My Journey into UTD Ratio Deco

[Nirvana]

so here is the problem as I understand it. Those who are anti-RD in this thread are looking for and expecting those who use RD to give scientific proof that it is the best. NEWSFLASH: Everything about decompression is THEORY! Even those who follow their fancy Perdix AI's aren't following Buhlmann ZHL16C - they are adding gradient factors - which are a best guess correction to overlay Buhlman's work! And who is doing the guessing? The individual Perdix AI diver! One year a low GF of 30 is popular, and then another 50. Did everyone who set their GF to 30 get bent? No. Why? Becaus deco is not that exact. No one really knows how fast tissues actually perfuse, and half times are arbitrary.

I DID NOT WRITE THE ABOVE TO DEBATE THE ACCURACY OF DECOMPRESSION THEORIES!!! The purpose of the above statement is to put depth averaging into perspective. How accurate does it need to be? Does it require an arbitrary grid to place over your decompression, and then calculate each point to the 10th degree? Or can you learn to get close?

RD gives you options. You can choose how precise to make your average depth calculation. The method Captain Sinbad detailed is NOT even in the book. The book details two methods, but doesn't say you have to limit yourself to only those two methods. And after getting your average, the book recommends you weight the average either deeper or shallower - depending on how conservative you think it should be. And there is nothing that says you can't compare the average you calculated with the average displayed on your bottom timer. If you are here to find a 'smoking gun' in depth averaging - you either aren't going to find it - or you have already found it and you can leave now - depending on how you look at it.

The point is to create a thinking diver. After you have learned the tool of RD, you can dive your computer if you want. But in a UTD class, you will practice RD so you can learn that it's not that hard, how useful it is, and have it as an available tool.

Well, I think that when someone chooses to adopt a procedure very different from what is commonly done on a given field, it is reasonable to ask why they think the new method is superior, and to get a rational explanation in response.

On the same vein, considering that gas absorption by the body is thought to be dependent on time and partial pressure, I would be interested in seeing an intelligent explanation on why it is reasonable to treat very differently the time spent on a given depth depending on the phase of the dive, as more weight is given to later phases of the dive in the method presented.

Finally, if one does not want to see their methods questioned, a first sensible step would be to not post them for examination on a public forum. Asking for explanations does not mean enmity.

 

[Patoux01]

NEWSFLASH: Everything about decompression is THEORY

I take it you are not familiar with science?

 

[tbone1004]

@sigxbill why would you spend $560 on a bottom timer??? That's insane when you can get a full trimix actual computer for not much more.
Save $200 and get this if you're running it in gauge mode and want a fancy screen. I like the Freedom, but spending that amount of money for something that tracks depth, time, and average depth is hilarious.
Deepblu COSMIQ+ (V3.0.1)
My objection to RD has nothing to do with the min-deco philosophy. My objection to it is that the UTD RD tables go in direct opposition to the current research in decompression theory. Same with anyone that still uses NAUI's RGBM, or really anyone that still uses VPM. They go against our current understanding of decompression stress and creates a less efficient ascent profile. It is much less about the principal of using ratios, calculating average depths, etc. it's all about the implementation of the actual ratios used and how the proponents of it who are not qualified to teach on the subject are preaching that they know better than the deco scientists which is 100% what AG does and that is NOT ok. If the ratios were adjusted to better reflect the current state-of-the-art in ascent profiles, then no problem, but he still claims to know deco better than MD/PhD's actively studying it

@LiteHedded if this isn't DIR, then what is? AG is the biggest voice of DIR right now. UTD and ISE are the only ones actually calling their diving DIR. Now, I do understand your WKPP argument, and I also understand why JJ stopped using the term, but if UTD and ISE are promoting ratio deco, and promoting DIR, then that is to me more "DIR" than anything that GUE is doing right now. Unfortunate, but annoyingly true.

 

[kelemvor]

So I wanted to address the issue of "mental mathematics" because some degree of criticism is generated by the idea that ratio-decompression requires very difficult mental computations. Before I proceed, I must state that mathematics has never been my forte and if there is anyone on this forum who should be apprehensive about messing up the mental mathematics then it is me. While I was trying ratio decompression during my test dives, I did not come across a situation that required anything more than taking the average of two numbers that would be very close. I am going to explain what mental mathematics go into ratio-deco and if there is anyone here who thinks that what I am describing below is prone to massive human error then please say so.

MIN-DECO TABLE (Nitrox 32):

All UTD divers will know these numbers at the back of their minds. Some are seen carrying a slate but most will have these numbers ingrained in memory as they are easy to remember.

60 ft = 60 mins
70 ft = 45 mins
80 ft = 40 mins
90 ft = 35 mins
100 ft = 30 mins

Unlike a conventional dive table which uses maximum depth, this table uses average depth instead.

Now the mental mathematics: Once the dive begins you are required to do a rolling average every 5 minutes. It would be something like this:

RT 5 mins = Depth 73 (Avg 73)
RT 10 mins = Depth 77 (Avg 75)
RT 15 mins = Depth 85 (Avg 80)
RT 20 mins = Depth 88 (Avg 84)
RT 25 mins = Depth 90 (Avg 87)
RT 30 mins = Depth 93 (Avg 90) = At this point you know that you have 5 more mins at this depth from the above described table.



If you think you can determine the bold number in the bracket without using calculator then the task loading aspect should not be over-whelming. For the particular dives that I was doing with simple straight profiles or gradual depth increases this was not over-whelming.

UTD Ascent Schedule

After finishing the dive, you ascend to 50% of your depth @ 33 ft / minute and then stop for 1 minute every 10 feet until you reach the surface. For a hundred ft average depth you are doing 5 stops of 1 minute each all the way up to the top so that would make it a 5 minute ascent schedule. For 80 feet dive your first stop will be at 40 feet and then 30, 20, 10 so 4 minute schedule.

Does anyone here think that this is too much task-loading as far as mental mathematics go? Thoughts?

It seems to me that accurately keeping track of average depth throughout the dive (without a computer) would be time consuming. I mean, you've got to sum a growing array of numbers and then calculate the average every 5 minutes? I guess it's doable if you had a slate, but it seems like this would take a significant bit of focus each time you do it right? I must be missing something obvious, what is it?

 

[tbone1004]

It seems to me that accurately keeping track of average depth throughout the dive (without a computer) would be time consuming. I mean, you've got to sum a growing array of numbers and then calculate the average every 5 minutes? I guess it's doable if you had a slate, but it seems like this would take a significant bit of focus each time you do it right? I must be missing something obvious, what is it?

I think the thing that you're missing is that the concept of this all came out when dive computers were terrible and I don't think the bottom timers actually spat out average depth either. Computers weren't available where you could muck with gradient factors, the Uwatec bottom timers didn't give you average depth, neither did most of the computers. What failed to happen in the last 10 years was a change to accommodate the technology. It continues to make them unique and arguably keep feeding AG's ego....

 

[sigxbill]

@LiteHedded Lol! I would be so heartbroken if no one’s name from utd is on an arrow in the wkpp! But I suspect there is....

Regarding posting detailed methods in a public forum, no one does that. If you want to read PADI methods - you have to pay - just like with GUE and most anyone else that has an investment in IP ...

Maybe you would like to share the correct DIR method of using a depth gauge / bottom timer!

 

[CAPTAIN SINBAD]

it quickly diverges from your computer once you start doing real (non min deco) diving. I'm curious how your class will explain it away. the gue answer for these situations is that ratio deco is wrong, because they just made it up...

I would really like to see when and where this happens. During my chat with Bob Sherwood (GUE) he also raised this concern that at certain exposure times you will deviate from established algorithms on ratio deco. From the test profiles I have been running on Multi-Deco, using standard gas (32%), using Min-Deco table while using UTD ascent profile, I have not come across such a situation at least in the Min-Deco depth and time limits but yes, I am open to seeing possibilities of where that could happen.

In fact I would encourage everyone to run a few Min-Deco single profiles as well as repeat profiles on your Deco-Planning software while following the guidelines I am posting below. These are from UTD Tech-1 Diver training manual which I am going through right now. For those who are new to this, some points should explain the UTD mindset.

• Unlike conventional tables the UTD Depth averaging table is a repeatable table. The bottom times do not change on this table and that is why it is one table committed to the divers memory.
  
• Instead of shrinking and expanding bottom times to fit within a moving No Decompression Limit, UTD will expand and contract its stop-times during ascent to ensure that you clear any deco obligation while repeating the table on consecutive dives.

1. For up to three dives a day you follow the same ascent schedule as long as you are putting 60 minutes of more of surface time between dives.
2. For up to three dives a day you double the stop times on each stop if your surface interval is less than 60 minutes between dives. In other words you are stopping to decompress twice as long after your recreational dives.
   
3. For more than three dives a day the audio-material suggests that you double all the stops no matter what the surface interval.

I have tested various versions of scenario A up there on Multi-Deco giving them only 60 minutes of interval to see if they would blow you out of the Buhlmann table and thus creating the departure that GUE community suggests caution against. For three dives a day, they get you out while keeping you within pure Buhlmann 100/100. On the fourth dive you are pushing it.

...

NOTE: THESE ARE AVERAGE DEPTHS

 

[tbone1004]

@LiteHedded
Regarding posting detailed methods in a public forum, no one does that. If you want to read PADI methods - you have to pay - just like with GUE and most anyone else that has an investment in IP ...

and yet, the decompression algorithms are public domain.... Anyone with excel can create the same profiles that Shearwater uses on their computers, for both VPM and ZHL....

@CAPTAIN SINBAD the min-deco tables basically follow established "guidelines". Rule of 120 or Rule of 130. The discussion against RD isn't about min-deco because that's not "decompression". The points against, including what Bob said, are about "exposure times" that are "real". I.e. multi hour dive profiles with trimix, multiple decompression gases, etc. not light backgas deco or NDL diving. Do not confuse the two because the point he and the rest of us are trying to make is there are plenty of profiles, if not most that it works just fine on and will match most accepted algorithms with little issue. It tends to fall apart on the "real" dives though where you have 1+hr bottom times are >100ft depth

 

[CAPTAIN SINBAD]

And yes ... it would have been possible to start this discussion in DIR section. We can even move this into the UTD section where everyone will obviously agree with the UTD manual. I purposefully invited some of the highest level technical divers on here from various decompression philosophies to offer their insights into this because if we are going to put an agency on trial then the jury has to be diverse right .

 

[PfcAJ]

I would really like to see when and where this happens. During my chat with Bob Sherwood (GUE) he also raised this concern that at certain exposure times you will deviate from established algorithms on ratio deco. From the test profiles I have been running on Multi-Deco, using standard gas (32%), using Min-Deco table while using UTD ascent profile, I have not come across such a situation at least in the Min-Deco depth and time limits but yes, I am open to seeing possibilities of where that could happen.

In fact I would encourage everyone to run a few Min-Deco single profiles as well as repeat profiles on your Deco-Planning software while following the guidelines I am posting below. These are from UTD Tech-1 Diver training manual which I am going through right now. For those who are new to this, some points should explain the UTD mindset.

• Unlike conventional tables the UTD Depth averaging table is a repeatable table. The bottom times do not change on this table and that is why it is one table committed to the divers memory.
  
• Instead of shrinking and expanding bottom times to fit within a moving No Decompression Limit, UTD will expand and contract its stop-times during ascent to ensure that you clear any deco obligation while repeating the table on consecutive dives.

1. For up to three dives a day you follow the same ascent schedule as long as you are putting 60 minutes of more of surface time between dives.
2. For up to three dives a day you double the stop times on each stop if your surface interval is less than 60 minutes between dives. In other words you are stopping to decompress twice as long after your recreational dives.
   
3. For more than three dives a day the audio-material suggests that you double all the stops no matter what the surface interval.

I have tested various versions of scenario A up there on Multi-Deco giving them only 60 minutes of interval to see if they would blow you out of the Buhlmann table and thus creating the departure that GUE community suggests caution against. For three dives a day, they get you out while keeping you within pure Buhlmann 100/100. On the fourth dive you are pushing it.

...


View attachment 460196

NOTE: THESE ARE AVERAGE DEPTHS


View attachment 460197

You can’t just ignore 7% difference in inert gas content.

Well...you can... but don’t expect the same DCS risk.