Multi Level Diving?

Could someone please explain to me how multi level diving works to increase your bottome time?

With a square profile, that is you plan your entire dive at the MAXIMUM depth, there is no allowance for time spent at a shallower depth.

With multi-level dive you plan the first part of your dive for you maximum depth. The subsequent levels are planned at shallower and shallower depths.

What this does is effectively reduce the nitrogen loading that one would experience at the max depth.

For example, let us say that you want to dive on a wreck that has a 85' max depth. The deck is at 70' and the pilot house is at 50'.

You could dive the bottom and check out the hull for say, 10minutes.
Then you could spend 15 minutes at the deck at 70'.
You would finish up your dive in the pilot house for 20 minutes.

This gives you a total dive time of 45 minutes.

Had you planned the dive based on your max depth of 85', your dive time would have been limited to a maximum of 27 minutes.

I see. Then to do this I would use the dive planner on my dive computer to pre plan the dive and then just follow what my dive computer says...right?

Also, depending on NDL depths and times, you may actually be offgassing on the second, shallower part of your dive. Dive computers, and to a lesser extent, PADI's wheel take this into account.

But remember that, with a computer, you are intersecting a fine line (your computer tracked dive profile) through a thick gray area (the no decompression limits). Don't use that as an excuse to right dive down to the NDL if you don't understand decompression diving.

Most dive computers, if not all (but don't quote me on this), don't allow for planning a multi-level dive.

A multi-level dive can be planned with the RDP (recreational dive planner), but it is MUCH EASIER ACCOMPLISHED by using "The Wheel".

I am a little confused then and would like to hear from more experienced divers on their thoughts. :06:

I was taught that all dives are to be planned based on the PADI tables (we did not do the wheel) so that it falls within the NDLs.

Given that most divers do not typically drop to their planned bottom and remain at that depth until their planned direct (slow/planned) ascent and safety stop does this mean that you use a computer just for dive information? I apologize as I do not have my tables here at work but let's assume you plan your dive for a certain depth and you know that you only have so many minutes. Once you reach the planned ascent point of the dive you look at your computer and due to multi-level diving it shows that you have more time available given your air, depth, time, etc. Do divers continue the dive based on the computer or stick to the plan and ascend?

I do understand the premise that the tables and the theory are instructed to be conservative and cautious rather than recklessly liberal but what do we do about the gap between dive planning based on tables that assume you are at maximum depth for the whole time and computers that are constantly making calculations throughout the dive?

I would hazard a guess that most divers who use computers don't plan their dives in the classical sense of the meaning.

I think most simply put in their max depth and jump into the water.

I'll probably get the business end of a flame thrower for this statement, but from what I've observed aboard dive boats that's what generally happens.

Plan your dive, dive your plan, and all that.

Lots of people will continue the dive based on the computer. Not everyone agrees with that. Some dive buddies will even be resentful when you call a dive and their computers show they have NDL time left. There is no easy answer.

In your case since you use PADI tables I would plan the dive on the PADI wheel (there is also a flat version but I couldn't find the link). I use different tables but apply the same principles. Nitrox makes a tremendous difference for the NDL times, esp. on repetitive dives, in my case I find that makes a bigger difference than anything. YMMV.

Ok. I understand about useing the dive tables and planning your multi level dive that way, but I thought that was one of the big advantages of having a dive computer is that it does all that for you. I know some of the dive shops in Cozumel say they use nitrox and multi level dives with a dive computer to increase the bottome time to around an hour or more. I am trying to figure out how to use my dive computer to do that. Am I understanding correctly that it is not recommended?

You won't find a pat answer. Most people, here and on dive boats, will tell you just to follow the computer. Some people (probably a minority, to be honest) disagree with that thinking. UP will tell you not to use the computer at all, except in gauge mode and as a tool for downloading your dive profile.

My advice if you *are* going to "fly" your computer, at least learn how it works and follow what it tells you. I dove in FLL last month and couldn't believe all the beeping computers (NDL, ascent rates, etc.). The people flying their computers had no idea why.