Rising GF99 after surfacing???

[inquis]

While supersaturation accounts for effects everywhere in the body including capillaries and non-circulatory tissues

The complication is surfGF does not provide insight into supersaturation "everywhere". It is specific to the peak tissue compartment and merely an upper bound on all others.

 

[rsingler]

Fun to speculate. Me, I am indebted to Shearwater for leading the way in providing SurGF to the diving community.

 

[b1gcountry]

I don't own a shearwater and I am not completely sure I understand gf99. Reading the documentation, and looking at the graphs, it sounds like it may be your current gradient for the ambient pressure. Does this sound correct? So it will go up as you ascend.

It sounds like shearwater is simply trying to round out the curve using a depth averaging algorithm over your latest few minutes. This might be more accurate seeing as your respiratory/pulmonary system doesnt immediately adjust to the ambient.

 

[rsingler]

Nothing further heard back from @Shearwater

 

[rsingler]

Now up to version 2.10.2 and the problem persists.
My graph is still truncated (now 60 sec after reaching surface) despite specifying Dive End at 360 sec.
My graphs still show an increasing GF99 over that one minute, and the listed surfacing GF in the dive statistics is often as much as 11% lower than the max GF99 graphed before Cloud truncated my graph.
On my last Deco dive, after dawdling at 10' an extra few minutes (I dive 50/70), the GF99 max on the graph was 62%, while the data summary says my dive's surfacing GF was only 51% (which was true the instant I hit the surface).
I have not heard anything further from @Shearwater after my inquiry. Count me disappointed in them. 62% vs 51% is not insignificant, even if we don't really know what it means.

 

[attue]

I've got a similar problem, but just dove my new Peregrine once - for what I've seen my last logging point was 1m below surface and then immediatly 0.0m - the end-surface GF was logged with the GF stated at 1m - i think it just stopped there, as I had ascending-rates between 3 and 6mtr/minute and logging-rate of 2sec. Does your graph also jump from 1m to 0m? As I am still logging my dives on paper I wrote down the surfgf which was 53 at the point of 1m instead of 41. Interestingly the gf99 at the end (my graph is trucated at 2x seconds after the jump to 0m) is what subsurface calculates as surfgf at the last logged data-point at 1mtr. So I think that this would be a more reliable value for surface-end-gf.
Cheers...

 

[rsingler]

Thank you for confirming this problem!
Interesting finding - yes, my dives all go from 3.3 or 3.1 feet to zero in a single step, even if my immediately preceding ascent rate was slower.
I note that the GF99's at 3.1 ft or 0.0 ft are not necessarily recorded as the end dive GF.
Of greater concern is that my graphs, which continue for another 15-30 seconds, all show an immediate jump in GF99 at the surface. Despite my plan on my last trip, I kept forgetting to watch GF99 on the display for the next several minutes.
But your observation that SurGF at 1m is significantly higher correlates with this jump in graphed GF99 immediately after surfacing.
I remain concerned that the logged end-dive GF bears no relation to either the graph, or apparently, your observed SurGF.
If you're still diving right now, watch the GF99 for two minutes after surfacing and see when it peaks.

Thanks again for your data!

 

[attue]

Hi, yes, that's why I will write down the last surfgf shown in subsurface, which i think is, if i remember right, the same as it was shown on the DC short before surfacing. I will try to have a look at how gf99-peaks after surfacing and how surfgf was right before surfacing.

I also noticed that ascending-rates are only logged in 3m/min-steps, so I have got constantly changing rates between 0m/min-3m/min and 6m/min while the graph shows quite steady and smooth ascent.

 

[L13]

The complication is surfGF does not provide insight into supersaturation "everywhere". It is specific to the peak tissue compartment and merely an upper bound on all others.

I don't know how I missed this earlier.

I disagree. While you are correct that SurfGF is the upper bound on all the others, "merely" undersells it. Unless your skipped your safety stop, or significantly shorted your deco, it will represent the tissue with the bulk of the remaining decompression stress. In any case, even as an upper bound, it gives insight into the supersaturation "everywhere relevant". Any tissue with a significantly lower GF is significantly less relevant.

 

[L13]

Thank you for confirming this problem!
Interesting finding - yes, my dives all go from 3.3 or 3.1 feet to zero in a single step, even if my immediately preceding ascent rate was slower.
I note that the GF99's at 3.1 ft or 0.0 ft are not necessarily recorded as the end dive GF.
Of greater concern is that my graphs, which continue for another 15-30 seconds, all show an immediate jump in GF99 at the surface. Despite my plan on my last trip, I kept forgetting to watch GF99 on the display for the next several minutes.
But your observation that SurGF at 1m is significantly higher correlates with this jump in graphed GF99 immediately after surfacing.
I remain concerned that the logged end-dive GF bears no relation to either the graph, or apparently, your observed SurGF.
If you're still diving right now, watch the GF99 for two minutes after surfacing and see when it peaks.

Thanks again for your data!

While I don't dive a Shearwater right now, I am curious as to how other DC's perform in this regard. I have made a conscious decision to monitor my Garmin on my next dives to see how it's behavior compares to what you are seeing with the Shearwater. The similarity or difference might be insightful.