Why you can't use the PADI RDP table for Multi-Level dives

[tursiops]

And all I've asked for is an example showing me that I'm wrong, and it doesn't work. If it's that hard finding an example of how it fails, I have a hard time believing that I can be so wrong.

You are asking for the comparison of an incorrect use of the tables with what a Buhlmann-based computer might say for the same dive? OK, assume 32% and 28 mins at 30m (NDL is 30 mins). Multi-deco (set at 85/85) says that requires 2 mins of deco at 3m......but according to your GUE table you don't need to do that. We don't even need to look at a multi-level dive; the GUE table is more aggressive than Buhlmann at 85/85.

 

[steinbil]

"We get it, we just don't want it": memorizing certain ratios that are "good enough" for certain gas mixes at certain depths may be great for one's brain development, but for actual diving: skip ten lunches and buy a computer.

I think I'll sign out of this thread now. I've lost track of how many times I've written that I use a Perdix for most dives.

 

[steinbil]

You are asking for the comparison of an incorrect use of the tables with what a Buhlmann-based computer might say for the same dive? OK, assume 32% and 28 mins at 30m (NDL is 30 mins). Multi-deco (set at 85/85) says that requires 2 mins of deco at 3m......but according to your GUE table you don't need to do that. We don't even need to look at a multi-level dive; the GUE table is more aggressive than Buhlmann at 85/85.

Ok. Fair game. Point taken. I wasn't aware of that, but it makes sense that it would be covered by the mindeco ascent, or for the PADI rdp by the safety stop. It also is in line with what I've learned about adding conservatism to diving tables. And you're not really interested in looking into what I'm actually asking about. It's fine. I'm over it.

 

[tursiops]

Ok. Fair game. Point taken. I wasn't aware of that, but it makes sense that it would be covered by the mindeco ascent, or for the PADI rdp by the safety stop. It also is in line with what I've learned about adding conservatism to diving tables. And you're not really interested in looking into what I'm actually asking about. It's fine. I'm over it.

Unfair. I started to produce a multilevel diving to satisfy your curiosity, but couldn't get by the first level without going into deco. Stopping at 18m did not help, there was still a deco requirement. Get MultiDeco and you can play all you want.

 

[inquis]

We don't even need to look at a multi-level dive; the GUE table is more aggressive than Buhlmann at 85/85.

The ascent rate assumptions differ, but I think your conclusion still holds. I do get a 1 minute stop for that 28 minute dive (26 mins at depth) for what I think is the min deco ascent profile (30 fpm to 50% depth, then 10 fpm from there).

@steinbil, Subsurface is a freely available, multi-level, Buhlmann+GF planner. You might try some of the edge cases on your own. The GUE ascent profile can be implemented in the Ascent configuration. (No need to manually define those levels.)

 

[steinbil]

Unfair. I started to produce a multilevel diving to satisfy your curiosity, but couldn't get by the first level without going into deco. Stopping at 18m did not help, there was still a deco requirement. Get MultiDeco and you can play all you want.

All right. I’ll retract my last statement. I was a little riled up by all the snarky replies.

Clearly my suggestion to do a straight comparison between Buhlmann GF85 and multilevel tables was not the right way to go about it, since the table in itself is more aggressive than GF85. Maybe a better way to go about it would be to compare the deco output Buhlmann of square profiles and multilevel profiles planned with the table. I’ll get the software and try to run a few simulations.

 

[tursiops]

All right. I’ll retract my last statement. I was a little riled up by all the snarky replies.

Clearly my suggestion to do a straight comparison between Buhlmann GF85 and multilevel tables was not the right way to go about it, since the table in itself is more aggressive than GF85. Maybe a better way to go about it would be to compare the deco output Buhlmann of square profiles and multilevel profiles planned with the table. I’ll get the software and try to run a few simulations.

Please start a new thread. Not appropriate to discuss deco profiles in this Basic forum.

 

[boulderjohn]

I know that my last comment on scientific method was not liked, but if I am going to trust an algorithm protect me from DCS, I would like to see a little more evidence of science than I am seeing in some of the procedures in this thread. People like Buhlmann and others spent thousands of hours testing their tables. PADI's work on the RDP was massive, with many test dives performed, and the results were published. I for one would like to see the testing done on an algorithm that is contrary to established practices because of my personal history with such algorithms.

I used to train with an agency that had its own ascent procedures. When I was trained on those procedures by the head of the agency, when we planned ascent profiles, we compared it with established algoritms, and since they always disagreed, he gloated that those disagreements proved that the established algorithms, including Buhlmann, were all wrong.

Here are a few points to consider related to this:

• The director said that altitude does not need to be considered when planning an ascent. I asked how he knew that, and he said he had dived at Lake Tahoe without making any adjustments, and he was fine. Therefore, no adjustments were needed.
• When I pointed out that Buhlmann and others had used more than one test subject, he said that no one had ever been bent at altitude using that algorithm unadjusted. It had a perfect record. I replied that I knew at least 5 people who had been bent diving at altitude using that algorithm. He said those didn't count, because there was some other reason they all got bent. What were those reasons? He didn't know, but there had to be other reasons, because no one gets bent diving at altitude with that algorithm.
• Finally, he commissioned a scientific study for the purpose of proving his algorithm was superior to Buhlmann. Even though it is very arguable that he skewed the test parameters to favor his algorithm, his algorithm lost the comparison to Buhlmann.

So, I guess I'm a little bit sticky on this. I want to know what kind of research is behind an algorithm before I either use it or endorse it.

 

[steinbil]

Please start a new thread. Not appropriate to discuss deco profiles in this Basic forum.

The idea is to compare the validity/risk of using depth averages with a table vs square profiles on the table vs using a buhlmann computer for no-decompression (or minimum deco) dives. I just don't know what a good metric would be. Can I use Subsurface or Multideco to show the SurfaceGF? Would that not be a good way to compare the methods?

 

[steinbil]

I know that my last comment on scientific method was not liked, but if I am going to trust an algorithm protect me from DCS, I would like to see a little more evidence of science than I am seeing in some of the procedures in this thread. People like Buhlmann and others spent thousands of hours testing their tables. PADI's work on the RDP was massive, with many test dives performed, and the results were published. I for one would like to see the testing done on an algorithm that is contrary to established practices because of my personal history with such algorithms.

I used to train with an agency that had its own ascent procedures. When I was trained on those procedures by the head of the agency, when we planned ascent profiles, we compared it with established algoritms, and since they always disagreed, he gloated that those disagreements proved that the established algorithms, including Buhlmann, were all wrong.

Here are a few points to consider related to this:

• The director said that altitude does not need to be considered when planning an ascent. I asked how he knew that, and he said he had dived at Lake Tahoe without making any adjustments, and he was fine. Therefore, no adjustments were needed.
• When I pointed out that Buhlmann and others had used more than one test subject, he said that no one had ever been bent at altitude using that algorithm unadjusted. It had a perfect record. I replied that I knew at least 5 people who had been bent diving at altitude using that algorithm. He said those didn't count, because there was some other reason they all got bent. What were those reasons? He didn't know, but there had to be other reasons, because no one gets bent diving at altitude with that algorithm.
• Finally, he commissioned a scientific study for the purpose of proving his algorithm was superior to Buhlmann. Even though it is very arguable that he skewed the test parameters to favor his algorithm, his algorithm lost the comparison to Buhlmann.

So, I guess I'm a little bit sticky on this. I want to know what kind of research is behind an algorithm before I either use it or endorse it.

I appreciate the change of tone, and the proper answer. I know who you're referring to, and I'm equally sceptical of those attitudes - if I'm not mistaken that was partly why said person had to leave GUE. I would hope that those attitudes are not connected to what GUE is teaching.

My problem is that I don't know exactly what research is behind it. However, if we can compare it to the Buhlmann algorithm and they align - we only have to trust Buhlmann and his research. If they differ to a significant degree, I have some thinking to do, which is why I'm trying to find out.

Can you at least agree that if the method aligns or is more conservative than Buhlmann, the origin of the method or the research (or lack thereof) is of less importance?