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Thread: Ascent rates on Deep Trimix dives

  1. #11
    So many CCR So little etc Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase's Avatar
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    Re: Ascent rates on Deep Trimix dives

    Quote Originally Posted by Lee Stroke  View Original Post
    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.


    With tables yes but with a dive computer ascending slowley just meens added time to your shallow stops

    The problem with ascending too slowly is leavnig the bottom with a TTS of 120mins and ending up with a TTS of 140mins due to on gassing during the slow initial ascent.

    No drama ona a CCR but a bit of a shock when your limited to OC gas.

    ATB

  2. #12
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    Re: Ascent rates on Deep Trimix dives

    Tell me where my logic fails. If you had no stops to make on a shallow dive, you would surface from a depth of 10 meters at the slow and safe rate of 3 meters per minute, thereby taking you 3:20 to surface. That's 3:20 to halve your pressure from 2 ATA to 1 ATA.

    If you dive to 110m (12 ATA) and didn't begin your deco until 50m (6 ATA), that would be the same 50% reduction in pressure. Ascending that distance in the same time of 3:20 would be an ascent rate of 18 meters per minute.

    I see no physiologic reason why 18 mpm from 110 meters until your first stop (almost certain to be at least 50m depth) would be unsafe. So certainly a 9 mpm rate or anything as fast as you could still feel in control should be fine.
    Ken

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  3. #13
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    Re: Ascent rates on Deep Trimix dives

    Quote Originally Posted by kwinter  View Original Post
    Tell me where my logic fails. If you had no stops to make on a shallow dive, you would surface from a depth of 10 meters at the slow and safe rate of 3 meters per minute, thereby taking you 3:20 to surface. That's 3:20 to halve your pressure from 2 ATA to 1 ATA.

    If you dive to 110m (12 ATA) and didn't begin your deco until 50m (6 ATA), that would be the same 50% reduction in pressure. Ascending that distance in the same time of 3:20 would be an ascent rate of 18 meters per minute.

    I see no physiologic reason why 18 mpm from 110 meters until your first stop (almost certain to be at least 50m depth) would be unsafe. So certainly a 9 mpm rate or anything as fast as you could still feel in control should be fine.
    Your logic fails simply because it is the same as my logic.

    This is my take for coming up from 500' also. I see absolutely no reason to come up so slow that any more ongassing happens and the pressure differential still stays less than from a slow ascent at shallower depths.
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    Re: Ascent rates on Deep Trimix dives

    Quote Originally Posted by Dsix36  View Original Post
    Your logic fails simply because it is the same as my logic.
    Yes, that is a scary thought.
    Ken

    Quote Originally Posted by Dsix36  View Original Post
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    Re: Ascent rates on Deep Trimix dives

    Quote Originally Posted by Lee Stroke  View Original Post
    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.

    Except that risk is more of a probability function. The slow rate probably has more risk due to intermediate tissue on-gassing during those added minutes. You probably won't know if its more (or less) risky based on 1 dive. Hence results like the NEDU test that had one profile with a 5% risk and the other with a 1.6% risk. The slower ascent in this case likely has a high risk. Statistically higher and by how much? nobody knows.

  6. #16
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    Re: Ascent rates on Deep Trimix dives

    Quote Originally Posted by heland707  View Original Post
    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.

    Attachment 41903

    Attachment 41904

    Attachment 41905

    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
    3.3m/min as you rightly surmised is way too slow

    9m/min sounds a tad slow to me also for rapid phase of ascent from a deep dive. i cant recall what i used in sra keow but from 191m up it was initially a heck of a hot faster than 9m/mins as that speed would have kept me sub 150m for far too long on gassing. i realy dont recall but perhaps it was 30m/min?? sounds familiar




    i have little patience for those who would contort themselves in order to shave 20 mins of a deco hang when all they would do with that 20mins is sit on the boat and drink tea. id suggest (where dive conditions permit) one shouldnt be stressing over trying to shave time especially when its as little as 20 mins. to me the goal of deco is not to get out the water as soon as possible, (dive conditions permitting) the goal is not to get a dci. but 61mins is quite a lot different to 130 mins lol

    Personally i suspect the last 6m, last few meters, how you get out the water, what you do right after the dive maybe as important as a lot of what we fret over on deco planning. on big dives ascent from 6m to surface i would do as slow as i could bare. it wouldnt be unusual for me on say a 100m dive to taken 20 mins to surface from 6m after clearing my dc indicated deco. i would also float on the surface and take my time de kitting to minimise exertion (dive conditions permitting)



    bottom line your deco plan appears more sensible but perhaps in practice personally id either add a 30 sec deep stop and or initially ascend a bit faster then slow ascent to first stop, id clear my deco at 6m then very slow ascent to 3m then do say 15mins there then very slow ascent to surface.
    Last edited by Drmike; 3rd August 2016 at 09:18.

  7. #17
    So Cal Tech Diver aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie's Avatar
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    Re: Ascent rates on Deep Trimix dives

    Nothing in deco diving is linear. Everything is exponential. It's the percent change in pressure that should be controlled, not the linear rate of ascent.

    On our 500 ft dive, we had scooters. We aimed our scooters straight up and ascended as fast as they would carry us up to 300 ft.

    Obviously this requires some solid buoyancy control. But it took over 2 hours off our deco time over the usual stupid 30 fpm rate recommended by textbooks. This is more than just shortening the deco time. It radically reduces unnecessary on take of inert gases, and gives you way better emergency responses should something go wrong as you get shallow far faster. In general, I would agree with Mike's points above about this being about more than exiting fast to drink tea.

    10 fpm is just asinine.
    Last edited by aainslie; 5th August 2016 at 23:53.
    Andrew Ainslie

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

    3m/min on a sub 100m is just stupid.... your simulations shows this - at that rate you are on gassing more than you are off gassing and are actually adding to risk of the dive (dc hit).

    There is no scientific backing reason for this - my experience so please do not do this . below 100m I do about 20m/min (to get out of the on gassing area) - 100m to 70m about 10-15m/min thereafter no faster than 9m/min and quite bit slower in the upper 50m (there is no rush here in any event.

  9. #19
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    Re: Ascent rates on Deep Trimix dives

    After Andrew had this discussion years back when I started going over 300' my ascents of the bottom became fast until about 200'
    It saves time on your runtime and not just a few minutes. I have not felt any negative affects. I have to upload my dives but generally I keep the shearwaters in the high yellow to red of the ascent warning.

    I also running 70/85 for last 3 years and feel much better then the last year I was doing VPM-0.
    Guys I am diving with also started bringing their low GF up and are feeling better and having less issues on multiday multiple dives in a day trips in the 200-300' range
    Deeper then 300' we do one dive only a day.

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