To integrate or not to integrate

[scubadada]

Could you elaborate about the Cobalt being RGBM but more liberal ? So far it has not penalised me even when I had shortish 45mn surface intervals. But I am soon going to bring it for for the first time 7 days at 3 to 4 dives a day on nitrox32...

The decompression algorithm is simply more liberal. See the attached information from a repetitive dive test done by ScubaLab in 2014, in which the Cobalt was tested against many other popular computers/algorithms
http://ads.bonniercorp.com/scuba/PDF/ScubaLab-Computer-Test-September-2014-data.pdf

@RonR has discussed the Cobalt algorithm on the Atomic Aquatics Manufacturers Forum. He has been very helpful in understanding the topic and is quite active on the Forum. I believe @drrich2 dives a Cobalt ,and maybe a VT3 also, he might be able to help you

Good diving, Craig

 

[stuartv]

@OP: I agree with what everyone has said on these things:

- modern hoseless AI seems to be pretty solid. My Oceanic Atom 3.0 w/AI has been totally reliable for the 21 months and 100+ dives I've done with it. And I haven't even needed to change the transmitter battery yet.

- if you can wait until DEMA, you will probably find there are new options available that you might like better than what is currently available.

I would add:

Since you have so much experience and mentioned doing deep and deco dives, I personally would stay away from all the recreational computers, and go for something that will work well for deco dives.

I would not buy the Eon Steel because, while it does support Trimix, it does NOT use a tech-friendly algorithm.

The only computer that is available right now (that I know of), that has AI, that I would be looking at (and actually I am looking at as a backup to my H3) is the Hollis TX1. It's a wristwatch style, but bigger (more puck-sized). It is a full-on, multi-gas, trimix-capable tech computer that uses the Buhlmann algorithm, with Gradient Factors. And it works with the Hollis/Oceanic/Aeris AI transmitters. The computer is selling for something like $550. They want $950 for a package with the AI transmitter, but you can get the transmitter separately for well under $400. Or you could probably get the package for cheaper if you call CaveAdventurers or email LeisurePro.

As a photographer, I would think that being able to check your tank pressure by glancing at your wrist, versus having to take a hand off your camera (or whatever), or even turn your head away from your work, would be a useful advantage.

My backup computer/dive trip watch is a Suunto Stinger. I'm not quite sure why I carry it, though, because if my Cobra craps out, I won't have a tank pressure reading anymore...

If my Atom crapped out on a single tank dive, I would only have my backup computer and no tank pressure reading. I'd still be glad to have my backup computer. For one, it would still be telling me my depth and ascent rate. And, for two, if I'm using a single 120 on a wreck dive off NC, and I have a solid buddy, I probably wouldn't even end my dive early. I know my SAC well enough to be confident that my NDL will run out way before I get low on air. I usually max my NDL, take a long safety stop on the way up, and still get out with over 1000psi left (when I'm actually back on the boat).

Plus, once I'm back on the boat, if I had to, I could swap my AI transmitter off for a physical SPG and do the next dive with my backup computer having the correct info regarding my current tissue loading.

The decompression algorithm is simply more liberal.

Small correction to this. The IMPLEMENTATION of the algorithm is more liberal. An algorithm is an algorithm. No algorithm is inherently conservative or liberal, I don't think. It's the implementation of the algorithm that makes it liberal or conservative. For a bubble model, one implementation could use a different critical radius than another. For a Buhlmann model, one implementation could use the equivalent of gradient factors with different values.

And, that is what RonR has alluded to before, here (on page 4 of the thread, if the link doesn't go straight there):

New dive computer for Divemaster internship

I feel like it's important to keep the distinction clear between an algorithm and its implementation. Many discussions here blame an algorithm for things that should be blamed on the implementation. Which is to say that, for example, one RGBM-based computer being very conservative should not be an automatic whitewash of all RGBM-based computers as being conservative. You've pointed out the Cobalt as the prime example. Similarly, not all Buhlmann-based computers should be presumed to be liberal.

However, I *think* that DSAT is a specific implementation of a Buhlmann algorithm. So, I do think it is appropriate to expect all DSAT computers to be very similar in how liberal/conservative they are. However, I could be wrong. Any OEM that puts DSAT in their computer COULD (I conjecture) be free to tweak parameters to make their computer more or less liberal/conservative than other computers that are also using DSAT.

 

[scubadada]

Suunto, Mares, Cressi, Atomic Aquatics, Deep 6...are all proprietary versions of a RGBM algorithm. I'm not at all sure the algorithms are the same and that it is only implementation that is different. Perhaps we also have a semantic difference. I readily admit my understanding is incomplete and would be glad to continue my education.

 

[stuartv]

Suunto, Mares, Cressi, Atomic Aquatics, Deep 6...are all proprietary versions of a RGBM algorithm. I'm not at all sure the algorithms are the same and that it is only implementation that is different. Perhaps we also have a semantic difference. I readily admit my understanding is incomplete and would be glad to continue my education.

I think you are right. Mares says they have a Mares-Wienke version of RGBM, right? Suunto has "Suunto Fused RGBM". They are clearly all different in some way. Whether you call it a difference in the algorithm itself or just a difference in the implementation is definitely a grey area.

Either way, it's also clear that you cannot, in fairness, just ASSUME that any computer that says RGBM is going to be conservative. The Cobalt is the proof of that. So, I still think it's appropriate to distinguish that what is conservative or liberal is the implementation, not the algorithm. Heck, Suunto could surprise us all and put out a new computer that is still the "Suunto Fused RGBM algorithm" but with different parameters that make it the most liberal computer on the market. You never know....

 

[scubadada]

The following URL links to an interesting article from Diving and Hyperbaric Medicine from 2014, comparing the performance of 43 dive computers for single, square-wave dives to a variety of different depths. No repetitive, or multi-level dives as was reported in the ScubaLab test. No Atomic Aquatics but Suunto, Mares, Cressi, Oceanic, Uwatec, and others are included.
http://www.sams.ac.uk/martin-sayer/pdfs/decompression-management-43-computers

 

[Storker]

The following URL links to an interesting article from Diving and Hyperbaric Medicine from 2014, comparing the performance of 43 dive computers for single, square-wave dives to a variety of different depths. No repetitive, or multi-level dives as was reported in the ScubaLab test. No Atomic Aquatics but Suunto, Mares, Cressi, Oceanic, Uwatec, and others are included.
http://www.sams.ac.uk/martin-sayer/pdfs/decompression-management-43-computers

That paper corresponds very well with my experience with my Suunto(s). For a square profile, non-repetitive dive, the Suunto RGBM NDLs are very, very similar to the PADI RDP NDLs. Sure, my Suunto has been pretty p'ed off with me when I've cut short a safety stop, or ascended way too quickly, but since I'm well into middle age and not quite in top shape (don't ever expect me to run a marathon!), I guess a little conservativism isn't a bad idea. Any issues that the Suunto RGBM algorithm has with short SIs don't bother me at all, since my diving is usually only one or two tanks per day, with at least a 2hr surface interval (partly since I was trained on the PADI RDP table, where the bulk of your residual nitrogen time clears after ~2hrs).

I realize that if you're on a liveaboard and want to do nearly half a dozen dives in a day, a Suunto computer will probably penalize you for the short SIs, but again, I'm getting old(ish). I'm pretty certain that that "excess conservatism" of the Suuntos gels pretty well with the body I'm currently inhabiting.

 

[scubadada]

That paper corresponds very well with my experience with my Suunto(s). For a square profile, non-repetitive dive, the Suunto RGBM NDLs are very, very similar to the PADI RDP NDLs. Sure, my Suunto has been pretty p'ed off with me when I've cut short a safety stop, or ascended way too quickly, but since I'm well into middle age and not quite in top shape (don't ever expect me to run a marathon!), I guess a little conservativism isn't a bad idea. Any issues that the Suunto RGBM algorithm has with short SIs don't bother me at all, since my diving is usually only one or two tanks per day, with at least a 2hr surface interval (partly since I was trained on the PADI RDP table, where the bulk of your residual nitrogen time clears after ~2hrs).

I realize that if you're on a liveaboard and want to do nearly half a dozen dives in a day, a Suunto computer will probably penalize you for the short SIs, but again, I'm getting old(ish). I'm pretty certain that that "excess conservatism" of the Suuntos gels pretty well with the body I'm currently inhabiting.

That's right on. That is why repetitive dive information, like the ScubaLab report (post 31), is complimentary to single dive information, like this article contained.

The OP is talking about being dissatisfied with the NDLs on his Suunto computer when doing multiple dives per day. I frequently dive with folks in Florida using Suunto or Mares computers for 3 or 4 dives per day. They're with me on the 1st dive but disappear early on subsequent dives. The SIs during a 3 tanker, or beween dives 1 and 2, 3 and 4 on a 4 tank day, are often on the shorter side and tend to get penalized by the RGBM computers.

The ScubaLab test actually had an hour SI between dives 1 and 2, 3 and 4, and 2 hours between 2 and 3. Ascent rates were also controlled to within acceptable limits. Perhaps there are additional factors contributing to repetitive dive performance

 

[RonR]

Small correction to this. The IMPLEMENTATION of the algorithm is more liberal. An algorithm is an algorithm. No algorithm is inherently conservative or liberal, I don't think. It's the implementation of the algorithm that makes it liberal or conservative. For a bubble model, one implementation could use a different critical radius than another. For a Buhlmann model, one implementation could use the equivalent of gradient factors with different values.

And, that is what RonR has alluded to before, here (on page 4 of the thread, if the link doesn't go straight there):

New dive computer for Divemaster internship

Stuart is right, a fuller discussion is in the link he provides. No algorithm is inherently liberal or conservative. All algorithms contain ways to alter the conservatism. The implementation is up to the manufacturer. For RGBM or other bubble models there is the additional factor of running an "iterative" or "folded" version. Iterative being the computer actually running in real time the bubble calculations, folded being an approximation of those results created by adding factors to what is basically a Buhlmann algorithm. Iterative is far more computationally intensive and difficult to code, and to my knowledge the Cobalt is the only recreational computer to offer an iterative bubble algorithm- and we only kick that in for over 150' dive depths. For shallower dives the Cobalt uses a folded algorithm as well. There are third party iterative bubble algorithms available for more technical computers.

Also correct is the observation that DEMA in November is likely to bring announcements of a new crop of AI computers. When they will actually be available is always a question, but I would expect more options after the first of the year.

Ron

 

[gassed]

Hey all,
Great info. Thank you for the viewpoints and updates. Looks like I will wait for DEMA.
I have a couple of thoughts now. Where as before I had concerns a failure of a single unit killing the whole dive (and subsequent) if it failed, I now remember that it is just the computer that controls that destiny. I can always keep the old trusty Suunto as a backup in pocket. And to be honest, most dive ops will have rental SPGs from what I have seen.
I guess the real question now is hose less or not. I really like the idea of less clutter to carry and pack. I have two bags devoted to camera gear now!
There was a comment about not dropping a hand off the camera to look at current stats. That is a real concern as I do that often. A recent cave trip actually led to limited access to reach my primary console (leading to thoughts of a wristmount).
As to questions of consumption rate and knowing my rate; when I shoot I hunt. I do a ton of stalking. Hide and seek as opposed to charge and shoot. My profile is so far from square I dont think geometry has a name for it. In areas of heavy current (Cozumel, Philippines) I may drift for 45 minutes and then kick against a 2 knot current for 10 and recover for another 15. My rates vary on the dive and subject so i am interested a single gauge for quick reference. Even if theoretical.
Good noted about Suuto's RGBM. I knew but had forgotten that they were ultra conservative.
Again, great info, keep it coming. I have already shifted my initial view point. Nice to be old enough to remember I dont know everything!

 

[scubadada]

Stuart is right, a fuller discussion is in the link he provides. No algorithm is inherently liberal or conservative. All algorithms contain ways to alter the conservatism. The implementation is up to the manufacturer. For RGBM or other bubble models there is the additional factor of running an "iterative" or "folded" version. Iterative being the computer actually running in real time the bubble calculations, folded being an approximation of those results created by adding factors to what is basically a Buhlmann algorithm. Iterative is far more computationally intensive and difficult to code, and to my knowledge the Cobalt is the only recreational computer to offer an iterative bubble algorithm- and we only kick that in for over 150' dive depths. For shallower dives the Cobalt uses a folded algorithm as well. There are third party iterative bubble algorithms available for more technical computers.

Also correct is the observation that DEMA in November is likely to bring announcements of a new crop of AI computers. When they will actually be available is always a question, but I would expect more options after the first of the year.

Ron

Maybe the Atomic Aquatics wrist mounted AI?