Suunto Cobra 2 in Nitrox Mode

[John Henry]

Just did my first diving using Nitrox. Throughout the dive, the O2 % was continuously displayed (32) and flashing in the bottom left corner, where Tank Pressure is normally displayed.

I thought this was odd, because I dont need to know O2 % every time I look at the computer, (It doesnt change, and I set it, so why display it?) I need to know tank pressure. To get tank pressure required paging through three displays each time.

Reading the manual, this seems to be normal. I think it is stupid.

Did I miss a step somewhere? I need to see tank pressure, not O2 % .

Any help?

[cbope]

Actually it is important, as most Suunto's like your Cobra 2 support multi-gas switching (2 gases if I remember correctly). It could lead to DCI if your computer "thinks" you are using a particular mix but in fact you have a different mix in your tank. So for that reason alone it's a good idea for the computer to show your mix on the main screen so that you KNOW which mix is being used for NDL caluculations (and resulting deco stops if you are deco diving).

I haven't used my D6 for mixes other than air since I got it but I'll check to see if it does the same thing. Of course the D6 doesn't support air integration so I think that other Cobra owners will have to chime in.

[John Henry]

yes, you are correct about setting it up for two gases. But I still would rather see tank pressure than mix %.

Maybe that's just me, since I am a relatively new diver.

[Diver Dave]

I would re-read the manual. I dive an air integrated Cobra 2 on Nitrox almost exclusively (28%-32%) and have never experienced this. Try manually setting your pp02 level warning function (I use 1.4 ata) and see if that doesn't solve the prolem.

[Jack Hammer]

I use a Gekko, mine shows the % always when in nitrox mode, they did this so you would know what gas you are breathing (or what you told the computer you are using). This is actually a good thing, a few times I forgot to set the % and noticed it as soon as I got ~5' down, I just surfaced and set it for what I was actually breathing.

After a while you get used to the different screen layout. One of my buddies used the cobra and IIRC you can hit one of the buttons to toggle to pressure, there might even be an option in the menu.

Jack

[RogerAg]

I have both a Cobra 1 and a Cobra 2. I never would have upgraded to a Cobra 2 if I know the problems with it in Nitrox 2 mode. When I dive I usually do a 2 or 3 tank dive and usually the last tank is Nitrox. So the Cobra 2 and mode 2 I thought was a good idea. In mode 2 I would have mix 1 at 21% and mix 2 set at the percentage of the last tank, usually around 32%. But in mix 2 the Cobra does not show tank psi. What it does show is the mix FLASHING such as 32%. I keep my Cobra console next to my chest usually facing me so I can see depth and tank psi at a glance. What I don't need to see is a flashing 32%, for Gods sake I know what percent oxygen I have because I entered it into the Cobra, what I don't know is what the tank pressure is. I really think that tank psi is more important information then oxygen percentage because that does not change but psi does. Some people say that it is a good thing to see the % of gas you are breathing and I say YES but once I see it I don't need to see it throughout the dive. What we should have is psi showing all the time and toggle to % if I want to make sure but then the computer should always go back to psi.

[nrembis]

I might be overlooking something, but but switching to another gas, wouldnt matter what your psi is showing on the computer as its another tank

[RogerAg]

Cobra 2

The real problem with the Cobra 2 is it is my opinion that it was misrepresented by Suunto. The Cobra 2 is advertised as “2 gas switching” but what Suunto does not say is what “2 gas switching” means.

When I dive I usually do my deepest dive first and I use Air.
On the second dive of the day I will usually use NITROX, which helps me to offgas, and I don’t usually fall asleep in my chair while watching TV in the evening, that is probably why they call NITROX “geezer gas.”

In the Cobra 2 User’s Guide it states that if the Cobra 2 is set at AIR then you can not switch to NITROX within 24 hrs. So since I use AIR on the first dive and NITROX on the second dive, the Cobra 2 is set on NITROX and the O2 is set at 21% which is the same as AIR.

The Cobra 2 has two (2) NITROX settings called “MIX 1” and “MIX 2”. And the Cobra 2 allows the diver to switch from “MIX 1” to “MIX 2” while on the surface or underwater. So I set the O2 “MIX 1” at 21% and “MIX 2” is set at the dive shop after I test the O2 of the tank which is usually 32%. This is quite convenient because I don’t have to enter new values on the Cobra 2 while on a pitching boat with the sun glaring down on the display.

The Dive

On dive 1 of the day I usually hook up my tanks myself. When done I check the tank psi then I turn the air off and take note of air leaks. When I’m ready to dive I turn the air back on, put on my gear including BCD do a buddy check and jump in the water while on the surface I do another check psi OK, Cobra 2 OK and BCD OK. As I descend I am always watching depth and psi. While in “MIX 1” the Cobra 2 works as expected.

After surfacing and back on the boat I hook up the NITROX tank and I switch to “MIX 2” which was preset at the dive shop, lets say O2 32%, then I do all the pre checks that I did on “dive 1”. On the boat and while floating on the surface the tank psi continues to show psi BUT when descending below 10 feet the Cobra 2 in “MIX 2” stops showing psi and only shows O2 32% in the place of psi.

Now I can switch under water from “MIX 2” to “MIX 1” and psi comes back and stays but the Cobra 2 now thinks that I am now at 21%. I can also switch from O2 32% to psi but only for 2 seconds and then the Cobra 2 go back to O2 32% and stays there until I surface. That’s right when I get above 10 feet psi comes back and O2 32% goes away!

My dive shop sent the Cobra 2 in for repairs and it came back as OK!
After my next dive I when back to my dive shop and they sent the Cobra 2 back in for repairs. It came back as OK! and this time they included a new User’s Guide!
This time I used the dive shop pool to check the Cobra 2 and the same thing happened, on the bottom of the pool (10 feet) “Mix 2” no longer showed psi but O2 32%. Then the Dive Shop owner took my Cobra 2 to the bottom of the pool and when he came back up he immediately called his tach at Suunto. As it turns out his tach is not the same as a users tach. My dive shop owner was told that the Cobra 2 is doing just as its supposed to do. “Mix 2” is used when a 2nd tank strapped to the divers side such as a deep dive when the 2nd tank is used for decompression.

“Mix 2” is used when the diver is breathing off of a second tank of air while the Cobra 2 is attached to the empty tank while decompressing.

The problem is that the dive shop does not know that because the “User’s Guide” does not say that! BUT the “User’s Guide” on page 6 does say “WARNING NOT FOR PROFESSIONAL USE! Suunto dive computers are intended for recreational use only.”
That is why I say that the Cobra 2 is in my opinion misrepresented by Suunto. I would not have paid as much as I did for the Cobra 2 because there are other problems that I did not mention.

[nrembis]

I would say you better find you a new dive shop/instructor before someone gets killed

any competent instructor/owner/salesman would have known that the 2 gas mixes on the Cobra 2 are settings for a deco mix during same dive, I dont think suunto mis-represented it, its just a matter of lack of education on someones part.

[thesmoothdome]

It's always been my understanding that a computer that does 2 mixes means that the switch is done during the dive. If you start a dive with 21% that would be Mix 1. If you switch to a higher O2 during a shallower part of your dive or for deco purposes, that would be Mix 2.

Sounds like it's a lack of understanding of the usage of computer able to switch gases rather than a misrepresentation by the company.