Multi level dive Question

[JamesH]

Okay I have the VT3 computer and Ocean log. I dive the old mine pits up here in Minnesota. Very multi depth diving. After I down load my dive from my computer into Ocean log. I'll get a max depth and an average depth. Which do I use for my pressure group?

Thanks
Jim

 

[philmayer]

I've never calculated pressure groups in multi-level. What did they teach you in class? For regular diving, you use maximum depth. Regular DSAT tables don't give you credit for multi-level diving.

Most people who use dive computers don't bother calculating their pressure groups any more.

 

[Dan Watkins]

Out of curiosity, what are you trying to figure out a pressure group for? The computer more accurately tracks your nitrogen loading (especially in a multilevel dive) so that you do not have to use your max depth with a table.

 

[yyidus]

Okay I have the VT3 computer and Ocean log. I dive the old mine pits up here in Minnesota. Very multi depth diving. After I down load my dive from my computer into Ocean log. I'll get a max depth and an average depth. Which do I use for my pressure group?

Thanks
Jim

You're gonna end up freaking out, but the correct answer to your question is to use 'max depth'. If you're using basic RDP tables, you compute the entire dive time until the safety stop at the deepest level you reached in the dive (even if you only spent one second there). For this reason, the dive tables are not half as nice as a computer that tracks what you're doing.

Often you will find that using the RDP tables, you must now call 911 and get transferred to a recompression chamber. So laugh a bit and keep using the computer...

 

[JamesH]

Well for multi-level your supposed to use the wheel. As far as what they told me in class. Didn't really go over it. That may be for advanced open water. I like the computer. I think it's great. I like to keep a written log cause I was told that if you go on a dive on a boat they want to see your log. See what kind of diving you've done. What kind of experience you have. I'm not real worried about it, just curious. Cause your right. I should be dead a few times over. Oh-well, thanks for the input.

Jim

 

[philmayer]

You can still record the dive in your log. You just don't need to worry about computing your pressure groups. Dive shops are going to want to see the max depths, dive times, and conditions you've been diving in.

 

[visibilityunlimited]

When you log your dives definitely notate the depth and time but if there is a comments section mark down that it was a computer assisted dive.
It is not only the dive stores and or dive boat personnel that want to see it. If something did happen emergency personnel would also like to see it. Not only will it let them know your past dive history but they will also know that you did dive with a computer which will give them the most concise information about you dive profiles. This information is also more immediate because you would probably not have logged the problem dive(s) as of yet.

 

[Dan Watkins]

Jim, definately keep a log. You just don't need to record pressure groups if you aren't using tables.

 

[Wayan]

Actually of you are really interested you can have a look at the Graver Method. This was used before computers became common place. Of course it is all theoretical and requires good knowledge of the tables.

This would not replace the theoretical models now used dive computers but is an interesting piece of history of man trying to spend as long as possible underwater

 

[TSandM]

James, I completely understand this question, and the first thing I want to say is kudos to you for keeping track of what you were taught, and trying to analyze your dives.

It isn't possible.

What your computer basically does, is run the calculations that determine the tables, on a continuous basis, using the data from your actual dive. The way the tables are constructed is to make them useful for what we call square profile dives. Those are the dives where you jump off the dive boat and go down to the wreck and stay there for a given amount of time, and then come up. You use maximum depth to determine your no-deco limits, and then go on to all the calculations you were taught in class.

But real life dives rarely look like that, unless you live somewhere where the diving is off charter boats and onto wrecks. If you shore dive, you're going to start shallow, work gradually deeper, and then reverse the profile. If you dive off charter boats onto native structure, you're going to do a descent onto some kind of topography, which may or may not fit a square profile chart.

Your computer tracks where you've been, and what the nitrogen loading at that depth for that time is, according to the model it uses. As with most computers, it has far more capacity to perform iterative mathematics than you do. Therefore, it can offer you a great deal more flexibility in your profile than the tables do. The problem is that, if you follow your computer, you can't log the dives in any sensible way in your book. Worse, you probably can't assess what the computer is telling you, to know whether it's functioning properly or not. It's VERY frustrating.

What I would recommend, at an early stage of diving, is to find out what you can about the dive you are about to do -- In other words, find out what the maximum proposed depth is, and what the contour is. Look at the tables and see what they say about that maximum depth; if the contour is roughly square, your computer should come close to what the tables say. If the profile is very different (eg. a quick descent to max depth, and then a fairly linear ascent along the topograhy) you may be given a great deal more bottom time, but you should understand WHY.

BTW, I asked this same question the year I learned to dive: http://www.scubaboard.com/forums/basic-scuba-discussions/115693-dive-planning-terrain-diving.html