Deco while cave diving

Got a question for everyone,

I recently got my discretionary apprentice and I'm looking to do lots of cave diving. - Which has got me thinking.... I've always used dive tables in my OW diving and I'm a little confused about how to use them correctly in cave diving. When planning a dive in the open water, using tables is pretty straight forward. You a pick a max depth and a max time and stick to the plan. In the OW, if you're diving a square profile - it's easy to plan ahead of time.

Cave diving is somewhat different I've learned, many sites (not all) have wildy varying depths throughout the dive. When using tables, how do you plan for the depth of the dive if the dive's profile varies from one moment to the next? Do you pick the max depth of the site or is there an averaging system used to find what depth you should be using in your plan? It would seem that picking the max depth of certain sites would give you ridiculous levels of conservatism on dives that only go deep for a few feet and then go shallow again for hundreds of feet. Finally, most confusing to me is deco diving in a cave, how do you plan for exact mixtures of deco gas and the amount you'll need, if you'd don't have an exact depth to work with? Thanks for any aid to my confusion!!

Should I just buy a computer? :D
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Does anybody know of a shorter word for yes?

I use a computer and back up with a bottom timer and tables based on worst case bottom times. It's super conservative if you have to go to the tables but it's safe.

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Originally Posted by andrebasso

Do you pick the max depth of the site? It would seem that picking the max depth of certain sites would give you ridiculous levels of conservatism on dives that only go deep for a few feet and then go shallow again for hundreds of feet.

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The Cave Diving Manual discusses various situations for diving and deco but max depth + time is the general rule when using the Navy tables.

Padi tables are multilevel capable but are incompatable with deco or any extreeme diving. The Bheulman tables may have a multilevel proceedure and is compatable with deco. Various dive table software programes allow you to specify an expected multilevel profile and will give a deco schedule to your specified conservatism.

The easiest solution is to buy a dive computer - but it is not a complete solution as you should have the capabiliy of estimating your deco ahead of time and/or having a backup method in case the computer deco looks weird or the computer fails. Some people use 2 computers so the can check against each other and a convienient backup in case one fails.

Most software programs that provide deco also can predict and track deco gas volumes which can be a useful feature as dives grow more complex - or just longer and deeper. Always a problem if you have a deco plan but not enough gas to accomplish it. ;)

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Originally Posted by Gary

Some people use 2 computers so they can check against each other and a convienient backup in case one fails.

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That is my solution. 2 multi-gas computers.

I am intro and this opinion might be worth the paper it is written on. Ahh..... the disclaimer is now out of the way.

This seems like a situation I shouldn't be diving until I have been specifically trained for it. Becuase we might be allowed to do something in the guidelines doesn't in any way mean that we should do it. Diving outside our training limits is one of those magic rules, yes? My understanding is that this is handled in full cave by the instructor and materials. Is this correct?

I think in this situation, I would call my instructor or go to dinner/lunch with him and ask him what he thinks. I expect to stay with him for all of my cave training. So we talk regularly to montior my progress, my decisions and of course my questions.

I am sure this didn't answer your question, the answer to you question is that I use a vr3, a watch, a cobra is guage mode and a set of navy tables. I monitor my depth and my time so in the event I have to switch to tables I can.

Hans

Have you had a decompression class yet? If not I strongly encourage you to take one, either in conjunction with your full cave class or before it with a local instructor. It'll be worth the money spent.

Good Luck!

All of the above posters are correct.

The path I followed was using a single gas computer and then started cutting tables at max depth using D-planner. I was being terribly punished with deco time but was learning. I learned how different tables worked and watched what others were doing with their various computers. I was doing Ginnie stuff, etc. I still did not 'really' understand deco procedures but was doing my best. The next step was to take an Extended Range or Advanced deco procedures type class IN ADDITION TO reading as much literature I could to better understand what is currently understood about decompression and the models. If you can understand the models, then you can better pick which computer will work for your type of diving.

You'll learn why diving on run time is far more sensible than stop times, etc. particularly when you are REALLY racking up the deco in a multi-level situation.

Finally I bought a multi-gas computer to help me follow a deliberate deco schedule / profile. The computer is a helper, especially for multi-level dives. Knowing the tables, what they mean and what to do with them is your backup and can save your butt.

It took me two years to work through this. I dive one weekend a month.

That being said - I now carry the multi-gas computer as primary and use my single gas computer as a bottom timer. Backup tables are always in my pocket. Yet I'm sure there are still more things to learn about deco procedures.

Just my 2 cents.

Back in the old days when I had a choice of air & US Navy tables, we'd stop at 40' and calculate deco based on max depth and run time to that point.

Multi gas computers are the best thing to happen to cave diving since.... well, the old days.

Here's my two cents:

I'm 47 years old and don't want to get bent. I have no interest in something that will "get you out of the water faster." A reasonably conservative multi-level computer is as fast as I want.

That said, I use two different computers (a Nitek Plus and a Nitek HE), and stay three minutes past when the slower one cleared.

Five minutes at 15' is a lot funner than five hours in a chamber.

And adding some sort of "deep stops" if you don't have a computer that provides them is a big plus. Lots of methods for that.