Translating the GUE T/1 Deco Curve

[ScubaInChicago]

I was reading the Ratio Deco thread and spun off this thread to not Hi/jack. After looking over Blackwood's chart http://www.scubaboard.com/forums/5053199-post32.html
I had a couple of questions on how it translated to our latest T/1 class and get a feeling for how our class teachings compare to the teachings of past.....Please let me know either good or bad how it translates..

-We were told to take advantage of the high PPo2 oxygen window at the 70' gas switch and to reverse engineer our curve from the 70'-30' then split 50/50 the deco from 20'-surface with the 70' mark getting the most time and 30' the least....20'-surface again because of the greatest pressure change to the surface.

ex of 30 min deco from 150':

150-110' assent rate of 30'/min

110' 15 sec stop and 15 sec slide
100' "
90' "
80' "

70 - 5
60 - 4
50 - 3
40 - 2
30 - 1
------------
20 - 10 (10'/min to surface assent rate)
10 - 5

-told to plan no more than 2/3rd's for cf consumption of deco gas bottle.

 

[rjack321]

The 50% of time above 20ft and 50% time below is typical.

Problem with the shape of the curve is that it doesn't scale to 2 deco gas dives where you want a backgas break at 30ft (on the long hose) before switching to O2. And there doesn't seem to be an actual rule for your reverse engineering. E.g. How would you distribute 17mins in that segment? The other issue I see is a huge time jump from 30ft to 20ft. On one deco gas I'm not sure that's really justifiable. That is nothing special is going on at 30ft that isn't also happening at 20ft. RD tries to keep time steps within a factor of 5.

RD would calculate a linear ascent:
15mins =
70-3
60-3
50-3
40-3
30-3

leave the 30ft stop as is
take 1/2 the time from 40 and 50ft and move it to 60 and 70ft
1/2 of 3min stops (1.5) can be rounded either way, to 2 or to 1
I round 1.5 to 2

so
70-4
60-4
50-2
40-2
30-3
20-10
10-5

Net, 30 to 20ft time step is a little over a factor of 3 and there's a backgas break in there if this were a 2 gas dive. And the "o2 window" is not weighted as heavily as your method. Honestly your's is the first profile I have seen from a GUE diver in many years that weights the "O2 window" heavier than AG's version of RD.

Don't feel bad GUE has bounced all over the place on the shape of the 70-30ft segment. At one time it was like I described, at one time it was straight linear time (3min each in your example), your version is the 3rd itteration I've heard. I am not sure where or why there are so many changes to the shape. Maybe cause it doesn't matter much, maybe there's some info behind it. Its not elaborated on outside of class via any sort of proceedures document I've ever seen.

BTW RD would have a slower asecent from 110ft, 30sec stops with 30sec slides. You slowed from 30ft min off the bottom to 20ft min from 110 up to 80. The RD way has 10ft/min sliding stops (or 30sec stop 30sec slide). I haven't done a 1 gas EAN50 dive in years but if I were, I would do all of the shallow time at 20ft and then 5mins up to the surface. I don't seem to get a "time credit" for doing deco deeper than something like Vplanner would suggest. So I do all the shallow time at 20ft and then use the 5min up as a little padding. My normal buddies are the opposite (they feel like crap without an extended 70ft stop) so we do an RD shape and then have all the deco done before leaving 20ft.

I can tell you for sure the lost deco gas contingency with UTD/AG is not like you were taught. Completely different conceptually. That is a topic for a different thread tho.

 

[TSandM]

That profile is interesting, SIC, because it's different from what I remember us doing when we went through creating decompression profiles with Decoplanner in Rec Triox. (We did all the T1 classroom work in that class, I think.) The profile we would have come up with would have resembled Richard's RD profile, in that we would have weighted the 70 and 60 foot stops by taking time from the middle ones, to "open the oxygen window". But we would have kept the 30 foot stop longer because it pushes the gradient more.

In my UTD class, we were allowed the shaped profile or "linear pragmatic", with the instruction that the longer the deco, the more important the shaping would become.

 

[ScubaInChicago]

Thanks RJ,

I've already heard that classes shortly before ours were taught the linear/pragmatic split between the 70'-30' stops like shown in your example. I wasn't sure how many schools of thought were actually out there...It was relayed to us that "The newest findings" lent itself to getting off the bottom and through the deep stops faster than previously taught. As for the 30' stop and 02 breaks, were limited to our single deco gas .....prob my only complaint of the curriculum but doesn't really cut much time off the overall deco at the t/1 level.


I think overall I want to get an idea of how to work with other teams who learned to put different emphasis on deco schedules before us.

 

[ScubaInChicago]

That profile is interesting, SIC, because it's different from what I remember us doing when we went through creating decompression profiles with Decoplanner in Rec Triox. (We did all the T1 classroom work in that class, I think.) The profile we would have come up with would have resembled Richard's RD profile, in that we would have weighted the 70 and 60 foot stops by taking time from the middle ones, to "open the oxygen window". But we would have kept the 30 foot stop longer because it pushes the gradient more.

In my UTD class, we were allowed the shaped profile or "linear pragmatic", with the instruction that the longer the deco, the more important the shaping would become.

Thanks Lynne,

I know it's not an exact science and has lots of wiggle room....I'm mostly interested in the why's that were taught for shaping the curves to help build an understanding with others before me.

-Dan

 

[rjack321]

In my UTD class, we were allowed the shaped profile or "linear pragmatic", with the instruction that the longer the deco, the more important the shaping would become.

In the olden days, it would have been a Fibonacci sequence up to 20ft. But nobody could spell Italian underwater so they ditched it

I didn't follow the exact strategy for shaping in UTD's Tech1. I thought you put half the time in the 30-60ft segment. Left the shallow time on O2 alone. Then took some 60min time and put it at 30ft. And a little of the 50ft time and moved that to 40ft.

so 15mins in the deep portion would start as:
30-4
40-4
50-4
60-3

and you'd move that around a little to something like:
30-6
40-5
50-3
60-1

net
10-5
20-10
30-6
40-5
50-3
60-1

which would be just about your max possible deco (1 O2 cycle) within that cert I think.

 

[rjack321]

I wasn't sure how many schools of thought were actually out there....

Apart from folks diving a modified decoplanner profile (those are out there too), I think 3:
1) your shape
2) linear
3) 1/2 time from the middle put deeper

It was relayed to us that "The newest findings" lent itself to getting off the bottom and through the deep stops faster than previously taught.

Yeah this is a topic of much dispute. You might want to check out Andrew Ainsle's posts about the subject of 500ft ascents on TDS. Some heavy hitter MDs weighed in at various points.

Basically it comes down to:
sure you may be racking up more deco in some (slow) tissues by ascending too slow.
BUT
the consequences for the fast neurological tissues like the CNS are too severe to push the gradient much through the deep stops no matter what the theoretical offgassing start depth might be.

I don't think its all that important at the Tech1 21/35 type gas level. Once you are really loaded (saturated in many medium+ time tissues) or are really deep with many ATAs for a bubble formed deep to grow ginormous is where trying to shave deco at the end by pushing the gradient early can bite you in the butt.

 

[liuk3]

I think overall I want to get an idea of how to work with other teams who learned to put different emphasis on deco schedules before us.

I had the same GUE Tech1 instructor as you. In class, he presented a number of different ways to run deco profiles, and he gave us his personal preference in shaping the deco. At the end of the day, the choice in terms of how we wanted to shape it was to be ours, and we ultimately had to take responsibility for it. At the GUE Tech 1 level, it probably really doesn't matter whether using a linear/pragmatic approach versus shaping the curve. In terms of working with other teams, all you have to do is talk about it before a dive. I haven't had a problem adapting or trying different schedules out so long as we talked about it as a team prior to a dive. In fact, I enjoyed keeping an open mind and trying out minor variations in deco schedules that seemed reasonable to me (including shaping the way rjack321 posted). They all seemed to work fine for me.

 

[AndyNZ]

Don't feel bad GUE has bounced all over the place on the shape of the 70-30ft segment. At one time it was like I described, at one time it was straight linear time (3min each in your example), your version is the 3rd itteration I've heard. I am not sure where or why there are so many changes to the shape. Maybe cause it doesn't matter much, maybe there's some info behind it.

Fresh out of T1, but with a fair chunk of that nasty deep air diving to think about....

Realistically, how much difference does it make (at the T1 level)? The diving is fairly conservative, the shape of the curve is somewhat immaterial - in the sense that as long as you know what your shape means in terms of fast/slow tissues and the impact of gas loading.... well you can probably shape it any way you like and still end up with a a reasonable deco schedule.

To my mind, Buhlmann 100/100 gives you one extreme (max out the pressure gradient) and VPM gives you another extreme (keep you deep to minimise the bubbling).... somewhere in between can potentially give you the benefits of each.

 

[rjack321]

Fresh out of T1, but with a fair chunk of that nasty deep air diving to think about....

Ummm please god tell me nobody left the door open here?

VPM gives you another extreme (keep you deep to minimise the bubbling).... somewhere in between can potentially give you the benefits of each.

Actually VPM is much closer to a Buhlmann shape than RD. Streetdoctor's example is actually pretty close to an inverted VPM profile. But (apologies to Erik Baker et al) if you force something like Vplanner into the shape you desire by inputing a multilevel multigas gas dive manually - you can see that for all practical purposes on 150ft dives like this example 1min at 70ft is equal to 1min at 40ft. The shape of 15mins over 5 stops don't matter much as far as VPM is concerned.