average depth and tables?

[SailNaked]

can you use the average depth from your computer to log dives with tables.

Lets not get into why I want to do this because it is not really relavant.

Would you consider this safe enough to use to make a subsequent table dive?

 

[SkimFisher]

Interesting question. I'm hope it gets some good responses.

 

[Blackwood]

Assuming you understand your inert gas loading and are running your ascents accordingly, it's a fine process. I do so routinely.

Depth averaging isn't voodoo, but you have to do it intelligently. Don't necessarily address 50 feet for 10 minutes followed by 100 feet for 10 minutes the same as you would 100 feet for 10 minutes followed by 50 feet for 10 minutes even though they have the same average.

 

[Rainer]

Sort of. It matters how the average was generated, though (e.g. was the dive done shallow->deep or deep->shallow). It's more complicated than just substituting the average depth your computer gives you for a max depth on a table.

You can learn more about this:

DIR-diver.com - Average depth for deco?

Ratio Deco - Unified Team Diving

 

[Walter]

Of course you can do it. Keep in mind, doing so violates a basic concept of working with tables and they are no longer valid. You increase your risk of DCS if you do so. I would recommend against it. I would rather use tables for multilevel diving, although that is also not recommended.

 

[Blackwood]

You increase your risk of DCS if you do so.

Source?

 

[atedeschi]

I have been using average depth for almost two years now. I just take from the bottom timer and use those tables. Most of my profiles are cave type therefore same in and out depths or saw tooth ones on wrecks where I'm up in down going inside down to say enigne room then back up to a deck above then down in to a cargo hold.
My max depths so far doing this have only been to 210' and beening doing it on closed and open circuit.
Buddy of mine have been doing this for years with max depths over 300'.

I recommend the bt and/ or a tec 2g they are the only ones on the market that do average depth on the fly.

 

[TSandM]

Remember that, when tables are generated, they undergo empirical testing (volunteer dives) to make sure that the incidence of DCS will be no more than the desired number (which is never zero!) Those tests are done using the tables as you were taught to use them . . . which means, using the maximum depth for the dive to determine the pressure group and limitations for the next dive. To my knowledge, NO conventional tables were designed for the use of average depth (which, of course, makes your dive look much shallower to the tables than the use of maximum depth). I don't believe even the GUE tables were designed that way (and I don't know how much, if any, testing has been done on the GUE tables).

So, if you plan your dives, and especially repetitive dives, using average depth instead of maximum depth, you are violating one of the assumptions of the model, and the information it gives you is no longer valid under that model. In other words, you can do this, but you're on your own as far as risk goes, because the folks who wrote the table didn't intend it to be used that way, and the predicted DCS risk won't be as low as they intended it to be.

 

[atedeschi]

But to be fair the tables assume square profiles when you may not be doing a square profile. If you run some multi level profiles in your dive planner and figure what your average depth is before ascent they are about the same.

 

[Herk_Man]

So, just so I understand the question, we're trying to determine if it would be ok, for instance, to take a dive that was 20 minutes at 100' and 20 minutes at 50' and base our next dive as if it were a 40 minute dive to 75'?

Since the pressure effects of sea water are linear with depth (not sure if the resultant effects of nitrogen loading are correspondingly linear though) then shouldn't this averaging be valid?

I'm not that experienced so consider all of this pretty much an addition to the OP's question.