My Journey into UTD Ratio Deco

[PfcAJ]

I think the idea is to learn to do it without the aid of a computer.

 

[northernone]

I've never heard decompression described as scientific mystery. So off the bat, I'm a tad puzzled.

As we join you on this journey, I'd be interested to learn your relevant history of decompression diving and training which will provide the context for your interpretation of the experience.

Cameron

 

[decompression]

Looking forward to this......thanks for taking us on this journey.

 

[CAPTAIN SINBAD]

I've never heard decompression described as scientific mystery. So off the bat, I'm a tad puzzled.

Really???

"Decompression is an area where you discover that the more you learn, the more you know that you really don't know what is going on. From behind the "black and white" exactness of table entries, the second-by-second countdowns of dive computers and beneath the mathematical purity of decompression models lurks a mysterious physiological jungle that has barely been explored."

Karl E. Huggins, PhD
Decompression Theory Researcher
University of Michigan.

 

[Scuba J7]

I am genuinely curious if UTD promotes the use of a bottom timer or solely the “computer between the ears”

 

[sigxbill]

I was under the impression electronics were not permitted. So to my next question, if you can use a BT why in tarnation would you try to track it in your head?

Like what PFcAJ wrote, the idea is to be actively involved in your profile by thinking about it. The rule isn’t no electronics; that would require wearing an analog depth gauge. I use this UTD recommended bottom timer / depth gauge, and it is clearly 'electronic.' Freedom Advanced Bottom Timer | Divesoft

"Why in tarnation?" LOL! Thanks for using that phrase! You don't ever hear that where I live. My grand dad used to say that... ;-)

The point is to practice being active in your profile, and learn how to survive without a computer. There is nothing that says UTD divers can't ever use computers - they just don't in class - so they can learn and practice diving without one. Once you learn it, it becomes so easy that you don't miss the computer, and when you realize how easy dive planning without a computer is, your whole team dives the plan - together - no need to ask each member if their computer cleared yet.

Relatively speaking, I am a new convert to ratio deco, thought I would hate it, and have ended up loving it! Surprised the tarnation out of me! - cheers

 

[sigxbill]

I just reviewed my 100' dive from Saturday - downloaded from my bottom timer. Using the rolling average method detailed by Captain Sinbad, I calculated my average depth to be 56', and my bottom timer calculated 58' ...

 

[northernone]

Really???

"Decompression is an area where you discover that the more you learn, the more you know that you really don't know what is going on. From behind the "black and white" exactness of table entries, the second-by-second countdowns of dive computers and beneath the mathematical purity of decompression models lurks a mysterious physiological jungle that has barely been explored."

Karl E. Huggins, PhD
Decompression Theory Researcher
University of Michigan.

Edge!

I've not come across that quote from 1992 before, reading the source now for context.

 

[CAPTAIN SINBAD]

I am sure you asked for the scientific basis for this approach. Could you provide that for us?

It would make a legitimate question if this method takes you out of the safety margin generated by your dive computer. If it accurately mimics your dive computer then whatever scientific basis you have for your computer will also support this method.

I think a different way to express your particular concern would be, what gradient factor would I be riding on BuhlmannZHL-16C if I did this to the most aggressive limits acceptable by UTD standards?

The most aggressive you could go on this method while still remaining within UTD agency standards would be to do 3 dives a day while keeping the same min-deco table and same ascent schedule and keeping the minimum surface interval to 60 mins. Even with surface interval being minimum, bottom times being maximum and ascent schedules remaining unmodified, it is hard to break gradient factor 100/100 which is what you hit when you dive conventional tables to their square profile, max limits. So in the end the scientific basis for this would be its ability to keep you within safety parameters defined by BuhlmannZHL-16C. No?

 

[Nirvana]

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.

I do not understand this average. I would imagine that any relevant average depth would be a weighted average with relation to time, something like:

D = (D1*∆t1 + D2*∆t2 +...+Dn*∆tn)/T

where D is the average depth, Dn is the nth measured depth, ∆tn is the time spent at depth Dn and T is the sum of all time intervals.

However, it appears you are just taking the average up to a given time, summing it up with the depth of the next 5min interval and dividing it by two. In the example above, if we take just the first three lines, we have 10min spent at an average of 75ft (I supposed the depth there is measured in feet) and then 5 min at 85 ft. All this is averaged to 80ft.

By this process, if I did a dive of 25min at 20ft and then 5 min at 90ft, my average would be 55ft. The same average would be found if I did a dive of 25min at 90ft and then 5min at 20ft.

Is the example correct?


edit: I see @huwporter raised more or less the same point on a previous post. Sorry for the repetition.