Simple surfacing GF question

[scubadada]

Assume you are diving X/95 and have 5 minutes of deco at 10 feet at the end of the dive. You make a normal ascent and fulfill the deco obligation. I assume, if you surface immediately, you would be at your GF high of 95. How much would 3 or 5 minutes of additional time at your stop lower your surfacing GF?

I'm hoping folks with Shearwaters will know this. I know it's a bit more complicated, just looking for approximate values.

 

[Graeme Fraser]

I'm thinking roughly 10% for 3 minutes. This is based purely on a dive from a few weeks ago. I was using my Perdix with GFhi 80, whilst my buddy was using an Eon Steel set conservatively. His comp kicked him 3 extra minutes at 3m and I hung around watching the GF99 field on mine drop from 80 to sub 70. No hard data, just my casual observations.

 

[scubadada]

This question applies equally to no stop dives just up to the NDL with direct ascent vs. 3-5 minute safety stop. I would guess some of you with Shearwaters have looked at this, I would.

 

[Macan]

If you have a Teric, it will provide real time Surface GF. I use it all the time.

 

[CWK]

Plan the sane dive on xx/95, xx:85, and xx/75 then compare deco times.

 

[scubadada]

If you have a Teric, it will provide real time Surface GF. I use it all the time.

So what is the answer to my question, how much does a 3 or 5 min stop lower your surfacing GF?

 

[scubadada]

Plan the sane dive on xx/95, xx:85, and xx/75 then compare deco times.

No

 

[CptTightPants21]

Are we talking about 100% O2 or backgas for deco? From my experience, 3-4 min of additional pure O2 will drop the GF by 5. So if you do a dive on 50/85, staying 3-4 min longer will clear deco on a 50/80 GF dive, ANOTHER 3-4 min will clear a 50/75 GF dive. Back gas would be completely different. I haven't tested out the GF lower on back gas, but depending on nitrox mix and number of dives performed on the day you would need at least 8-10 min of back gas to lower the GF 5 for the first dive and a little longer if it was a 2nd/3rd dive of the day.

 

[hammet]

great question. I was actually thinking about safety stops and its effect on gf99 after reading the article posted by shearwater. Was hoping to test this on my teric next chance I get to dive.

 

[CWK]

There is no simple answer. It depends on leading tissue group, deco gas and depth.