Why are my Vytec and Cobra so different?

[SM Diver]

I use the Vytec with AI as my primary, but also use the Cobra as a redundant computer.

Yesterday I had multiple dives and noticed a fairly significant disparity between the two computers. Yes, I had remembered to program the correct mix in BOTH computers for each dive, h/e, immediatly after the third dive my Cobra was showing 80% 02 exposure, and the Vytec only 20%. On my last dive, in 133 fsw, I left when my Vytec showed 2 minutes of no-deco bottom time. It never went into deco. H/E, upon hearing my Cobra, I looked and saw that I had 10 minutes with a 10ft ceiling. I wasn't too concerned about locking out the computer since it was my last dive, but made the stop just to be safe.

Hmmm, why is one computer giving me a mandatory deco stop, and the other is not? Are these not the same algorithms?

Scott

 

[SM Diver]

And an even better question: Why in the hell did I put this in the regulator area?


Edit note: Moved to the Computers, Gauges and Watches forum by DivingGal

 

[Genesis]

Suunto does some VERY bizarre things with O2 exposure on the Vyper/Cobra (the Cobra has the EXACT SAME firmware as the Vyper, except for the AI - having now tested both, and now having one of each, I can say that with some certainty.)

I dive a Vytec as my "regular" computer.

The Cobra/Vyper grossly accelerate the O2 clock in some cases if you approach (and definitely if you exceed) a 1.4 PO2, even for a very short period of time.

"Grossly exceed", by the way, means TEN TIMES the proper exposure calculation according to the NOAA tables!

 

[SM Diver]

I did get a P02 alarm on my first dive. Dove a 35 mix down to 110. Strange that the Vytec would only show 20% total exposure, when the Cobra showed 80%. That's one hell of a difference.

Still does not explain the mandatory deco stop on the Cobra.

I guess what you are saying is they are not the same algorithim. I thought they were, and that Suunto held it out as being the same.

 

[Genesis]

on the NDL computations and deco obs. Realize that the Cobra was probably a foot or so BELOW the Vytec the entire dive (especially if you're spearing!), and believe it or not, it makes a difference!

BUT, they are VERY DIFFERENT on the PO2 loading if you approach or exceed 1.4.

My Cobra and Vyper are typically set in Gauge mode; my Vytec is my primary computer. The others are for my g/f, her daughter, and anyone who "comes to play" and wants better gear to dive with than the crap that is usually rented. As such a nice digital gauge pack works really well - and I got a nice price on the Cobra (and had the Vyper "left over"), so it worked out well for me.

 

[KrisB]

tampascott once bubbled...
I guess what you are saying is they are not the same algorithim. I thought they were, and that Suunto held it out as being the same.

Same algorithm, but Suunto has added a feature to the Vytec that lets you "turn down" the RGBM modeling. This would allow you more bottom time at the supposedly higher risk of DCS. *shrug* who really knows, though.

Perhaps this setting has been changed on your Vytec?

 

[Genesis]

They are NOT the same.

I have both, and have, like TampaScott, dove both side-by-side.

There are subtle differences in the NDL computation, and VERY NOT SUBTLE ones in the CNS loading.

 

[jplacson]

To those who have the Vytec and Vyper... what are the main differences in data output? Which one is more conservative? Or which one can be set for a more conservative/aggressive dive?

If you had to choose between the Vyper or Vytec... and have only ONE computer to depend on... which one would it be?

 

[SM Diver]

I doubt you'll find many people that dive the vytec and vyper side by side, simply because they are both wrist computers. Most people that use a wrist computer who want redundancy will have their second computer on a console.

Genesis- I had thought about the fact that the Cobra hangs lower, especially since it's not clipped to a d-ring and just hangs freely. If a foot or two makes that much difference, that would be surprising.

I will have to go back and check the diver setting. I know you have three choices, with the third being the most liberal. I believe they are both set the same, but if I am mistaken, and the Vytec is set more liberal, then mystery solved.

 

[Genesis]

you're near the deco limits..... especially if its there for the entire dive!

I've dove a Vyper and Vytec side-by-side (intentionally, as I was testing the PO2 stuff), and there are differences. Not major (in the NDL computations), but they're there.

The Vytec can be set to be LESS conservative (the RGBM50 .vs. 100 setting) while the Vyper/Cobra lack the latter option - they can only be set to be MORE conservative than the base settings.