The flat wheel

[ChillyWaters]

I have found only limited discussions on the differences of the PADI Wheel vs the PADI Tables for multilevel diving. I'm a new diver (20 dives) without the need of a computer. We mainly do single dives at known locations.

I find reading the PADI Tables extremely simple. I can't figure out what all the fuss is about the "math." Not much math really needed.

Anyways, I found the link to the "flat wheel," the conversion of the Wheel to a table, along with the associated rules for multilevel diving. http://www.scubaboard.com/gallery/showphoto.php/photo/3142

Can anybody comment on using the "flat wheel" as a diving tool? I've heard of people using the Tables for multilevel diving, by simply using a 0minute surface interval. While I realize this isn't exactly safe, does the safety as shown in the "flat wheel" enough? Is the "flat wheel" really equivalent to using the Wheel?

- ChillyWaters

 

[Mako Mark]

by simply using a 0minute surface interval. While I realize this isn't exactly safe,

Using a zero minute surface interval would work if you actually surface between the levels, which effectively make them different dives. If you dont surface, you have an error in your calculations. Although this error may be a fairly small margin, getting DCS by a fairly small margin hurts just as much as getting it by a lot.

If you aproximate you NDL calculations, you can be aproximately sure that you aproximately may or may not get dcs.

I have seen the flat wheel before, but havent used it to plan any dives with.

safe diving dude,

 

[Charlie99]

The "Flat Wheel" is just the PADI wheel sliced apart and put down in table form. The PADI RDP is also the same as the wheel, except for lack of multilevel instructions and the additional "ML" or multi-level NDL limits.

To generate the 5' depth rows, and also because I was too lazy to type in all the numbers, I generated the Flat Wheel numbers with a couple of simple equations in Excel. To do that I had to reverse engineer the PADI RDP. My assumptions as to 1.6fsw H2O pressure and the 3% steps of the 60 minute HT M values for the PGs seem to be correct since my entries are within +/-1 minute of what is on the RDP.

I ran through all of the examples in the PADI Wheel instruction book and got the same answers except for a couple cases where, because the example was right on the edge between two pressure groups, my Flat Wheel gave one answer and the PADI Wheel came up with an answer that differed by 1 pressure group.

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While using the "zero minute SI" method with the PADI RDP gives you a general idea of the agressiveness of a planned dive profile, you can indeed exceed the PADI/DSAT model limit using this method. That is why PADI/DSAT introduced the "ML" limits that you see on the wheel. You can violate the limits for the faster tissues if you plan a multilevel dive using the zero minute SI method on the PADI RDP (or the flat wheel) without the additional limits of the wheel.

To properly use the PADI RDP you must
1. Follow all of the dive profile rules of the wheel manual (things like what is an acceptable 2nd and 3rd depths, based on the previous depths.)
2. Follow the ML limits, and the mandatory 3 min SS if you come within 3 PGs of any ML at any level.

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As I cautioned in the text below the Flat Wheel table: "Don't use it unless you understand it. "

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On a related note, if you look at the PADI RDP more closely, you will see that the various tables are redundant. Except for a couple entries that differ by 1 minute, Table 3, the repetitive dive timetable is just a repeat of table 1 (The 2 entries in each spot in Table 3 always sum to the NDL for that depth).

The incredibly hard to read SI Credit Table, Table 2 can really just be replaced by the single row of numbers in the Z row, provided that you can add 2 numbers together. That's what that single "SI" row on my Flat wheel is. I figured if you couldn't figure out how to use that row to calculate SI ending PG, then you shouldn't be using the flat wheel.

Charlie Allen

 

[ChillyWaters]

As I cautioned in the text below the Flat Wheel table: "Don't use it unless you understand it. "

Thanks for the reply. I find the tables (including the "flat wheel") very intuitive, and can't understand the big deal about the Wheel. Perhaps I haven't given it enough of a chance, but at the cost of it, I doubt I will. You might as well put that money towards a computer.

Though, I don't like blindly trusting a computer. I like to know the theories -- the scientist in me. I guess adding a computer would provide additional safety, if you used it as a secondary tool, rather than the primary.

I'm considering purchasing a book on dive physiology for some reading. Time to check out the FAQ.

- ChillyWaters

 

[DepartureDiver]

You're right, there should be no big deal with the wheel. If you know the concepts, the table can generate the exact same results.

 

[Diver0001]

The "Flat Wheel" is just the PADI wheel sliced apart and put down in table form. The PADI RDP is also the same as the wheel, except for lack of multilevel instructions and the additional "ML" or multi-level NDL limits.

To generate the 5' depth rows, and also because I was too lazy to type in all the numbers, I generated the Flat Wheel numbers with a couple of simple equations in Excel. To do that I had to reverse engineer the PADI RDP. My assumptions as to 1.6fsw H2O pressure and the 3% steps of the 60 minute HT M values for the PGs seem to be correct since my entries are within +/-1 minute of what is on the RDP.

I ran through all of the examples in the PADI Wheel instruction book and got the same answers except for a couple cases where, because the example was right on the edge between two pressure groups, my Flat Wheel gave one answer and the PADI Wheel came up with an answer that differed by 1 pressure group.

--------------------------------

While using the "zero minute SI" method with the PADI RDP gives you a general idea of the agressiveness of a planned dive profile, you can indeed exceed the PADI/DSAT model limit using this method. That is why PADI/DSAT introduced the "ML" limits that you see on the wheel. You can violate the limits for the faster tissues if you plan a multilevel dive using the zero minute SI method on the PADI RDP (or the flat wheel) without the additional limits of the wheel.

To properly use the PADI RDP you must
1. Follow all of the dive profile rules of the wheel manual (things like what is an acceptable 2nd and 3rd depths, based on the previous depths.)
2. Follow the ML limits, and the mandatory 3 min SS if you come within 3 PGs of any ML at any level.

--------------------

As I cautioned in the text below the Flat Wheel table: "Don't use it unless you understand it. "

------------------

On a related note, if you look at the PADI RDP more closely, you will see that the various tables are redundant. Except for a couple entries that differ by 1 minute, Table 3, the repetitive dive timetable is just a repeat of table 1 (The 2 entries in each spot in Table 3 always sum to the NDL for that depth).

The incredibly hard to read SI Credit Table, Table 2 can really just be replaced by the single row of numbers in the Z row, provided that you can add 2 numbers together. That's what that single "SI" row on my Flat wheel is. I figured if you couldn't figure out how to use that row to calculate SI ending PG, then you shouldn't be using the flat wheel.

Charlie Allen

`

That's an awfully clever bit of work. Did you make a metric version?

R..

 

[Charlie99]

`
Did you make a metric version?

The easiest way it to simply use table 3 of the metric RDP, after copying from the metric wheel the ML values and the restrictions on allowable depths for the different levels.

I hadn't bothered dong a metric RDP or wheel until today. The attached files are similar to the metric RDP. For comparision, I've also attached excel version of the flat wheel.

The NDLs are manually entered --- the calculations are all based on the 60 minute halftime compartment. The NDLs at other than 10.5 and 12 meters are determined by faster compartments. The first row reads 10.7m, because it turns out that on the PADI metric RDP they actually calculated for 10.7m for the first row even though it's labeled 10.5. It had me confused for a while

To get the equivalent of the wheel, you would have to add the rows corresponding to the extra depths available on the wheel, whatever they are, and add the extra info such as ML values and what the profile depth rules are for the metric version. Just copy one of the cells to get the the entries for how long to get to a particular PG.

There is also a cell for changing from air to nitrox to make the equivalent of the metric nitrox RDPs. Again, the NDL cell will have to be entered manually.

All the values I checked were +/-1minute from RDP, but I haven't done an exhaustive check of every cell. Use at your own risk.

Charlie

 

[Diver0001]

The easiest way it to simply use table 3 of the metric RDP, after copying from the metric wheel the ML values and the restrictions on allowable depths for the different levels.
Charlie

You're the man. Thanks.

R..