drop some knowledge on me: algorithms

[Fred R.]

I have to be a heretic here,

I take great exception on the concept of ‘conservative’ vs. ‘liberal’ computers. There really is a difference between ‘inaccurate’ and ‘accurate’ information. So called liberal computers are trying to give you the best in nitrogen loading information. Conservative computers are cutting your dive short to try and ‘save’ you from your own stupidity.

The fact of the matter is, all decompression information is based upon an incorrect assumption. Since that incorrect assumption is at the base of all tables and algorithms, of course the experience is that the tables or computers do not ‘work’ all the time. In fact each different model comes with an observed relative risk factor. And the relative risk is never zero.

Personally, I want to have the most ‘liberal’ computer I can get. Then I can use my brain and my good sense to be as conservative as I am comfortable with.

 

[Diver0001]

Fred, I think we agree about one thing, which is that every computer needs to be dived intelligently. Where we disagree would be where to set the baseline (liberal vs conservative). Strangely, your argument for using a liberal computer (best guess) is negated by what you say about the model being full of holes. That's the reason I would choose not to use them.

It might be relevant to point out that extreme divers use algorithms that are more "conservative" than the most conservative models made for sport divers. The way I see it, if the *real* hot-shots in this sport are doing that, why would we as mere plebes do anything less?

Just a thought.

R..

 

[WarmWaterDiver]

i think you know what i mean by "trustworthy". that (above) is not it.

No, I don't - as I and others including TS&M have posted, it's an individual choice on risk management, similar to so many other aspects of our lives. I can think of no other greater risk of personal injury and death than routine travel along the roadways to use as a fitting analogy. But I don't know each individual's definition, and frankly, don't personally care to. But I did think you were looking for info to help you become more educated in both absolute and relative differences, which has been provided.

Enjoy!

 

[ThatsSomeBadHatHarry]

No, I don't - as I and others including TS&M have posted, it's an individual choice on risk management, similar to so many other aspects of our lives. I can think of no other greater risk of personal injury and death than routine travel along the roadways to use as a fitting analogy. But I don't know each individual's definition, and frankly, don't personally care to. But I did think you were looking for info to help you become more educated in both absolute and relative differences, which has been provided.

Enjoy!

sorry, i didnt see the metaphor at the time but i really do appreciate the help. It just seemed to me that computers that are carrying out the job that they do, would make more sense to be using a standard algorithm. it seems like different computers using different algorithms leaves alot of room for error, and with the addition of everyone's different chemistries, it makes the variance between the plethora of computers and their algorithms less "trustworthy". i should probably stop using that word... lets just say i have a cautious approach to the whole thing

 

[Fred R.]

Hi all,

I did not say that computer algorithms were full of holes, those computer models are some very elegant mathematics.

What I did say is that ALL of the decompression models have at their base an incorrect assumption. That assumption is that there is a certain time that one can stay at pressure and come directly to the surface.

There is no time that one can stay at pressure if that pressure is released too fast. Non divers get bent flying in unpressurized aircraft. There was a case on the island here, where a scuba instructor on her first dive of the day, did 20 minutes at 45 feet and ended up spending the evening in the chamber. She came up too fast.

The problem with computers is that they do not know how fast you will actually come up at the end of your dive. So they give you the best math for you to stay down and come up as fast or as slow as the ascent meter will tell you. In this aspect, computers are much better than tables as they meter your ascent rate. Even so, each table and computer will get you to the surface with a certain risk factor, 4 in a 1000, 1 in 1000, or 3 in 10,000. If you dive as much as my wife and I, 1 in 1000 is very bad odds, one of us would be in the chamber at least once a year. Therefore, based on years of research with some of the best hyperbaric people, I developed my own ascent procedures for recreational diving.

By following my liberal computer and a very conservative ascent procedure, I have stayed unbent for all of my 13,000 + dives. More importantly, the 100,000 or so dive events that I guided have the same complete lack of incident.

 

[ThatsSomeBadHatHarry]

Therefore, based on years of research with some of the best hyperbaric people, I developed my own ascent procedures for recreational diving.

By following my liberal computer and a very conservative ascent procedure, I have stayed unbent for all of my 13,000 + dives. More importantly, the 100,000 or so dive events that I guided have the same complete lack of incident.

you should post it. i'd really like to see a sample one.

 

[mozz]

By following my liberal computer and a very conservative ascent procedure, I have stayed unbent.

okay fred, im intrigued. please share your gear config. as well as 'ascent procedures'?

 

[Fred R.]

Hey all,

Mozz, At the risk of alienating most of the board, Genesis Cobra II BC, I only use jacket style in open water, Atomic Titanium regulator (check out their website under 'testimonials') an old Sherwood full sized octo, with a left hand hose entrance, worn on the right side, 40" hose (that's an 'exclusive', but should be the standard). I've got three USIA dry suits, two Henderson Hyperstretch 7MM wet suits and am getting a pair of TUSA fins. I won't say what fins I am using now, the sole reason I have them is that they don't suck too bad and they were BRIGHT yellow-green. Reasons for my choices would be cause for another thread.

Back to ascents, the latest Navy research, which I am told will never be published, (but hey, what do I know, I live on an island) called for 'parabolic' ascents. The closer you get to the surface, the slower you should ascend. Because it is nearly impossible for a diver to finely control ascent speed, you go up as slow as possible and stop two to three times, with each stop getting closer to the surface being significantly longer than the deeper stop.

On any given day, my morning starts with either a seventy five or a hundred foot dive, followed by a forty to fifty foot dive. Afternoons is either a fifty footer again or very very shallow, 15 foot, a very long safety stop. (but it is an incredible dive)

Any dive shallower than one hundred feet, up slow 20-30 fpm, stop at 25 for 1 full minute, 10 fpm to 15 feet stop for 4 full minutes, spend one or more minutes angling up from the safety stop to the boat ladder.

When we break a hundred feet, as we do on our big wreck dives, we add one minute at half the max depth to the above procedure.

It is very simple and it has worked, so far, so good.

 

[brianstclair]

It is very simple and it has worked, so far, so good.

Thanks for sharing that, Fred.

Brian

 

[mozz]

fred r,

i share your enthusiasm for atomic's breathers. i have breathed off the t2 for almost a year now and would sooner part with my mother-n-law. oh, come to think of it, i'll give you her for free. seriously, thank you so much for sharing. i would love to come dive with you and pick your brain some more.

thanks again.