I think GF were created well after A, B and C
Eric Baker mentions them in this document btw
Gradient factors explanation from E Baker, he references the previous paper so must be written afterwards.
Why 2 gradient factors ?
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Eric Baker mentions them in this document btw
Gradient factors explanation from E Baker, he references the previous paper so must be written afterwards.
I've learned a lot reading this thread, thanks for all of the informed input.
For OC Rec dives, do y'all have any opinions on whether the Shearwater default of 40/85 is reasonable, versus something like 75/85? I understand that for no-stop dives, GFLo does not enter the picture, but every now and then s--- happens and a no-stop dive becomes a deco dive. For that situation, I'd like to have my computer set to what I think is the safest option.
I tried punching several dive profiles that go a few minutes into unplanned deco into Subsurface, using its default of 0.7 cuft/min. For example: using air in a HP100 tank, 2 minutes to descend to 90 feet, remain at 90 for 25 minutes. With 40/85, there's a 20' stop for 2 minutes and a 10' stop for 4 minutes, diver surfaces with 646 psi. With 75/85, there's a 10 foot stop for 5 minutes, diver surfaces with 687 psi. I found several cases like this where you end up with ~50 psi more gas in the tank. Which, for an untrained diver in a mandatory deco scenario, could make a difference.
Thoughts? Maybe I'm in the weeds here, I dunno.
For OC Rec dives, do y'all have any opinions on whether the Shearwater default of 40/85 is reasonable, versus something like 75/85? I understand that for no-stop dives, GFLo does not enter the picture, but every now and then s--- happens and a no-stop dive becomes a deco dive. For that situation, I'd like to have my computer set to what I think is the safest option.
I tried punching several dive profiles that go a few minutes into unplanned deco into Subsurface, using its default of 0.7 cuft/min. For example: using air in a HP100 tank, 2 minutes to descend to 90 feet, remain at 90 for 25 minutes. With 40/85, there's a 20' stop for 2 minutes and a 10' stop for 4 minutes, diver surfaces with 646 psi. With 75/85, there's a 10 foot stop for 5 minutes, diver surfaces with 687 psi. I found several cases like this where you end up with ~50 psi more gas in the tank. Which, for an untrained diver in a mandatory deco scenario, could make a difference.
Thoughts? Maybe I'm in the weeds here, I dunno.
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For the untrained deco diver, I think it's a good idea to try to stop at 20 ft, at least briefly, regardless of which of those 2 GFs you use. There's less of an impact for an inadvertent overshoot. After that, they're largely similar for such a short obligation.
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Hi Brett,
Those are good questions, I have asked them several times myself. I am mainly a rec diver and do mostly no stop dives. However, about 5% of my dives are planned light, backgas deco, and have been for about 15 years. Nearly all my deco is <10 min, occasionally a touch more.
Initially I dived just an Oceanic computer running DSAT and never had a stop deeper than 10 feet. I started diving a computer running Buhlmann in 2016 and chose a GF high of 95, to approximately match DSAT. Running the preset of 45/95, I would occasionally get a min or two at 20 feet. After the Doolette article, I switched to 80/95 and get all my deco at 10 ft. I do actively use the SurfGF on my Teric and surface no higher than the low 80s from dives very close to the NDL or deco.
For my simple diving, these settings work fine. I believe much of the controversy and debate concerns much more serious decompression diving, for which I have no experience or opinion.
Best of luck in your diving
No, you're correct. It takes a really dumb setting, like 10/90, to make a practical difference (I wouldn't call 50 psi "practical"), but that's the way it works: lower GF Low will generate more/deeper deco in the situation where you're likely already low on gas.
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@Brett Hatch
Like you, I am always tempted to run simulations, this one on MultiDeco. stop time at 1 min.
Like you, I am always tempted to run simulations, this one on MultiDeco. stop time at 1 min.
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Mostly weeds...
But assuming you have at the very most 10 mins of deco. And probably more like 5mins. And you are on the leftovers of your gas supply. Getting shallow and hanging out at 15-20ft - which is what every recreation table ever made recommends, is the prudent strategy. The minute or two you might spend at 30-40ft is pretty inconsequential one way or the other DCS wise. But you're using a little more gas, and that much further from the surface if you do run completely OOA and are forced into a CESA
My honest thought,
If you are planning deco dives with a single tank, it doesn't matter what GF you put in. The Gradient factor isn't what will wind up killing you.
What is this **** that happens making your no stop dive a deco dive?
Stop doing that. I have done a lot of no stop dives, can't say I have ever had one turn into a deco dive unexpectedly. You are diving too close to the edge if this is something you run into.
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