Planning multi-level dives with the RDP

[SNorman]

OK, they really didn't go over this in class, but I was just sitting here at work looking over my RDP and I just realized this (let me know if there is any reason this would NOT work).

Let's say I dive to 80 fsw for 25 minutes. That puts me in pressure group N. From what I've learned so far, it's time to end the dive. But, if I wanted to then ascend to say 50 feet and keep diving, table 3 tells me I can spend 36 minutes there starting at pressure group N.

Or would it be better to get the "wheel" to do this?

 

[PerroneFord]

I love awakenings...

 

[Charlie99]

Using the RDP like this can lead to some dive profiles that are slightly beyond NDL.
The pressure groups are accurate and can be used for repetitive dive planning.

The wheel and the RDP are similar, but the wheel has a few additional restrictions on allowable combinations of depths, and has some slighly reduced no-deco times for use with multilevel profiles.

Although I have made some flat table equivalents of the RDP that include the multi-level no-deco limits, when planning a dive that I will then execute using a dive computer, I just use the backside (table 3) of the RDP.

http://www.scubaboard.com/showpost.php?p=2187851&postcount=27 lists the multi-level no-deco limits, aka ML values, as well as info on the allowable combinations of depths.

 

[Scuba_Steve]

I love awakenings...

LOL, I brought that up for kicks and grins during my IDC...........lol.

Nothing like tossing in a grenade and then walking away...

I think it's important to note that that profile is not only seriously aggressive, but you wouldn't have enough gas on a single 80 or 100 to do it properly anyway, so the point is moot in a proper dive plan.

 

[HowieDean]

All these years I thought the wheel gave you more dive time by elimating all that rounding when using the RDP tables.....

If you round your times and numbers as the tables want you to I don't know how you could ever get anywhere near an agressive profile........

That's just my opion I could be wrong...............

 

[ffestpirate]

Computer..............

 

[amascuba]

To do multi-level dives with your RDP tables where is what you do:

Plan your max depth and find the max bottom time.
Plan to do that depth, but stay conservative with the bottom time.

Say 80ft for 15 minutes.

From there find which nitrogen group that puts you in on table 1.
Continuing on table 1 scroll up the nitrogen group until it intersects with your second planned depth.
Dive at that depth within the NDL limits.
End your dive within the NDL limits of your second planned depth.

That's basically all the wheel does for multi-level dives, except it stays a bit more conservative by creating a MDL (multi-level dive limit) in place of a NDL. They are essentially the same thing though.

*Disclaimer: Also keep this more conservative because diving the tables weren't intended to be dove this way. I would end the dive within 3 pressure groups of the NDL at a minimum. If you don't feel comfortable doing that dive then don't do it. Dive it at your own risk and take responsibility for yourself.

 

[SNorman]

I think it's important to note that that profile is not only seriously aggressive, but you wouldn't have enough gas on a single 80 or 100 to do it properly anyway, so the point is moot in a proper dive plan.

If you mean the original profile I posted, I just made something up to show what I was thinking. A real dive would be much more conservative

And yes, I know a computer can do all this for me but I like to know the tables.

 

[Charlie99]

All these years I thought the wheel gave you more dive time by elimating all that rounding when using the RDP tables.....

If you round your times and numbers as the tables want you to I don't know how you could ever get anywhere near an agressive profile....

What you say is somewhat true, if you are comparing the Wheel and the RDP table on a single level, aka "square profile", dive. But the depth and time rounding is just a minor difference.

Where the big difference shows up is in a multilevel dive, such as going to 80' for a while, and then coming up to 40' for a while, then surfacing. Per the standard rules for tables, the entire dive must be treated as if it were all at 80', thereby limiting the total bottom time to 30 minutes per the RDP. The wheel OTOH, shows that a dive of 15 minutes to 80' followed by a full hour at 40' is an acceptable dive.

 

[Scuba_Steve]

LOL, well, I can see you just made it up

And for the record I never said use a computer , it'll rot your brain doncha know.

I prefer to just roll the the dice for SI and NDL.

Clipped off, right pocket.