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Your Gradient Factors?

Discussion in 'Technical Diving Specialties' started by CAPTAIN SINBAD, Nov 20, 2020.

  1. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

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    I have about 85 light deco dives on Oceanic computers running DSAT. Deco is usually 10 min or less but as long as 14 min. I've never had a stop deeper than 10 ft. About 30 of these were run with a Buhlmann computer in parallel run at 80/95. No stop deeper than 10 feet here either.
     
    KenGordon likes this.
  2. dmaziuk

    dmaziuk Regular of the Pub

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    Yeah, I guess it's a function of number and spacing of half-times: more TCs will result in finer granularity of deco stops. DSAT has noticeably bigger "gaps" than ZH-L16 in the 10..40-minute range so if that's your leading TCs, it's probably how it works out. And who knows what zoop has: my leo apparently has 9 going from 2.5 to 480 minutes (cf. DSAT's 14 for 5..480) but I don't know if RGBM TCs are fixed or you can pick your own like ZH-L16.

    Still, if you have a 1-minute stop at 9' before a 14-minute stop at 6', it's less weird than one 25-minute stop at 6'.
     
  3. KenGordon

    KenGordon Rebreather Pilot

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    Suunto will tell you what they have in terms of half times and number of compartments, but you may be forgetting that the faster compartments have higher over pressure limits so are not always limiting shallower than the slower ones. I did a load of short deco dives in the 30 to 45m range with maybe 20 minutes of stops recently and only a couple got a brief stop at 9, mostly the first actual stop was at 6. These were 50/85GF and according to MultiDeco I ought to have had stops at 12 and 9 but of course my ascent is never as fast and the computers have a different idea of where GF lo applies.
     
  4. BLACKCRUSADER

    BLACKCRUSADER Manta Ray

    # of Dives: I'm a Fish!
    Location: Taiwan
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    Well it happened. I believe she went into deco on her Suunto and missed a deco stop. For whatever reason her Suunto had her do 25 mins at 5m. I'm not one for telling porky pies just stating what happened. It was the second dive of the day and she had done multiple dives each day over the last 5 days prior to that day. It was a very boring 25 minutes that went so slowly.

    This dive log I posted is not her dive with me it's just one I use showing my GF factor where I get longer times to NDL on Shearwater than Sunnto over many days of diving.. Sorry for confusion with that. My error.
     
  5. BLACKCRUSADER

    BLACKCRUSADER Manta Ray

    # of Dives: I'm a Fish!
    Location: Taiwan
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    Halo glare gets less as time goes by. Bit annoying when you get very bright lights that some traffic lights and car lights have. Yeah not too many on the forums who did their tri focals in Sydney when some chap was asking how to fix his bad eyesight when he cannot even see his Perdix display underwater lol. Overall very happy with the eye surgery a huge lifestyle change. Old age aint for sissies.
     
    Mike1967 likes this.
  6. dmaziuk

    dmaziuk Regular of the Pub

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    They are, but they also off-gas the fastest, so if you stick to safe ascent rate and a TC is fast enough, it's possible for it to never kick in at all (in theory anyway). Middle compartments are getting the blame for DCS hits for a reason: the fast ones "cancel out" unless you blow the ascent rate, and slow ones never kick in on no-stop/"light deco" dives.
     
    NothingClever likes this.
  7. 100days-a-year

    100days-a-year Solo Diver

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    So is there evidence available that the tissues those compartments are analogous to get bent more often? That would seem helpful for divers to plan thier deco.
     
  8. dmaziuk

    dmaziuk Regular of the Pub

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    I've seen it in some DAN EU study that I'm pretty sure did not include deco dives and I should've highlighted and stressed no-stop up there. Although ZH-L16 was "adjusted" from A to B to C also in the middle compartments, and that was after the trials. Or at least A to B was I believe.

    Note that this is only how numbers work out. How much faith an actual diver should put in them for actual deco is another story.
     
  9. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

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    Nobody knows what actual tissues in the body have a medium 30min half-life or what is a long 90min half-life or what corresponds to what. They are theoretical compartments with made up numbers across a likely range, not actual tissues. And even within a 'single' tissue like bone, or the CNS, parts of it probably act differently than other parts. For instance, there is lots of postulating that the CNS or spine is "fast" but the actual spinal cord is surrounded by fat cells and when people experience a type I hit nobody really knows where the impacting bubble(s) actually are in real time. There are some symptoms which can be clearly related to a specific tissue, like the optic nerve. But knowing the actual half life of the optic nerve, nobody knows. And many symptoms can't be related to such a specific tissue at all.
     
    Nirvana, RyanT, NothingClever and 2 others like this.
  10. beester

    beester DIR Practitioner

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    The GF part has already been answered. The computers I use (both on rebreather and for OC) try to keep you safe but they will keep calculating an ascend even if you dangerously change the parameters.

    For example I also use a computer as gauge (depth and time). I've had times where I forgot to change my breathing gas from last dive (deco on O²) back to a trimix gas. So then you arrive at the bottom breathing your trimix mix but your computer still has O² as breathing gas set. Yes you'll see bright red warnings flashing your PPO² stating you are about to die ;-) but it will keep calculating a 60m dive even if you keep the settings on pure 100% O². Same with missing deco stops. If I elect to skip a stop, or just drop the last 5 minutes of the last stop and go up, it will warn me that I'm missing stops, but if I confirm this it will keep calculating, instead of crashing out.

    I really like this...
     
    NothingClever likes this.

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