost uncontrollable rate until my first stop or 200' which ever is first. I have no real science to back me up and it may well kill me one day. My dive logs show it at an average of 125 fpm.

    I doubt that many others will do this and even less will admit to it.
    Ha ha back in my OC days I'd often to a 80m dive with a 50m reel and effectively lift myself 30m!!! Good fun but my unit doesn't like it as much!
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    PS admitting to things is how we can all learn
    Last edited by turtle dude; 29th July 2016 at 11:49. Reason: damn auto correct

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    RBW Member rjack will become famous soon enough rjack will become famous soon enough rjack will become famous soon enough rjack's Avatar
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    Re: Ascent rates on Deep Trimix dives

    I've been diving with various buddies that are "too slow" at some point you just gotta say "thanks but no thanks" and decide not to dive together. 3m/min up from 100m is way too slow for me, I'd either skip the dive or accept that a quarry is a training exercise and doodle around in the shallows for an especially long time to compensate.

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    RBW Member techintime is an unknown quantity at this point techintime's Avatar
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    Re: Ascent rates on Deep Trimix dives

    Our technique:
    9m/min off of the bottom. In practice very difficult to achieve because it feels like you are out of control. When we looked back at our profiles off of the computer (a years worth of diving in 70-112m) we found that we only rarely achieved 9m/min, maybe 20% of the time. Despite out best efforts the usual ascent rate was about 5-7m per minute.

    non-computer driven deep stop at half the difference between the bottom and the ceiling as you left the bottom. Short pause there until ceiling increases or TTS increases (usually takes less than 30 seconds) then resume the ascent at 6m/min to the ceiling.

    then follow the ceiling (not the stops)

    last stop at 6m

    After clear...1m/min from 6m to the surface
    Last edited by techintime; 29th July 2016 at 06:51.

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    RBW Member Lee Stroke is an unknown quantity at this point Lee Stroke's Avatar
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    Re: Ascent rates on Deep Trimix dives

    If you reached the surface and had no DCI then that is the correct rate. Now saying that, your next dive all conditions being the same you can make small changes and see how you or your buddy do. You may have to have two different schedules. I usually dive my own schedule, we are in sight of each other but usually a stop apart or so. Off the bottom at 18m/min first stop 9m/min, to 6m. 6m to surface as slow as possible. On board stay on O2 till I am sure I am not doing IWR.
    Last edited by Lee Stroke; 30th July 2016 at 03:03.

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    Re: Ascent rates on Deep Trimix dives

    I try for 9m/min ascent to first stop at 60GF depth but its not often i can get mooving that fast.

    9m/min is (or at least apears to be) damed fast to me bordering on the uncontrolable without a shot line for stabuility and loads of alarm warnings from my back up computer :D

    My average ascent rate is about 7 id guess.

    Blue triangles are ascent rate warnings


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