actual NDL calculations

[captain]

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.

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.

 

[scc135]

The OP is asking about calculating NDL, not how to appropriately use dive tables.

I'm not talking about what they (PADI/their tables) instruct divers to do, I'm talking about what ascent rate is assumed for the purposes of establishing NDL.

As far as I know, for a dive to 60 feet, the PADI/DSAT NDL assumes the diver will have at a minimum one minute of in water decompression, not two minutes.

Also, FWIW, I dug my PADI RDP out of the garage. Ver 1.2 (Rev 02/03) states under General Rules: "Ascend from all dives at a rate not to exceed 60ft per minute."

While that doesn't mean that 60fpm is used in the algorithm, I find it highly unlikely that they would suggest that 60fpm is okay if the algorithm is based on 30fpm.

well, I think the part about calculating ndl was pretty much nixed since someone mentioned about how the calculations were done. Right now, I'm still trying to figure out how to log a multi-level dive that most seem to be (at least the majority of my dives are).

 

[muddiver]

I use the Navy table to log my dives, because if I blow the N0-D table when diving on a computer, one can always check the Air Decompression table to see how it compairs.

 

[Blackwood]

PADI Max Ascent Rate = 60 fpm
NAUI Max Ascent Rate = 30 fpm (as does pretty much every other agency I've trained with)

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.

[URL="http://precisiondiving.net/blog/wp-content/uploads/2009/04/padi_rdp.jpg"][/URL]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

 

[NC Wreck Diver]

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.

 

[scc135]

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?

 

[peterbj7]

I only asked because the PADI Dive Planner, and all tables PADI, as is mentioned by the OP has a 30fpm ascent rate

I'm not going to say you're wrong as you seem quite positive in your statement, but I have always believed that all PADI tables (which have not changed in decades) are based on an ascent rate of 60 fpm. That includes the new eRDP, which is merely a low grade computer based on the same parameters.

A more acceptable ascent rate these days, at any rate between about 60 and 15 feet, is 20 ft/min. Below 60 ft it hardly matters what rate you ascend at, and above 15 ft you should ascend even slower. If you go from 15 feet to the surface in a minute that's about right.

Going back to the original question. Even on the highly simplistic PADI model calculating the "true" NDL is very complex, and not something any diver would be expected to do. From a more general perspective, there is no such thing as an absolute NDL, as whatever NDL you choose is a product of the compression/decompression algorithm you have opted to use.

Being even more general, we are only talking about a mathematical model simulating a "typical" adult in good health. What applies to any particular person on any particular dive is likely to be quite different. So the very concept of an "accurate NDL" is spurious anyway.

 

[Peter Guy]

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?"

 

[scc135]

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?"

Ah, so I can't. That's the answer I was looking for. As interesting as it was, all the talk about ascent rates kinda threw the discussion off the original question.

I was not looking for a kludge, but an a viable non-computer method. I was hoping to use what was already available to me, which was a regular OW RDP. Is there anything that is similar to the eRDPml? I'd like to know what options there are.

 

[boulderjohn]

I was not looking for a kludge, but an a viable non-computer method. I was hoping to use what was already available to me, which was a regular OW RDP. Is there anything that is similar to the eRDPml? I'd like to know what options there are.

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.