Average Depth Diving?

[RTodd]

You know, the first image that came into my mind was of a guy playing Russian roulette and saying, "well the revolver feels a little heavier on the right hand side so I'll spin the chamber again". One day his feeling is going to let him down.

Just follow your computer chief and ignore what the crazy man is saying.

Althought I don't know UP, I think that we are fairly far apart on the deco risk spectrum. (His "typical" dive is more conservative than my "typical" dive.) However, we both understand what the other is doing. And, other than the time spent on the shallow side of the dive, based on his posts I suspect our diving practices are very similar. Now, I wonder why that is? Maybe you should try to spend some time figuring that part out. Not needing to rely on a computer or tables doesn't mean someone doesn't know what they are doing. It means you don't understand what they are doing. Big difference.

 

[RTodd]

Another thing is that if you're doing this you should be able to recognize the symptoms of subclinical DCS and use that as feedback that you're doing something wrong. I've followed my computer on a few air dives and nearly fallen asleep on the drive back home (and afternoon diving -- not just due to ***-crack-of-dawn diving...). And this was on a fairly conservative profile that did go deepish (80 fsw) but was not a reverse profile and had a lot of 40 fsw time and came nowhere near the NDL limits... The computer was also happy with my stop...

I'm starting to really distrust computers for NDL diving, I think they're right up there with the "bend and mend" Navy Tables for deco diving, although the "mend" part isn't a long 10 ft hang, but its the nap you take when you get home...

Yeah, but once you have been whacked a few times your shoulder starts to hurt when you are filling your tanks with helium and it gets confusing all over again.

 

[Tavi]

.........................[snip]................................................. Not needing to rely on a computer or tables doesn't mean someone doesn't know what they are doing. It means you don't understand what they are doing. Big difference.

:rofl:

 

[Walter]

Not that assumption.

 

[miketsp]

lol... talk about a misplaced metaphor
..snip..

And I thought I was expressing an analogy and not a metaphor. Shucks.

..snip..
that's not what Pug said at all. and by the way, if you are tired, dehydrated,
ill, haven't gotten good sleep, etc., and don't take that into account and dive
more conservative than usual, you *might* just get bent whether you are
following tables or a computer. i'm sure you've heard of these aspects of DCS.
so how you "feel" *is* extremely important.

How do you quantify the weighting factors to dive more conservatively?
Come to that, how do you define a conservative factor in %?

One of my computers is a Beuchat Maestro Pro (made by Cochrane) and among the settings you can choose 10% or 20% more conservative. But I've never managed to figure out the real effect of choosing these percentages in terms of bottom time.
It certainly isn't linear. Which brings us back to the exponential characteristic of gas transfer.

 

[mempilot]

Plan a multilevel dive instead so that you can stay a little closer to your plan. The multilevel plan will credit you for time spent shallower. If you have a cx, then it is already doing this for you.

I'm no expert in deco theory, but long shallow dives affect certain tissue compartments differently than short deep dives. I don't think it is as easy as blending the depths. Not all tissue compartments absorb and offgass at the same rates.

 

[RTodd]

Plan a multilevel dive instead so that you can stay a little closer to your plan. The multilevel plan will credit you for time spent shallower. If you have a cx, then it is already doing this for you.

I'm no expert in deco theory, but long shallow dives affect certain tissue compartments differently than short deep dives. I don't think it is as easy as blending the depths. Not all tissue compartments absorb and offgass at the same rates.

I think you are at least shooting at the correct side of the barn, but it isn't entirely clear. Depth averaging and multi-level dives are not exlcusive. Depth averaging would be used for each level of a multi-level dive. However, for recreational depth dives, you really only need it for the deepest level.

 

[mempilot]

for recreational depth dives, you really only need it for the deepest level.

True. But I figured they wanted credit for the shallow portion of the dive. To plan a dive to 60' because you plan on hitting 80 for half the time and 40 for the half the time doesn't really make much sense. Planning a dive to 80' and only spending half the time there and the other half at 40 isn't efficient planning. Planning a multilevel dive at 80 and 40 would make sense and be efficient. It would also allow one to know their N2 loading more precisely for repetitive dives. Balancing the depths for use in the charts is not supported.

 

[lamont]

I'm no expert in deco theory, but long shallow dives affect certain tissue compartments differently than short deep dives. I don't think it is as easy as blending the depths. Not all tissue compartments absorb and offgass at the same rates.

If you're doing multilevel diving with a non-reverse profile, as you spend time shallower you'll start to offgas in the fast compartments that got hammered when you were deep and they stop being the controlling compartments and you can start to ignore those. Your controlling compartment will become a slower one, but it'll be a bit faster than the compartment which would normally control that depth, and your time spent deep will have had a higher delta-P into that compartment so it will have ongassed more N2 than a dive at that depth with the same runtime to that point. I've found a pretty good correlation by taking time spent at 100 fsw, doubling it and adding it to time spent at around 50/60 fsw and using that as runtime for a dive to 60 fsw on the PADI charts to get pressure group and surface interval time and comparing it to what my computer was telling me for surface intervals and repetitive diving.

I'm just guesstimating exponentials in my head, though, and don't recommend actually using that as some kind of rule to plan dives that way. Just pointing out that what the computer is doing isn't voodoo at all...

 

[To_Narced]

We average our depth all the time, but we know how to do it. Becareful what you say here because there are people who have a lot more experience than you and who are doing successfully the things that you say will get someone bent.

Hey I am interested in how the average depth diving you do works. Can you go into more detail i find it very interesting. Thaniks.