Multi-level repetitive dives

[Brett1971]

My dive group is going to Bonaire in 2 weeks. We're planning on diving as much as possible while there but also want to make sure that we remain safe.

We all have computers but I'd like to use this opportunity to double check my comp against the tables, and because I'm a total geek. I only went through the 'whiz bang' 5 minutes of PADI table instruction when I took the class but I do remember the basics. My question is; how do I work the tables for 4 or more dives per day? We're thinking about early morning, midday and night diving while there.

We only worked through the initial dive and 2 repetitive in class. Is it just a matter of figuring subsequent dives like the 3rd? e.g. Find pressure group after first dive, use it to calc for the second dive, use the second PG to calc for the third dive, use the third to calc for the fouth dive, etc. ad nauseum?

Any suggestions?

 

[Pearldiver07]

Yes - you calculate the subsequent dives just like figuring dive 2, then dive 3, etc.

If you have a 6-hour surface interval, then start as dive 1 again.

 

[rstofer]

Just like that... Around and around the table we go!

However, your question asks about multi-level diving and tables won't get you there without some undocumented and untested heuristics (wild a$$ guessing). But PADI does have The Wheel for calculating multi-level dives. It's a lot harder to use and more error prone. Then there is the PADI eRDP-ML, a calculator for evaluating multi-level dives. I say evaluating because I don't see how you you can know in advance what your multi-level profile will look like. I suppose you could use The Wheel while underwater but the calculator is barely splash proof. Keeping track of all your depths and times is going to be a PITA.

Using tables and treating each dive as a square profile is going to seriously limit your bottom time.

About the only satisfactory way to deal with multi-level diving is in real time and that requires a computer.

Richard

 

[vjanelle]

They stopped teaching the wheel in 2008, afaik.

 

[scubadada]

???This is an advanced scuba discussion??? Sorry, but this is somewhat frightening. Compared to the computer calculations, the table calculations will be very inaccurate for the multilevel profiles but wiil be a very conservative estimate of NDL. Isn't this something that should be reasonably clear following OWD certification?

Good diving, Craig

 

[rstofer]

They stopped teaching the wheel in 2008, afaik.

Yes but there are still Wheels around to purchase and they come with an instruction book.

I would just use the computer for multi-level diving.

Richard

 

[NCadiver]

Brett1971 if you are using you computer dive most likely you will be at the limits or over the limits for the table. Let say you start you dive at 80 ft and you are their for 15min then you go to 40ft for 30 mins what letter are you? Tables are meant for a square profile not multilevel diving. PS I hate the Padi wheel to do they still have a warehouse full of those things.

 

[Graeme Tolton]

If you are concerned with redundancy, get a second computer....

 

[DA Aquamaster]

Brett1971 if you are using you computer dive most likely you will be at the limits or over the limits for the table. Let say you start you dive at 80 ft and you are their for 15min then you go to 40ft for 30 mins what letter are you? Tables are meant for a square profile not multilevel diving. PS I hate the Padi wheel to do they still have a warehouse full of those things.

I have not played with the Wheel for a year or two but it only took a minute to refresh my memory and with the multilevel profile you specify, you are group G after the 80' for 15 min segment and are group P at the end of the dive after the 40' for 30 minute segment. You are actually right on the line for group O, but following the rule where you use the first PG arrow that pireces the line, you get a slightly more conservative group P.

Which is interesting, because if you run the same dive on the regular RDP you are the same group G after the 80' for 15 min segment and if you plan a repetetive 40' for 30 minute dive using 0 mminutes for an SI, you have 34 minutes of RNT at 40', which brings you to 64 minutes TBT which is the extreme limit to still be group O on the RDP. Or in other words, you are right on the same line between O and P that you get with the Wheel. So in effect, if you are at the maximum time in a box, step up to the next greater time to accomplish the same thing as pirecing a line on the wheel rather than being on the line.

The short story is that the Wheel, despite the whining and lamentations of legions of probably incompetent DM candidates, is really easy to use.

However, if you follow the same basic rules regarding minimum differences in depths and use the shorter ML NDLs from the Wheel on the RDP you would get the same answers off the RDP by planning a 2 or 3 depth mulitlevel dive as 2 or 3 dives with 0 minute surface intervals between dives.

This is not a surprise as the Wheel is the same basic table as the RDP, just adapted to shorter ML limits and packaged in a circular slide rule format. It isn't rocket science and the Wheel makes a great back up to a computer provided you have fairly significant steps in your multilevel profile as listed below.

Deepest depth / next deepest depth no deeper than:
130-120ft / 80 ft
110-95ft / 70 ft
90-80 ft / 60 ft
75-65 ft / 50 ft
60-50 ft / 40 ft

 

[merxlin]

Padi now makes a multi level electronic dive planner eRDPml. Electronic version of the wheel.