Cobra vs. Cobra 3 - "Consumed Bottom Time" vs. "Dive Time in Seconds and Minutes."

[lawtyger]

I know these computers have been compared many times based on my search of past threads. But, to sum up the differences as I understand them:

Cobra
- No compass
- No matrix display
- No deep stop
- No gas switching during dives

Cobra 3 does all of the above. The other difference that I was hoping someone else could explain to me (in terms of benefit or use during a dive) is the Cobra says it has a "consumed Bottom Time Graph" and the Cobra 3 does not. But, the Cobra 3 has "Dive Time in Seconds and Minutes" when in gauge mode.

I'm trying decide on whether to buy a used Cobra or Cobra 3 and just want to make sure I understand this which I don't at the moment. I'm assuming that the Cobra 3 will tell you exactly how many minutes and seconds you have left based on the air in your tank but I don't know if that is correct. I guess it could just mean it will tell you at the end of the dive exactly how many minutes and seconds your dive actually was.

If anyone wants to chime in on which would be the better purchase, I'll just say that I'm I'm not opposed to foregoing the digital compass and I am a very beginner diver so I don't think I'll be missing much with if I don't have no deep stop and no gas switching during dives.

 

[reefduffer]

Cobra 3 does all of the above. The other difference that I was hoping someone else could explain to me (in terms of benefit or use during a dive) is the Cobra says it has a "consumed Bottom Time Graph" and the Cobra 3 does not. But, the Cobra 3 has "Dive Time in Seconds and Minutes" when in gauge mode.

I'm trying decide on whether to buy a used Cobra or Cobra 3 and just want to make sure I understand this which I don't at the moment. I'm assuming that the Cobra 3 will tell you exactly how many minutes and seconds you have left based on the air in your tank but I don't know if that is correct. I guess it could just mean it will tell you at the end of the dive exactly how many minutes and seconds your dive actually was.

You have misunderstood this a little. Gauge mode is a mode of operation in which the computer is not attempting to track either nitrogen loading (remaining no-deco time), or estimated air time remaining. In this mode, it functions as a "bottom timer" with integrated SPG, that is, it will tell you about your depth, how long you've been under, and your tank pressure, but it's not computing anything from these about how much longer you can stay at depth, which is what many buy a dive computer for. A bottom timer, or gauge mode, is used by technical divers or others using tables etc. who are computing their nitrogen and tank gas situation themselves, and not depending on the computer for that.

Most would not buy a Cobra or Cobra3 to use primarily in gauge mode, but if you have one already it's nice not to need another instrument when all you want is the raw data. Gauge mode is also entered automatically in Error Mode, when you have violated a required decompression stop and the Cobra/Cobra3 has given up on computing remaining no-deco time because you don't have any. It will report time, depth and tank pressure so you aren't "flying blind" trying to get back to the surface.

In normal (not gauge) operation modes, dive time is reported in minutes. Since the big center display isn't needed in gauge mode, that is used for a more precise display, in minutes and seconds. My guess from your profile is that gauge mode, or a higher-resolution dive time display in gauge mode, should not be a big factor in a Cobra/Cobra3 decision.

I have a Cobra. The "Consumed bottom time" graph is a representation of your current cumulative nitrogen loading. Think of it as roughly what pressure group you're currently in when diving tables. During a dive, I pay a lot more attention to the remaining no-deco time display as a measure of my nitrogen loading. If the graphical CBT display were gone (like a Cobra3) I wouldn't miss it much.

My serious recommendation is that before you spend the several hundred dollars to buy either, even used, download the manuals and read them. You'll have to (or at least should) do this before using them, so you'll end up doing it anyway, and doing it before purchase might prevent buyer's remorse.

Edited for terminology clarification; "no-deco" vice "bottom" time.

 

[lawtyger]

Yes, it does seem I misunderstood. I'm actually in the process of watching a review how how the Cobra operates so that should help as will trying to read the manuals ahead of time.

I did use a Cobra when I got certified but at that point everything was so new. I also dove once after getting certified and used a Cobra again. No issues and served it's purpose, I think where my confusion is/was is how the Cobra 3 would be better for my needs. It sounds like, especially as a beginner, the Cobra is just fine.

I haven't purchased anything yet but have been monitoring used Cobras and Cobras 3 to see what they are going for. I don't think I'm willing to spend the money on something new.

 

[Hatul]

I have the Vyper but I presume the Cobra uses the same terms. Consumed Bottom Time is just a graphical representation of the non deco time. When the graph is full the non deco time is 0. It provides no new information and is useless IMO. In fact it's not available when you use the computer in Nitrox mode or in surface mode.

The is contrast to computers that display a graph of the nitrogen loading of the max loaded compartment. This one is much more useful and it does correspond to the pressure group of the tables.

Adam

 

[DiveNav]

we have online classes for both models: lots of videos to show how they operate in various diving situations.