tables and multi-level dives

[pengwe]

Apparently there is a PADI wheel to help you plan multi-level dives. I don't think I've seen one (maybe they waved it at us in my course, and I missed it). Could you just use tables though?

Say you go to 25m for 20 min. That would put you in pressure group K. Then you go up to 15m. Table 3 gives you a NDL of 38 min, so you could happily spend 25 minutes there. Would the fact that you had no actual SI make any difference?

I was going to say that you happily spend 30 min at 15m in the above situation. Then I noticed that would give you a TBT of 64min (at 15m), which would put you in the grey. Do people who dive tables try to avoid the grey boxes on the table? Or is it common to go to the limit and do your safety stop?

 

[MoonWrasse]

You can buy the wheel for about $40-50 or so on Ebay or many dive shops.

If you want to dive safer, avoid diving the "grey" or with a dive computer when it indicates single digits of NDL.

All of these are just mathamatical models, you need to consider the other factors to keep you safe. People have gotten bent without exceeding their tables/wheel/computer.

 

[pir8]

You cannot use the tables for multilevel diving! DO NOT TRY! The wheel is constructed similar to a slide rule whereas the tables are straight charts and do not work for multi level dives. Wheel would be taught in the Multi level specialty. But I would just get a computer instead.

 

[riguerin]

As I recall, the Wheel may have been mentioned in lower level PADI curriculums, but wasn't formally taught until the Dive Master level.

 

[Fastmarc]

Is it that it is more complicated to understand that it isn't taught in OW?
From my experience most dives turn out to be multi-level dives anyway, it would be a real asset to have that knowlege.

 

[MoonWrasse]

You can take the PADI multi-level specialty course, or as one of the 5 dives in AOW.

There is a bit more to know than just how to use the wheel.

OW is just a minimal (but not the most minimal of course) to get you into the water.

 

[bradshsi]

You cannot use the tables for multilevel diving! DO NOT TRY! The wheel is constructed similar to a slide rule whereas the tables are straight charts and do not work for multi level dives. Wheel would be taught in the Multi level specialty. But I would just get a computer instead.

I'd disagree with that. You can use the tables for multi level dives by treating each section as a separate dive with a 0 minute surface interval. Computers that are based on the PADI RDP also do extrapolation between table values, so I don't see anything wrong with a manual extrapolation (and a very simple one at that). Rocket science it isn't.

However one important caveat. Using this method it is possible to exceed the wheel ML limits, you should therefore check to see you don't exceed them. In addition you should follow the wheel rules for allowable depth combinations

The following threads are useful:

http://www.scubaboard.com/showthread.php?t=115912
http://www.scubaboard.com/showthread.php?t=129234

Charlie99's flat wheel is also a useful tool (it's attached in one of the above threads)

Personally I try to avoid hitting the max limits on the table, but that's just me. Your risk acceptance and mileage may vary.

 

[TSandM]

I totally empathize with your question, and in fact, I asked something very similar myself shortly after I found SB. The answer is not trivial. You need to read about decompression theory and understand where the tables came from, and where the computers are coming from, in order to decide how YOU want to order such dives. YOu will not get a recipe from anybody on line.

 

[riguerin]

Is it that it is more complicated to understand that it isn't taught in OW?
From my experience most dives turn out to be multi-level dives anyway, it would be a real asset to have that knowlege.

No it is not. It's basically an analog computing device similar to a slide rule. It's taught at the PADI DM level because this is where dive planning and management start to become emphasized.

You can take the PADI multi-level specialty course, or as one of the 5 dives in AOW.

There is a bit more to know than just how to use the wheel.

OW is just a minimal (but not the most minimal of course) to get you into the water.

I never realized that this specialty existed ... or didn't remember. It's been a while. Thanks for the info.