Is SSI more conservative/The wheel

[oceandjinn]

After doing some research I have come to the conclusion that the SSI tables are more conservative.Am I correct in my assumption? Second point or rather question.Where is it possible to find more info about the PADI WHEEL or to purchase one in metric(and is it woth getting as oppossed to a decent dive computer).I am living in Japan and getting any of the resources(waterproof SSI,PADI RDP or the wheel) is close to impossible.
Thanks in advance

 

[amascuba]

SSI's tables are based on the U.S. Navy Tables with Doppler and are a 12 hour table. They have been changed slightly from the navy tables to make them more conservative, but are a good table. Learn your tables and you can use them to do multi-level dives with out any issue.

The PADI tables are a 6 hour table. Upon inspection they look pretty similar to the SSI tables, but the PADI tables have more resitual nitrogen groups for shorter surface intervals.

So to answer your question, yes the SSI tables are more conservative, but that doesn't make them bad tables.

The PADI wheel, while a good concept, is a piece of poo poo. The implementation of it is flawed. If you compare your dive profiles to the PADI tables and the PADI wheel you will most likely get conflicting information. This is because the PADI wheel is somewhat hard to read and operate precicely because of the small lines, numbers, letters, and arrows. Again learn how to operate the tables correctly and efficiently and you can get the same information out of your tables as you can the wheel, even for multi-level dives.

 

[oceandjinn]

Thanks I appreciate the update. I have been using SSI but did my Advanced thru PADI and in the lit. they mention the wheel for multi level dives so that is why I asked.The second part is getting the watreproof Tables in metric. Any Ideas?

 

[Doc Intrepid]

..."is it worth getting as opposed to a decent dive computer"?

No. For recreational diving you will be better served by a decent dive computer.

The reason is precision.

When diving with a computer, the computer 'samples' data (depth, elapsed time, temperature, etc.) according to a periodic interval set by the diver. The computer takes the data and enters it into an algorithm which "quantifies" gas absorption in various tissue groups.

Therefore the computer offers, all else being equal, a reasonably accurate record of both data readings as well as decompression information derived from them.

A Wheel involves estimates - both during the pre-dive planning as well as on the post-dive analysis.

(In fact, any tables - whether PADI, SSI, NAUI, etc. - all involve estimates of both depth and elapsed time during multi-level diving. This is why tables can be problematic if your dives are not square profile dives.)

The Wheel is intended to allow the planning and analysis of "multi-level" diving, however, in terms of measuring how long you were at depth X and then afterwards at depth Y, obviously the Wheel relies on your estimates. Your estimates may be close, but even under the best of circumstances your estimates will not be as accurate as the data sampling performed by the computer. Then if something happens to distract your concentration, your estimates may also be wildly off base.

Considering that the computer also tracks Surface Interval duration, so that multi-level diving is performed with a cumulatively more accurate measurement of total residual nitrogen (which can also be over several days in a row, not merely several dives in one day), and you can see clearly that for most recreational diving situations a decent dive computer will be a much safer alternative than a Wheel.

FWIW. YMMV.

 

[herman]

I have the opposite opinion of the wheel. It's a little different to learn to use but once you learn it, it's easier than tables for me. The wheel AND the PADI tables are based on the same research-RDP. You can interchange the data between the wheel and the PADI table (this is not true for other tables). The wheel if used properly gives you much more accurate information than any table can. There is no need to round up or down times like you must do when using tables and the wheel has smaller depth graduations. You can do multilevel dive planning on tables but I find it easier on the wheel and I am unaware of any agency that teachs divers how to do it. While the navy tables may be more conservative than the PADI tables they may be overly so. It is different than the other tables because it was designed specifically for rec divers, unlike most other tables which are more or less navy tables. Navy diving and rec diving are different and have differnet objectives. There is a good description of the RDP and it's development in the PADI dive master manual, chapter 5.
They do exist in metric.
Given the choice between spending the money on a wheel or a computer I would opt for the computer and a set of PADI tables. Last I heard the wheel was in the $45 range, while I like them, thats more than I am willing to pay for them.

.

 

[AstroDad]

No. For recreational diving you will be better served by a decent dive computer.

AMEN! After doing tables for twenty years I finally broke down and bought a dive computer a few months ago. What the hell was wrong with me for so long? Get the computer - it just makes life so much simpler...

 

[amascuba]

I have the opposite opinion of the wheel. It's a little different to learn to use but once you learn it, it's easier than tables for me. The wheel AND the PADI tables are based on the same research-RDP. You can interchange the data between the wheel and the PADI table (this is not true for other tables). The wheel if used properly gives you much more accurate information than any table can. There is no need to round up or down times like you must do when using tables and the wheel has smaller depth graduations. You can do multilevel dive planning on tables but I find it easier on the wheel and I am unaware of any agency that teachs divers how to do it. While the navy tables may be more conservative than the PADI tables they may be overly so. It is different than the other tables because it was designed specifically for rec divers, unlike most other tables which are more or less navy tables. Navy diving and rec diving are different and have differnet objectives. There is a good description of the RDP and it's development in the PADI dive master manual, chapter 5.
They do exist in metric.
Given the choice between spending the money on a wheel or a computer I would opt for the computer and a set of PADI tables. Last I heard the wheel was in the $45 range, while I like them, thats more than I am willing to pay for them.

.

The PADI Wheel takes the math out of using the tables. It takes the "Thinking" out of "Thinking Diver", which IMHO can get people in trouble.

Using the wheel isn't more accurate at all. In fact it's supposed to give the same results as the PADI RDP. Ever try to use the PADI RDP for multi-level dives? If you do it correctly it gives you the same information.

The PADI Wheel is also less accurate than the PADI RDP because the numbers, lines, letters, arrows, etc are all small and when doing repeditive dives it's impossible to produce the same information as the PADI RDP for every dive. This is because you can't properly align the wheel were it needs to go. That's why I say that the PADI RDP and the PADI wheel are supposed to display the same information. In reality, it rarely does, especially for repeditive dives.

Infact PADI reconize must this flaw because on the PADI divemaster decompression theory exam it states in the Instructors grading instructions that the answers using the wheel may vary within a given range.