Spisni study

[Diver0001]

I think I see where you are going here. I only have an anecdote to offer but since I started diving CCR 4 yrs ago all of my adjusted and tweaked RD has basically been tossed. I still do an average depth in my head. I still carry GUE/UTD standard gases. If everything poops out I could do an RD ascent like I used to do on OC.

Where it gets interesting is what happens side by side with an RD diver. My on CCR using 40/70 or 40/80 (depends on the dive) and them on OC using RD. We actually have fairly comparable total deco times. They end up about halfway through that time by 30ft. My deco doesn't even start until ~50ft (some of the deeper 1-2min buhlmann stops clear before getting to 50ft). At 30ft they are halfway done, have ~65+% of my deco time to go. They will be "done" after 10-20mins at 20ft. I still have an 12-18min 10ft stop overhead.

Essentially, if you do a deeper stop profile how much longer do you have to clear a buhlmann profile? For 20-25 min BTs in the 140 to 200ft range, quite a bit.

I think you're sniffing up the same tree I am. I was, however, completely unable to pose the question to Simon in a way that made it clear what I was interested in seeing. My inability to communicate accurately using the proper scientific jargon made me sound like an intoxicated nascar fan trying to ask a technical question about the nuances of a space shuttle engine.

You seem to know what I meant. Can you help pose the question in clear concise accurate language?

R..

 

[huwporter]

What I did may not work for you but I would like to challenge you to at least strap on a Buhlmann computer for a few dives and see what kind of mop up times it gives you.

From my experiences over the last year or so for OC dives between 45-85m with up to 90 minutes of deco using GUE ascent standards with also a Buhlmann computer strapped on, the computer normally clears 0-10 minutes before the original plan. (Personally I'm totally happy to accept maybe 10 minutes extra time in the water in return for computer failure being a total non-event.)

(Please do note, GUE ascent standards are NOT the same as UTD RatioDeco (TM), I do not speak for that.)

 

[Diver0001]

From my experiences over the last year or so for OC dives between 45-85m with up to 90 minutes of deco using GUE ascent standards with also a Buhlmann computer strapped on, the computer normally clears 0-10 minutes before the original plan. (Personally I'm totally happy to accept maybe 10 minutes extra time in the water in return for computer failure being a total non-event.)

(Please do note, GUE ascent standards are NOT the same as UTD RatioDeco (TM), I do not speak for that.)

I haven't tried it but this is eyebrow raising. I would intuitively expect exactly the opposite as was Richard's experience as posted above.

R..

 

[huwporter]

Further to the above. It would be very interesting to see what kind of "mop up" times (I hope I've made sufficiently clear what I meant by that) the Buhlmann model would have calculated if the NEDU deep stop ASCENT STRATEGY was applied while running on the Bulhmann model.

In other (I'm sure, very sloppy) words, it would be interesting to see what Buhlmann would do if you ignored the suggested ascent strategy and did MOST of the ascent using the stops that BVM(3) calculated and just did the last couple of stops (the required stops) with the Bulhmann model and "let the tail wag" as it were.

My curiosity is what kind of "mop up" Buhlmann would calculate for the BVM(3) dive after the first required stop..... what the difference in run-time would be.... and even more interesting, what the post dive heat maps would look like.

I made two attempts to pose this question to Simon but I was utterly unable to make myself clear. If anyone else sees what I'm saying and can say it better than I can then please help me pose the question again.

R..

I did a rough analysis of both of the NEDU profiles through a Buhlmann lens here: UTD Ratio deco discussion

The NEDU shallow stop profile is fairly close to GF 93/43
The NEDU deep stop profile is 'kinda something like' GF 42/70 (though the gradient factors of the consecutive stops don't fit a normal GF progression)

...so both profiles look 'OK' according to Buhlmann.

 

[Diver0001]

I did a rough analysis of both of the NDEU profiles through a Buhlmann lens here: UTD Ratio deco discussion

The NEDU shallow stop profile is fairly close to GF 93/43
The NEDU deep stop profile is 'kinda something like' GF 42/70 (though the gradient factors of the consecutive stops don't fit a normal GF progression)

...so both profiles look 'OK' according to Buhlmann.

Thank you, I'm going to try chewing through that for a while.

R..

 

[rjack321]

@Dr Simon Mitchell a question from the peanut gallery ...

If in repeating a NEDU dive:
1) one were to do the BVM(3) profile up until it intersected the dissolved/buhlmann profile
2) switched models at this intersection (with the new total gas loading)
3) how much extra time would you have to add shallow to get the same heat map as if you had just followed the dissolved/buhlmann model in the first place?

I.e. is it possible to change the heat map output to instead of showing a gas load difference to showing an overall time "penalty" created by the extra deep stop/time? Seems like it would be possible to model the gas loads accumulated in those intermediate half time tissues and then calculate how long it would take to get rid of them by extending the shallow stops. At least to the point where they roughly matched the original buhlmann ascent, although not all the tissue loads are going to match up perfectly the sum gas load could be matched.

Hopefully I captured our dutch friend's inquiry correctly. @Diver0001

 

[Diver0001]

@Dr Simon Mitchell a question from the peanut gallery ...

If in repeating a NEDU dive:
1) one were to do the BVM(3) profile up until it intersected the dissolved/buhlmann profile
2) switched models at this intersection (with the new total gas loading)
3) how much extra time would you have to add shallow to get the same heat map as if you had just followed the dissolved/buhlmann model in the first place?

I.e. is it possible to change the heat map output to instead of showing a gas load difference to showing an overall time "penalty" created by the extra deep stop/time? Seems like it would be possible to model the gas loads accumulated in those intermediate half time tissues and then calculate how long it would take to get rid of them by extending the shallow stops. At least to the point where they roughly matched the original buhlmann ascent, although not all the tissue loads are going to match up perfectly the sum gas load could be matched.

Hopefully I captured our dutch friend's inquiry correctly. @Diver0001

Thank you Richard. This question has been burning a hole in my brain for weeks. I sincerely appreciate your help.

R..

 

[huwporter]

@Dr Simon Mitchell a question from the peanut gallery ...

If in repeating a NEDU dive:
1) one were to do the BVM(3) profile up until it intersected the dissolved/buhlmann profile
2) switched models at this intersection (with the new total gas loading)
3) how much extra time would you have to add shallow to get the same heat map as if you had just followed the dissolved/buhlmann model in the first place?

I.e. is it possible to change the heat map output to instead of showing a gas load difference to showing an overall time "penalty" created by the extra deep stop/time? Seems like it would be possible to model the gas loads accumulated in those intermediate half time tissues and then calculate how long it would take to get rid of them by extending the shallow stops. At least to the point where they roughly matched the original buhlmann ascent, although not all the tissue loads are going to match up perfectly the sum gas load could be matched.

Hopefully I captured our dutch friend's inquiry correctly. @Diver0001

This isn't precisely what you asked, but in order for the deep stop profile to surface with the same surfacing gradient factor as the shallow stop profile (about GF45) you'd need to add roughly an additional 90 minutes to the 3m stop, making a total run time of about five hours.

=========================================================================

 Phase                Depth   Time       RunTime   Mix O2/He Ceiling GF
 -----                -----   ----       -------   --------- ------- --
 Descent To:          51m     2.8 min    2:50      21/0      0m      0
 Bottom Phase:        51m     27.2 min   30:0      21/0      13m     0
 Ascent To:           21m     3.3 min    33:21     21/0      12m     42
 Stop:                21m     12.0 min   45:21     21/0      8m      42
 Stop:                18m     17.3 min   62:39     21/0      6m      20
 Stop:                15m     15.3 min   77:57     21/0      5m      9
 Stop:                12m     18.3 min   96:15     21/0      4m      14
 Stop:                9m      23.3 min   119:32    21/0      2m      23
 Stop:                6m      17.3 min   136:51    21/0      2m      36
 Stop:                3m      163.3 min  300:8     21/0      0m      64
 Stop:                0m      1.0 min    301:8     21/0      0m      45
 Surface:                                301:8                       45

 =========================================================================

 

[rjack321]

I was going to guess "hours" so was on the right track
Seems like a big penalty on a 30min dive.

 

[Diver0001]

From my experiences over the last year or so for OC dives between 45-85m with up to 90 minutes of deco using GUE ascent standards with also a Buhlmann computer strapped on, the computer normally clears 0-10 minutes before the original plan. (Personally I'm totally happy to accept maybe 10 minutes extra time in the water in return for computer failure being a total non-event.)

(Please do note, GUE ascent standards are NOT the same as UTD RatioDeco (TM), I do not speak for that.)

You know something.... I think I know what's happening here.

When I think back to when I first started technical diving, I dove on tables with a computer (a vytec) that I put in gauge mode to use as a bottom timer. I was cutting tables using Vplanner (I know... but we all did it back then... admit it!) and learning about RD, deep stops and how bad computers were at everything except getting you killed. It was in this period of time that I also picked up the habit of ascending at 3m/min (max) in the shallow zone (after the 50% switch).

The first time I remember ever using a "live" computer during a dive I was diving on a wreck in the North Sea. The dive was to 36m and I was using ean32 and ean50.

I forgot to put the computer in gauge mode before the dive. I noticed it during descent but decided to keep on diving anyway.

The bottom profile was about 36m-50min@ean32 and about 35min of hang time IIRC. I had made quite a few dives like this already so I was pretty sure what to expect. Wreck dives are pretty easy to control in this sense.

Because the computer was turned on it gave me a run time of about ... something like 1:45 min. (it was a while ago but this is probably in the ball park). The run time according to tables was about 90 minutes. I followed my plan and bent the computer but then got curious about what it would have done if I had switched gasses. I had never used the vytec in computer mode during a technical dive up to that point. I bought it for that but then got sucked into the rhetoric online.....

So a few weeks later I was diving on the same wreck. Same protocol, same gasses but this time I put the computer in computer mode and turned on the deco gas. I made a similar profile but this time I changed gasses on the computer and it did, indeed, clear earlier than my "tables".

Then I got to thinking about why....

At first, I thought what you did..... That the computer and the table dive could be compared on equal terms.

But then I remembered the one most important thing about computers.... they give you longer bottom times because they eliminate the rounding errors built into the tables! We all preach that to our students now. Buy a computer for longer bottom times... nobody makes a bucket profile.....

Even though this was a wreck dive I clearly didn't spend 100% of my time at the maximum depth and the computer knew that. The table was based on an erroneous assumption that this would be the case. The deco times were different because (aside from differences in deco model) the computer knew what I had ACTUALLY done... I, however, did not.

Even calculating average depth on the fly you're going to be off. You have a data point every now and then but the computer samples your depth every few seconds and recalculates the entire dive based upon a very accurate average depth. A human could never come close to that. My conclusion, after thinking it all through, is that, like tables, the average depth calculation has enough "slop" in it to have a significant effect on your deco times.

Maybe not enough to get you bent (on every dive) but enough that trusting in-your-head-average-depth-calculations isn't sounding wise to me when you can strap something to your wrist that does it perfectly.

Just a thought.

R..