calculating multi-level dives?

[amascuba]

I'm curious how to calculate multi-level dives using the tables. I was looking around for some information about it on google, but haven't really found any information about it, other than people offering classes on it. Then I got to thinking about it and wondered if you would calculate the dives with tables like you would a repeditive dive, but with a 0 time surface interval?

I don't have tables with me, but if somebody wants me to elaborate on my thinking then I'll do it when I get a chance.

 

[Charlie99]

See this previous thread for a typical discussion that has been repeated several times.

The bottom line is the zero SI method is reasonable, but can result in dive profiles that are slightly outside of NDL.

With a few minor tweaks, you can do the same multilevel planning on the PADI RDP that you can do with the PADI Wheel.

 

[Scuba Brad]

I'd suggest a dive computer...............I've not seen anyone lately actually doing the calcs. Its sort of an lost art.

Happy Diving

 

[CD_in_Chitown]

Isn't the 120 rule dynamic enough to support multi-level dives?

 

[amascuba]

I'd suggest a dive computer...............I've not seen anyone lately actually doing the calcs. Its sort of an lost art.

Happy Diving

I have a computer and I like my computer, but I like to know exactly how things work rather than relying on something to do it for me.

 

[amascuba]

Isn't the 120 rule dynamic enough to support multi-level dives?

120 rule? Can you elaborate?

 

[kidspot]

I know the RDP Table doesn't support multi-level, even though it's possible to calculate based on a 0 minute SI. What about giving yourself a "negative" SI of 1 or 2 pressure groups? would that fall within the limits of the Wheel RDP? I don't have a wheel to check, so just curiosity?

 

[CD_in_Chitown]

120 rule? Can you elaborate?

My understanding is it calculates deco on the fly, but I've only heard and read what others say, haven't taken a class where it is taught. If you'll search the DIR forums you'll know what I know, MHK wrote a synopsis here somewhere I believe.

 

[Jason B]

I know the RDP Table doesn't support multi-level, even though it's possible to calculate based on a 0 minute SI. What about giving yourself a "negative" SI of 1 or 2 pressure groups? would that fall within the limits of the Wheel RDP? I don't have a wheel to check, so just curiosity?

Hey Kidspot, I have the PADI tables and the Wheel. I get the same pressure group for multi level dives using both and also by using depth averaging (it may vary by 1 pressure group at most).

 

[Charlie99]

I know the RDP Table doesn't support multi-level, even though it's possible to calculate based on a 0 minute SI. What about giving yourself a "negative" SI of 1 or 2 pressure groups? would that fall within the limits of the Wheel RDP? I don't have a wheel to check, so just curiosity?

No need to play around by backing off on pressure groups. You can get exactly the same results between RDP and Wheel with a couple tweaks. To fall within the limits of the wheel, you also have 1) follow the allowable depth level combinations and 2) to stay within NDL at all time, you need to stay within the slightly reduced "Multilevel Limits", which are a few minutes shorter than the RDP NDLs.

Using the RDP with 0 SI gives the correct ending pressure group, even if you violate those MLs.

When planning a multilevel dive, one must also of course, do gas planning.

Here's an excel spreadsheet with the PADI Wheel limits. Instead of repetitive dive times, there is a second row for each depth for "surface equivalent minutes" or "ata-minutes". As you go through the table to track N2 load, you just keep a running total of "ata-minutes". For 0.4 cfm SAC, 65 cu feet (2500psi of an AL80) has 160 ata-minutes.