I'm Concerned! Oceanic VT PRO question

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RoadWarrior

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Below is text from a DiverNet review of the Oceanic Versa Pro - So far as I know the only difference between the Versa and the VT Pro is the VT is hoseless. I was just about to buy the VT Pro, knowning it's less conservative, but reading this review concerns me. I don't plan to ever go below 130 feet but I do want to be at that depth at least once in my life. So far 109' is my deepest dive. I know there are arguments for being very conservative and arguments for not being so anal. Reading this review makes it appear the Oceanic is way off base, perhaps wrong, when diving deep. I'm less interested in opinions but very interested if anyone knows something specific.

"Decompression-stop dives are the type of dives I commonly do, and I took the Versa Pro on a series of 12 such dives (many repetitive) alongside a Cressi Archimede and a Suunto Vytec.
Only once did the Oceanic momentarily show me entering deco-mode, though the other two had me into deco-mode on nearly every dive.
Not only that, but the discrepancy between the amount of no-stop time remaining on the Oceanic Versa and the deco-stops demanded by the other two was alarming.

However, I can state that there were times on dives when the Suunto and Cressi were showing the first stop at 3m while the Oceanic Versa Pro showed 45 minutes of no-stop time remaining.
On one particular 38m dive, the Suunto showed eight minutes and the Cressi five minutes of total ascent time needed, while the Versa Pro still showed 15 minutes of no-stop time remaining."

Read the whole review here: http://www.divernet.com/equipment/0602divertests.htm#versa





 
As far as I know, all Oceanic computers use a modified Haldanean decompression algorithm. The Haldanean decompression theory is the oldest one, and it has been modified (tweaked) to greater and lesser extents by most modern users. The basic problem is that it assumes that gasses leave your blood and tissues at the same rate that they entered (this has been disproven and caused many modifications) and it does not consider the formation of microbubbles (a proven fact that considerably slows off-gassing) in the blood and tissues. The result is that unless the Haldanean model is PROPERLY modified, it gives extremely liberal no-stop times.

Theory (and I stress that word) number 1 - This is the theory I feel best about - The Oceanic VT PRO is using one of the more liberal Haldanean modifications. This might not be great if you are pushing its limits for no-stop times. However, I have not seen any reports of Oceanic computers routinely causing Decompression Sickness.

Theory #2 The test computer was a lemon. This is also not a good thing, but I consider it less likely because an electronic failure would more likely lead to non-operation or lock-out of deco information than to "slightly" wrong calculations, but I am operating by gut feeling with this one.

Another fact is that almost any computer is going to look liberal when stacked up against a RGBM-algorithm unit, like the SUNNTO in that article. The Reduced Gradient Bubble Model was specifically designed to deal with microbubble formation, using sonar to actually monitor the blood and tissues after surfacing from a dive to detect microbubbles which were -apparently- not causing any immediate problems, but were nevertheless forming in many divers. Because these microbubbles are easy to form, it takes a great deal of conservatism to reduce or eliminate their formation. Some consider this to be unnecessary, but it is undoubtedly safe.

Disclosure: I use a SUNNTO and choose to live with its shorter no-deco times. However, there's a large school of thought (especially in Europe and among certain Tech divers) that the RGBM is an overreaction.
 
MrConclusion:
Another fact is that almost any computer is going to look liberal when stacked up against a RGBM-algorithm unit, like the SUNNTO in that article.

See http://www.scubaboard.com/showthread.php?t=91622 and many other threads dealing with Suunto’s “RGBM.”

To quote Charlie99, “The ‘Suunto RGBM’ is NOT a bubble model. It is a neo-Haldanean dissolved gas model with no parameters or estimates for any bubble related phenomena such as free gas (bubble) volume, bubble diameter, etc. The Suunto Cobra will give you credit for deep stops in exactly the same way as will the Oceanic Veo. Fast tissues will be offgassing, slow tissues will be ongassing.”

“The Cobra and other Suunto computers do a crude emulation of RGBM by adjusting the limits (aka M-values) of the dissolved gas model in response to the history of your previous dives. In other words, it is still a dissoved gas only (not bubble) model, but with even more conservative limits, if your previous dives were deeper than 100', had a rapid ascent, your SI was short, or the dive is a reverse profile.”

“Hydrospace Engineering has a true bubble model computer. Mares might have upgraded the M1, although it might be an emulation like Suuntos. Suunto will soon release a full-up RGBM computer, if it hasn't already done so recently. But the Vytek, Vyper, Cobra, Mosquito, et al ARE NOT TRUE RGBM.”

“Look more closely at the manual and you can confirm my above statements.

Quote: Page 65 of the Cobra Manual: Tissue Calculation Model
• Suunto RGBM algorithm (developed by SUUNTO and Bruce R. Wienke, BS, MS and PhD).
• 9 tissue compartments.
• Tissue compartment halftimes: 2.5, 5, 10, 20, 40, 80, 120, 240 and 480
minutes (on gassing). The off gassing halftimes are slowed down.
• Reduced gradient (variable) "M" values based on diving habit and dive violations. The "M" values are tracked up to 100 hours after a dive.”

“Most Oceanic computers use straight, unpadded PADI/DSAT limits. I dive an Oceanic, but choose not to exit the water until I've gotten a bit more margin. DCS risk vs exposure is not a sharp well defined curve, but instead rather gradually increases with increase time-depth. Just compare the original Haldane table, USN/Workmann tables, and later tables like DCIEM. Each table author thought his table was correct, and indeed they have been used with acceptable DCS risk, but they vary widely in no-stop times.” End quote from Charlie99.
 
Thank's for the comprehensive reply. I assume you would not be concerned using the VT Pro?

MrConclusion:
As far as I know, all Oceanic computers use a modified Haldanean decompression algorithm. The Haldanean decompression theory is the oldest one, and it has been modified (tweaked) to greater and lesser extents by most modern users. The basic problem is that it assumes that gasses leave your blood and tissues at the same rate that they entered (this has been disproven and caused many modifications) and it does not consider the formation of microbubbles (a proven fact that considerably slows off-gassing) in the blood and tissues. The result is that unless the Haldanean model is PROPERLY modified, it gives extremely liberal no-stop times.

Theory (and I stress that word) number 1 - This is the theory I feel best about - The Oceanic VT PRO is using one of the more liberal Haldanean modifications. This might not be great if you are pushing its limits for no-stop times. However, I have not seen any reports of Oceanic computers routinely causing Decompression Sickness.

Theory #2 The test computer was a lemon. This is also not a good thing, but I consider it less likely because an electronic failure would more likely lead to non-operation or lock-out of deco information than to "slightly" wrong calculations, but I am operating by gut feeling with this one.

Another fact is that almost any computer is going to look liberal when stacked up against a RGBM-algorithm unit, like the SUNNTO in that article. The Reduced Gradient Bubble Model was specifically designed to deal with microbubble formation, using sonar to actually monitor the blood and tissues after surfacing from a dive to detect microbubbles which were -apparently- not causing any immediate problems, but were nevertheless forming in many divers. Because these microbubbles are easy to form, it takes a great deal of conservatism to reduce or eliminate their formation. Some consider this to be unnecessary, but it is undoubtedly safe.

Disclosure: I use a SUNNTO and choose to live with its shorter no-deco times. However, there's a large school of thought (especially in Europe and among certain Tech divers) that the RGBM is an overreaction.
 
Vie, I really appreciate your reply and MrConclusions as well.
"You said you use an Oceanic but choose not to exit the water until you've gotten a bit more margin." What exactly does that mean? When it finishing counting down the stop time you give it a little more anyway? Would you mind explaining?

By-the-way: I travel internationally in my work - Sales. I'm in Bangkok 1 or 2 times a year. Construction materials industry. Customers are company's such as CPAC, Siam City Cement, Hanson, Boral, etc. Small world huh!!?! I've been wanting to stay a weekend and dive. Before I head that way again I'll see if I can look you up here and get some suggestions and advice.

Don J



Vie:
See http://www.scubaboard.com/showthread.php?t=91622 and many other threads dealing with Suunto’s “RGBM.”

To quote Charlie99, “The ‘Suunto RGBM’ is NOT a bubble model. It is a neo-Haldanean dissolved gas model with no parameters or estimates for any bubble related phenomena such as free gas (bubble) volume, bubble diameter, etc. The Suunto Cobra will give you credit for deep stops in exactly the same way as will the Oceanic Veo. Fast tissues will be offgassing, slow tissues will be ongassing.”

“The Cobra and other Suunto computers do a crude emulation of RGBM by adjusting the limits (aka M-values) of the dissolved gas model in response to the history of your previous dives. In other words, it is still a dissoved gas only (not bubble) model, but with even more conservative limits, if your previous dives were deeper than 100', had a rapid ascent, your SI was short, or the dive is a reverse profile.”

“Hydrospace Engineering has a true bubble model computer. Mares might have upgraded the M1, although it might be an emulation like Suuntos. Suunto will soon release a full-up RGBM computer, if it hasn't already done so recently. But the Vytek, Vyper, Cobra, Mosquito, et al ARE NOT TRUE RGBM.”

“Look more closely at the manual and you can confirm my above statements.

Quote: Page 65 of the Cobra Manual: Tissue Calculation Model
• Suunto RGBM algorithm (developed by SUUNTO and Bruce R. Wienke, BS, MS and PhD).
• 9 tissue compartments.
• Tissue compartment halftimes: 2.5, 5, 10, 20, 40, 80, 120, 240 and 480
minutes (on gassing). The off gassing halftimes are slowed down.
• Reduced gradient (variable) "M" values based on diving habit and dive violations. The "M" values are tracked up to 100 hours after a dive.”

“Most Oceanic computers use straight, unpadded PADI/DSAT limits. I dive an Oceanic, but choose not to exit the water until I've gotten a bit more margin. DCS risk vs exposure is not a sharp well defined curve, but instead rather gradually increases with increase time-depth. Just compare the original Haldane table, USN/Workmann tables, and later tables like DCIEM. Each table author thought his table was correct, and indeed they have been used with acceptable DCS risk, but they vary widely in no-stop times.”
 
The pelagic computers (Aeris, Oceanic) are just more liberal than the Suunto's, which tend to be some of the more conservative computers. I have dove Suunto's. (the favor, the favor air and the cobra) I have dove the Pelagics (Datamax Pro plus, Aeris 500AI, Atmos300G and the VT). I have gone into DECO with all of the above computers, having done quite a few dives with all of them in various conditions, except the VT, which I just bought 3 dives and 1 week ago. I have not been bent.

That being said, no computer can guarantee you won't get a hit. The only way to be sure of not getting bent is not to dive. No computer or table can take into account factors like diver health or metabolism. Obviously, the more conservative a computer is, the less likely you are to take a hit. You have to decide what you are comfortable with. I prefer the liberal computers because I like the longer times and they seem to work for me.

One thing, though- approach your computer's limits slowly and cautiously. Be sure you are familiar with it before you try deco.
 
Vie - Thanks, I didn't know about the difference between an actual bubble model and the "Sunnto RGBM" algorithm. Do you know any more specifics about the differences?
 
djanni:
Vie, I really appreciate your reply and MrConclusions as well.
"You said you use an Oceanic but choose not to exit the water until you've gotten a bit more margin." What exactly does that mean? When it finishing counting down the stop time you give it a little more anyway? Would you mind explaining?

I was actually quoting Chalie99, a member of this board. I would assume that Charlie99 meant that he waited until the “tissue loading bar graph” dropped to well below the green/yellow border, i.e. well into the green (assuming he has enough breathing gas), before he surfaces. You should PM him for clarification. I myself (and my gf) have used an Oceanic Datamax Pro Plus on hundreds of dives with no problems. I now use an Atom and have experienced various problems (which I have posted in various threads on this board). Am now on my third Atom and the problems have been rectified by Oceanic.

djanni:
By-the-way: I travel internationally in my work - Sales. I'm in Bangkok 1 or 2 times a year. Construction materials industry. Customers are company's such as CPAC, Siam City Cement, Hanson, Boral, etc. Small world huh!!?! I've been wanting to stay a weekend and dive. Before I head that way again I'll see if I can look you up here and get some suggestions and advice.

Don J

Feel free to look me up—I’ll be happy to help. PM me for contact info.
 
MrConclusion:
Vie - Thanks, I didn't know about the difference between an actual bubble model and the "Sunnto RGBM" algorithm. Do you know any more specifics about the differences?

I think there are many on this board, such as Charlie99, who can perhaps answer this question well AND properly. My own understanding of the subject is quite limited... You could perhaps PM Charlie99.
 
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