Mares HD Icon and Atomic Cobalt...compatible algorithms?

[citycountryguy]

Hello--

New to diving, looking to buy computers once and be "done with it" if we buy the first time. And yes, I know the ones we are looking at aren't cheap ...

My wife has become enamored with the Atomic Cobalt--which is of course, a hose air-integrated computer. I really love the display it has, but overall I lean toward a wrist mounted computer...I also want air-integrated, so that means a transmitter based system. Since I had lasic surgery, I need reading glasses, so in looking at the options, the Mares HD Icon (now with the air integrated option available as I understand) seems to offer the best easiest reading screen for a wrist based system. (I know I could get a "reader" mask, and may well do that regardless to make sure, but for now that is not my question.)

The question is this: I've read a lot about the different algorithms of computers and how they allow for different dive times, etc...some being more conservative, some being more liberal. I've read that sometimes buddy pairs have different dive profiles based on their computer algorithms.

All other things being relatively equal (breathing/air use, etc.) would buddies using these two computers (or one person carrying both of them for testing/comparison's sake) end up with different dive times/profiles based on these two computer algorithms? I don't want either of us to be losing bottom time merely because one or the other's computers has a different algorithm that doesn't really impact on safety (since presumably, all profiles on all dive computers have safety considerations and tolerances built in). Any advice or information here about these two computers in particular would be appreciated.

I've also looked at Oceanic hoseless, and I understand that the OC1 can adjust the diving algorithm/profile to more closely match other gear, but I'm not sure how easy it would be to read for a close-vision challenged individual.

Finally, I would say that our goal is not to have the most aggressive profile/algorithm--the whole point of getting good gear is to decrease risk and increase safety margins. We're looking for a sweet spot, and general compatibility should we choose different gear.

Thanks in advance for information/feedback/advice...

Michael

[DiveNav]

Welcome to ScubaBoard.

You can see how the Mares RGBM algorithm compares to other computers in the 2009 Scuba Lab test, or in our article Fine Tuning a Decompression Algorithm

So far I have not seen a comparative test for the Cobalt.

We are integrating the Mares Icon HD into our simulators and expect to release the Icon HD online class next month.

Alberto (aka eDiver)

[Hatul]

There's a new on coming out, the Liquivision Lynx.

[NCadiver]

They are both using RGBM but I believe Mares is using a customize version for their computer. But they should be very close. If you go to dive planning on both computers you can see if there is any major time difference.
But it going to come do to air time and most likely she will have more.

[Kern]

At recreational depths both the Cobalt & the Mares use their own proprietary recreational version of RGBM. Usually? Buhlmann single phase with so called bubble factors thrown in.

I don't know how much faith I put in any of the comparisons I'v seen, but according to at least 1, the Mares version is more "conservative" than the Suunto, & according to RonR, Suuntos is more conservative than the Cobalt.

A single dive, for real or simulated, probably won't show a great deal of difference between algos. However, once you start factoring in, surface intervals between multiple dives per day, ascent rates, how close you came to NDL's, consecutive days of multiple dives, things start to change.

I wouldn't be too concerned about the differences, it's all voodoo & arcane arts really.

[RonR]

Well, you are unlikely to get identical profiles, but I doubt they will be wildly different, either. Typically the Cobalt is middle of the road, neither the most conservative or the most liberal. The Mares has a reputation of being a bit more to the conservative side.

They are both RGBM, but RGBM is more of a framework that takes bubble theory into account, and specific implementations can be quite different between computer models. As a new diver, these are not likely to be significant to you- I'm assuming you are not planning to do a lot of decompression diving- if you are, that does change things. As NCDiver says, air consumption is likely to vary more. And other differences, like the interface or battery life, are likely to be more significant.

Both computers have adjustments to conservatism, so you could try to persuade them to be similar over time. The Cobalt will demand deep stops if you get close to your no-deco limits, that might put one on a different ascent profile.

The biggest differences between RGBM implementations will tend to show up in repetitive or multi-day diving scenarios, not on single dives. Be very skeptical of any simple tests- there are a lot of variables, I've never seen test that covered more than a few. It's not that they are wrong, just incomplete. Is a computer that puts you into deco sooner (shows shorter no deco times) but gives a shorter overall ascent profile, or clears more quickly on the way up, more or less conservative? I certainly don't know. One of the hallmarks of RGBM or other bubble models is that they tend to penalize repetitive or multi-day diving, because they are trying to reduce bubble formation, not re-absorb bubbles. It is a complex subject. If you can get them side by side in a shop, you can run simulated dives on the computers using the planning functions.

Where these two will definitely diverge is on deeper decompression dives. Over 150', the Cobalt implements the fully iterative RGBM algorithm. The Mares (and all other recreational RGBM computers on the market) use a "folded" RGBM- essentially a Haldanian model with some tweaks to limit bubble formation. Full, iterative RGBM can give decompression schedules that are quite different- typically more and deeper stops, but of shorter duration with possibly a lower overall ascent time. The Cobalt, to my knowledge, is at present the only dive computer that has the full RGBM running in real time- it's very computationally intensive and has usually been used to generate tables in dive planning software. It's not anything to be concerned about as a new diver.

Some divers like to get very nerdy about algorithms. My favorite algorithm quote is from Eric Baker, to the effect that all dive algorithms are attempts to "draw a sharp, clear line through a fuzzy gray area". I'd get the computer that fits your needs best- especially your eyes- and not worry overmuch about the algorithm variations.

Ron

[citycountryguy]

Helpful information, thanks. I get almost all of it, although I will be reading a bit more to have this be part of my normal vocabulary....I appreciate it a lot...Now it becomes about spending money....

[Dr. Lecter]

Over 150', the Cobalt implements the fully iterative RGBM algorithm. ... The Cobalt, to my knowledge, is at present the only dive computer that has the full RGBM running in real time- it's very computationally intensive and has usually been used to generate tables in dive planning software.

Ron, bit of a dumb question but I wanted to know for sure: does the Cobalt's algorithm shift over when planning dives below 150', too, or just when we actually hit that depth? Guess I'm wondering too whether it was ever meant to be used as a dedicated deco diving computer. Thanks.

[RonR]

Ron, bit of a dumb question but I wanted to know for sure: does the Cobalt's algorithm shift over when planning dives below 150', too, or just when we actually hit that depth? Guess I'm wondering too whether it was ever meant to be used as a dedicated deco diving computer. Thanks.

The on board planner uses exactly the same algorithm routines as the Cobalt does during diving. That, and the fact that the Cobalt knows your current saturation state is one of the advantages of using the Cobalt's planner vs. a PC based planner. Simulating dives deeper than 150' will give full RGBM tables (there is a = "Show Deco" button in the planner, intended for viewing schedules and writing out backup tables).

Our philosophy in developing the Cobalt was very much in the "all dives are deco dives" mode- some dives come with recommended or required stop schedules. So yes, it was intended to be used for deco diving, within the limits of an air/ EAN computer.

Ron