Recreational Ascent Rate in the last 15 feet

[rsingler]

I don't think anyone is arguing that in suboptimal conditions, maintaining a very slow ascent just may not be possible above 8 feet due to boat traffic, surge or other factors beyond your control. That said, this is still a valid process discussion to have: is there really any value in an ultra-slow final ascent, or is it just window dressing? Where I stand on the issue is obvious by now.

But here's another thought: with the advent of SurfGF in Shearwater computers, it should now be possible to choose one technique or the other. That is, if you can't do an ultra slow continuous ascent from the safety stop to minimize the red in that theoretical heat map, it should be possible to do an extended safety stop at whatever depth is stable, until the SurfGF shows the value you want. Your offgassing will still "bloom", but to a lower (safer?) end point. Of course, that then requires us learning what SurfGF really means, and what value is "safe." Here comes another decade of argument and controversy, lol!

Here's a shameless plug for Subsurface: a great, FREE program that allows you to look at the consequences of all sorts of dive profiles. Plus it's a reasonable dive long, and a great deco computer. Yes, it shows "heat maps".
Downloads | Subsurface

 

[Fastmarc]

Through many discussions on here, I've adopted doing at least 5 mins on my SS usually at 15'. I then slowly drift up and get to the ladder last. This would be less than 10 fpm.
I haven't bought my perdix yet, so can't see what it's doing, but I can definitely feel the difference

 

[dmaziuk]

... it should be possible to do an extended safety stop at whatever depth is stable, until the SurfGF shows the value you want. Your offgassing will still "bloom", but to a lower (safer?) end point. Of course, that then requires us learning what SurfGF really means, and what value is "safe." Here comes another decade of argument and controversy, lol!

Your fastest TC is the fastest to react to pressure change and should be the first one to go red on ascent. On a no-stop dive you should be able to reach the surface without going over M0 in any TC, which I think in practice translates to in the fastest TC -- or at least in ZH-L16 where the fastest is 4 or 5 minutes it should. So what you're effectively talking about is modifying your ascent profile to protect the fastest TC from the large overpressure gradient permitted by the base model. Sound familiar?

 

[rsingler]

Sound familiar?

Sounds logical. Straight deco theory.
Are you thinking of a specific model or concept that I should be focusing on?

 

[Jay]

Here's a shameless plug for Subsurface: a great, FREE program that allows you to look at the consequences of all sorts of dive profiles. Plus it's a reasonable dive long, and a great deco computer. Yes, it shows "heat maps".
Downloads | Subsurface

Additionally here's @EFX's spreadsheet which shows which theo tissue is leading at various points during a dive: Dive Calculation Spreadsheet

 

[dmaziuk]

Sounds logical. Straight deco theory.
Are you thinking of a specific model or concept that I should be focusing on?

The deep stop argument is that M-values based on empirical observations were right after all and that fast tissue does not require extra protection. Why is that not also true of no-stop dives? -- GF99 shows large overpressure bump in fast tissue on your first-and-only-not-decompression stop, that is as designed. Many goats gave their lives for this design, was their sacrifice in vain? </straight faced>

 

[rsingler]

The deep stop argument is that M-values based on empirical observations were right after all and that fast tissue does not require extra protection. Why is that not also true of no-stop dives? -- GF99 shows large overpressure bump in fast tissue on your first-and-only-not-decompression stop, that is as designed. Many goats gave their lives for this design, was their sacrifice in vain? </straight faced>

Regardless of the validity of Deep Stop theory (or not), no stop diving requires no stop at all to remain below critical leading compartment supersaturation. What M0 is, in this case, is not clear to me. Compartment overpressure is a simple function of the ascent. What various deco theories are attempting in their search for "most efficient profile" is an added safety margin that reducers supersaturation, which the incidence of occasional DCS seems to indicate is warranted.
What GF99 attempts to show, and what SurfGF attempts to predict, is a theoretical leading compartment supersaturation. If we can attach a number to that which is less than whatever GFHi you have set for your "no-stop dive", then we can theoretically have the best of both worlds: extended no-stop bottom times (with a high GFHi), and safer overall dive profiles by pausing or slowing near the surface to allow our fastest compartments to offgas, since there is a good suggestion that the faster compartments tolerate overpressure perhaps better than the slower ones, as you alluded to above. This ascent profile, (essentially higher GFLo's) is rather the opposite of deep stops or slower ascent rates from depth, isn't it?
This is all very soft, since by definition, the algorithms don't require any stop at all, and GFLo is never reached! But I think the heat map concept of visually displaying offgassing can add a lot to our safety, in the absence of a blinded (military) study that deliberately bends divers. Unless you disagree with what the heat maps are portraying...

How else to look as a no stop dive that is below NDL, yet shows an alarming GFSurf after an "instantaneous" ascent. That is showing us that ascent rate matters, and we can continue to argue about where the slowing (or stop) should be...

 

[Jay]

One thing I've found when playing with a new wetsuit / different weighting, in my 5mm if I've very neutral at SS / possibly slightly + , then even with large exhales in the last 1-2m it can be somewhat difficult to stop a small pop when I need to inhale ... if I time it correctly then I can get it to work (at the surface at the end of an exhale). I think this is being a bit too much of a 'weight perfectionist' and just add an extra pound to prevent that 'effort'.
I'm curious if others find something similar in thicker wetsuits.

 

[dmaziuk]

How else to look as a no stop dive that is below NDL, yet shows an alarming GFSurf after an "instantaneous" ascent. That is showing us that ascent rate matters, and we can continue to argue about where the slowing (or stop) should be...

It's the "alarming" part that I'm not buying, but OTOH you're right: if it alarms people into making proper stops when they didn't before, more power to it.

 

[rsingler]

One thing I've found when playing with a new wetsuit / different weighting, in my 5mm if I've very neutral at SS / possibly slightly + , then even with large exhales in the last 1-2m it can be somewhat difficult to stop a small pop when I need to inhale ... if I time it correctly then I can get it to work (at the surface at the end of an exhale). I think this is being a bit too much of a 'weight perfectionist' and just add an extra pound to prevent that 'effort'.
I'm curious if others find something similar in thicker wetsuits.

If the Optimal Buoyancy Computer taught me anything, it is what you just said above. Neutral at the last stop carries a penalty, in everything but 3mm neoprene or less.
I concur. I am now aiming for 2# heavy at my stop, for a more controlled final ascent.