Ascent from Minimum Deco Dive

[Charlie99]

In another thread (http://www.scubaboard.com/t77610-.html) it has been posted that the ascent method taught in DIR-F course and supplemental materials is a series of 1 minute stops starting at 80%max ata / 75% max depth , including just 1 minute at 20' and 10'.

OTOH, the Minimum Deco Tables (http://www.dir-diver.com/pdf/minimum-deco-tables/english_imperial_A.pdf) at www.dir-diver.com use (for all depths and times) a standard set of stops of
1 minute at 40'
1 minute at 30
3 minute at 20'
3 minute at 10'

The same GUE-trained individual that posted the linear ascent method also says that the dir-diver tables are not considered the DIR approach to minimum deco.

It appears to me that the series of 1 minute stops at all depths is an approximation of a 10fpm linear ascent, while the dir-diver.com stops are more in line with an efficient "shape of deco" ascent.

What really is being taught in DIR-F for the optimum ascent profile?

Do different instructors teach different methods?

What is the concensus as the better ascent profile?

[jonnythan]

My DIRF class taught 1 min at each of 30', 20', and 10'. It also stressed the importance of a slow controlled ascent, especially for the last 10 feet.

[boomx5]

I'm sure this thread is going to be another "hot topic". However, may I suggest you PM any one of the GUE instructors who tends to hang out here that way you get the straight answer you seek. Sometimes one can look so hard for that "one correct answer" that they can miss the forest throught the trees...and that is why I would recommend PMing one of the instructors.

[jonnythan]

I'm all for going straight to the source, but I know what I learned in my DIRF class and would be eager to hear if anyone had any markedly different experiences.

[Soggy]

What I posted was what I was taught. There is some other profile being discussed taught over on the FifthDx Yahoo Group which AG talked about that I'd never heard before....I believe it is a profile taught in Tech 1. I have always seen that Tech 1 minimum deco profiles and DIRF min deco profiles do not seem to line up.

The dir-diver tables say (C) Peter Steinhoff, Sweden, 2003. Last I knew, GUE copyrights their own stuff.

If you want to know the real answer, email one or many of the GUE instructors. There are several here, and all the email addresses are available on GUEs site under "instructor database."

[Soggy]

There is an interesting discussion on the FifthD-X yahoo group regarding this topic. Mike Kane has provided some good information that is very different from what I was taught in either of my DIRF classes (one with him, interestingly enough).

[Spectre]

That's because he's obscuring it with conservatism to keep you safe until you take your next class. ;)

[Soggy]

That's because he's obscuring it with conservatism to keep you safe until you take your next class. ;)

I can see my next nickname...Fizzy Wigglie Soggy Wogglie.

[MonkSeal]

In another thread (http://www.scubaboard.com/t77610-.html) it has been posted that the ascent method taught in DIR-F course and supplemental materials is a series of 1 minute stops starting at 80%max ata / 75% max depth , including just 1 minute at 20' and 10'.

I was taught to use either:
a) 80% max ATA rounded to shallower depth
b) 70% max depth rounded to deeper depth

[CRDiver]

From Michael Kane:

Rather then introduce certain concepts at the Fundamental level,
specifically 80% of ATA's, we recommend for an otherwise recreational
profile, to start the deep stops at 50' from the max. depth. In other
words, if you did a 120' dive, start the deep stops at 70'. Then do 30
second stops, with 30 second moves until you start your "safety" stops. In
lieu of the industry standard of 3 minutes at 15', we recommend doing an
additional minute at 30', then a minute at 20' and then a minute at 10'.

So to summarize, you do 30 FPM ascent rates, you start your deep stops at
50' off the max. depth, continue "deep stops" at 30 second stop- 30 second
move intervals until you get to 30'. Then do 1 minute at 30', 1 minute at
20' and 1 minute at 10'.

Bear in mind, this ascent rate strategy applies to no mandatory
decompression diving within otherwise defined recreational limits. If you
plan of progressing to deeper then "recreational" limits and/or doing
mandatory decompression diving, this strategy is inapplicable.

[Soggy]

This is the post I was referring to on the FifthDX yahoo group. It is interesting to note that it is not what was taught in any fundies class that I have attended, including the one he taught. So, I don't know what the 'real' answer is. I have email correspondence from another GUE instructor saying very explicitly stating that one is to start deep stops at 80% ATA and then proceed at 10fpm up from there.

Who knows. I guess I'll learn the real stuff in Tech 1, eh? :)


From Michael Kane:

Rather then introduce certain concepts at the Fundamental level, specifically 80% of ATA's, we recommend for an otherwise recreational profile, to start the deep stops at 50' from the max. depth. In other words, if you did a 120' dive, start the deep stops at 70'. Then do 30 second stops, with 30 second moves until you start your "safety" stops. In lieu of the industry standard of 3 minutes at 15', we recommend doing an additional minute at 30', then a minute at 20' and then a minute at 10'.

So to summarize, you do 30 FPM ascent rates, you start your deep stops at 50' off the max. depth, continue "deep stops" at 30 second stop- 30 second move intervals until you get to 30'. Then do 1 minute at 30', 1 minute at 20' and 1 minute at 10'.

Bear in mind, this ascent rate strategy applies to no mandatory
decompression diving within otherwise defined recreational limits. If you plan of progressing to deeper then "recreational" limits and/or doing mandatory decompression diving, this strategy is inapplicable.

[jonnythan]

The point I take home from the whole thing is that when you take GUE's deco procedures and extrapolate them to the low end of no required deco, you can go a lot of ways with it.. none of which are necessarily any better than the others. Don't fret over where you do your stops as long as you plan them and they make sense to you.

Worry about the numbers and real procedures when they teach them to you.

[Spectre]

I think the thing to realize here is the building in of a conservative approach. Sure, with an NDL dive you should be able to run 60fpm to the surface with no stopping. A 'safety stop' is just that... a method to add a little bit of security to be safer [hense the 'safety' part of it]. If you look at something like the PADI tables [from memory here], they have ranges within the NDL limit where your safety stop becomes a required safety stop, and then longer safety stops if you get too close to the limit.

It's not meant to be 'the way the big boys do it', it's just meant to add a little conservativeness to the ascent to increase your chances of getting out if you screw up.

Along the same lines, the linear approach that Soggy is being given isn't necessarily the way the 'big boys' do it, as will be learned in later classes I assume, but it's a more conservative approach to other methods.

Let's look at the profile in question. 1 minute from 100 to 70, then 1 minute every 10 feet from there on. That's 8 minutes. Sure, that extra minute from 70-60 might add a little on-gassing, but you still have 6 more minutes from there to the surface, rather than a traditional 1 or 2 minutes from 60 up.

Even going PADI style, 30 ft/min from 60 to the surface with a 3 minute safety stop.. that's 5 minutes. Soggy's doing 6. adding a minute at 70 isn't going to give you an extra minute obligation... so he still comes out ahead if he ongasses for that minute at 70. [even saying 1:40 or so for the time from 70 to you get past what V-planner says the offgassing point is isn't going to give you an extra minute of deco when you're sitting in an NDL scenario].

Another thing to remember is that there's no 'line' between ongassing and offgassing. It's different compartments that ongas and offgas at different speeds. Continued ongassing of slower compartments on deeper stops isn't going to be much of a deal when doing recreational dives unless your doing a liveaboard or something to that effect where the slow tissues never get a chance to offgas like they would in regular weekend divers.

I don't know for sure what MHK is truely saying for a profile in his response. 1 minute stops generally mean 30 second stop, 30 second moves. Since he references both, I can only assume he's saying 1 extra minute at 30, 20, and 10. So that'd be saying 1 minute to 70, another 4 minutes to 30, and then another 6 minutes to the surface.... which pads the safety even more. 8 minutes from 50 up is -more- than enough to cover that minute or two below v-planner's magic line.

Now... the only part I don't quite get is why some feel that 80% and 50% in ATA is too complicated for a Fundies student to grasp ;)

[reubencahn]

This is not the ascent strategy taught in Recreational Triox--which deals only with recreational depths and no deco profiles.

[MHK]

I think that point that appears to be missing from this thread is one that we try as hard as we can during the DIR-F classes to bring home. Noting that scuba forums aren't necessarily the most productive method of communicating this type of information, I'll do my best to address the issue(s).

One of the initial goals of our introduction to ascent rate strategies in the DIR-F class is to begin to move the student off of the industry way of thinking. In other words, we believe every dive has an element of "decompression" associated with it, accordingly we try to move the student from a "No Decompression Limit" way of thinking towards a view that no such thing exists. Once the students accepts that premise, we can then move towards the notion of various ascent rate strategies. Those of you that are weighing in on what one instructor said versus another in different DIR-F classes, are largely missing the broader scope, which is to say that it isn't an exact science, and it's all about knowing how to shape the ascent rate curve. The difference between 80% of ATA's versus 50' of max. depth [ assuming a recreational profile] is a distinction without a difference and should be viewed from the prism of a different means to the same end, as opposed to a stark inconsistency.

Overall, the recomendation in the recreational setting [ Please do NOT confuse this approach with a dive that required accelerated decompression as the strategy will differ], but for the average Joe diver, doing a dive within otherwise defined "recreational" limits is as follows:

Use a 30fpm ascent rate;
Initiate deep stops at 50' of the max depth;
Continue deep stops using a 30 second stop- 30 second move approach at 10' incriments;
Commence your "safety stop(s)" at 30' for 1 minute, then 20' for 1 minute and lastly at 10' for 1 minute

There are various other ways to achieve the shape of the ascent curve that we like, but rather then parsing language, please appreciate that the end goal is to understand and implement an ascent rate that will maximize off-gasing and allow for bubble reduction in a complimentary fashion. Those that are worrying about whether instructor A said to start deep stops at 80% of ATA's and/or start the "safety stops" at 40' is missing the larger picture, and that larger picture is what is infinately more important then the minutae of what is being written so far in this thread.

I caution once again, as your diving habits progress, and you extend depth and/or extend acceptable bottom times and mandatory decompression obligations accumulate the above referenced ascent rate strategy will be inapplicable, and may very well lead to adverse consequences. For that reason you don't see many GUE instructors posting on scuba forums any additional "advanced" ascent rate strategies, since we don't believe it's effective or efficient to post an incomplete picture, which could be easily misunderstood and misapplied by someone who does not posses the requisite training or skill level.

For those that have taken my class, and something still isn't clear, please feel free to e-mail me and I'll try to clear up any confusion, but I'm reluctant to go any further on a scuba forum.

Hope that helps.

Michael H. Kane

[MHK]

So, I don't know what the 'real' answer is. I have email correspondence from another GUE instructor saying very explicitly stating that one is to start deep stops at 80% ATA and then proceed at 10fpm up from there.

Who knows. I guess I'll learn the real stuff in Tech 1, eh? :)

Soggy,

If you compare 80% of ATA's with 50' of max. depth I suspect you'll find that they tend to be a few feet apart ;-) It's just a different way of saying the same thing. Think of it if you lived 60 miles away from someone, and one day I said drive 60 mile per hour and the next day I said I'll see you in an hour..

Again, I go back to look at the bigger picture rather then focusing in on the differences amongst how different instructors explain the issue. At the end of the day, the results are the same. The 80% of ATA "rule" is more applicable in the "technical diving world", but applies equally as well in the recreational world and as I noted, I suspect you'll find that 80% of ATA and 50' of max. depth are pretty close in dives of 120' or shallower..

Regards

[Soggy]

So are you saying I should just continue doing what I'm doing and that I'm not too far off base? ;)



If you compare 80% of ATA's with 50' of max. depth I suspect you'll find that they tend to be a few feet apart ;-)

[Spectre]

If you compare 80% of ATA's with 50' of max. depth I suspect you'll find that they tend to be a few feet apart ;-)


Somehow I think if anyone was 23 feet off on a stop, they'd fail your class.



I suspect you'll find that 80% of ATA and 50' of max. depth are pretty close in dives of 120' or shallower..


Doesn't seem to get close in my eyes until around 210'.

It's kind of funny. One of the senses I got from GUE was that they prepare you for the further steps. You might not know the full reasoning right off the bat; like why your compass is best on the left wrist instead of the right wrist; but it's there so when you get further along, you don't have to change anything; you just realize the reasoning behind each little thing.

So why is it on this issue, GUE feels the need to confuse the issue rather than doing something as simple as "Pause at 80% of the max ATA, and then begin 1 minute stops at 65%, or 40 feet, whichever is deeper"... which prepares them to start being aware of 80%, 65%, and the other percentages who's significance will become apparent as they get further down the road?

[lamont]

If you're doing rolling stops from 100' starting at 50 feet, that should add 2 mins to your ascent time compared to a simple 1@30/20/10 profile (i get 9 mins vs. 7 mins). Should this get added to rock bottom times as well?

[Soggy]

If you're doing rolling stops from 100' starting at 50 feet, that should add 2 mins to your ascent time compared to a simple 1@30/20/10 profile (i get 9 mins vs. 7 mins). Should this get added to rock bottom times as well?

Of course. If it takes longer to get up, it takes more gas to get up....x2 :)

[Spectre]

If you're doing rolling stops from 100' starting at 50 feet, that should add 2 mins to your ascent time compared to a simple 1@30/20/10 profile (i get 9 mins vs. 7 mins). Should this get added to rock bottom times as well?
The point of rock bottom is to reserve enough gas to get you and your buddy up through the planned ascent. So whatever your planned ascent is should be the ascent used in calculating your rock bottom.

[MHK]

It's kind of funny. One of the senses I got from GUE was that they prepare you for the further steps. You might not know the full reasoning right off the bat; like why your compass is best on the left wrist instead of the right wrist; but it's there so when you get further along, you don't have to change anything; you just realize the reasoning behind each little thing.

So why is it on this issue, GUE feels the need to confuse the issue rather than doing something as simple as "Pause at 80% of the max ATA, and then begin 1 minute stops at 65%, or 40 feet, whichever is deeper"... which prepares them to start being aware of 80%, 65%, and the other percentages who's significance will become apparent as they get further down the road?

I thought we were making real simple by saying:

"Start your deep stops 50' from max. depth and do 30 second stop, 30 second move until you hit 30'". I'm not sure how much simplier we can make it. Certainly as you progress the 80% of ATA rule is more realistic, but at the DIR-F level our goal is to introduce ascent rate strategies that more often then not are the first time students encounter any such dialogue. I can't tell you how many times I ask a student to compute how many ATA's at 100', and all I get is blank stares.

The big picture that is our goal to communicate to students at this level is to begin the process of changing the way they view ascent rates. We move them from the concepts of getting up quickly, ie; 60fpm to slowing down there ascent to 30fpm. We then walk them through why incorporating deep stops is a good idea, as opposed to what most have been taught which is that by slowing the ascent down you are not on-gasing, We then move them off of 3 minutes at 15' and into a 30',20',10' viewpoint. We discuss RGBM -v- Buhlman so I guess I'm confused what you'd like to see added. The teaching paradigm we use is very much a building block approach, and by building the blocks the way we do it seems to have been a productive approach.

The other thing to consider on your point respecting "GUE confusing the issue" is that our goal has always been multi-faceted, in that we like to address how the industry teaches it, how we teach it for purposes of comparing and contrasting, and then most importantly the WHY's behind it. I don't see offering a variety of ways to approach the issue as confusing it. I like to give students more credit then that, in that we're not trying to train robots, we're trying to train divers to think and show them that once you understand the mechanics behind the approach there may very well be more then one way to do it. Perhpas it's a little more then semantics, but I believe at the end of the day the picture we are trying to fill in is the shape of the curve, and the tools needed to be understood to create your own shape. I hope everyone recognizes that point.

Let me know if that clarifies the point.

Later

[Charlie99]

What hasn't been addressed is the relative merit of the different ascent profiles.

In the doppler study (https://www.daneurope.org/eng/whatascent2.pdf) done by DAN (8 different ascent profiles from a 25m 25min dive followed by 25m 20 minute repetitive dive) the 10fpm linear ascent comes out as the worst possible ascent even though it is not the shortest total time to ascend, and at least one of the GUE recommended ascents is pretty much a stepwise approximation of that same linear ascent (after the initial 30fpm ascent to 80%ata).

The fixed stops on the www.dir-diver.com website better match my understanding of the proper shape of deco, they better match what you get out of various deco programs by cranking up the conservatism very high, and the better match the profiles with low bubbling on the DAN study.

To me they look like that is a much better way of "doing it right", even if others post that it isn't DIR.

[boomx5]

What hasn't been addressed is the relative merit of the different ascent profiles.

To me they look like that is a much better way of "doing it right", even if others post that it isn't DIR.

No one ever said they were not DIR. I still think you are missing what Mike was saying Charlie. Furthermore, I think trying to get the answers you seek off of the internet is a less than optimal way of satifying your curriosity...IMHO.

[Charlie99]

If you compare 80% of ATA's with 50' of max. depth I suspect you'll find that they tend to be a few feet apart

Doesn't seem to get close in my eyes until around 210'.Independent of the creative math, in the recreational range of depth and times, the 50' off of max depth appears to be a better rule of thumb as the place to slow the ascent from 30fpm to 10fpm.

[Charlie99]

No one ever said they were not DIR. I must have misinterpreted Soggy's statement "For the record, these tables are not DIR." on ************.

His post in the Safety Stops thread (http://www.scubaboard.com/showpost.php?p=844277&postcount=49) "They are not considered the DIR approach to minimum deco, regardless of his affiliations, and that fact has been stated here by more than just me, I believe." can indeed be interpreted as merely meaning the overall table approach being not DIR.

The reason I started this thread was to determine whether his depiction of the GUE taught ideal ascent profile was accurate, or whether is was a case of an enthusiastic DIR-F graduate passing along mistaken info.

Comments as to the relative merits of the dir-diver approach (slow to 10fpm at 40', further slowdown shallow with 3 min stops at 20' and 10') vs the 10fpm all the way to the surface approach would be greatly appreciated.

[lamont]

it seems like a major problem with this discussion is that people are overly focusing on a given schedule and not the principles behind deco. people are taking the deco schedules way too literally...

[boomx5]

I must have misinterpreted Soggy's statement "For the record, these tables are not DIR." on ************.


Yes, I have read what Soggy wrote. However, just because they did not teach it in a 2 1/2 day class doesn't mean it's not DIR. There are a number of ascent profiles that would make sence in the DIR scheme of things, however they may not be taught in a fundamentals class. I think the misinterpretation here is that GUE teaches one and only one ascent profile and that that way is the ONLY way to "Do It Right"; and to fixate on this without understanding the big picture is going to leave you wanting. I assure you it is very simple, but there is just to much to discuss on a message board...unfortunately.

[CRDiver]

I believe some of the confusion with different profiles is the result of people spending too much time focusing on how dogmatically GUE handles gear configuration, and expecting the same out of ascent/descent profiles. Some people (including many over-anxious newbies) are attracted to the DIR philosophy because it gives clear-cut and definitive answers to practical questions related to gear, emergency procedures, safety procedures, etc., with little room for dissent within the community. When it comes to questions of decompression and physiology, there really aren't definitive and clear-cut answers yet (as GUE readily admits), only various recommendations based on scientific measurements and observations which are subject to change, unlike which side to sling a deco bottle or wear a canister light.

[Spectre]

I thought we were making real simple by saying:

"Start your deep stops 50' from max. depth and do 30 second stop, 30 second move until you hit 30'". I'm not sure how much simplier we can make it.


Well first off the confusion is the lack of consistancy, with different instructors giving different statements. Yes, that is simple... sort of. I mean, even this itself is confusing. i.e. you talk of 30 second stops, 30 second moves, and then you talked about 1 minute stops at 30, 20 and 10.

Well, technically a stop is the time you arrive at the stop to the time you arrive at the next stop. So a '1 minute stop' vs. '30 second stop, 30 second move' really -is- the same thing, with two different terms being used.

So the confusion still gets propagated with some people interpreting that as 1 minute stops every 10 feet from 50 to the surface, while others may interpret that statement as 1 minute stops every 10 feet from 50 to 30, then 1:30 stops from 30 to the surface [1 minute stops, 30 second moves].

Now then it gets even -more- confusing when you compare that with the DIR-F lecture that discusses 1 minute from 100 to 70 with a pause at 70.

So as you see... there is different things being said, and while yes... they are all conservative enough to be perfectly fine; they definately confuse people as not every one with the same training is on the same page.



I can't tell you how many times I ask a student to compute how many ATA's at 100', and all I get is blank stares.


That is definately the most disturbing thing I've heard in quite a while. ATA to Depth and Depth to ATA is a skill that is taught in OW class. In a Fundamentals class, which is, as I understand it meant to teach students the fundamental skills that they -should- have learned in their OW and AOW programs, I can't believe that you can just brush off the anability to make such calculations; let alone -require- it to be done.

When is it that they are taught that skill? In tech 1? When they have quite a bit more task loading that they to focus on?

But ok... let me hypothetically assume that I accept that disability as acceptable. So how about tell them to pause at 75% of their depth, and start their stops at 50% of their depth, or 30 feet; whichever is deeper. That hits them pretty close in recreational depths, gets them familiar with making those calculations, and considering they damn well better be able to learn how to divide their tank pressure by 3, I don't think it's much to ask to expect them to be able to divide their depth by 4.



We move them from the concepts of getting up quickly, ie; 60fpm to slowing down there ascent to 30fpm.


I think if you look around, you will find that 30fpm ascents are what is being taught. There are some threads on other boards that asks specifically 'what ascent rate were you taught, and what methods were you taught to gauge that'. There were quite a few that were very surprised to learn that my OW book [(c) 1999] still stated 60fpm. I would be quite surprised if you found many DIR-F students that weren't already running 30fpm ascents, if not aware to some level of 'slower ascents' and 'deep stops'.



I like to give students more credit then that, in that we're not trying to train robots, we're trying to train divers to think


See... that's exactly the point I'm trying to make. You say you like to give students more credit, but in the same post you don't expect them to able to convert depth to ATA and knock off 20%, or even to be able to take 75% of their depth.

You speak of building blocks; but you don't seem to think that teaching them to be aware of the depths where later you will expect them to be able to not only calculate but calculate ascent profile changes at. Don't you think a better building block to learning to be aware of a curve shape is to start getting them used to the points on the curve, rather than giving them a linear ascent for 50 feet, and then another linear ascent for the rest?

[VTernovski]

Well first off the confusion is the lack of consistancy, with different instructors giving different statements. Yes, that is simple... sort of. I mean, even this itself is confusing. i.e. you talk of 30 second stops, 30 second moves, and then you talked about 1 minute stops at 30, 20 and 10.

Well, technically a stop is the time you arrive at the stop to the time you arrive at the next stop. So a '1 minute stop' vs. '30 second stop, 30 second move' really -is- the same thing, with two different terms being used.

So the confusion still gets propagated with some people interpreting that as 1 minute stops every 10 feet from 50 to the surface, while others may interpret that statement as 1 minute stops every 10 feet from 50 to 30, then 1:30 stops from 30 to the surface [1 minute stops, 30 second moves].

Now then it gets even -more- confusing when you compare that with the DIR-F lecture that discusses 1 minute from 100 to 70 with a pause at 70.

So as you see... there is different things being said, and while yes... they are all conservative enough to be perfectly fine; they definately confuse people as not every one with the same training is on the same page.



That is definately the most disturbing thing I've heard in quite a while. ATA to Depth and Depth to ATA is a skill that is taught in OW class. In a Fundamentals class, which is, as I understand it meant to teach students the fundamental skills that they -should- have learned in their OW and AOW programs, I can't believe that you can just brush off the anability to make such calculations; let alone -require- it to be done.

When is it that they are taught that skill? In tech 1? When they have quite a bit more task loading that they to focus on?

But ok... let me hypothetically assume that I accept that disability as acceptable. So how about tell them to pause at 75% of their depth, and start their stops at 50% of their depth, or 30 feet; whichever is deeper. That hits them pretty close in recreational depths, gets them familiar with making those calculations, and considering they damn well better be able to learn how to divide their tank pressure by 3, I don't think it's much to ask to expect them to be able to divide their depth by 4.



I think if you look around, you will find that 30fpm ascents are what is being taught. There are some threads on other boards that asks specifically 'what ascent rate were you taught, and what methods were you taught to gauge that'. There were quite a few that were very surprised to learn that my OW book [(c) 1999] still stated 60fpm. I would be quite surprised if you found many DIR-F students that weren't already running 30fpm ascents, if not aware to some level of 'slower ascents' and 'deep stops'.



See... that's exactly the point I'm trying to make. You say you like to give students more credit, but in the same post you don't expect them to able to convert depth to ATA and knock off 20%, or even to be able to take 75% of their depth.

You speak of building blocks; but you don't seem to think that teaching them to be aware of the depths where later you will expect them to be able to not only calculate but calculate ascent profile changes at. Don't you think a better building block to learning to be aware of a curve shape is to start getting them used to the points on the curve, rather than giving them a linear ascent for 50 feet, and then another linear ascent for the rest?


Jeff, why are you publicly attacking MHK on this forum on that subject? We all know that you know this stuff, hence it just seems that you are playing devils advocate and if I would be a mod here I would have closed this thread and sent you a PM asking to take such discussions directly with MHK and to stop this trolling.

[MonkSeal]

I can't tell you how many times I ask a student to compute how many ATA's at 100', and all I get is blank stares.

Maybe it's because of imperial units ;) - in metric system it's much easier. Also, using 70% of max depth (rounded to deeper) is quite easy in both systems.

[rossh]

...<snipped - see above>...
Michael H. Kane
Hello Michael, Good to see this issue in the public area for discussion.

I would like to comment on the 80% ATA rule (70% max depth) first stop depth and particularly for these shallow dives. The 80% rule forces a diver to stop deeper with reduced depth. i.e the 80% is linked to a proportion of max depth, when in fact is I think it should be linked to distance from max depth alone. The 80% creates increasing obligations, for dives wich have a reduced gas load? That would appear to be applied in a reversed order, and introduces errors into the shallower dives.

In current deep stop bubble models (vpm,rgbm,others), the first stop depth is primarily a function of supersaturation, gas choices and inert gas loadings, ascent rate and limits set to prevent onset of bubbling. This typically resolves to a distance of about 2 ATA off the bottom. Also a check of many NDL tables, will show that the 2 ATA value has significant impact on tables, as they begin to limit NDL times around this pressure offset.

For a quick and easy "rule of thumb" first stop placement, I would use a distance of 50 or 60 ft off the bottom value applied to all dives including deco dives. You can see this also fits neatly with the WKPP 300 ft dives (first stop typical at 240). This would give a much different first stop for many dives from 0 to 200ft bottom depth than your currently using, and eliminate all the extras stops that your organizations procedures add on to existing model and plans. WKPP experience has found that 2 ATA works at 300 ft. NDL testing and data shows the same 2 ATA at the shallow end. Why would we want to employ different value for dives between these two extremes of depth?

On any dive, when a diver is slow to leave the bottom, he experiences additional gas loads. His achieved profile will look very much like a multilevel dive which will require additional deco obligations, or reduced NDL's. If we take the slow ascent procedures, coupled with the overly deep 80% first stops on a shallow dive plan, then it's probable a divers body will register this as a multilevel dive, or an extended bottom portion. These two items coupled (slow ascent, too deep stops), will subject the diver to an increased gas load and deco obligation - more so than had he used the conventional ascent profile and safety stops. The too deeper stop when used in this area, is likely adding obligations unnecessarily to a basic dive.

Not too many years ago, a deep stop was anything deeper than a basic Bulhman table. Then came Pyle stops and WKPP deep stops, and then bubble models computed the deep stops for an accurate first stop value. Now GUE standards is promoting the deepest stops of all.

I think the GUE standards has overshot the mark with the 80% ATA / 70% depth idea when used on dives in the 0 to 150ft range. As pointed out in a post above, the linear ascent method has been well tested and shown to be unsatisfactory. I think GUE's procedures are getting too close to this situation. Our bodies will not distinguish the subtle difference from a linear type ascent in the deep portion versus the slow ascent and too deep first stops. The only saving item here on these shallow dives, is that they have a small gas load, and can afford a large error factor.

Regards
Ross Hemingway

http://www.v-planner.com

[MHK]

Jeff, why are you publicly attacking MHK on this forum on that subject? We all know that you know this stuff, hence it just seems that you are playing devils advocate and if I would be a mod here I would have closed this thread and sent you a PM asking to take such discussions directly with MHK and to stop this trolling.

Vadim,

I think part of the reason that many GUE instructors are reluctant to engage in scuba forums is evidenced in this thread. We try as hard as we can to communicate the notion that decompression theory isn't an exact science, and the methodolgy and tools we provide to help divers understand and shape their ascent rate curve is the end goal. George, and by extension the WKPP, have been using 80% of ATA's for some time with great success. As GUE moved into offering a DIR-F class many students only had access to information procured from George's postings and the WKPP site. The 80% of ATA rule is very applicable to the diving done in Wakulla, as a way to introduce the same methodology to recreational students many had already become accustomed to the 80% of ATA rule. Frankly, 50' of max. depth is more applicable in the recreational environment, but anyone that is fixating on the distinction is severly missing the larger point, which is that either way it's simply a tool to use as a starting point for a more complete ascent rate strategy. Similiarly, by way of example, we teach a 120 rule, as a methodology to compute NDL's. I say all the time if you want to use 115 instead of 120 I could care less, the point is that we offer the methodology, not necessarily a myopic fixation on 120, or in the instant case 80% of ATA. As you note, it makes little sense to engage in discussions of this subjective nature with professional contrarians on a scuba forum.

I note someone else in this thread pointed out that we are rigid with respect to standardized gear configuration, but are more flexible respecting decompression theory. Those that can't distniguish the reason why have either missed the boat, or just want to argue semantics. I'm happy to help those that don't see the point, but I'm loathe to engage debates for self-serving purposes..

Anyway I'll see you in 2 weeks..

Later

PS. did you get my PM??

[Charlie99]

Ross -- thanks for actually addressing my question as to what would be a good ascent profile from a minimum deco aka NDL aka recreational dive.

As a reminder, I started this thread with some questions:


The same GUE-trained individual that posted the linear ascent method also says that the dir-diver tables are not considered the DIR approach to minimum deco.

It appears to me that the series of 1 minute stops at all depths is an approximation of a 10fpm linear ascent, while the dir-diver.com stops are more in line with an efficient "shape of deco" ascent.

What really is being taught in DIR-F for the optimum ascent profile?

Do different instructors teach different methods?

What is the consensus as to the better ascent profile?


Your comments about 50', 60' or 2ata off of max depth being a good spot to slow the ascent from 30fpm to 10fpm makes a lot of sense to me.

The remaining thing I'm trying to puzzle out has to do with the length of 20 and 10' stops compared to the overall time to ascend. I can see some logic in replacing a 30fpm + 3 minutes at 15' with a 30/20/10' set of 1 minute stops if you are just going to allocate 3 or 4 minutes to the ascent.

But once one starts doing longer total ascent times with 1 minute stops (or 10fpm average ascent) starting deeper (either 80% ata, 75% d3pth, or what appears better --- 50' to 2ata off of max depth) it appears to me that one should lengthen the time in the 20'-10' range. Again, the fixed stops as shown on dir-diver.com match up with what appears to me to be the better ascent strategy.

Any comments on 20' and 10' lengths?

Charlie Allen

p.s. Yes, all of the discussed ascent strategies will work. So did a 60fpm pop to the surface with no stop of any sort. As long as I'm going to spend X amount of time in an ascent, there isn't any reason to use an ascent strategy that doesn't get me out of the water as clean as possible.

[Soggy]

As a reminder, I started this thread with some questions:

I think all of your questions have been answered.