oceanic computers - what's up with the deco algo?

[edupress]

Hello
I've recently bought Oceanic Geo computer for my wife but then I stumbled upon Divernet article describing Oceanic Versa Pro and then another one with Oceanic Veo. Unfortunately, theirs algorythm (DSAT) was described as the least cautious and sometimes even "It revealed a Jekyll and Hyde character in that at times it seemed to be working with two entirely different algorithms" http://divernet.com/cgi-bin/articles.pl?id=4177&section=2083&action=display&show=.
So, did I make a mystake and should have looked some other way? Thanks.

 

[DandyDon]

Hello
I've recently bought Oceanic Geo computer for my wife but then I stumbled upon Divernet article describing Oceanic Versa Pro and then another one with Oceanic Veo. Unfortunately, theirs algorythm (DSAT) was described as the least cautious and sometimes even "It revealed a Jekyll and Hyde character in that at times it seemed to be working with two entirely different algorithms" http://divernet.com/cgi-bin/articles.pl?id=4177&section=2083&action=display&show=.
So, did I make a mystake and should have looked some other way? Thanks.

I can't tell who wrote that 3 year old article, but a great many divers prefer the more liberal Oceanic over the more conservative makes. The algorithm used by Pelagic, makers of Oceanic and Aires computers, is no more liberal than the very similar one used in the Padi RDP chart. The more conservative makes simply penalize you of safe dive time, IMO - a very unneeded loss.

Try the Oceanic slide show on how computers work for more info: http://www.oceanicworldwide.com/flash/OCE_dc101_files/frame.htm

I dive a Versa Pro and a VEO both, actually. If you want to forfeit safe dive time to exaggerate your margin safety, fine - take 10% off of the dive time remaining on the screen. I would never, ever bother.

 

[Rick Murchison]

The Oceanic algorithm tends to give you more dive time on "typical" recreational profiles than others, but will penalize you more for reverse profiles (deeper late in the dive) and on repetitive deco dives.
As for the article, whoever wrote it doesn't like those properties of the algorithm. For what it's worth, I could write an article whining about what I don't like about SUUNTO's version of the RGBM, and how much more I like the Oceanic, and have good points - from my perspective.
One man's preference is another man's whine.
Bottom line - don't sweat the article. The Oceanic algorithm has been working fine for divers ever since its introduction 15 or so years ago, and is still working fine today.
Rick

 

[Charlie99]

Rick, although the articles mentions the extraordinarily long deco times as ocurring after a 50m/165' dive following a 30m/100' dive I'm pretty sure that the Oceanic/Pelagic computers completely ignore the reverse vs. forward profile issue.
The article also mentioned that SI less than 2 or 3 hours on deco dives were involved in the long deco obligations.

My guess is that the strange long deco times observed are a combination of 1) Oceanic using DSAT/PADI model (same model upon which the PADI tables are based), which is significantly more conservative than ZHL-16 in the 60-100 minute compartments (which don't affect recreational NDL profiles, but do come into play in some deco profiles) and 2) since the DSAT/PADI model is an NDL model only (no delta-M values), Oceanic had to cook up some on their own, and probably chose some very conservative values, which could easily result in long hang times at 10' when using air.

Edupress --- the short answer is that the Oceanic computers use an algorithm that has been extensively tested for repetitive NDL dives but they are not designed or optimized for decompression diving.

 

[Thalassamania]

Rick, although the articles mentions the extraordinarily long deco times as ocurring after a 50m/165' dive following a 30m/100' dive I'm pretty sure that the Oceanic/Pelagic computers completely ignore the reverse vs. forward profile issue.
The article also mentioned that SI less than 2 or 3 hours on deco dives were involved in the long deco obligations.

My guess is that the strange long deco times observed are a combination of 1) Oceanic using DSAT/PADI model (same model upon which the PADI tables are based), which is significantly more conservative than ZHL-16 in the 60-100 minute compartments (which don't affect recreational NDL profiles, but do come into play in some deco profiles) and 2) since the DSAT/PADI model is an NDL model only (no delta-M values), Oceanic had to cook up some on their own, and probably chose some very conservative values, which could easily result in long hang times at 10' when using air.

Edupress --- the short answer is that the Oceanic computers use an algorithm that has been extensively tested for repetitive NDL dives but they are not designed or optimized for decompression diving.

I think that Charlie has it dead to rights, and while the penalty the Oceanic selected for reverse deep decompression profiles may be a mite harsh, I'm not convinced that they're unreasonable ... I really, really, really like my spinal cord.

 

[divermatt]

The Oceanic VEO lines (I have a 180) are NOT designed for deco diving, they're a rec tool. Any SI calculations or safety stop extensions these computers give are, and should be, very conservative, as the computer, and the average diver who uses said comptuer have NO business in deco.

 

[edupress]

Thanks you very much for the contribution, I actually feel much better (safer) now!
But it's interesting that Oceanic uses the same algorithm for the full line of theirs comps, including, as I understand, more advanced Atom, which if I'm not mistaken, can be used to change gases during the dive.

 

[Charlie99]

But it's interesting that Oceanic uses the same algorithm for the full line of theirs comps, including, as I understand, more advanced Atom, which if I'm not mistaken, can be used to change gases during the dive.

The dissolved gas algorithms used in the majority of computers just tracks the ppN2 (partial pressure of nitrogen). Handling air and multiple types of nitrox is a trivial modification to the programming, no more complicated than the equivalent-air-depth equation that you learn in a basic nitrox course.

The algorithm for trimix is slightly more complicated, but as long as the only inert gas is nitrogen, then the basic algorithm is identical whether the gas is air or nitrox

 

[rakkis]

All Oceanic and Aeris computers use the same algorithm.

You also have the option of bumping up the "conservative" setting if you feel the times are too liberal for you.

 

[DandyDon]

Excerpts from the Oceanic sit on the GEO...

Oceanic Personal Dive Computer Algorithm
Decompression theory can be trusted only as far as it has been demonstrated by actual test dive data. In 1987 a unique series of experiments were conducted by Diving Science and Technology (DSAT). Commissioned by the Professional Association of Diving Instructors (PADI), these Doppler ultrasound monitored human experiments conducted by Dr. Michael Powell produced the most comprehensive data set that exists for recreational divers to this day. These data were used to validate the PADI Recreational Dive Planner and are the basis of the algorithm used in all Oceanic Personal Dive Computers (PDCs).


Personal Conservative Factor Adjustment
When the Conservative Factor is set On, the no-decompression limit times are reduced to values equivalent to those that would be available at the next higher 3000 foot (915 meter) altitude.

"The Ultimate Adjustable Algorithm"
That's the way divers, instructors and Authorized Dealers refer to Oceanic PDCs. Our tissue loading bar graphs provide complete control of your margin of safety for each dive. Want to be a bit more cautious? Make it a personal rule to never enter into the caution zone; or stay one or more pixel away. Now you can even program several of our PDCs to do it for you with our patent pending Nitrogen Bar Graph Alarm; set it once and let the GEO alert you when your bar graph reaches that level.