What's your SurfGF and how does it compare to your (Rec) GFHi?

[FreeFlyFreak]

That last bit's debatable, but you do understand that GF99 is plotting one moving target relative to another moving target, yes? For one tissue compartment out of 16, subject to change without notice?

Yes, I believe I understand.

At the beginning of ascent its the fast tissues leading, toward the end or ascent and after the safety stop its the medium tissues leading.

Its all deco stress to the body, even if it's a NDL limit dive.
Sliding scale, bottom of the scale as far as I can tell is wanting to nod off on the drive home.
Or as I have heard said "every dive is a deco dive"
NDL just means less chance of getting bent. Diver pfo, workload, temperature, depth time and ascent rate etc could all make not getting "bent" on a NDL dive not true.

 

[Jay]

You must have a Teric.
I have a Petrel.
The row options are not exactly the same.

Ah ... my bad (assumption).

FYI there's a very nice spreadsheet done by EFX which shows which theo tissue compartment is leading at different points during the dive: Dive Calculation Spreadsheet

When I first did this poll I checked (only) one other divers data to set the SurfGF input ranges. It seems our data was generally a bit low ... perhaps for next year's poll I'll widen them out and ignore the GFHi question ... that question was only to establish a pre vs end of dive relative 'risk' comparison.

 

[Fastmarc]

Having just received my Perdix AI, I'm once again going through this thread.
Did I mention before this is such a good thread? Why isn't this a sticky.

 

[FreeFlyFreak]

Before everybody jumps on @FreeFlyFreak for what seems like improbable GFs at the end of his dive, note his total dive count. If true, perhaps he's not as aggressive or deep as you are right now. Let's be thoughtful here...
I think he's to be applauded for knowing this much of the science this early in his dive career.

Ah ... my bad (assumption).

FYI there's a very nice spreadsheet done by EFX which shows which theo tissue compartment is leading at different points during the dive: Dive Calculation Spreadsheet

When I first did this poll I checked (only) one other divers data to set the SurfGF input ranges. It seems our data was generally a bit low ... perhaps for next year's poll I'll widen them out and ignore the GFHi question ... that question was only to establish a pre vs end of dive relative 'risk' comparison.

Since my original posts in this thread I have done more diving, and some deeper, longer NDL dives in nice warm water.

Single dive.
Average depth 50 ft
Deepest on that dive 73 ft
Dive length 46 mins
Lowest NDL 4 mins on the way up @ 50ft, where we had hung out for a while, and 37 mins, that was with GFHi set at 75 (was supposed to be 85 forgot to change it d'oh)

I still saw just 1% GF ascending initially following the reef up.
It came off the 1% peg at 43 mins, 27 ft depth 4% GF99
At Safety Stop oscillating between 17-13 ft due breathing and some surge GF99 range was 15-30%
Highest GF upon surfacing was 63%, the highest I have seen.

Very interesting to look at the graph though. Presuming the algorithm is accurate (I know). The majority of the excess N2 tissue over pressures happened in the last 25 is feet, and 50-75% of that was from the safety stop to the surface.

 

[rsingler]

The majority of the excess N2 tissue over pressures happened in the last 25 is feet, and 50-75% of that was from the safety stop to the surface.

Which brings us right back to
Recreational Ascent Rate in the last 15 feet
SurGF is turning out to be a fascinating parameter to study!

 

[FreeFlyFreak]

Which brings us right back to
Recreational Ascent Rate in the last 15 feet
SurGF is turning out to be a fascinating parameter to study!

Indeed!

I cant do it on these guided boat dives, where they want everyone to surface together. But when I cold water shore dive now with my buddy we have started just following the bottom up or gradually swimming up almost horizontally from the 15ft safety stop. Often taking 8 mins to transition from SS depth to the surface.

I can't say if its useful/helpful or not as they have thus far been shallower dives, but I do it anyway. I did learn there is a lot of cool stuff in the shallows that I used to not see.
Last time we found a leopard shark on the bottom next to a rock in less than 10ft of water. Never would have seen it before.

 

[stuartv]

Indeed!

I cant do it on these guided boat dives, where they want everyone to surface together. But when I cold water shore dive now with my buddy we have started just following the bottom up or gradually swimming up almost horizontally from the 15ft safety stop. Often taking 8 mins to transition from SS depth to the surface.

I can't say if its useful/helpful or not as they have thus far been shallower dives, but I do it anyway. I did learn there is a lot of cool stuff in the shallows that I used to not see.
Last time we found a leopard shark on the bottom next to a rock in less than 10ft of water. Never would have seen it before.

Don't ever let anyone (boat crew or other) make you surface more quickly than what you feel is best/safest for you! "Everyone else is going up now" is not an acceptable reason for them to tell you you have to come up more quickly.

 

[scubadada]

Don't ever let anyone (boat crew or other) make you surface more quickly than what you feel is best/safest for you! "Everyone else is going up now" is not an acceptable reason for them to tell you you have to come up more quickly.

However, you may have to occasionally modify your dive plan to comply with operator rules/regulations. If there is a hard dive time and you need more time than others for your ascent, you may have to leave the bottom earlier than others. If you can't do this, you may have to find a different operator. A few minutes may be easily tolerated, a significant amount of time, may not be. It would seem that this common sense would not be difficult in no stop diving.

 

[FreeFlyFreak]

Don't ever let anyone (boat crew or other) make you surface more quickly than what you feel is best/safest for you! "Everyone else is going up now" is not an acceptable reason for them to tell you you have to come up more quickly.

Understood, and agreed.
They didn't rush me but my buddy surfaced with the group, I was the only one left slowly ascending. I figured it was safer to ascend than to stay down much longer on my own, especially with a boat inbound for pick up. .
If the boat is tied off i usually wait untill I see people climbing the ladder to come up the last 5ft, and then get on last or close to it.
In this case the boat wasn't tied off, I still reached the surface probably a minute after the group, and was getting some "whats up" hand signals on the way.
I should probably bring it up with my buddy more than anyone.
I did tell the person that had been signaling me, after the first dive, that I prefer to come up very slowly from the safety stop and that I didn't have a problem/deco obligation.

 

[FreeFlyFreak]

It would be really great if @Shearwater could some how incorporate an indication of when you are net off-gassing.

GF99 only tells you percentage wise where the leading compartment is between the point of it (it alone) off gassing and the M value.

I would like to know, at what point I am off gassing overall more than I am on gassing, taking into account all compartments.
Something simple like a small green open circle to indicate net ongassing and the same circle turns solid green to indicate net off gassing.

Is that even possible?
Would it even be useful?

In otherwords, during ascent down deeper I may be off gassing faster compartments lets say the first 1, then 2, etc but still on gassing the other compartments. At some depth this would change to where lets say the amount of off gassing in the x fastest compartments would out pace the on gassing of the slower y compartments.
The compartments would change depending on depth time and if it was a repetitive dive or first dive.

I guess it has something to do with the integral of supersaturation I have heard @Dr Simon Mitchell mention in the past.

It may turn out that it really doesn't really matter for a lowly Rec diver like me, but it may be useful info for a Deco Tech diver. Or it may not be useful to anyone. But I don't know without seeing it.

Just thinking out loud, mental masturbation if you prefer, feel free to tell me where I am wrong. I know you guys aren't shy.