The other issue then is -- and I'm talking about how the computer works, not the actual human diver, of course -- that on a no-stop dive the fastest tissue compartment is taken care of by slow ascent rate and it doesn't really matter anyway except on a very short bounce dive. It will be a slower compartment that's controlling, in ZH-L16 they've 8, 12.5, 18.5, etc. minute half times. I've no idea how much delta-pressure it has to lose in order to make a difference to surfacing GF, nor which was controlling on that particular dive, but I would not expect to see any drop in surfacing GF until after at least a 3-4 minute stop. Ascent won't cut it unless you're so slow your leading compartment is off-gassing faster than the ambient pressure's going down. I doubt 40' in 7 minutes is slow enough even for the 8-minute TC.
What's your SurfGF and how does it compare to your (Rec) GFHi?
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The other issue then is -- and I'm talking about how the computer works, not the actual human diver, of course -- that on a no-stop dive the fastest tissue compartment is taken care of by slow ascent rate and it doesn't really matter anyway except on a very short bounce dive. It will be a slower compartment that's controlling, in ZH-L16 they've 8, 12.5, 18.5, etc. minute half times. I've no idea how much delta-pressure it has to lose in order to make a difference to surfacing GF, nor which was controlling on that particular dive, but I would not expect to see any drop in surfacing GF until after at least a 3-4 minute stop. Ascent won't cut it unless you're so slow your leading compartment is off-gassing faster than the ambient pressure's going down. I doubt 40' in 7 minutes is slow enough even for the 8-minute TC.
Anthony A.
Contributor
This thread has some great info. Im curious though how to determine what surface gf percentage I should be getting on a no deco rec dive that would be considered safe. Let's say med (40/85 gf) conservative mode. Would it be safe to ascend at 85% and after 3 min ss 75, or should I be off gassing more to reach under 70. Im confused how to determine what percentage is safe.
First, GF Low does not matter on a no-stop dive. Second, nobody's going to tell you what's "safe": these things are statistically-derived and come with "expected incidence of clinical DCS". Last I looked several models seemed to agree on the statistics in about 70-85 GF range, which doesn't make it "safe", it only means they agree on expected DCS incidence. Last but not least DSAT is the only model designed specifically for no-stop diving; it has been used for it a lot and with great success, and it roughly corresponds to GF in high 90s (although the differences tend to accumulate with repetitive diving).
IOW what's "safe"? -- you decide.
IOW what's "safe"? -- you decide.
Anthony A.
Contributor
I get that its very personal and kind of trial and error, but for a typical rec diver what range should one be looking at? For example, would anywhere from 80% and lower be fine and considered "safe"?
I dive GF 50/70 for both no-stop and deco.
It's uncommon for me to have a no-stop dive where I surface with greater than 60%, and I try to take 2-3 min to ascend the last 15 feet where GF99 is blooming.
I am uncomfortable with GF Hi in the 80's, though many are not. My deep dives might be 3 min shorter than a buddy's with 50/70, but with Nitrox, it's more common to be gas limited than NDL time limited.
All you'll get is personal opinions. But it's interesting to see the number of tech divers who are now diving 50/70 when 30/85 used to be the standard. Change comes slowly.
My 2 cents?
Always dive Nitrox.
Try a lower GF Hi and see if your dive style is even cramped.
It's uncommon for me to have a no-stop dive where I surface with greater than 60%, and I try to take 2-3 min to ascend the last 15 feet where GF99 is blooming.
I am uncomfortable with GF Hi in the 80's, though many are not. My deep dives might be 3 min shorter than a buddy's with 50/70, but with Nitrox, it's more common to be gas limited than NDL time limited.
All you'll get is personal opinions. But it's interesting to see the number of tech divers who are now diving 50/70 when 30/85 used to be the standard. Change comes slowly.
My 2 cents?
Always dive Nitrox.
Try a lower GF Hi and see if your dive style is even cramped.
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Hi @Anthony A.
My Teric is set at a GF high of 95, to approximately match my other computer, an Oceanic VT3, running DSAT. Many of my dives are limited by dive time or gas. However, not infrequently, I'm pushing the NDL and about 5% of my dives are light deco.
The Shearwater GF high setting does not include your safety stop, it reflects a direct ascent to the surface, just as SurfGF does. If you perform any safety stop, you will surface below your GF high from a no stop dive. You can always lower your surfacing GF by extending your safety stop or by padding your last deco stop and you can follow this with your SurfGF
I have downloaded my last 160 dives to the Shearwater Cloud. Among other things, it gives you your End Surface GF for every dive. My highest end surface GF has been 80, with an average of 59 (25-80).
I have been successfully executing dives using a computer running DSAT for nearly 20 years, 2000 dives. Now, I have additional information from my Shearwater computer to assist me in diving safely. As per @rsingler I do my final ascent slowly, at least a minute from the safety stop or last deco stop. Watching the final ascent GF rapidly rise on the Shearwater graphic is quite eye opening.
My Teric is set at a GF high of 95, to approximately match my other computer, an Oceanic VT3, running DSAT. Many of my dives are limited by dive time or gas. However, not infrequently, I'm pushing the NDL and about 5% of my dives are light deco.
The Shearwater GF high setting does not include your safety stop, it reflects a direct ascent to the surface, just as SurfGF does. If you perform any safety stop, you will surface below your GF high from a no stop dive. You can always lower your surfacing GF by extending your safety stop or by padding your last deco stop and you can follow this with your SurfGF
I have downloaded my last 160 dives to the Shearwater Cloud. Among other things, it gives you your End Surface GF for every dive. My highest end surface GF has been 80, with an average of 59 (25-80).
I have been successfully executing dives using a computer running DSAT for nearly 20 years, 2000 dives. Now, I have additional information from my Shearwater computer to assist me in diving safely. As per @rsingler I do my final ascent slowly, at least a minute from the safety stop or last deco stop. Watching the final ascent GF rapidly rise on the Shearwater graphic is quite eye opening.
Cool analysis! I just went and did a similar analysis from my dives for this year. My Max End SurfGF was 65%, my Min End SurfGF was 1% (Blue Heron Bridge), my Avg End SurfGF was 52%. I have my Perdix AI set to 70/85.
Massively confused about what's meant by the SurfGF -- always understood it to mean that should you immediately bolt for the surface, that will show you the percentage of the M-value. For example, mine read SurfGF=219 on the 15m/50' stop the other day. When it drops to 80 -- my GF-hi -- the deco clears.
My GFs profile is, and always has been, 50:80.
My GFs profile is, and always has been, 50:80.
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