UTD Ratio deco discussion

[boulderjohn]

Almost 20 pages to establish that neither UTD nor GUE currently teaches altitude diving using RD.

I am still trying to figure it out for sure, but there is actually a HUGE difference between the two--at least as I understand it. In fact, it is that difference that I am still trying to understand.

• GUE primarily teaches that RD is used to plan a dive on the fly when the primary plan goes awry, with the goal of recreating a DecoPlanner profile. A GUE diver at altitude would not use RD, but would instead simply input the altitude into DecoPlanner and follow the adjusted DecoPlanner schedule. No problem.
• When I was with UTD, we were told DecoPlanner was wrong, and we should use the UTD version of RD at any altitude. I am told now that this has changed, but I am still trying to figure out how. What has become clear is that no one representing UTD in this thread knows what to do when diving at altitude. They all know they should do something different, but they don't know what that is.

 

[mikeny9]

No, you never said that UTD does not teach altitude adjustment in any of its classes.

Really? Have you been reading?:

John, altitude not having an effect in decompression is definitely a 180 degree turn from what I've been taught in my time with UTD, for what it's worth.

Fair enough John. I can say at least now, they don't teach that RD is the same for all altitudes.

To be clear, again UTD doesn't teach altitude diving as part of ratio deco.

I've also stated I think for the third time or fourth time now, that UTD doesn't teach altitude diving in ratio deco.

In my courses I was explicitly taught one can't use RD strictly the same when it comes to altitude diving.

UTD does not teach altitude diving in any class that I know of. It's not hard to answer, I've answered it 6 times now I think?

You did say that you personally would make some adjustments to Ratio Deco, but it seems to me you would make those adjustments based on your own guesswork as to what would be the right thing to do, because UTD does not offer any official guidance for this. Is that correct?

Yes, and you still have not told me whether my "guesswork" is acceptable. I'm also "guessing" that by now if you haven't objected it is. So it seems my method of depth adjusting RD for the purposes of determining total deco obligations works close enough, but probably errs more on the side of caution and would prevent some from doing a dive if not using GFs or VPM-B; I'm cool with that.

So, as I understand it, you are certified by UTD to dive to 150 feet at sea level, but UTD is silent as to what that means at altitude. If you were visiting in the Rocky Mountain region and were invited to join us at Rock Lake in Santa Rosa, NM, and do a dve to 150 feet, you could not do it according to your understanding of how to make an adjustment. Is that correct?

160' feet at sea level. And for the 7th time (yes I was correct it appears about the 6th time before, see the quotes), UTD isn't "silent" about it. The courses teach explicitly that RD can't be used the exact same way for altitude diving. That's not the same as being silent.

Regarding a dive to 150' in Santa Rosa, isn't the elevation around 4600 ft? To answer your question, no I personally wouldn't do that dive.

What has become clear is that no one representing UTD in this thread knows what to do when diving at altitude.

Because there is no official position that I've heard of. They give you tools. What a diver does with the tools to make an informed decision is up to them.

 

[boulderjohn]

160' feet at sea level. And for the 7th time (yes I was correct it appears about the 6th time before, see the quotes), UTD isn't "silent" about it. The courses teach explicitly that RD can't be used the exact same way for altitude diving. That's not the same as being silent.

But it doesn't tell you how to adjust it, so it is silent on that point. That means if you choose to dive at altitude, you are on your own to decide how it should be done.

 

[mikeny9]

Precisely, only they aren't silent about using the same exact profile as one does at sea level. Might as well call the local chamber and tell them you'll be there around noon.

 

[Rainer]

• GUE primarily teaches that RD is used to plan a dive on the fly when the primary plan goes awry, with the goal of recreating a DecoPlanner profile. A GUE diver at altitude would not use RD, but would instead simply input the altitude into DecoPlanner and follow the adjusted DecoPlanner schedule. No problem.

I took my GUE tech training (with Bob Sherwood, at the time, the GUE training director) about ten years ago, but I can state:

(1) We were first introduced to decompression theory by cutting a lot of tables using DecoPlanner in class. We learned how to modify those results to incorporate what were then considered by GUE to be best practices (deep stops, oxygen window, s-curve, etc). We then were introduced to Ratio Deco. Since the RD profiles so closely mirrored the modified DP results, we planned the experience dives using RD (but confirmed that they matched closely with DP). After class, we used RD for any profiles that fit within the general parameters covered in class and our prior experience. For any profiles outside that range, we were encouraged to use DP and look for new patterns that could be applied algorithmically.

(2) Our training never covered diving at altitude.

 

[decompression]

John, if you ask a baker how to cook a steak your gonna get an umbrella........in other words, no one here can legitimately answer your question about UTD and altitude. I understand you would have a reluctance to contact UTD directly but that would seem the only way to give you what you want. Or, take the new RD 2.0 class and have the ability to ask the question there. Unfortunately in the big picture, diving at altitude isn't near as popular as sea level and that's where the efforts are made.

When I was first introduced to RD, prior to UTD in 2006, it was simple, you have the knowledge to adjust and place your deco as you see fit. But, again, that was in the beautiful Pacific Ocean.

 

[stuartv]

You're really confusing me. You mentioned:


What dive are you talking about that doesn't ever exceed 160' that you planned? Did you share it?



You're not comparing apples to apples. You changed the BT to 15 min and the depth to 200' at 0 ft elevation. Also I think there's a difference in what we are considering "deco time." I consider it the time spent from 50% of your depth up to the surface. Using MultiDeco set to 50/80, 6000ft of elevation, 21/35 for back gas and 50% for deco gas, a dive to 160' for 25 min gives 46 min of deco. A dive to 200' at 0 ft of elevation gives around 35 min of deco time. Both of those are well over 30 min. If I was using GFs I still wouldn't do this dive. That was the point I was trying to make when I said earlier, "RD is not the reason I couldn't do the dive."

You said that, at 6000' elevation, you would regard a dive to 130' to be the equivalent of diving 160' at sea level.

I asked what sea level depth equivalent would you use in order to plan a 160' dive at 6000' elevation. You never answered.

I extrapolated your earlier statement (of 130' == 160') and ran a plan based on 160' == 200'. I.e. planning a dive for 200' at sea level as the equivalent of diving to 160' at 6000' elevation. Since you never answered the question about the sea level equivalent depth, I had to come up with a number on my own in order to run a plan that would tell me whether you could do a dive to 160' at 6000' elevation while having less than 30 minutes of deco.

And, I did not change the BT to 15 minutes. I arbitrarily chose that. You said you could not plan ANY dive to 160' at 6000' elevation (using RD or Buhlmann) because it would be more deco time that you are certified for. So, I just picked a BT and then ran a plan to verify that your statement was wrong.

The result was the conclusion that you could EASILY do a 200' dive at sea level and have less than 30 minutes of deco. Therefore, you can do a dive to 160' at 6000' of elevation and also have less than 30 minutes of deco. At least, you can while using Buhlmann - and even with the arbitrary and huge number of planning as if it were 200'. So, your statement that cannot do a dive to 160' at 6000' of elevation with less than 30 minutes of deco, using Buhlmann, is just wrong. Well, given that I chose 200' as the sea level equivalent because you won't answer the question of what sea level depth is equivalent to 160' at 6000'.

Your statement that your deco time is longer because you start counting when you get to 50% of max depth is just ignorant. The dive I planned, with 25 minutes of deco, is counting the deco time starting from as soon as the diver leaves the bottom. I planned 15 minutes of BT and got a total runtime of 40 minutes. So, 25 minutes of deco (i.e. total ascent time).

You said that you can't do the dive but it's not because of Ratio Deco and that is clearly just nonsense. If you were using Buhlmann, you would plan the dive for 160', instead of some made up sea level equivalent, you would tell it the altitude, and you could easily plan a dive to 160' at 6000' of elevation with less than 30 minutes of deco. So, you can't do it precisely because you are using RD.

And you still haven't answered boulderjohn's question: How did you determine that 130' at 6000' of elevation is the same as diving to 160' at sea level? What process did UTD teach you that you used in order to come up that number of 130'?

And my earlier question that you still haven't answered: What depth at sea level is equivalent to diving to 160' at 6000' of elevation? What number and how do you calculate it?

 

[decompression]

Stuart, I can't answer for Mike, but I can say that altitude tables (pick an agency or USN) generally advise the addition of 30' above 4000-6000. So a 160' dive at 6000' would be a 190' dive at sea level. And that is beyond tech 1, and AN/DP, tec 50 et al.

 

[decompression]

Further, and I'll have to check, but at 190-240 it becomes a 3:1 ratio for RD, and that adds considerable Deco time.

Checked, depth is 220-290 for 3:1,

Regardless, at 2:1 , with a BT of 15 minutes that puts deco at 30 minutes before adjustments, so yes that could put it beyond tech 1 level.

Could you post the profile of the 200' BT 15 buhlmann dive with less than 30 mins of Deco, for info.

I ran one with 50-80 GF but I had to put it at conservative 1 to get a 30 min Deco.

 

[lv2dive]

No, but if a baker is adamant about how experienced he is compared to everyone else, it's really not that unreasonable to expect said baker to handle, say, a chocolate soufflé... ok but since that's too much of a specialty dish, it does seem like someone could get one of the other more Sr Bakers or even the Head Baker himself to come to this thread to set the record straight. Really I think at this point the primary outstanding (simple) question is when one would expect to learn about adjusting for altitude in the UTD RD curriculum.

John, if you ask a baker how to cook a steak your gonna get an umbrella...