More conservative: RDP or the Wheel?

[indigoscuba]

I think this is a newbie question so I'm posting this here. During my open water and subsequent certifications, I was only taught how to use the PADI RDP. But after my OW, I purchased gear and have been using a computer ever since. Lately though, I've put some thought into really planning my dives with tables or the wheel and having the computer as a backup. My question is that, which is more conservative between the two, the RDP table or the Wheel? Thanks in advance.

BTW, I searched for similar topics concerning the RDP and the Wheel but I haven't found any definite answer on my query.

 

[BabyDuck]

i'm sure you'll get more informed answers, but it's my understanding that they use the same numbers. the extra conservatism would be time-related (because not all dives are square profiles) due to having to round up, so i'd answer that the tables are more conservative, but not because of different numbers, because of having to round up when using tables.

 

[The Kraken]

The RDP is more conservative because it's tabulated on 10' depth increments whereas the "Wheel" is tabulated on 5' depth increments.

So if you're making a 55' dive with the RDP, you must plan your dive to 60'. That would give you 10 minutes less dive time.

NDL for a 60' dive on air is 55 minutes. NDL for a 55' dive on air is 65 minutes.

That same dive on the "Wheel" would be planned at 55'.

 

[BabyDuck]

thanks for the clarification, k. i meant 'same numbers' as in 'same algorhythm', but i didn't know the wheel had more choices of depth.

 

[Charlie99]

My question is that, which is more conservative between the two, the RDP table or the Wheel?

Both are based on the same decompression model, as are Oceanic dive computers. On a square profile dive (straight to the bottom, and more or less the same depth for the entire dive), all three will have the same level of conservatism and will give the same calculations.

On multilevel dives (deep at the beginning, then shallower later) the table becomes more conservative since you have to treat the dive as if it were all at the deepest depth. This "conservatism" is highly variable since it is just due to the inability of the standard table to properly track a multilevel dive.

The wheel improves the tracking of the dive a bit, and falls in between the RDP and the computer in terms of the ability to fully track a dive profile.

Edit: and as Kraken notes above, the wheel also better tracks and calculates the dive because it has 5' resolution rather than 10'. Same sort of effect ---- more round off of the table means that for some dives there will be extra conservatism.

 

[indigoscuba]

In your opinion which would be better in planning dives? I presume the Wheel is better since it offers more flexibility?

 

[The Kraken]

I prefer the wheel. Even though I dive a computer, I calculate my dives before the dive. It's just a good thing to do.

Those 5' increments add a lot of bottom time to many recreational dives if you're diving an SPG as opposed to a computer.

the K

 

[DiverBuoy]

Here is a brilliant archive that really addresses the issue most of us have with simplifying things to RDP vs Wheel:

http://www.scubaboard.com/archive/index.php/t-42987.html

 

[drbill]

Although many can plan their dives well in advance, especially if diving a wreck or some other offshore feature, there are others like myself whose dive profiles are unpredictable due to the activity we are engaged in.

As a videographer, I take advantage of opportunistic events and film unexpected subjects when encountered. On numerous events these opportunities have taken me well away from any initial dive plan I may have had before entering the water.

Given this kind of diving, planning using the tables may still be a good idea... but the plan goes out the window as soon as that giant sea bass swims by and I follow it. Therefore I rely entirely on my computer which is conservative and more accurately reflects my actual profile.

Unless you are certain you can dive your plan, the Wheel and RDP tables can only approximate best case scenarios. On the other hand, if I'm diving a deep wreck at a given depth in a square profile, they can be very good planning devices.

 

[DandyDon]

Both are based on the same decompression model, as are Oceanic dive computers.

It's my understanding that Oceanic computers do calcualte a little differently.

BTW, the RDP can be used to plan or track muli-levels dives, just by using 0:00 suface intervals, but it's challening.

I use my Oceanic computer to plan a multi-level, on the Sim mode.