Recreational Ascent Rate in the last 15 feet

[NAM001]

This is probably non-linear because of the switch in the leading tissue compartment. I expect you can smooth it out by using more tissue compartments up to the infinite number of infinitely small ones, a la integral. With Buhlmann's idea of deriving M-values from properties of the gases, this may actually be doable, and modern cellphone-level CPU shouldn't have a problem running it in what passes for real time in our case. Well, except those Buhlmann's numbers turned out to be too much and had to be tuned down in the middle compartments...

I bet it's so much easier to calculate the upper bound... which may just happen to be 30 fpm.

I would agree ,,,,I was speeking conceptionally for the most part as I would explain to REC divers at a level they can follow with out a lot of proior reading . One of the big things is when trying to use a table You have to ask its it a table for the first dive or the 2nd or the 3rd or a less than accurate one that covers all combo's. The answer is the last for the most part. Tables for the most part when put into practice is much akin to saying you will put your eye out if you run with a stick.

I have similar conversations about using levels of conservaton. A point you made(regarding lead tissues) fits right into that discussion. You have to ask first dive type of dive and much more to GUESS what may be appropriate. Mostly I suggest if all else is good you can use low on a nice drift dive under good water conditions. perhaps on your second or third dive that level should be reconsidered. You can push the limits maybe once with out cost but many times,,, at that level,,, can be a formula for desaster. There is a lot that we take for granted and trust when it comes to global rules of thumb created by others. They all error on the side of what is considered safe. Even some old navy tables had 45 minute NDL's at 100 ft. the surfacing protocol was different and not 30 ft per minute and go home.

Use of 30 fpm make it simple such that any one can told one rate is good for all.I would think that if I did 30 min at 100 ft on air I wold have a no stop surface if I did it at 10 fpm or so. Numbers being not important but rather that the slower ascent rate being used to counter the exposure with out stopping. Yes there is a bunch of things in print covering this and other aspects ,,,and what is the most effective etc. It does not have to be the most effective to be sound and workable in principle. Look at how much discussion and research was done on the idea of deep stops. And those were mostly relating to the tech side and not rec diving.

 

[Frontpointer1000]

I would have voted that my safety stops are usually about three minutes, and then I more or less jettison to the top. Out of curiosity I went back and looked at my computer to get the specifics. I was pleasantly surprised. I dive a Perdix but have not updated the firmware so I have no comments on GFSurf.

My last five dives:
A: SS 4 min 40 sec then 8 min to surface
B: SS 9 min 50 sec then 6:40 to surface
C: SS 4:20 (after Ss@20 ft for 3 min) then 1 min to surface
D: SS 4:40 then 4 min to surface
E: no “SS” however after reaching 15 ft, it took another 19 min to surface

 

[chillyinCanada]

I would have voted that my safety stops are usually about three minutes, and then I more or less jettison to the top. Out of curiosity I went back and looked at my computer to get the specifics. I was pleasantly surprised. I dive a Perdix but have not updated the firmware so I have no comments on GFSurf.

My last five dives:
A: SS 4 min 40 sec then 8 min to surface
B: SS 9 min 50 sec then 6:40 to surface
C: SS 4:20 (after Ss@20 ft for 3 min) then 1 min to surface
D: SS 4:40 then 4 min to surface
E: no “SS” however after reaching 15 ft, it took another 19 min to surface

Intetesting, that you'd thought without checking that you were "jettisonjet for the surface".

Well done

 

[tursiops]

I would have voted that my safety stops are usually about three minutes, and then I more or less jettison to the top. Out of curiosity I went back and looked at my computer to get the specifics. I was pleasantly surprised. I dive a Perdix but have not updated the firmware so I have no comments on GFSurf.

My last five dives:
A: SS 4 min 40 sec then 8 min to surface
B: SS 9 min 50 sec then 6:40 to surface
C: SS 4:20 (after Ss@20 ft for 3 min) then 1 min to surface
D: SS 4:40 then 4 min to surface
E: no “SS” however after reaching 15 ft, it took another 19 min to surface

Were you boat or shore diving? My impression is that shore diving ascents from a SS are usually slower, because you often are going a horizontal distance as well as a vertical distance, whereas boat diving is usually just vertical from the SS

 

[Frontpointer1000]

Intetesting, that you'd thought without checking that you were "jettisonjet for the surface".

Well done

I will be honest, I wasn’t driving this kind of profile out of safety. I had the gas and I had the time, and I was just enjoying everything around me. However, I am going to dive more conscientiously now. I’ll make sure I’m really hitting the SS well. And excited to start using GFSurf. When I dive with a buddy, it’s almost always with a guy whose computer requires him to do two safety stops. He hits one around 25 feet and again at 15 feet. Or maybe his first one is 20 feet. So I’m hanging around Anyway.

Were you boat or shore diving? My impression is that shore diving ascents from a SS are usually slower, because you often are going a horizontal distance as well as a vertical distance, whereas boat diving is usually just vertical from the SS

Yeah, I thought this too. So I went back and looked at my last five boat dives. Here’s what I found.

D: (above, was Actually a boat dive. It was on the Hilma Hooker in Bonaire. I didn’t realize this dive was from a boat because I was just pulling the data from the app, and did not correlate it with my dive log (which is hand written). So that was 4:40 safety stop, then 4 to surface.
E: shore dive
F: 2:30 SS then 10:10 to surface
G: 6:30 SS then 3 min to surface
H: 8:30 SS then 4:50 to surface
I: 11 min SS then 3 min up
J: 11 min SS then 2:30 to surface

A few notes on the above diving. This was last month in Bonaire. Obviously pretty easy diving. Most of the safety stops Began around 45 - 65 min into the dive. My computer starts the safety stop at 20 minutes, but I did not count that time in the above calculations until I was at 15 feet. We were doing six dives a day on nitrox 32-38%.

My dive log is hand written. I started using the Shearwater app on this last trip, mostly for the graphing capabilities. I did not have the firmware upgrade, so do not have the GFsurf, That would’ve been such a great piece of data for this diving. We were always the last to come out of the water, but we were diving with a very experienced group of Divers, and no one was ever upset that we took longer to come out of the water. This was certainly a benefit, and I think our diving would’ve been cut by 15 to 20 minutes per dive if the boat has not been supportive.

A huge takehome for me is the power of the app and going back to really analyze this data. I’m especially interested in how all of you use post dive data analysis to better your diving.

 

[Brett Hatch]

I was taught 3 min safety stop at 15-20', then surface like a cork. Thanks, PADI.

This thread has me thinking I really ought to at a minimum slow that final ascent dramatically (like 10x or 20x slower), and perhaps increase the safety stop window by several minutes as well.

Thanks for the fruitful discussion.

 

[tursiops]

I was taught 3 min safety stop at 15-20', then surface like a cork. Thanks, PADI.

That may be what you remember, but I doubt that is what you were taught.

 

[Brett Hatch]

That may be what you remember, but I doubt that is what you were taught.

My recollection is <=60 fpm up to safety stop, stop for 3 minutes, then head to the surface. All the while not exceeding the rates / stops required by my computer. It could be the case that this is not PADI canon and I simply do not remember correctly.

In my case, my computer likes a 15-35 fpm ascent rate, and goes berserk if I exceed 40 fpm. On the face of it, that seems a reasonable level of conservatism for NDL OW diving to me, but of course I'm not at all an expert this area and would be happy to learn more here.

For me, the eye-opener in this thread is that not all ascent rates are the same, and in particular are not linear -- a good ascent rate is a decreasing function of one's depth. Seems obvious in hindsight, like so many other things in life .

 

[tursiops]

My recollection is <=60 fpm up to safety stop, stop for 3 minutes, then head to the surface. All the while not exceeding the rates / stops required by my computer. It could be the case that this is not PADI canon and I simply do not remember correctly.

In my case, my computer likes a 15-35 fpm ascent rate, and goes berserk if I exceed 40 fpm. On the face of it, that seems a reasonable level of conservatism for NDL OW diving to me, but of course I'm not at all an expert this area and would be happy to learn more here.

For me, the eye-opener in this thread is that not all ascent rates are the same, and in particular are not linear -- a good ascent rate is a decreasing function of one's depth. Seems obvious in hindsight, like so many other things in life .

My doubt was that you were taught to surface like a cork after your SS. Apparently that was hyperbole?

 

[Brett Hatch]

My doubt was that you were taught to surface like a cork after your SS. Apparently that was hyperbole?

I see. Maybe I should have said, <=60 fpm post-safety stop as well. In the context of this thread's posts and poll results, that 60 fpm during final ascent seems pretty cork-ish, and is what I meant. Does not seem like hyperbole to me, but if you found it to be misleading, then maybe you have a point.