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  1. #1
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    Gradient Factors

    Good evening all,

    I hope you are all well and enjoying your respective bunkers!

    I did a presentation the other week about 'tech' diving to a group of varied ability divers in a club setting, one the things I always bang on about is expanding knowledge by getting information from multiple sources.

    As an example, if you are in a club and all the club are taught by the same instructors, those members become instructors and teach the same way and repeat. After a while the entire clubs standard of diving can be on its arse...

    ...which brings me to the point of this thread, I have used GFs for years, started with 40/70 and over time have moved to 80/80 as my understanding of M values, GFs and decompression theory evolved. Over this time I was also doing extended range dives and I moved further and further away from the 'deep stop' ethos.

    My diving tends to be beyond that of the people I occassionally dive with (mostly solo here), so I rarely have conversations with a 'peer group' and in the interests of staying true to my own presentation of drawing from many pools of knowledge I wondered what the great and good are using on here?

    So what is your chosen deco model and why?

    No flaming!

  2. #2
    Sorry for being a dick jb2cool's Avatar
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    Probably similar to most people in that i use ZH-L16 + Gradient Factors. Back in the day when i was fairly new to diving VPM-B was the go-to model but that started to be thought of as too aggressive. I've used Suunto's RGBM model purely as that was what my Gekko/Zoop had but i wouldn't use it out of choice, i don't like the opaqueness of the model and as an advocate of Free or Open Source software (these are different things) then i prefer the fact that the Buhlmann algorithm is more openly published and understood even if i don't understand it myself.

    Why?

    Mainly because it's probably the model that's had the most dives done on it for the kind of diving i do and due to the sheer number of people using it the community can tweak the gradient factors and then that knowledge gets fed back into the community, effectively finding the most suitable settings for me.

    I currently use 30/85 but am thinking my GF-High is a little too aggressive for me so am thinking of lowering this a bit. My GF-Low may appear to be too low for some people but for the kind of diving i do with limited deco raising this would make little difference to the deco schedule.
    Last edited by jb2cool; 26-03-2020 at 08:04 PM.

  3. #3
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    This is worse than the virus - another GF thread haha

    I use 20/85 for routine stuff - run the numbers ... there is very little difference between that and 30/70 or whatever the current flavour of the month is - particularly since it is rare that people actually follow their schedule (ascend too slow and say too long in the shallows). For the stuff where it really makes a difference ... say 5h of deco I usually do 20 lo and play around with the hi or in reality not follow the GF profile at all. There's a huge leap from 30min of weekend warrior deco to 5h+ and I don't think you should be learning about how to do those kind of decos but any other method than building up slowly to them - there are lots of tips and tricks to learn from experienced people .

  4. #4
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    50:80

    Was taught by a well known instructor and author who uses this for all types of diving. It optimises deco time. If it's good enough for him, it's good enough for me.

    Spent last season doing longer OC dives in the 30 to 60 metre range with 30 to 90 mins of deco using 50% and 80% deco gas, or just 80%. I modified the final stop to 3 metres giving me the flexibility of moving up as conditions permitted. This definitely helped with post dive tiredness.

  5. #5
    Gobbie squaddie, average diver timmyg's Avatar
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    50:80

    However as Graham said, run the numbers of different GF on planning software. You’ll see that the first stop depth will change as will the final stop length based on your Low/High figures but for the ‘average’ diver the overall TTS is generally within one or two minutes of each other.

    PS. If you use the search bar you will see a bunch of other similar threads so all this does is repeat the same debates.

    TPG


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  6. #6
    Established TDF Member Wardy_uk's Avatar
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    65:75 or 65:85 depending, with 95:95 dialled in as my Get out of Dodge GF if the sh1t hits the fan...

    All for <50m dives

  7. #7
    TDF Member IainC's Avatar
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    50:70 or 50:75, mostly 40 - 50m diving , but up to 60m 2hrs RT ish

  8. #8
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    80/70 for air or nitrox with less than half an hour decompression, 70/60 for longer dives.

  9. #9
    Coastal Member dwhitlow's Avatar
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    It is so long ago......I just checked my dismantled rebreather (with disconnected cells and no batteries) and it was set to 75/80 with an option to switch to 100/110 if I really want to surface.

  10. #10
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    Quote Originally Posted by timmyg View Post
    50:80

    However as Graham said, run the numbers of different GF on planning software. You’ll see that the first stop depth will change as will the final stop length based on your Low/High figures but for the ‘average’ diver the overall TTS is generally within one or two minutes of each other.

    PS. If you use the search bar you will see a bunch of other similar threads so all this does is repeat the same debates.

    TPG


    Sent from my iPhone using Tapatalk
    Yes I could have used the search function, but if we all did that then this place turns into a library instead of a community...and it's quiet enough already!

    But I appreciate your full reply and contributions from everyone, interesting that I seem to be on the more aggressive side so far.

    Out of interest has anyone specifically increased their own safety margins as their health has deteriorated or as they grew older?

    Im 36, no health issues and reasonably fit, I have used 80/80 for dives up to 125m with 5hr run times. I also dive on a box which (for those unfamiliar with CCR) gives some further information around off-gassing by monitoring loop volume during deco.

    I would echo other comments on running a 100/100 back up, I do the same for when the shtf.


 
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