Computerless Multi-Level dives

[Uncle Pug]

DA Aquamaster once bubbled...
It always amazes me that some divers who will go to great lenghts to eliminate relatively small risks in terms of their equipment selection and configuration will often be the same ones who play it fast and loose with dive tables where the risk of getting bent is very real. It's an odd contradiction.

I'm amazed at the folks who will follow a dive computer to 100' with a short fill and a pony.

 

[Charlie99]

The real problem about using the PADI RDP for multi-level planning is that the RDP tracks one and only one compartment, the 60 minute one.

Using the PADI RDP to plan a multilevel dive will keep the 60 minute compartment below 95% gradient factor, but the 20/30/40 compartments will go a few percent beyond the M0 value, ie. gradient factors somewhere around 105%.
This means that you have a few minutes of deco obligation.

Running multiple profiles through GAP, I have yet to find one that requires more than 3 minutes of deco with GAP conservatism totally turned off, but that doesn't mean that there isn't one.

I find the PADI RDP is good for a rough sanity check on a proposed dive profile, but prefer to verify it with either a PC or a dive computer simulator.

 

[Charlie99]

grunzster once bubbled...
5 Seriously how do you read the table sideways?

Table 3, The Repetitive Dive Timetable on the back of the RDP doesn't have any info that isn't on the front table 1, provided you can subtract 2 numbers.

One method of calculating repetitive dives starts off using Table one to get the PG at end of dive 1 in the normal manner. Then use Table 2 to get PG at end of SI. Now, rather than turning over the RDP, just find that post-SI PG in the vertical column of Table 1. Go "sideways" into table 1 over to the depth of the 2nd dive. The number you find there is what is called RNT on Table 3.

The difference between that RNT number and the NDL is the number of minutes allowed for your 2nd dive.

 

[Charlie99]

Doof bubbled long ago...
My PADI Wheel and my PADI RDP can't even agree what the the PG is for a dive to 90 feet for 15 minutes is.

The RDP says it's H.
The Wheel says it's I.

A 1 minute different between the Wheel and RDP difference isn't too surprising. I reverse engineered the PADI RDP. With the assumptions I, made PG H corresponds to GF of 41%, I to 44%. H is 14.4 minutes at 90', I is 15.6 @ 90'. In other words, 15 minutes falls right on the H to I division. My excel spreadsheet has the same numbers in most boxes, with a few that are +/-1 minutes. 90' H and I are 14 and 16 minutes on my table.

PM me if you are truly a geek and want an Excel spreadsheet for the PADI table, and similar ones but for 10/20/30/40 halftime compartments.

 

[DA Aquamaster]

Charlie99 once bubbled...
Using the PADI RDP to plan a multilevel dive will keep the 60 minute compartment below 95% gradient factor, but the 20/30/40 compartments will go a few percent beyond the M0 value, ie. gradient factors somewhere around 105%.
This means that you have a few minutes of deco obligation.

The PADI Recreational Dive Planner REQUIRES a 3 min "saftey" stop for all to dives to 100 ft or greater as well as 3 minute stops for the last 4 time intervals for all lesser depths. This is quite consistent with what you are noting for the shorter half lifed compartments.

In my opinion a mandatory "saftey" stop is in effect a deco stop and we are really talking about overhead diving with some of the profiles allowed by the RDP.

 

[Braunbehrens]

DA Aquamaster once bubbled...

In my opinion a mandatory "saftey" stop is in effect a deco stop and we are really talking about overhead diving with some of the profiles allowed by the RDP.

A 30 fpm ascent rate is not much different, you still can't
"blow to the surface".

It goes back to the same old broken record...every dive is a deco dive.

 

[TRIG]

Or maybe you need a brush up on your Dive Tables. You can do that by downloading the shareware version of The Computerized Table Tutor. This PC based software lets you practice doing first table, surface interval, repetitive dive and missing surface interval questions for 9 different dive tables - metric or imperial. And you can even input your own questions!

I spent about an hour with this fast paste, question/answer,
show me how, software and the Vis got remarkably better.

If the above link " The computerized Table Tutor " doesn`t
work, go to scubatoys.com , click Education and find it, it`s
worth it.

Trig

 

[Charlie99]

DA Aquamaster once bubbled...
The PADI Recreational Dive Planner REQUIRES a 3 min "saftey" stop for all to dives to 100 ft or greater as well as 3 minute stops for the last 4 time intervals for all lesser depths. This is quite consistent with what you are noting for the shorter half lifed compartments.

LOL. Yes, I'm aware of the rules for use of PADI RDP.

I just used that description of 3 minutes deco stop on GAP with no conservatism as a shorthand way to indicate that multilevel dives planned on the RDP load up the fast tissues to a higher level than does just running out to the NDL at any single depth. Using the same setup conditions, the PADI single depth NDLs did not create any deco requirement whatsoever in GAP.

Perhaps I should have stated the less intuitive "planning multilevel dives on RDP may run 20 minute compartment up to around 70fsw". (Higher than DSAT'87 and Buhlmann '90 ZHL16B&C, but lower than Workman '65. This was even with using a 30fpm ascent rate to offgass the fast compartments a bit
more.)

DA Aquamaster once bubbled...
In my opinion a mandatory "saftey" stop is in effect a deco stop and we are really talking about overhead diving with some of the profiles allowed by the RDP.

The flip side of "every dive is a deco dive" is that "a few minutes of deco does not an overhead make".

I wouldn't classify any PADI RDP profile as "overhead"; the same way that I wouldn't classify deco imposed solely by running ZH-L16C with a gradient factor of 85 as an "overhead".
Indeed, since deco is a probablistic calculation, even 5 or 10 minutes of "required deco" doesn't really present very much of an overhead risk.

Don't blow away deco stops on a whim, but also don't be like the Rescue Diver student mentioned in another post that stopped for his Suunto's 3 min SS on the way up with a simulated casualty.

 

[newdiverAZ]

Does anyone now what the tissue haltimes are corresponding to the compartment #'s. I'm a lil confused I thought that the compartments move 50% closer to equilibrium every halftime, as long as depth remains constant, this does not seem to follow suit with the software.

 

[newdiverAZ]

are the compartments figured as different solubility's or by halftimes or both?