actual NDL calculations

[scc135]

Other agencies use something similar to the eRDPml then? I'm just trying to get a fuller understanding on what it means to plan a multi-level dive, not just in PADI, but under broader terms.

 

[NAM001]

I only asked because the PADI Dive Planner, and all tables PADI, as is mentioned by the OP has a 30fpm ascent rate. And no I don't know when that changed, but it was definately before 2003 when I finished my Divemaster course, and the U.S. Navy table for No-Decompression dives, Revision 5 (latest revision is 6) is also 30fpm.

I just want to make sure we are all taking the same certification agency here, and not mixing in ratio-deco or some other theory.

Thanks all.

it seems like only a couple of years ago that my lds was talking to padi about the 30/60 ascent rate. at that time they were in the progress of changing the policy to 30. somehting about law suits and changing to 30 with the other agencies would apear to admit fault. i want to say 2007--2008

 

[NAM001]

Rate of ascent...interesting. I would need to check but I think PADI still teaches 60fpm. I will also need to recheck te user manual for my suunto but I think it is based on 60 fpm up to 60 ft and then 30 fpm afterward...

that is the latest i have heard of. my computer runs on that ascent rate for the ascent alarm.

 

[Thalassamania]

I'm sorry, but where do you keep coming up with 60fpm?

60 fpm is inherent to the model that PADI used to create their tables, it is also the old ascent rate for the U.S. Navy Tables.

The recommended ascent rate with the Edge was 20 FPM, the max ascent rate was 40FPM not 60 FPM, Navy tables and most others back then were 60 FPM.

If you are speaking of the ORCA Edge, it has an ascent warning, but it really did not care, e.g., it doesn't lock you out. But, as I recall, the manual specified 60 fpm or slower.

Ken -

Do you happen to know if that 30fpm is applied to the decompression tables?

It doesn't look like it. Superficially comparing it to the RPD, NAUI's table and PADI's table are more or less in the ballpark (suggesting similar ascent rates and m-values).

There are only two instances in which the NAUI table lists a longer NDL (which I'd associate with a slower ascent rate), the greatest difference being 16% more bottom time at 80 feet on the NAUI table.

PADI     NAUI
 
140/8    
130/10   130/8
120/13   120/12
110/16   110/15
100/20   100/[U]22[/U]
90/25    90/25
80/30    80/[U]35[/U]
70/40    70/45
60/55    60/55
50/80    50/80
40/140   40/130

PADI and NAUI tables are based on complete different assumptions. The PADI tables are designed to be more "friendly" (e.g., less conservative) and permit more repetitive diving with shorter surface intervals and have a good safety record. The NAUI tables are nothing more than the U.S. Navy Tables dialed back one click, to produce a more conservative table than the U.S. Navy tables, but with no theoretical basis.

Post #21 & commented on by "Captain:"

Originally Posted by NC Wreck Diver

Years ago, I was taught 60'/minute. My Edge used this model. Now, I've did some review a while ago, and it's 60'/minute up to 60 feet. Then 30'/minute from 60 feet to the surface (with a safety stop at 15' for 3-5 minutes). My computer seems to follow this algorithum (Uwatec Aladdin Nitrox Pro). I follow this procedure, and my computer seems to follow.

I do incorporate a deep stop on my deeper dives. The is about a minute or two at half my deepest depth. I have read the pros and cons of deep stops, and still feel it is a good program. There has been some interesting articles in DAN's magazine. I'm sure it's covered on DAN's website too.
__________________________________________________________________________

My EDGE by Orca was a software 4. It's been years since I've used it. It's now used in a SCUBA class as a 'history' of dive computers, and how they have advanced over the years. The computer still works.

I never remember 20' per minute. Maybe my software was an old revision. I do come up slow from all dives. It never gave me any pixel warning as I came up faster than 20' per minute, but slower than 60' per minute. Since Orca has been closed for many years, I can't really find any information, since my manual is long gone. I'll search the net.

Perhaps my software is an older version, I don't know I'll have to check.

ok, ascent rates aside, how do I plan a multi-level dive profile without a comp? Is it possible with just the dive table provided me in my OW class?

There are two techniques, one is known as "repping up," the other in know as the "Graver Method." Frankly it has been almost 20 years since I used either and so it would be irresponsible for me to try and reconstruct either without going back to my notes. All that I remember for sure is that the "Graver Method" had been shown to be dangerous.

scc135 -- I think you are asking the wrong question regarding dive planning.

THE question is, How do I plan a dive that is safe for me at my level of training and with the dive gear I have?

The simple PADI RDP table is specifically designed for planning square profiles -- it is NOT designed for planning multi-level profiles. IF that is what you want to do AND IF you want to use the PADI/DSAT tables/data, you should probably spend the $35 to get the PADI eRDPml which is specifically designed to plan multi-level RDP profiles.

Can you devise a kludge to allow you to use the simple RDP table to plan a multi-level profile? Yes. Will it plan a dive that is as safe as the one for which is was designed? Who knows?

"Do you feel lucky? Well, do you?"

The Wheel was the way to do multilevel calculations for the RDP. Repping up is the way to do so using U.S. Navy, or U.S. Navy based tables. Both have good science behind them and have nothing more to do with luck than any other decompression calculation does.

PADI used to have a table-like version of the RDP called The Wheel. They have stopped using it because, frankly, almost no one ever used it. (I saw one in use one time in my life.)

The eRDPml works very easily and eliminates the most common error in using the tables--reading the wrong column. You can use it to plan a multi-level dive. PADI even has multilevel test questions now for that purpose.

-------------
I would also like to settle the ascent rate issue definitively.

The PADI RDP was created after a long and very expensive series of tests on actual divers. They tested the blood of divers after dives using Doppler Bubble Imaging and published the results in peer reviewed journals. Michael Powell, who is Dr. Decompression on ScubaBoard, was one of the scientists involved. That is where the numbers come from on the RDP, not from some basic formula.

All dives were done with an ascent rate of 60 fpm, which was then the standard used by just about everyone. The numbers on the RDP therefore assume the diver will ascend at that rate.

Since that time, research, especially a 2004 study, has indicated that a 30 fpm ascent rate is somewhat safer than a 60 fpm ascent rate, so other agencies have gone to that number. If PADI were to change to 30 fpm, the numbers in the RDP would no longer be valid. The studies indicate that 60 fpm is still a safe ascent rate, so I assume (admittedly a guess) that PADI still maintains the 60 fpm rate because it retains the validity of the RDP. Research on actual divers has shown that those profiles with that ascent rate are safe, so there is no reason to change.

To my knowledge, other agencies with different tables have not made it clear how they got their numbers. I don't know much about how all the other agencies do things, so I could be wrong in some cases. I have read speculations about the science behind some tables, so I know that science is hidden in at least those cases.

Other agencies use something similar to the eRDPml then? I'm just trying to get a fuller understanding on what it means to plan a multi-level dive, not just in PADI, but under broader terms.

BoulderJohn is correct. The 60 fpm ascent was a "given" value that was used in the calculation of the PADI tables.

 

[wve]

PADI and NAUI tables are based on complete different assumptions. The PADI tables are designed to be more "friendly" (e.g., less conservative) and permit more repetitive diving with shorter surface intervals and have a good safety record. The NAUI tables are nothing more than the U.S. Navy Tables dialed back one click, to produce a more conservative table than the U.S. Navy tables, but with no theoretical basis.

And if memory serves me, one of the reasons PADI/DSAT designed and tested a new table was because of the observation that recreational dives are usually different from Navy dives.

At the time, Navy divers were doing repetitive long, shallow dives, presumably working on equipment and boats that were just underwater. On the other hand, recreational divers tended to make fewer deeper, shorter dives. The question arose whether the different diving styles might be different enough to tweak the tables in favor of the recreational goals.

DSAT developed the algorithms then tested lots of divers to validate the predictions. So the different tables are both based upon theory and experience, but with the different assumptions in mind as you point out.

 

[boulderjohn]

And if memory serves me, one of the reasons PADI/DSAT designed and tested a new table was because of the observation that recreational dives are usually different from Navy dives.

The problem with the Navy tables was that they called for very long surface intervals. This fit Navy diving, but not recreational divers ready to jump back in after a relative short and shallow dive.

that was because when they were built, the Navy tables added a 120 minute (half time) compartment to the original ones from Haldane and made that the controlling compartment. Surface intervals were based on clearing that compartment, which is why they were so long. PADI/DSAT's research indicated that for the kind of diving done in the recreational limits defined by their table, the appropriate controlling compartment was the 40 minute compartment, but they chose the 60 minute compartment for the table in order to be more conservative. They also made the NDLs for the first dive shorter than the Navy tables for that reason.

Compartments clear in 6 iterations of their half time. If you look at the PADI table, you will see that the table clears in its longest surface interval at 6 hours, or 6 iterations of the 60 minute half time.

With certain exceptions, surface intervals are based on the 60 minute compartment. The exceptions are for repeated long dives that put the diver near the NDL. In that case, you have the WX and YZ rules, which dictate longer minimum surface intervals.

 

[NC Wreck Diver]

If I read the documents correctly, 60 fsw a minute from 60 feet to the surface has a higher degree of micro bubbles in the bloodstream based upon doppler testing. I'm sticking with 30 feet per minute from 60 to zero, with my 15 foot safety stop at 3-5 minutes.

As I know it, awhile ago, it changed from a safety stop at 10 feet to 15 feet mainly due to ocean swells. I remember being at 12-14 feet at certain times, and 6-8 feet at others, when the ocean was kicking up on a rough day.

 

[Thalassamania]

First of all, Doppler detectable bubbles have not been shown to actually have anything to do with DCS.

Second of all, the ascent rate is integral to the tables you choose to use. If you do not follow the advisable ascent rate you must deal with the difference time in the way the tables suggest, usually that is to add the discrepancy to bottom time.

 

[Mike Boswell]

First of all, Doppler detectable bubbles have not been shown to actually have anything to do with DCS.
Second of all, the ascent rate is integral to the tables you choose to use. If you do not follow the advisable ascent rate you must deal with the difference time in the way the tables suggest, usually that is to add the discrepancy to bottom time.

Thal, does this mean there is probably no connection between Doppler bubbles and DCS, or does it mean that it is difficult to get data?

 

[Thalassamania]

Neither, it means that no link between the two has been demonstrated and so we should, until it is (and I expect it will be) demonstrated we must take Doppler findings with a grain of salt.