Average depth finder

[boulderjohn]

I have to say I am baffled by a lot of what I read there. tbone1004 is being kind in saying it does not make sense. The one thing I can say is that the thinking seems to come from that time about 10-15 years ago when people were first going wild about deep stops and bubble theory, an enthusiasm that has waned considerably in the last decade or so.
let's look at one portion of what you wrote:

COMPUTER: Well I can not be sure because at the time that I was designed, people who designed me were not sure either. I do have that old research that was done prior to the invention of Doppler radar. I can project to you the table limits that were developed during the era of dissolved gas models. That table stuff they did back almost a hundred years ago did reduce visible symptoms in a lot of people. It is very possible that you could be one of them. Would you like me to project those NDL limits?​

You seem to be acting like Doppler bubble imaging is the latest and greatest thing that made all tables obsolete. In fact, Doppler bubble imaging was used in the research that created the PADI tables, and we are approaching the 40th anniversary of that research. The PADI tables are thus based on the results of Doppler bubble imaging, which is the opposite of what you seem to think. We are well past the era when bubble theory was so new and exciting and we are looking beyond that thinking now.

 

[KenGordon]

From what I can tell, there is NOBODY that is trying to make a case that on-gassing or off-gassing is linear.

Thalmann did, for off gassing See about page 205 in your copy of Deco for Divers.

 

[CAPTAIN SINBAD]

uhhh what?
you do realize that the NDL is essentially the same as "your stops have cleared" right? I.e. I dive to some point and my NDL is based on a theoretical tissue loading of 90. I can do the same dive, but do it 10 minutes longer where I have a 5 minute decompression stop but that 5 minutes is determined by how long it takes for my tissues to calm down to 90, and I am surfacing with theoretically the same amount of nitrogen in my body.

Yes and what you just described is an M-value. Robert Workman used the term M-value to describe maximum level of over-pressurization that could be tolerated without excess bubble formation. Let us look at the controversy that was generated by Doppler studies on the concept of M-value that you just described above.

Below I am quoting Mark Powell word by word ...

"So traditional Buhlmann table will bring you as close to the surface as possible in order to get you as close to, but not exceeding, the M-value and keep you there until you could either move up to the next decompression stop or to the surface without exceeding the M-value. This is reflected in profiles calculated from Buhlmann tables or using dive computers which use Buhlmann algorithm which are characterized by fast initial ascents followed by long deco stops at shallow depths.

However we saw that Doppler bubble detection has shown that bubbles form on a large number of dives. This includes dives where the diver does not approach critical super-saturation and where he shows no traditional signs or symptoms of decompression sickness. This shows that our M-value is at best an attempt to delineate a sensible limit where the number of bubbles produced is small enough to avoid the appearance of signs or symptoms of decompression sickness.

This provides a significant challenge to the traditional view of decompression theory. If bubbles are formed well within our M-value limit then what use are M-values? And if bubbles form and yet there are not signs or symptoms of decompression sickness then how can we say bubble formation causes decompression sickness. If it is not bubble formation that causes decompression sickness that what does cause ?"

(Mark Powell "Deep into Deco" page 109 - 110)

 

[tbone1004]

ok, so what does Mark say about deep stops?

What does he recommend using for decompression algorithms and profiles?

What was the basis for this ratio deco based on average depths?

 

[CAPTAIN SINBAD]

You seem to be acting like Doppler bubble imaging is the latest and greatest thing that made all tables obsolete. In fact, Doppler bubble imaging was used in the research that created the PADI tables, and we are approaching the 40th anniversary of that research. The PADI tables are thus based on the results of Doppler bubble imaging, which is the opposite of what you seem to think. We are well past the era when bubble theory was so new and exciting and we are looking beyond that thinking now.

No it did not make tables obsolete but Doppler bubble detection split the scientific community into two religions. The first religion continued with dissolved gas models and attempted to to improve them. They felt that whether bubbles or no bubbles, since limits and stops generated by dissolved gas models were good in reducing symptoms, let us tweak them. The second group of scientists like Brian Hills created the Bubble Mechanics community.

"Even after Doppler testing proved the existence of silent bubbles most scientist continued down the trail that Haldane first blazed. Brian Hills however decided to pursue a different path.

Further research led Hills to develop a new approach to decompression theory he called "Thermodynamic" or "Zero Super saturation." Hills Thermodynamic approach attempted to predict the behavior of both dissolved gas in solution and gas in free state (bubbles.) This new concept was the birth of what we now call Dual Phase or Bubble Models."

(TDI Decompression Procedures page 74-75)

Mark Powell describes the havoc Doppler research caused in decompression science circles.

"We can see that the discovery of silent bubbles threw quite a large spanner into the theoretical basis of traditional (dissolved gas) decompression theory. Two alternate views developed on how best to deal with this spanner. The first view was that the dissolved gas model has served us well for many years and and many millions of dives have been conducted with an acceptable level of safety. As a result there is no need to completely reject the dissolved gas model. Instead a number of modifications can be made to take into account the existence of silent bubbles.

The alternative view was that the discovery of silent bubbles highlighted such a fundamental flaw in the dissolved gas model that a mere tweak was not sufficient to solve the problem. Nothing less than a new theory which attempted to explain the formation of silent bubbles as well as the cause for decompression sickness was the only way forward."

(Mark Powell "Deep into Deco" Page 111)

As of now we do not have that new theory. The closest attempt to this are bubble models like VPM etc.

Since there is no scientific consensus, designing a dive computer is like designing a Catholic Computer (Buhlmann with gradient factors) and a Muslim computer (RGBM) and a Protestant Computer (VPM). The guy doing ratio deco is the one who is saying "What the heck! I am going athiest here!!!" Then everyone gangs up on scubaboard to burn the "freakin athiest" and the number of unwarranted decompression hits they have all accumulated under their own religions never ever occurs to them.

I am not saying Ratio Deco has the answer. I am saying let us open ourselves to all perspectives up there.

 

[tbone1004]

@CAPTAIN SINBAD what you are implying is that Mark advocates for VPM?

Have you read the accounts of DCS when diving on VPM and who is still actually using and advocating for it? Same with GF Lo's that are below 30? or the general trend of the GF-Lo getting higher and higher?

You say that you're an atheist, but you aren't explaining why you chose to be an atheist or what this atheism is based on... Where did the ratios come from? Do you know?
Do you know why they chose them?
Do you know what research caused them to have the concepts that they have?

 

[stuartv]

Since there is no scientific consensus, designing a dive computer is like designing a Catholic Computer (Buhlmann with gradient factors) and a Muslim computer (RGBM) and a Protestant Computer (VPM). The guy doing ratio deco is the one who is saying "What the heck! I am going athiest here!!!" Then everyone gangs up on scubaboard to burn the "freakin athiest" and the number of unwarranted decompression hits they have all accumulated under their own religions never ever occurs to them.

I am not saying Ratio Deco has the answer. I am saying let us open ourselves to all perspectives up there.

In your analogy, I don't think it's correct to say RD is the atheist. More like AG is L. Ron Hubbard and the RD users are the Scientologists.

 

[Kevrumbo]

. . .
What was the basis for this ratio deco based on average depths?

. . . Where did the ratios come from? Do you know?
Do you know why they chose them?
Do you know what research caused them to have the concepts that they have

Here's that monograph again on Ratio Deco so y'all can find & quote the basic tenets about the method that you find questionable and want to discuss. . .

http://www.ultimatedivelog.com/articles/8.pdf

 

[tbone1004]

Here's that monograph again on Ratio Deco so y'all can find & quote the basic tenets about the method that you find questionable and want to discuss. . .

http://www.ultimatedivelog.com/articles/8.pdf

i'm very aware of the answers to the questions that I asked, but my knowledge of ratio deco isn't what I'm questioning. What this sounds like is blind faith in something because of various snippets of information that have caused doubt in the OP's mind. Completely different than " I believe ratio deco is OK, and this is why". I was trying to get him to answer the why

to the OP. Buy this, set to VPM+2 or Buhlmann 20/85 and turn on the deep stops function. Have fun.
Ratio Dive Computers - iX3M Deep

 

[stuartv]

What this sounds like is blind faith in something because of various snippets of information that have caused doubt in the OP's mind. Completely different than " I believe ratio deco is OK, and this is why".

Why is it so often the case on SB that wanting to know more about something is automatically presumed to mean that you are going to do it?

I have heard nothing of blind faith here. What I have heard is a pretty educated person seeking even more education. That includes quoting sources who promote a certain way of doing things, in order to solicit counterpoints. That seems way better than him giving us "his own" understanding of how RD works and then asking for a critique. Quoting sources does not mean he agrees with them. Asking questions that are predicated on stipulating that what someone else said is true, also does not mean he agrees with them. It just means he is seeking better understanding.