Y.A.A.T. (Yet Another Ascent Thread)

[DivesWithTurtles]

From another lively thread that wasn't generally about this topic:

... where can we get information on the 'latest' best assent profile?

Stan

Information on the 'latest' best ascent profile? Why, right here, Stan.

(First, I always like to remind you that I don't know what I'm talking about. Really. I'm not an expert. I'm not even very experienced. I have only about 350 dives, and about 300 of those are the proverbial "1 dive done 300 times". I've read a bit, but I have had no formal training in deco or deco theory.)

Importantly, I drift dive South Florida reefs. We don't have nice slopes or walls to work our way up. Most of my dives are relatively square profiles, running from about 50 feet to 90 feet max depth. I use Nitrox, 36 - 40%. Since we are usually asked to be back on the surface in 60 minutes or less, that is usually what limits my bottom time, not NDLs. My ascents are mid-water drifts.

I want get shallow as fast as I can to maximize off-gassing and I want to get shallow as slowly as possible to minimize bubbling. I want to spend time deeper where the faster compartments (and therefore, theoretically, my tissues that on- and off-gas quickly [like my spinal cord]) get rid of nitrogen adequately without bubbling, but don't want to increase my load on the medium compartments much by staying deeper. It's all trade-offs.

And, because of some vague references to older studies in recent DAN studies about discreet step-ladder stops being better than slow constant ascents (assuming they both come out to similar times to surface), I want to move up to my stops with alacrity, not slowly meander up for a few feet and then stop for short while (i.e., 30 second travel, 30 second stop every 10 feet).

So, here is my "'latest' (this week's) best ascent profile" from, say, 60 feet:

- ascend to 30 feet at 30 feet per minute (2 seconds per foot)
- stop for 1 minute
- ascend to 20 feet at 20 feet per minute (3 seconds per foot)
- stop for 3 minutes
- ascend to 15 feet really slowly, about 10 feet per minute (6 seconds per foot)
- stop for 5 minutes
- ascend to the surface really, really slowly. I try to take at least 2 minutes from 15 feet to the surface. This is done in little stops and starts because there is no way I can move that slow smoothly.

Total time to surface from 60 feet: about 13 minutes.

If I start at 75 to 90 feet, I'll add a 1 minute stop at 40 feet, then quickly (30 feet per minute) move up to 30 feet.

I do seem to piss-off many folks I dive with that want to do 3 minutes at 20-15 feet, then get out of the water quickly. Oh, well. They do what they do, I do what I do. Neither of us gets bent. Their way is probably quite adequate. I don't mind hanging out alone. (I solo a lot, though I don't generally recommend that for anyone else.)

I think this is pretty conservative, especially considering I'm not usually pushing anything close to NDLs. Surely more conservative than it needs to be. But, then again, I'm getting old, old, old. (Though still younger than some that may respond to this post.)


I'm WAY open to suggested modifications to my method. Slam away, please. Or validate my method if you will.

 

[Charlie99]

I want get shallow as fast as I can to maximize off-gassing and I want to get shallow as slowly as possible to minimize bubbling. I want to spend time deeper where the faster compartments (and therefore, theoretically, my tissues that on- and off-gas quickly [like my spinal cord]) get rid of nitrogen adequately without bubbling, but don't want to increase my load on the medium compartments much by staying deeper. It's all trade-offs.

That's a pretty good summary of the dilemma.

And, because of some vague references to older studies in recent DAN studies about discreet step-ladder stops being better than slow constant ascents (assuming they both come out to similar times to surface), I want to move up to my stops with alacrity, not slowly meander up for a few feet and then stop for short while (i.e., 30 second travel, 30 second stop every 10 feet).

This is the only part of your post I take issue with. I think you are misinterpreting the DAN studies. They did show that the instantaneous rate of ascent over short periods and depths are not important, but IMO did NOT say in any way that a slow continuous ascent is inferior to a stepwise ascent. They did show that a slow continous LINEAR ascent of 10fpm was bad, but as I interpret the study, that was because it spends the same amount of time shallow as it does deep.

<snipped the profile info>I'm WAY open to suggested modifications to my method. Slam away, please. Or validate my method if you will.

Looks good to me. You note that you add a minute at 40' for the deeper dives. I'd probably do that for all, even if it took away a minute from shallower. Or to put it another way, I distribute times in the same general way, but more like 40', 25' and then 20' to 10' slide. I'm also generally not willing to spend 13 minutes unless I'm loaded to the gills. My ascents are more typically 8 minutes or so from leaving the bottom. But the overall "slower as you get shallow" approach is IMO the best ascent.

I do have one practical and site specific suggestion: what works for me is to go check out the sand, sea fans and gorgonian on the reef top at about 45 or 50' for a while before starting the ascent, particularly after diving the deeper outside ledge of the 3rd reef. You also see a different mix of critters than what hangs out at the ledges.

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How do you keep track of the stop times?

As posted my method in an another thread, I decide upon leaving the bottom how many minutes I'll take going to the surface, figure out what elapsed dive time that will be on my computer, and then run everything backwards from that.

 

[DivesWithTurtles]

This is the only part of your post I take issue with. I think you are misinterpreting the DAN studies. They did show that the instantaneous rate of ascent over short periods and depths are not important, but IMO did NOT say in any way that a slow continuous ascent is inferior to a stepwise ascent. They did show that a slow continous LINEAR ascent of 10fpm was bad, but as I interpret the study, that was because it spends the same amount of time shallow as it does deep.

My statement is based on:

http://www.diversalertnetwork.org/news/article.asp?newsid=514
"What is interesting, and not necessarily intuitive, is that an in-water stop with a relatively rapid ascent rate appears to be more effective at eliminating inert gas than a very slow ascent rate. As can be seen from Table 2, a five-minute in-water stop is much more effective than simply slowing the ascent rate, even though the total ascent time is not much different (6.6 minutes vs. five minutes)."

and

https://www.daneurope.org/eng/wathascent1.pdf
"Lewis showed that the stop is in fact preferential to slowing the ascent rate."
(Reference to Lewis' publication is included in that document.)

As well as one other DAN reference that I cannot find right now.

 

[DivesWithTurtles]

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How do you keep track of the stop times?

Sundial.

 

[Charlie99]

My statement is based on:

http://www.diversalertnetwork.org/news/article.asp?newsid=514

"and

https://www.daneurope.org/eng/wathascent1.pdf

OK, it looks like DAN either misinterprets their own study, or oversimplifies the analysis in those particular statements.

Seriously, if you go back and look at the specific profiles those statements are referring to, you can see that the "simply slowing the ascent rate" profile results in disproportionately little time shallow. Or if you look at the profiles in terms of the tradeoffs you have in your very first post, all of the continuous constant rate ascent profiles are too much biased towards the deep and too little shallow.

My hypothesis is that the ideal/most efficient ascent is a continuous ascent, with a variable rate-of-ascent that continuously and gradually slows as one gets shallower. The series of stops of your ascent protocol are a reasonable, and more easily executed, approximation of that ideal continuous, but slower-as-shallower ascent.

 

[Thalassamania]

You have a very clear understanding of the issues. Your ascent procedure seems overkill to me, but overkill is much better than kill, if you know what I mean. I am also very attached to the the good things that my spinal cord does for me and try to take good care of it. Much better safe than sorry!

 

[grazie42]

This link should give you (one) view on most of the things that have been discussed in the recent AAT´s...

http://www.hhssoftware.com/v-planner/decomyths.html

 

[DivesWithTurtles]

... Your ascent procedure seems overkill to me, but overkill is much better than kill, if you know what I mean. ...

The Colin Powell Doctrine Ascent Profile?

 

[boulderjohn]

The Colin Powell Doctrine Ascent Profile?

Which beats the Donald Rumsfeld profile--start the dive with just enough air to have a really good, effective dive, but not enough to maintain the ascent.

 

[Thalassamania]

I'm shocked and awed!