The view in my area is to use something around 80/80 for anything without helium. Interesting difference imo.
Decompression controversies
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I agree. Many think deep stops are an inherent property of bubble models, but they aren't. I'd say the early deep stops are just a random artifact of a particular unfortunate simplification and choice of parameters in VPM.
VPM has a bubble model for each compartment with a few parameters such as the surface tension or the volume of tolerable bubbles. Our body has a lot of tissues, each with different physical properties regarding bubble formation, and each with different tolerance to bubbles before DCS symptoms show. So there's a large number of parameters for a bubble model to tune; many more than for a Haldanian style model with M-factors.
Looking at Dr Yount's paper on VPM ( http://www.divetable.de/workshop/Yount_Hoffman_1986.pdf ), you see that he wants to reduce the number of parameters and does so simply by using the same bubble model parameters for every compartment. Secondly, the parameters are not calibrated to a probability of DCS by experiments, but are just tuned to match the US Navy table's total decompression time. The result is a model (VPM) that produces ascent schedules with a similar runtime as the USN tables, but no idea about the DCS risk.
Obviously, compared to the experimentally fitted ZHL model and USN tables, VPM has more tolerant slow compartments and less tolerant fast compartments, resulting in earlier deeper stops and shorter shallower stops. That does not mean VPM discovered something new (deep stops being good). A more plausible explanation is: the way how VPM uses the bubble model is a too coarse oversimplification and conflicts with experimental results on the human body.
Divetech99
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RGBM is a bubble model algorithm. Yet, the few times I've taken my Suunto to 45/50 meter deco dives, I kind of noticed that the first stop of a Suunto is nearly the same as a Petrel on a gf lo of 40. This is anecdotal and I wasn't paying that much attention to the Suunto since the petrel is primary. Does anyone with a Suunto have observations on how it plots the first stop on a real deco dive?
The problem with Suunto's "RGBM" is that it's proprietary, and nobody except Suunto knows what it's doing. It might or might not be running an actual implementation of RGBM. There has been discussion in the past about their using something called "folded RGBM", at least on the less powerful recreational computers, which is a Haldanean model with some tweaks to make it act more like RGBM.
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I think it depends on the model you have. I'm using a Vytec from 2002 (I think) and it doesn't calculate any stops at all. All I can read from it is the TTS and I make up my own stops from just looking at the total deco obligation. Even the ceiling it calculates for the first stop longer than 1 min is ridiculous.
My buddies both use Suuntos as well (one as primary and the other as a backup). One is a D-series and one is a Helo2 and both of them seem to calculate a stop at +/- half of the maximum depth on the dives we normally do, which are profiles up to about 50m using Nitrox or air.
The buddy who uses the Suunto as a backup also has a petrel 2 that he uses for his primary. He normally sets it to 30/70 and it calculates a deep stop at about the same depth as the Suuntos do. It also seems to calculate another longers stop 1/2 way between the first stop and the first long stop. So, for example on a 50m dive it will normally show a deep stop somewhere between 20-25m and then another one at about 12m.
All of this is anecdotal, of course, and very specific to the small range of profiles that we dive pretty much every week.
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...provided you increase the shallow stops to compensate for slow tissue loading during the deep stops(s), that is?
That's what Pyle do and he felt better this way. There's little to say against Pyle stops except that it may not be the most efficient way, but at least it's safe.
But in the VPM paper, the total decompression time is matched to the USN table; so going from USN table to VPM means: redistributing stop time from shallow to deep. For the sensitive medium and slow tissues that means more on-gassing *and* less time for off-gassing. And that compared to a table that's not very conservative to begin with, as it was made for people who have a chamber right on the ship and can accept a 5% DCS risk.
VPM didn't go so well for many early adopters AFAIK.
VPM works well for a friend I dive with. I don't understand it and think the reduced deco is crazy but it works for him thus far. We were doing a dive last year with a max 117', average probably 95' and runtime 169 mins. I was on 30/85 and him using VPM. I ended up doing 25 more mins deco than my buddy and still suffered a DCS hit. We've yet to figure out the exact cause. I went to 30/70 and recently changed to 40/70.
Depending on depth, GF30/85 can be more aggressive in the deep stops than VPM-B.
Let me try to guess your profile and settings: 117' (36m) for 55minutes BT makes 169min runtime on GF30/85, and 140min on VPM-B+1 (ran with GNU subsurface), that are about your times.
GF30/85 starts with stops 1min@70' , 5min@60' , 6min@50' , ...
VPM-B+1 starts shallower with 3min@60', 6min@50', ...
So if this are your numbers, then GF30/85 is even more on the deep stop side than VPM-B; your DCS hit would suggest that staying deep for too long is not good for you.
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