Deco dive plan sheet

[rongoodman]

And I personally would prefer a set of empirically derived and empirically verified tables to plan my dives with, than software which uses algorithms based mostly on the most modern/advanced decompression theory!

I don't understand what you mean by this. I have several sets of tables, both for Nitrox and Trimix, that I can carry as a last back-up, but they're all derived from standard models, either VPM or Buhlmann. The only difference is that I can tailor the versions cut on the laptop/smartphone to match specific dives, gases, and conservatism settings more precisely. I suppose there might be differences in the software used to derive the tables as opposed to the version running on the computer at home, but how would you know, and why would you think one was more correct than the other?

 

[ucfdiver]

Back when I was doing "modest" deco dives (say, for 200 ffw, plus-or-minus, with 20-25 minute bottom tmes), I would always plan these by hand. I would check my hand solutions by doing my calculations a second, different way. And then check again by comparing my solutions to my buddy's hand-calculated solution.

Whenever I would check my solution against a software-computed solution, I would sometimes observe significant differences. Closer inspection invariably revealed that the software made some assumption here or there that my hand solution did not make. Being a former computer programmer (my first degree and my first job), I *know* there are hidden assumptions coded into computer programs. When I generated my solutions by hand, I was more confident about the presence or absence of hidden assumptions.

I continue to believe there is a great deal of value in planning tech dives by hand.

Ronald

I bet you'd find that most of the difference comes from variables such as air density, water vapor, etc. To my knowledge, vplanner and decoplanner make very few assumptions, but they do have defaults that most people never modify. Frankly I don't think deco is enough of an exact science to justify learning the exact dive site value for every calculation, but some may disagree.

 

[Jax]

I bet you'd find that most of the difference comes from variables such as air density, water vapor, etc. To my knowledge, vplanner and decoplanner make very few assumptions, but they do have defaults that most people never modify. Frankly I don't think deco is enough of an exact science to justify learning the exact dive site value for every calculation, but some may disagree.

If you take a SWAG for the physiology of decompression, create a theory from sample data, apply several iterations and maybe even cross-pollinate several algorithm's calculations to several significant digits,







. . . you still have a SWAG.

 

[rx7diver]

I don't understand what you mean by this. I have several sets of tables, both for Nitrox and Trimix, that I can carry as a last back-up, but they're all derived from standard models, either VPM or Buhlmann. The only difference is that I can tailor the versions cut on the laptop/smartphone to match specific dives, gases, and conservatism settings more precisely. I suppose there might be differences in the software used to derive the tables as opposed to the version running on the computer at home, but how would you know, and why would you think one was more correct than the other?

Rongoodman,

My wish is for a set of tables that are derived using animal and human-subjects testing--empirically-derived tables. It's been a very long time since I've read about tables, but I think I remember learning that the US Navy tables and the DCIEM tables are two examples of empirically derived and/or verified air tables. (Please correct if I've got this wrong.)

Empirically-derived and/or verified tables work, usually, in spite of sophisticated mathematical models (so long as the diver doesn't extrapolate beyond the table development limits).

Developing such tables might seem daunting, but I think it can be done. Might start first by identifying some "standard gases" and then developing tables for these. Maybe such tables already exist for certain tri-mixes (for example), but are proprietary and not generally available.

Ronald

 

[ScubaFeenD]

Rongoodman,

My wish is for a set of tables that are derived using animal and human-subjects testing--empirically-derived tables. It's been a very long time since I've read about tables, but I think I remember learning that the US Navy tables and the DCIEM tables are two examples of empirically derived and/or verified air tables. (Please correct if I've got this wrong.)

Empirically-derived and/or verified tables work, usually, in spite of sophisticated mathematical models (so long as the diver doesn't extrapolate beyond the table development limits).

Developing such tables might seem daunting, but I think it can be done. Might start first by identifying some "standard gases" and then developing tables for these. Maybe such tables already exist for certain tri-mixes (for example), but are proprietary and not generally available.

Ronald

Tables, such as those, would invariably be far more conservative than necessary, because the measurable endpoint would either be full blown DCS or some measurement of bubble formation, which we know can occur in healthy individuals too.

Validation for the models you seem to not trust comes from the countless number of dives executed successfully with the models. And, in all honesty, the models are probably more accurate than tables based on the most fit individuals possible. Now, if we took a real sample of divers (obese body habitus and all) then maybe subjecting a bunch of test subjects to potentially dangerous conditions might be more trustworthy.

 

[rongoodman]

I'm having a mental image of a large pile of exploded goats!

 

[rjack321]

Do people really need this much "backup" for every dive? Multiple tables, multiple algorithms, multiple computers... Even for depth/time combinations they have done before or are close to what they have done before?

Seriously my buddies and I can easily splash to 200ft in the ocean with no more written, validated plan than:
O2? check
EAN50? check
18/45? check
60mins max deco right? check

Plan done, lets rock and roll.

Yes we could write this all down, but rewritting the same answers and contingencies is rather dreary. Ditto consulting various supposedly "authoritative" sources which we don't exactly follow anyway. And yes we can and have covered a lost deco gas (twice IIRC, both were reg issues despite the bottle being full and breathable).

In caves or beyond 200ft in OW we end up increasingly gas limited and have to think about stages or a 3rd deco gas more so there's "more" planning for those. Although its still way more about the gas volumes and much less about "the deco" time. Time is the easy part. I don't know any software doing gas plans which incorporate required horizontal travel in an overheard so we do that by hand or guesstimate 1/3rds, 1/4ths, 1/6ths etc.

 

[Blackwood]

Do

Seriously my buddies and I can easily splash to 200ft in the ocean with no more written, validated plan than:
O2? check
EAN50? check
18/45? check
60mins max deco right? check

Plan done, lets rock and roll.

You're afforded that luxury by diving a select few gas combinations. Some folks would use a different bottom mix for 200 as they would for 180. For them, such abbreviated planning would be a daunting if not impossible exercise.

 

[Cave Diver]

You're afforded that luxury by diving a select few gas combinations. Without standard gases, that would be a daunting if not impossible exercise.

Seems like another good argument for standardized gases, no?

 

[Blackwood]

Seems like another good argument for standardized gases, no?

Really it's a cost/benefit analysis.

Best mix may get you out of the water faster. Standard gases facilitate familiarity with deco obligations.

My arbitrary limit for in water deco is 1 hour, and within that realm, I prefer the standard gas approach. If I were diving profiles where obligations became whole number multiples of 1 hour, and where one-off gas selections may make sizable changes to my deco, I may feel differently.