Multi-level Dives

[Snowbear]

Al Mialkovsky once bubbled...
I really didn't trust the computer at first so I always did the plan with the wheel. Of course if you're in an interesting area it's easy to screw the plan up anyway. So the faithful computer is there to save your butt.

I dive with two computers of the same make and model.

If I plan a dive outside rec limits I use a software planner. My trusty Vyper is usually more conservative than that, so I tend to follow it, but if it ever craps out, I have my plan to finish up with.

If I'm doing a "recreational limits" dive, I always know if my computer crashes, slow ascent with 3 min @ 20, 3 min @10 *should* keep me unbent....

 

[Arnaud]

I'm training for DM and have to learn how to use the Wheel. I went through all my past training without it. None of my instructors liked it and its use is (was?) not mandatory.

Going through the manual, I felt like an auditor at the Florida recount. Pierced arrow, pointing arrows, which one is in, which one is out?

Worse part: even though I'm able to align the Wheel according to the book, I'm one pressure group short in several of the tests. I look at my Wheel and the one pictured in the examples found in the manual, and they don't give the same result. And this is on dry land, in the comfort of my home. I can't imagine what it must be to actually look at this UW with thick gloves and bad light. Could they make those numbers any smaller?

The Wheel may not be a bad idea, but the actual execution is IMHO terrible. It should really be called the Wheels because there's more than one wheel to play with. On top of it, the Wheel, like a computer, can be used to ride the NDL's, with an increased risk for human error.

So, since I never dive a square profile, I use a computer. I never come nowhere near the NDLs and I always know pretty much how much air I have left before looking at my gage. My dive profiles are all very similar, so I never have to reinvent the... wheel.

 

[Iruka]

you CAN bring the wheel along with you during the dive, but it's likely to get sand & grit (from other divers stirring up the bottom if not yourself) between the wheel disks, and as you turn it, you eventually scratch up the surface & make it almost unreadable. Probably not a big problem unless you dive for a living & are using it very often. You can try to shake it around underwater a little, like you're trying to wave down a taxi in a bad neighborhood, and get out most of that grit before doing your calculations. Generally, I'd plan & write down the multilevel profile on my slate & try to avoid actually USING it during the dive.
By the way, Arnaud, you think you have it bad learning to use the wheel? Our DM trainer made us do some sort of "pre-test" before the DM course....just handed me a wheel, which I'd never seen/heard of at that time (about 8 years ago) and expected me to do dive problems with no explanation whatsoever regarding its use!

 

[Knavey]

The one problem in the book that I had problem with was 120 feet for 11 minutes. The show it as a PG of H, but no matter how I look at it, H only touches the line, and I pierces it. I would have called it an I.

I only recently ordered a computer and have not used it yet, so it will be interesting to see how much more it has to offer.

I do think that the wheel is better to use than the tables. It is only slightly more difficult to learn, and the increased ability to plan a multilevel dive gives you more "return" on your training. When I certified, the table was the only option. When my wife went through OW certification, the LDS let me sit in on her class free of charge, and I was able to pick up the wheel.

Its not really that hard to use, you just have to do it often enough to get comfortable with it. I have actually never carried it down on a dive with me...I plan for a couple of PGs around my target, and write them on a slate. If I go outside of that dive plan, my dive is over.

Just my couple of pennies on making the transition to the wheel, and soon to the computer.

 

[Arnaud]

The Wheel is not difficult to use. It took me about 30 min. to read the whole manual and do the exercises. However, I don't find the thing very precise or even practical, especially if you're on EAN>21...

 

[jiveturkey]

While it may not be exact, you're not really going to lose that much time if you go with the more conservative pressure group. Either way your assets are covered for NDLs.

 

[Arnaud]

jiveturkey once bubbled...
While it may not be exact, you're not really going to lose that much time if you go with the more conservative pressure group. Either way your assets are covered for NDLs.

Frankly, I'm just interested in the Wheel because I would like to pass the test and it's an unfortunate requirement. I am interested in preparing my dives better, but I don't think the key is in the Wheel or the RDP...

 

[Phish-phood]

I am curious about these manuals that say go to 15' if your computer bails or is that to do your safety stop and then finish the dive? Mine tells me to abort the dive if the computer bails unless I have a back up computer. Until recently I used the PADI tables and I asked why I couldn't plan the dive on the tables and use that as a back-up if the computer died. Well I swiftly learned after this weeks diving how uncompatible the tables and my computer are! After every dive this week I was well within the limits set by my computer but when I decided to check my tables for comparison I found that I was off the tables on all dives. I was worried about this at first but was advised that it is generally the case for diving with tables versus computers.

Having seen the discrepency between the two I can see why you are recommended to abort the dive if your computer bails. Even though the tables are more conservative than the computer the difference is such that I wouldn't want to take the risk of switching from one to the other during a dive as one miscalculation and you could find yourself in trouble.

 

[diverbrian]

Stopping at fifteen ft. is to allow for off-gassing of an undetermined amount of nitrogen (seeing your computer just went belly up). In fact some manuals and users advise hanging out there for five minutes or as long as your air supply allows.

My training manuals say that you should refrain from diving for 24 hrs as well. This is to start with a "clean slate" on saturated nitrogen before going to a new computer or the tables.

 

[Charlie99]

Phish-phood once bubbled...
I am curious about these manuals that say go to 15' if your computer bails or is that to do your safety stop and then finish the dive? Mine tells me to abort the dive if the computer bails unless I have a back up computer.

"Abort" means to safely end the dive. Popping directly up to the surface isn't a safe abort. Hanging for a while at 15' is better. 1 minute at 40 and 30, then 3 minutes at 20 and 10 is even better.

Until recently I used the PADI tables and I asked why I couldn't plan the dive on the tables and use that as a back-up if the computer died. Well I swiftly learned after this weeks diving how uncompatible the tables and my computer are! After every dive this week I was well within the limits set by my computer but when I decided to check my tables for comparison I found that I was off the tables on all dives.

That's why a lot of people would like to have reasonable ways of planning multilevel dives using the tables.

As you noted, if you just use max depth and total bottom time, you will very easily exceed PADI table limits on a rather conservative dive on a computer.

If on the other hand, you use table 3 and trace your multilevel dive as a series of separate dives with 0 SI between them, you will find the table is less conservative than your computer. This "multilevel on PADI RDP table" can generate dives that are a few minutes past NDL since the RDP track one and only one HT compartment, but this crude planning tool as a validity check of your computer sure beats doing nothing at all.