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#21 kriptap

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Posted 03 August 2006 - 03:37 PM

Agree with Mike, Sunnto are nice looking computers but crap on time, day after day the first up the line are the Sunnto users while the rest carry on diving, Sunnto have to be the most conservative computer on the market and for this reason I never recommend them to divers, Sunnto if your listening that's 100's per year in sales you miss out on. What's worse is I have a Sunnto D9 but have it set to 27% Nitrox which is still a little behind my Oceanic on air!

#22 jcfig

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Posted 03 August 2006 - 03:44 PM

Kriptap have you tried setting the RGBM model on your D9 to 50%?

#23 Glasseye Snapper

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Posted 03 August 2006 - 05:26 PM

Agree with Mike, Sunnto are nice looking computers but crap on time, day after day the first up the line are the Sunnto users while the rest carry on diving, Sunnto have to be the most conservative computer on the market and for this reason I never recommend them to divers, Sunnto if your listening that's 100's per year in sales you miss out on. What's worse is I have a Sunnto D9 but have it set to 27% Nitrox which is still a little behind my Oceanic on air!

<{POST_SNAPBACK}>


We all have our own level of safety tolerance and in these litigation-prone times I think it is a reasonable assumption that even the most liberal computer (or a computer set to its most liberal setting) is safe, just with less of a safety margin for intentional or unintensional exceeding the deco limit. However, if you try to fool the computer by setting it to 27% nitrox while diving on air I think you are only fooling yourself. Dive computers are calibrated against a large set of "normal dives" and are only guaranteed to be safe when your dives stay within those boundaries. Everyone can make their own decisions but I thought a warning would be in place so that kriptap doesn't get sued ;)

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#24 kriptap

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Posted 03 August 2006 - 06:01 PM

Yes I've set the RGBM, really doesn't make much of a difference. Also I said that "I" set "my" D9 to 27% not that anyone else should ;)

I suppose it's a fine line, but if you enjoy diving don't you find it annoying when you have to get out of the water while the other divers continue? We all want to be safe while diving but we all want the time to enjoy it.

#25 Graham Abbott

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Posted 04 August 2006 - 08:35 AM

I have to agree with a few of the comments here -- these newer Suunto computers really do punish you on dives when your dives are less than a few hours surface interval. I have used Suunto Favor's for years and loved them, though now I can't get another. I've tried their newer models which have me way into deco when my group are not, I have even had times when I have to set the thing up as if I was diving Nitrox when on air so it doesn't go too far into deco! Needless to say I am now probably going to get the new Aladin, this seems to be the way forward for a reliable and well priced computer, however I do prefer a consol computer, it's too easy for me to forget a wrist mounted version!

#26 John Bantin

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Posted 05 August 2006 - 09:54 AM

Why not just do the stops?

I buy my own photographic kit. Diving equipment manufacturers and diving services suppliers get even-handed treatment from me whether they choose to advertise in the publications I write for or not. All the equipment I get on loan is returned as soon as it is finished with. Did you know you can now get Diver Mag as an iPad/Android app?

 

#27 MikeVeitch

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Posted 05 August 2006 - 02:57 PM

that would take too long... hahaha

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#28 frogfish

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Posted 05 August 2006 - 09:53 PM

Agree with Mike, Sunnto are nice looking computers but crap on time, day after day the first up the line are the Sunnto users while the rest carry on diving, Sunnto have to be the most conservative computer on the market and for this reason I never recommend them to divers, Sunnto if your listening that's 100's per year in sales you miss out on. What's worse is I have a Sunnto D9 but have it set to 27% Nitrox which is still a little behind my Oceanic on air!

<{POST_SNAPBACK}>


Following on Drew's comment above, the RGBM algorithm used in newer Suunto (and other) computers is very different from the Buhlmann-based "Haldane" models used in the most other dive computers. Calling it "more conservative" may be correct (if misleading), but complaining that it "punishes" the diver doing repetitive dives misses the point. As for intentionally setting the computer to a nitrogen percentage less than the actual N2 content of the breathing gas in order to avoid doing deco stops you should do, thus overriding the computer's best efforts to keep you alive ... that strikes me as (avoiding the "S" word) ... a potential example of Darwinism at work in our species and the modern world.

Buhlmann models assume that all nitrogen in body tissues is in solution. The reality is that nitrogen in our bodies during a dive exists in solution and in free gaseous phase, namely bubbles. The modified version of the "Reduced Gradient Bubble Model" (RGBM) algorithm used in newer Suunto computers, developed by Dr. Bruce Weinke at Los Alamos National Laboratory, takes phase transitions between nitrogen in solution and gaseous form into consideration, which Haldane models cannot do.

It's not that RGBM "punishes" repetitive dives or short surface intervals. Rather, Buhlmann models fail to take into account the additional risks of repetitive multiple-day repetitive diving, inadequate surface intervals, and/or 'bad' profiles (saw-tooth, bounce, and reversed profile dives).

Setting a RGBM computer to 27% nitrox while diving on air to avoid having to make decompresion stops is asking for trouble, in my opinion, and may be riskier than just using an older and cruder Buhlmann-based computer. As someone in this thread has already asked [RD: it was John Bantin], what's wrong with just doing the stops? (Or to put it another way, what is it that you really like about decompression sickness?)

If you prefer the additional risk of doing repetitive dives with a Buhlmann computer (or if you're one of those divers who think driving your computer all the way to the no-dec stop time edge on every dive is smart diving), then I'd have to ask why you bought one of the very few RGBM computers that anyone makes in the first place? There are still plenty of aggressive dive-at-your-own-peril computers for sale in every dive shop, though Mares and other manufacturers have also released new RGBM-based computers or are about to do so. Something to do with those pesky lawsuits from the estates of dead divers.

None of this is meant to suggest that RGBM is perfect or that it guarantees you will not take a hit. I do think RGBM is superior (and safer) than Buhlmann models, but there are cases where divers using RGBM have taken DCS hits, though most if not all were technical divers doing very deep dives with rebreathers and/or exotic gas mixes.

I should also make it clear that even though I believe RGBM is safer, I use two DiveRite computers (Duo and a Nitek Plus), both Buhlmann-based - I carry both of them on every dive. They both still work and don't require replacement yet. I also have reliability issues with Suunto due to bad experiences with a Solution Nitrox that I owned years ago. But I am aware of the limitations of the Buhlmann algorithms and do what I can to compensate. For example, deep stops (starting at half the difference between the max depth and first deco-stop depth, or half the maximum depth on no-stop dives), avoiding bad profiles, and never driving the computers to the edge, particularly for multiple day repetitive diving (for example, on a liveaboard).

By not driving the computer to the edge, I don't mean that I limit my bottom times more than you. It means that I do my stops, and I take extra time on the safety stop on any dive that has pushed near or beyond the no-stop limits.

It would be interesting if someone here started a poll - who has ever taken a hit, or more than one, were they using a computer at the time, what compuer (and what decompression model), what gas, and was the dive part of a sequence of repetitive dives on multiple days.

Frogfish

P.S. RGBM isn't the only non-Haldane decompression model around, but it is the probably the best, and the only one (to my knowledge) that has been implemented on a commercial dive computer suitable for recreational diving. Other non-Haldane models include the Canadian Series model (implemented in the DCIEM Kidd-Stubbs dive tables), the EL model developed by the US Navy and implemented as a military computer for combat divers, the Slab model developed by Dr. Tom Hennessey for the British Sub-Aqua Club (implemented on tables), and the Varying Permeability Model (aka Tiny Bubble Model), and its successor, VPM, developed by Yount and Hoffmann at the University of Hawaii, implemented on tables and in software, which is generally viewed as the progenitor of Wienke's RGBM model.

Jolie Bookspan's excellent "Diving Physiology in Plain English" has a short discussion of the non-Haldane models.

Wienke has a book about RGBM out..

Wienke's book on Amazon

... and it is also covered in his Basic Diving Physics and his textbook on decompression theory and Technical Diving in Depth.

There's also a very interesting piece about Deep Stops by Richard Pyle, the University of Hawaii/Bishop Museum ichthyologist who independently discovered the value of deep stops about ten years before Wienke uncovered the theory behind them.

Richard Pyle on Deep Stops
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#29 John Bantin

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Posted 05 August 2006 - 10:27 PM

Not wishing to blow my own trumpet (wot, me?), Bruce Weinke has personally shaken me by the hand and said that my side-by-side comparison tests of computers are spot-on. John Lippmann has also found scientifically exactly what I discovered in my own way and has been in communication with me about these articles. One computer manufacturer looked for a way to suppress the information revealed but has had no luck! I am not an expert, I am merely a witness, but howmany divers regularly take ten or more computers side-by-side on a dive?

You can see them all archived on the www.divernet.com comparison tests pages. The latest is at: http://www.divernet....ompsextra.shtml

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#30 frogfish

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Posted 05 August 2006 - 10:49 PM

John,

I'm duly impressed (by what Wienke said when he shook your hand), but hardly surprised). I'm sure everybody here knows (or at least they should know) that the side-by-side equipment comparisons you've run as technical editor at Diver magazine are the best, and absolutely unique in the industry. How many diving publications, other than yours, have ever run a negative review or evaluation of any piece of dive equipment, particularly when it is an advertiser?

I was also interested to see that you cited Pyle and included an explanation of ad hoc deep stops at the end of your excellent comparison test of computers from the March 2006 Diver issue.

Since what I've just posted above could be read as advocating that users of Haldane computers practice ad hoc deep stops (which it is, and I do), it might be worthwhile printing Bruce Wienke's remarks in 2003 urging caution about the practice. This is from Another scuba-related website:

Folks,
-
The business of "P/1.6", "halving", and "gradient factor" rules for juxta-positioning deep stops (first and following afterward) are all ad hoc measures imposed on Haldane deco. Sometimes they work for very limited diving and ranges, but in general they are without real physical basis. They are attempts to get a dissolved gas (only) algorithm (Haldane M-values) to mock up bubble dynamics. And such rules are not self consistent for diving. They are also risky when they miss requisite deeper stops, but give shorter overall deco in the shallow zone.

They are a poor way to mock phase dynamics when dual phase tables, meters, and software are now available to do this self-consistently over a whole dive profile.

Diver, beware.

Bruce Wienke, Program Manager Computational Physics, C & C Dive Team


In another post, however, Wienke does make it clear that he endorses the idea of short ad hoc deep stops for all recreational no deco stop diving:

"Deep stops for recreational no-deco diving are safety stops, and the 1/2 rule holds up fine in this regime. This is a coupled rule for the new NAUI Rec Tables and it has been correlated in RGBM and by Bennett at DAN. Plus Marroni. Plus others. It extends to ALL recreational Tables, RGBM, Navy, etc that we use. The rule is "one minute at half the bottom depth" Remember, this is for recreational, no-deco diving.."

Those of us who mainly dive on coral reefs usually end up doing more than one minute at half the max depth as part of our normal multi-level ascent anyway.

Frogfish
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#31 mattdiver

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Posted 05 August 2006 - 11:28 PM

P.S.  RGBM isn't the only non-Haldane decompression model around, but it is the probably the best, and the only one (to my knowledge) that has been implemented on a commercial dive computer suitable for recreational diving. 


Excellent post, Robert. Very thorough and educative.

Just a small note to say that the DCIEM model is implemented in the Citizen Cyber Aqualand series of dive computers.

#32 Drew

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Posted 05 August 2006 - 11:44 PM

Hey John
Bruce shook your hand for the review. He shook his fist at me when I told him that the record of RGBM having a clean record was not so clean because I took a hit diving within RGBM in PNG. Then a few others came to pour more rain on the RGBM party.
However, for dive guides and professionals, the computer quagmire is a very real dilemma. I mean, someone comes with a clean computer for 1 -2 weeks and leaves loaded, expecting the guide to stay with them or worse the company expects them to stay with the clients.
Now many dive ops switch DMs so they don't dive 4 dives a day 350 a year. But there are many who don't.
As for the EAN % switchers, I wish you all the best of luck and hope you stay out of the can. However, please let me know which trips you're on so I can avoid the same boat. I like having not to stop a trip for medical emergencies.

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#33 DeanB

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Posted 06 August 2006 - 01:02 AM

I must admit, when I was diving in Malta we were diving as a threesome ;) two of us were on Aladins one on suunto. At first we took the piss out of our mate who had to stop up to 3 mins longer than us (macho diver banta) but one of us would stay with him for safety purposes, well that was me as I thought, in the long run its obviously better.

Anyway what do people think of the VR2-VR3 computers ???

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#34 frogfish

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Posted 06 August 2006 - 01:41 AM

Hey John
Bruce ... shook his fist at me when I told him that the record of RGBM having a clean record was not so clean because I took a hit diving within RGBM in PNG. Then a few others came to pour more rain on the RGBM party.
However, for dive guides and professionals, the computer quagmire is a very real dilemma. I mean, someone comes with a clean computer for 1 -2 weeks and leaves loaded, expecting the guide to stay with them or worse the company expects them to stay with the clients.
Now many dive ops switch DMs so they don't dive 4 dives a day 350 a year. But there are many who don't.
As for the EAN % switchers, I wish you all the best of luck and hope you stay out of the can. However, please let me know which trips you're on so I can avoid the same boat. I like having not to stop a trip for medical emergencies.

<{POST_SNAPBACK}>


But Drew, didn't you hit the hot tub (or have a hot shower) that time?

By now I think we all know that isn't such a great idea, but it wasn't that long ago that most of the Aggressor fleet actually had hot tubs that people were jumping into right after coming in from diving.

You're absolutely right about dive guides. There are lots of boats that do same day turn-arounds, which doesn't allow the diving personnel much off-time for off-gassing. My friends on a boat here just had a customer (Russian nationality) who decided to take his newly certified 12-year old son on a bounce to 60 meters. Obviously without telling the dive master ahead of time, who sensibly did not follow them all the way down. Both of them were banned from diving the rest of the trip, but it was almost over. This was in Komodo, where there is no chamber - the closest is Bali, almost a two hour flight.

There is a line of thinking that the only reason more dive guides don't get hit is that beyond a certain point, repetitive diving can lead to a higher resistance to DCI, the result of a reduction in microbubble nuclei. Wienke has written about this.

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#35 kriptap

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Posted 06 August 2006 - 03:18 AM

Following on Drew's comment above, the RGBM algorithm used in newer Suunto (and other) computers is very different from the Buhlmann-based  "Haldane" models used in the most other dive computers.  Calling it "more conservative" may be correct (if misleading), but complaining that it "punishes" the diver doing repetitive dives misses the point.  As for intentionally setting the computer to a nitrogen percentage less than the actual N2 content of the breathing gas in order to avoid doing deco stops you should do, thus overriding the computer's best efforts to keep you alive ... that strikes me as (avoiding the "S" word) ... a potential example of Darwinism at work in our species and the modern world.

Buhlmann models assume that all nitrogen in body tissues is in solution. The reality is that nitrogen in our bodies during a dive exists in solution and in free gaseous phase, namely bubbles. The modified version of the "Reduced Gradient Bubble Model" (RGBM) algorithm used in newer Suunto computers, developed by Dr. Bruce Weinke at Los Alamos National Laboratory,  takes phase transitions between nitrogen in solution and gaseous form into consideration, which Haldane models cannot do. 

It's not that RGBM "punishes" repetitive dives or short surface intervals.  Rather, Buhlmann models fail to take into account the additional risks of repetitive multiple-day repetitive diving, inadequate surface intervals, and/or 'bad' profiles (saw-tooth, bounce, and reversed profile dives). 

Setting a RGBM computer to 27% nitrox while diving on air to avoid having to make decompresion stops is asking for trouble, in my opinion, and may be riskier than just using an older and cruder Buhlmann-based computer.  As someone in this thread has already asked [RD: it was John Bantin], what's wrong with just doing the stops?  (Or to put it another way, what is it that you really like about decompression sickness?)

If you prefer the additional risk of doing repetitive dives with a Buhlmann computer (or if you're one of those divers who think driving your computer all the way to the no-dec stop time edge on every dive is smart diving), then I'd have to ask why you bought one of the very few RGBM computers that anyone makes in the first place?  There are still plenty of aggressive dive-at-your-own-peril computers for sale in every dive shop, though Mares and other manufacturers have also released new RGBM-based computers or are about to do so.  Something to do with those pesky lawsuits from the estates of dead divers.

None of this is meant to suggest that RGBM is perfect or that it guarantees you will not take a hit.  I do think RGBM is superior (and safer) than Buhlmann models, but there are cases where divers using RGBM have taken DCS hits, though most if not all were technical divers doing very deep dives with rebreathers and/or exotic gas mixes.

I should also make it clear that even though I believe RGBM is safer, I use two DiveRite computers (Duo and a Nitek Plus), both Buhlmann-based - I carry both of them on every dive.   They both still work and don't require replacement yet.  I also have reliability issues with Suunto due to bad experiences with a Solution Nitrox that I owned years ago.  But I am aware of the limitations of the Buhlmann algorithms and do what I can to compensate.  For example, deep stops (starting at half the difference between the max depth and first deco-stop depth, or half the maximum depth on no-stop dives), avoiding bad profiles, and never driving the computers to the edge, particularly for multiple day repetitive diving (for example, on a liveaboard). 

By not driving the computer to the edge, I don't mean that I limit my bottom times more than you.  It means that I do my stops, and I take extra time on the safety stop on any dive that has pushed near or beyond the no-stop limits.

It would be interesting if someone here started a poll - who has ever taken a hit, or more than one, were they using a computer at the time,  what compuer (and what decompression model), what gas, and was the dive part of a sequence of repetitive dives on multiple days.

Frogfish

P.S.  RGBM isn't the only non-Haldane decompression model around, but it is the probably the best, and the only one (to my knowledge) that has been implemented on a commercial dive computer suitable for recreational diving.  Other non-Haldane models include the Canadian Series model (implemented in the DCIEM Kidd-Stubbs dive tables), the EL model developed by the US Navy and implemented as a military computer for combat divers, the Slab model developed by Dr. Tom Hennessey for the British Sub-Aqua Club (implemented on tables), and the Varying Permeability Model (aka Tiny Bubble Model), and its successor, VPM,  developed by Yount and Hoffmann at the University of Hawaii, implemented on tables and in software, which is generally viewed as the progenitor of Wienke's RGBM model.

Jolie Bookspan's excellent "Diving Physiology in Plain English" has a short discussion of the non-Haldane models. 

Wienke has a book about RGBM out..

Wienke's book on Amazon

... and it is also covered in his  Basic Diving Physics and his textbook on decompression theory and Technical Diving in Depth.

There's also a very interesting piece about Deep Stops by Richard Pyle, the University of Hawaii/Bishop Museum ichthyologist who independently discovered the value of deep stops about ten years before Wienke uncovered the theory behind them.

Richard Pyle on Deep Stops

<{POST_SNAPBACK}>



Frogfish I think you missed what I said, so I'll say it again slowly "What's worse is I have a Sunnto D9 but have it set to 27% Nitrox which is still a little behind my Oceanic on air!" I use an oceanic on air...... the Sunnto is on 27% so I can use it or it would permanently be bent, so yes do avoid the "s" word and read the post. ;)

#36 pmooney

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Posted 06 August 2006 - 03:51 AM

I have been using an old "blue" alladin nitrox as my primary computer since they were released.
It has had absolutley no care or attention other than a bi-annual serive and battery change.

For the last few years this old wristmount has been backed up by an air nitrox cable tied to my contents gauge.

Both have performed flawlessly.

#37 frogfish

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Posted 06 August 2006 - 04:02 AM

Frogfish I think you missed what I said, so I'll say it again slowly "What's worse is I have a Sunnto D9 but have it set to 27% Nitrox which is still a little behind my Oceanic on air!" I use an oceanic on air...... the Sunnto is on 27% so I can use it or it would permanently be bent, so yes do avoid the "s" word and read the post. ;)

<{POST_SNAPBACK}>


If I misunderstood what you wrote, then my deepest apologies, but I don't think I have. You've said (twice) that you are have set your D9 to 27% Nitrox while your Oceanic computer is set on air. I assume that means you are diving on air (=EANX21, not EANX27) and that by "behind" you mean that the Suunto set on EANX27 still gives you less bottom time and/or requiresa longer decompression stops than the Oceanic set on air does.

I can only interpret your explanation that you dive with the Suunto set to EANX27 while diving on air "so I can use it or it would be permanently bent" to mean that the Suunto computer - not you - would be permanently "bent" (i.e., that it would lock you out) because you've chosen to follow the the least conservative of your two computers rather than adhering to the Suunto's decompression limits and instructions.

Most of the people I dive with would adhere to the principle that, when multiple computers are used, one should follow the most conservative computer regarding no-stop times, deco stops, etc. not the least.

If I understand you correctly, what you're doing here is the same as diving with two computers, following the least conservative profile of the two, and then putting the computer that is still "in deco" when you come up back in the water on 4 meters of line and hanging it over the side of the boat so it can "decompress" while you have a hot shower. If so, then I'm afraid the "s" word still does apply, as might the reference to Darwin. If I've misunderstood what you're saying, then don't be angry, just point out how I've misconstrued your meaning.

Frogfish
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#38 Drew

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Posted 06 August 2006 - 07:51 AM

Yes Robert I did take a hot shower. But after talking to a few doctors, they think I was probably already in non-clinical DCI and the hot shower pushed it to clinical.

Kriptap, I think what Frogfish was trying to say (and which I wholly agree with) is that using a precision instrument that is designed to keep you out of trouble in a dangerous way isn't something to be joked about.
I sure you know the consequences of your own actions, which at the end of the day is your own responsibility.
Frogfish is trying to emphatically deride that practice as unsafe and let people know exactly what the bad consequences are for messing with the EAN% settings to get bottom time.

But Drew, didn't you hit the hot tub (or have a hot shower) that time? 

By now I think we all know that isn't such a great idea, but it wasn't that long ago that most of the Aggressor fleet actually had hot tubs that people were jumping into right after coming in from diving.

You're absolutely right about dive guides.  There are lots of boats that do same day turn-arounds, which doesn't allow the diving personnel much off-time for off-gassing.  My friends on a boat here just had a customer (Russian nationality) who decided to take his newly certified 12-year old son on a bounce to 60 meters.  Obviously without telling the dive master ahead of time, who sensibly did not follow them all the way down.  Both of them were banned from diving the rest of the trip, but it was almost over.  This was in Komodo, where there is no chamber - the closest is Bali, almost a two hour flight.

There is a line of thinking that the only reason more dive guides don't get hit is that beyond a certain point, repetitive diving can lead to a higher resistance to DCI, the result of a reduction in microbubble nuclei.  Wienke has written about this.

Frogfish

<{POST_SNAPBACK}>


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#39 Alex_Mustard

Alex_Mustard

    The Doctor

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Posted 06 August 2006 - 08:01 AM

One thing I have noticed is the importance of surface intervals in determining the no-deco times given by the different models.

The Suunto algorithms are particularly cautious with short surface intervals. In cayman, where Kriptap dives it is routine to have short 45 minute surface intervals between dives on two tank trips. When I am diving in this the Suunto is very conservative.

When I dive in other places, such as the Red Sea, where it is routine to leave 1.5 hours or more between dives I find the Suunto can actually be more agressive than other brands.

Anyone else noticed similar patterns?

Alex

Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D4 (Subal housing). Nikon D7100 (Subal housing). Olympus EPL-5 (Nauticam housing).


#40 timoma

timoma

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Posted 06 August 2006 - 08:29 AM

One thing I have noticed is the importance of surface intervals in determining the no-deco times given by the different models.

The Suunto algorithms are particularly cautious with short surface intervals. In cayman, where Kriptap dives it is routine to have short 45 minute surface intervals between dives on two tank trips. When I am diving in this the Suunto is very conservative.

When I dive in other places, such as the Red Sea, where it is routine to leave 1.5 hours or more between dives I find the Suunto can actually be more agressive than other brands.

Anyone else noticed similar patterns?

Alex

<{POST_SNAPBACK}>


This is due to the Suunto algorithm which - and Suunto says it themselves - is NOT a purebred RGBM implementation, but a fuzz factor hack on top of a Haldanean model(*). One way Suunto has simulated RGBM is to tamper with the surface interval off-gassing model to make it (much) more conservative.

There has been plenty of discussion on this at various tech. diving forums like Decostop etc, so I'll let you read it yourselves.

There is a paper by Suunto on the algorithm at http://www.dive-tech...suunto-rgbm.pdf

Also, a nice comparison of various models is at ftp://decompression.org/pub/Maiken/

timo

(*) I am not familiar with RGBM, but I am fairly familiar with VPM and as a rule, a real-time (=diving computer) implementation of a full bubble model would be prohibitively expensive in terms of processor and power consumption.
It was already broken when I got here