Deep Stops Increases DCS

[RyanT]

I mean, isnt that what experts do...ask questions, challenge assumptions....and sometimes they are wrong and need to adjust their work. Updating an error should be applauded, not ridiculed.

Absolutely! If we look at this debate in its entirety, Doolette, Mitchell, and Watts, have challenged an assumption (deep stops). While there has certainly been some back and forth over the details, Hemingway has generally attacked the work as "junk science" and launched a variety of ad hominem attacks. This is very telling.

 

[igor p]

I find this to be an odd quote from someone that does "research" and is touted as one of the experts....Did he try to "deny" it or did he challenge the assertions and then quickly correct a mistake once he was convinved. Truthfully- I find it refreshing when "experts" can admit they made a mistake and update their work.....I mean, isnt that what experts do...ask questions, challenge assumptions....and sometimes they are wrong and need to adjust their work. Updating an error should be applauded, not ridiculed.

Exactely.

 

[shoredivr]

I find this to be an odd quote from someone that does "research" and is touted as one of the experts....Did he try to "deny" it or did he challenge the assertions and then quickly correct a mistake once he was convinved. Truthfully- I find it refreshing when "experts" can admit they made a mistake and update their work.....I mean, isnt that what experts do...ask questions, challenge assumptions....and sometimes they are wrong and need to adjust their work. Updating an error should be applauded, not ridiculed.

Rossh is not a researcher, or a scientist. I have a difficult time seeing him as an expert, considering the actual decompression researchers are pointing out his errors.
He is the owner of a popular decompression software that uses deep stops.

*Edit* if you have followed the NEDU study and Rossh's response to it on the internet (the Rebreatherworld thread comes to mind) over the past few years, you"ll notice that he attempts to use science to support deep stops. Now it appears that from the actual decompression researcher's point of view he does not adequately understand decompression models. That is of interest to me as he sells decompression software.

But the science seems to be moving away from deep stops. Rossh also sells another program called Multideco, which uses gradient factors. Why he will not move with the science and stop promoting bubble models is beyond me, as are the many ad hominem attacks made on the actual researchers. I just don't get it. Why not go with the research?

 

[UWSojourner]

I find this to be an odd quote from someone that does "research" and is touted as one of the experts....Did he try to "deny" it or did he challenge the assertions and then quickly correct a mistake once he was convinved. Truthfully- I find it refreshing when "experts" can admit they made a mistake and update their work.....I mean, isnt that what experts do...ask questions, challenge assumptions....and sometimes they are wrong and need to adjust their work. Updating an error should be applauded, not ridiculed.

I understand that it's very difficult to discern the difference in the truth value of statements made by different parties when they're mixed with technical language that the reader hasn't been immersed in. It's very difficult.

So let me try to put things into perspective. Let's say you arrive in a forum discussing mathematics. And let's say David Hilbert and Bernhard Riemann (famous math guys) are there (amazing in itself) trying to explain to novices the implications of their findings. These guys were AMAZING mathematicians.

And then it becomes obvious that one guy, let's call him Sor, is very strongly combatting everything they say. And this person's main argument is that these guys are ridiculous because much of their work relies on calculus and calculus relies on nonsense ideas like infinitesimals and "converging to infinity". What nonsense! These guys are just trying to mislead with their eye-candy symbols and fancy "proofs". Those reading who've had no exposure to calculus might have a hard time distinguishing what's right just because infinitesimals and converging to infinity, after all, are pretty foreign concepts and because Sor seems so sure of himself.

Now in the "debate" here, Hilbert and Riemann are to Sor as Doolette and Mitchell are to Ross. It's that simple. And the "arguments" being used by Ross to oppose the preponderance of evidence now available that deep stops have been oversold to the diving community, have about the same truth value and credibility as the "reasoned arguments" Sor used in the analogy above.

Not being an expert is not a fault -- I put myself in this category compared to Doolette/Mitchell. But what IS a fault is accosting the experts with already answered meritless "arguments" and perpetuating those same meritless arguments in forums like SB.

 

[Dr Simon Mitchell]

I find this to be an odd quote from someone that does "research" and is touted as one of the experts....Did he try to "deny" it or did he challenge the assertions and then quickly correct a mistake once he was convinved. Truthfully- I find it refreshing when "experts" can admit they made a mistake and update their work.....I mean, isnt that what experts do...ask questions, challenge assumptions....and sometimes they are wrong and need to adjust their work. Updating an error should be applauded, not ridiculed.

Hello,

This is a fair question, and to be honest, my playing a "look he made a fundamental error" game feels a bit childish for my own liking. However, you have to understand that these debates with Ross about David's study have played out over years now, and have involved hundreds of time consuming posts on multiple forums. We have generally afforded Ross the courtesy of debating him as though he is someone with a legitimate viewpoint that has to be worked through and properly examined. On this basis genuine progress has been made, and I do think the community is better educated about the issues as a result.

However, you (meaning me) do get a bit worn down by it all. Ross frequently becomes overtly abusive, and some deep flaws in his arguments are extremely difficult to tease out in a clear understandable manner because his confident pronouncements and copious production of complicated looking diagrams are often sufficient to sow the seeds of doubt in readers who are struggling to get their heads around it.

In this milieu, when he produces one of his trademark diagrams that is clearly wrong, then the temptation to point that out is obviously strong. This is particularly so when it is obvious that this diagram is a prelude some some new tangent he is going to go off on in an attempt to discredit a presentation on deep stops I recently gave using similar diagrams to illustrate some basic principles.

The fact that he made a major error in a very basic definition (of supersaturation) is undeniable. You would not know it now though because he changes the diagram on his website which means it updates on this forum without a change in the edit time / date stamp of the post itself. Luckily I kept a copy of the original before it changed (see my post 854).

You ask "did he try to deny it" and the answer is unequivocally yes. His original diagram appeared in post 823. In post 824 I pointed out the error. He changed his diagram on his website to remove the error and it updated on this forum without a change in time and date of his post. Then, in post 829 he quoted my post about the error and wrote "Really? David seems to think it is OK now". Anyone reading the thread, seeing no evidence of the error on his diagram, and looking at the sequence of posts and their dates / times would therefore be very confused about what I was making a fuss about and would have thought his denial was legitimate.

I put it to you that this was not an example of a discussant allowing persuasion to change their mind and legitimately acknowledging that change (which I completely agree is laudable). Indeed, I believe it was disingenuous in the extreme, and we have seen this sort of thing before in these debates. Hence I gave in to the temptation to point it all out.

Simon M

 

[AlexL]

His original diagram appeared in post 823. In post 824 I pointed out the error. He changed his diagram on his website to remove the error and it updated on this forum without a change in time and date of his post.

Just to expand and confirm this on technical aspects: Post 823 was posted on Friday, the 5th of Aug at 10:05am GMT, edited at 10:44am GMT, and the image in question was updated on Monday, the 8th of Aug at 6:32am GMT.

~/ $ curl http://hhssoftware.com/images/deco101_base.png -o /dev/null -v -s
*  Trying 66.154.116.236...
* Connected to hhssoftware.com (66.154.116.236) port 80 (#0)
> GET /images/deco101_base.png HTTP/1.1
> Host: hhssoftware.com
> User-Agent: curl/7.47.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Cache-Control: max-age=86400
< Content-Type: image/png
< Last-Modified: Mon, 08 Aug 2016 06:32:44 GMT
< Accept-Ranges: bytes
< ETag: "cef8ddab3ef1d11:0"
< Server: Microsoft-IIS/7.5
< Date: Mon, 08 Aug 2016 20:18:31 GMT
< Content-Length: 90695
<
{ [1192 bytes data]

 

[David Doolette]

What is the address of this thread? Did you forgot?
This is not deep stop efficiency debate but thread trying to answer to the question if Deep Stops increases DCS.
When some of you started jet again deep stop vs shallow stops fight and campain against dèep stops...

I think since this thread began in response to NEDU TR 11-06, it is unequivocally about efficiency.

I want to clarify a point that has been made before on the various deep stops threads but may have gotten lost in the heated debate. I (and I think the other ‘anti-deep-stops’ crowd) am not arguing that deep stops per se are bad. I am arguing against the notion that “at the same risk level, deep stops get you out of the water faster than shallow stops” (equivalent to deep stops schedules are more efficient than shallow stops schedules). My reply to NetDoc (post #826) encapsulates my point of view: his deep stop at half depth would not allow him to shorten his shallow decompression stops and overall decompression time – but that that deep stop in combination with additional shallow decompression time is probably a good thing. Similarly, I am not trying to “kill” (not my words) VPM-B. The argument has been advanced in these threads that VPM-B (and RGBM) does produce deep stops schedules that are more efficient than shallow stops schedules, and I have argued that there is no evidence to support that contention, and my synthesis of the available evidence supports the contrary. I do believe that a VPM-B schedule is not the optimum distribution of stop time, and the true optimum is some (as yet unknown) shallower distribution of stop time. That is not equivalent to saying do not use VPM-B, it is equivalent to saying if you choose to use VPM-B (or other ‘deep stops’ algorithm), it is prudent to use a higher conservatism level rather than select a lower conservatism level in the mistaken belief that “deep stops get you out of the water faster”.

 

[Divetech99]

Dr. Doolette, Dr. Mitchell, using Net Doc's example, would he be better off forgoing his deep stop at half depth and just follow a GF that will start his stops shallower such as say GF 40/70?

 

[Dr Simon Mitchell]

II (and I think the other ‘anti-deep-stops’ crowd) am not arguing that deep stops per se are bad. I am arguing against the notion that “at the same risk level, deep stops get you out of the water faster than shallow stops” (equivalent to deep stops schedules are more efficient than shallow stops schedules).

Absolutely. This message often gets lost. You and I have both made posts like this multiple times through the various debates.

I do believe that a VPM-B schedule is not the optimum distribution of stop time, and the true optimum is some (as yet unknown) shallower distribution of stop time.

Again, completely agree. Both of us have been reluctant to give guidance on this but (and I speak for myself here), based on the Kevin's analyses of the supersaturation patterns resulting from VPM-B+4 and GF 40-74 decompressions (equal length of decompression) for a typical deep mixed gas constant PO2 rebreather dive, and the comparison of those patterns to those produced by the two NEDU test profiles with their known outcomes, I would suggest that the GF40-74 approach is somewhere closer to that ideal.... but we still don't know what "ideal" is.

Dr. Doolette, Dr. Mitchell, using Net Doc's example, would he be better off forgoing his deep stop at half depth and just follow a GF that will start his stops shallower such as say GF 40/70?

I think one of the points that David made in his original answer to Net Doc implied that if he allowed the GF program to recalculate the shallow decompression to account for the half depth stop then there is probably no harm in it, and potentially even some good (though we don't know that). However, if I had pre-planned a GF 40/70 ascent and planned to stick to it without padding shallow, I would not be inserting any arbitrary extra stops deeper than prescribed by the 40/70 plan. Hope that makes sense.

Simon M

 

[manni-yunk]

Rossh is not a researcher, or a scientist. I have a difficult time seeing him as an expert, considering the actual decompression researchers are pointing out his errors.
He is the owner of a popular decompression software that uses deep stops.

This seems categorically incorrect. Im not defending Ross here, Ive never met him and dont know him at all - but - from a motive standpoint - I cant find any motive for him to fight one way or the other. Whether you choose to use a GF software, or a VPM based software for your dive planning - he has both options and from my own experience.....its the one that most people use. So he doesnt care what profile you use....he gets paid either way.