Can Suunto Cobra 2 be used for deco diving?

[rstofer]

A very interesting discussion. I hope guys like 40F and NWGD don't stop posting on such topics.
I am having the opposite problem. I'm looking for a simple (cheap) BT/DG and can't find one. Everywhere I look I find a fancy (expensive) model or a computer (expensive) that can be put into gauge mode. I've got a Gekko that can't be put into gauge mode damn it.
I find even as a rec diver I am over reliant on my computer to tell me about my NDL's and have started using tables to pre plan some dives (I feel the pull of the dark side).

I went looking for the same thing and the Uwatec was all I could find. I don't think the Uwatec battery is user replaceable. The user manual states that it will last 13 years at 50 dives per year and 10 years at 200 dives per year. In any event, it was so pricey that I just decided to get the Nitek Duo.

Unfortunately, there is some button pushing required to get to the secondary screen for maximum depth with the Duo. The same button pushing is required in Gauge mode. Bummer... Those little buttons are a PITA with cold water gloves. Especially if I wear it on my right wrist. I'm right handed...

Or, buy the LiquiVision X1 with V-Planner Live. It has a mode for NDL diving that shows the max depth, current depth, dive time, NDL and %O2 all on the same screen. That's perfect!

In a year or so, my grandson will outgrow his back-inflate BC and I will get him a BP/W. At the same time we can walk away from the Veo computer in his console. I will give him my Duo and buy the X1 for me. Gee, it's nice to have an upgrade path!

Richard

 

[Hatul]

I have a Cobra that I have used since being certified last summer. My understanding of the Suunto manual is that the Cobra (not familiar with the Cobra2) does provide for routine "deep" diving, where "deep" is the 60' to 120' range allowed for recreational divers. As i understand it, the Suunto Cobra is not intended to be used as a full decompression computer. It will calculate decompression stops and floors and ceilings in the event that you inadvertantly find yourself in a decompression dive (which should not happen if we pay attention to our depth and time)

...

I use the Suunto Vyper and an old Prodigy as backup. The Suunto is quite a bit more conservative than the Oceanic. A couple of points to add.

For a professional divemaster who has to make repetitive dives every day it may be too restrictive. I mentioned above about a dive guide who sold his Vyper and bought a Uwatec for that reason. He sets his Uwatec to 24% O2 to increase his dive times -- not advisable, but that's his decision.

The Oceanic has a nice nitrogen loading odometer, which the Suunto lacks. The Vyper only shows the number of minutes left in non deco time.

The Suunto has a great simulator mode, so you can see exactly what the display looks like in any dive. It's one of the nicest features of this computer in my mind.

The floor, in the Suunto, is only displayed when the computer enters the deco mode. For some reason, unfortunately it does not display the floor -- the max depth at which there is net off gassing of nitrogen, when in non-deco mode. I guess when the computer enters the deco mode they don't want you to continue with your dive and go below the "floor". And conversely when in non deco mode they figure you don't care, as long as you stay within the non deco limits.

Adam

 

[eponym]

I've used two Suuntos, the Vyper and the Vytec, on deco dives. I put them in gauge mode and follow a deco schedule cut in V-Planner. (In gauge mode the Suuntos display runtime in minutes and seconds, which is good; while I don't do enough deco diving to justify a new computer, they allow me to manage my deco stops efficiently.)

But I have never considered doing (planned) deco dives using the Suunto software. To begin with, how would you know your gas needs if you don't have a run table (stop depths and times) to work with before you dive? Seriously--anyone?

The Oceanic has a nice nitrogen loading odometer, which the Suunto lacks. The Vyper only shows the number of minutes left in non deco time.

At least on my (older) vyper and vytec, the series of bars on the left side of the display will light up progressively from bottom to top, from green to red, to show how much of the no-deco time you've consumed. I think that's the same as the Oceanic's loading bar graph, which is also on the left side of the display. I will admit that I seldom take notice of that nitrogen loading graph: I just look at remaining no-deke time. And when diving nitrox this graph is assigned to ox-tox instead of nitrogen loading.

But I could be wrong on this cross-model comparison--let me know.

The Suunto has a great simulator mode, so you can see exactly what the display looks like in any dive. It's one of the nicest features of this computer in my mind.

I agree. The simulator makes it easy to explain the unplanned deco features to a new user. It's critical to understanding the floor and ceiling dispays before you run into them underwater.

The floor, in the Suunto, is only displayed when the computer enters the deco mode. For some reason, unfortunately it does not display the floor--the max depth at which there is net off gassing of nitrogen--when in non-deco mode. I guess when the computer enters the deco mode they don't want you to continue with your dive and go below the "floor". And conversely when in non deco mode they figure you don't care, as long as you stay within the non deco limits.

I would say instead that as long as you're in no-deco mode, there is no floor. Of course, sawtooth profiles and shallow-deep profiles have their (theoretical) problems, but as long as I'm not into deco, I can't think what a recreational dive computer could have to say about a "floor." I'd be interested to hear more from anyone on this.

-Bryan

 

[eponym]

Adam:

After posting, it occurs to me that I missed your actual point at the end of your post:

The floor, in the Suunto, is only displayed when the computer enters the deco mode. For some reason, unfortunately it does not display the floor -- the max depth at which there is net off gassing of nitrogen, when in non-deco mode.

I would agree that there is a depth for "net off-gassing" which reflects the level of saturation of your tissues versus the ambient depth. This is what causes concern with sawtooth and shallow-deep profiles.

So I went to the Oceanic website and looked at the VT3 manual. I couldn't see a mention of a "floor" display. I'm hoping you can point me in the right direction, as I'm interested in that feature.

Thanks,
Bryan

 

[Hatul]

Adam:

After posting, it occurs to me that I missed your actual point at the end of your post:



I would agree that there is a depth for "net off-gassing" which reflects the level of saturation of your tissues versus the ambient depth. This is what causes concern with sawtooth and shallow-deep profiles.

So I went to the Oceanic website and looked at the VT3 manual. I couldn't see a mention of a "floor" display. I'm hoping you can point me in the right direction, as I'm interested in that feature.

Thanks,
Bryan

I have to play with the computer (Vyper) to see exactly what it does when you descend below the floor. But the hint of Suunto's philosophy can be seen from the name "floor". It's a depth they do not want you to go below. In other words, once you're in deco mode they don't want you to take on any more nitrogen; they want you to start decompressing and ascend.

In non-deco mode there is still a depth at which you're taking on more nitrogen, but they don't display that depth, because you're free to dive below that as long as you don't exceed the non deco limit. Nevertheless it would be useful to know that depth even if it's not called the "floor", if you want to make a deep stop and not be at a depth at which you're taking on more nitrogen.

Adam

 

[Hatul]

I have to play with the computer (Vyper) to see exactly what it does when you descend below the floor. But the hint of Suunto's philosophy can be seen from the name "floor". It's a depth they do not want you to go below. In other words, once you're in deco mode they don't want you to take on any more nitrogen; they want you to start decompressing and ascend.

In non-deco mode there is still a depth at which you're taking on more nitrogen, but they don't display that depth, because you're free to dive below that as long as you don't exceed the non deco limit. Nevertheless it would be useful to know that depth even if it's not called the "floor", if you want to make a deep stop and not be at a depth at which you're taking on more nitrogen.

Adam

Hello Bryan,
I just simulated a deep dive on my Vyper to 150 ft and put it into deco mode. The display shows the ceiling and the total ascent time. There is no direct indication of the depth of the floor, rather, when below the floor it displays an upward arrow and the label "ascent time" flashes. As soon as you get above the floor the arrow disappears and the flashing stops. That's the only way to know exactly what the floor is.

Also the "floor" was only 10-15 ft below the ceiling. With a ceiling of 10 ft, the floor may be 19 ft. So it does not really allow for deep stops. If you make a deep stop the Suunto considers that diving below the floor and increases your decompression obligation.

Once you enter deco mode the computer wants you to ascend to a narrow band below the ceiling (between the floor and ceiling) as long as it stays in deco mode, which goes along what the others are saying that it's not meant for decompression diving.

Adam

 

[eponym]

I just simulated a deep dive on my Vyper to 150 ft and put it into deco mode. The display shows the ceiling and the total ascent time. There is no direct indication of the depth of the floor, rather, when below the floor it displays an upward arrow and the label "ascent time" flashes. As soon as you get above the floor the arrow disappears and the flashing stops. That's the only way to know exactly what the floor is. Also the "floor" was only 10-15 ft below the ceiling. With a ceiling of 10 ft, the floor may be 19 ft. So it does not really allow for deep stops. If you make a deep stop the Suunto considers that diving below the floor and increases your decompression obligation.

Thanks for the details. I know just what you're referring to. I've seen it twice on deep recreational dives with an initial ascent portion too fast for the Suunto's liking. The amusing thing is that by the time I ascended to near the floor, the deco (mandatory stop) obligation cleared completely. That flummoxed me the first time, and led me back to (a fourth) re-reading of the manual.

-Bryan

 

[Hatul]

Thanks for the details. I know just what you're referring to. I've seen it twice on deep recreational dives with an initial ascent portion too fast for the Suunto's liking. The amusing thing is that by the time I ascended to near the floor, the deco (mandatory stop) obligation cleared completely. That flummoxed me the first time, and led me back to (a fourth) re-reading of the manual.

-Bryan

I can see that happening if your deco obligation is small. Don't forget that the acent time can appear large even with a small deco obligation, because it includes time for slow ascent, time at the ceiling, if any mandatory safety stop, 3 minute safety stop and time to reach surface. So once you get above the floor to the decompression zone the time may be very small and can clear quickly.

Adam

 

[eponym]

I have to play with the computer (Vyper) to see exactly what it does when you descend below the floor.

The Suuntos will blink and bark at you to get your gas back above it. If you don't do that within three minutes the unit will, at the surface, display "error" and shut down for 48 hours.

In non-deco mode there is still a depth at which you're taking on more nitrogen, but they don't display that depth, because you're free to dive below that as long as you don't exceed the non deco limit. Nevertheless it would be useful to know that depth even if it's not called the "floor", if you want to make a deep stop and not be at a depth at which you're taking on more nitrogen.

Understood. I followed an SB thread recently which debated ascent rates and offgassing results.

Since this thread is in the Basic Scuba Discussions forum, I'll state without getting into the details of deco theory that on a deep stop some of your tissues may be ongassing while others are offgassing. So for non-decompression dives, can theory give us a single clear-cut floor in the sense you use it ("a depth at which you're [not] taking on more nitrogen")? And you have to be quite a bit above that floor to get any significant pressure difference and offgassing. I've heard most recreational deep-stop proponents speak to bubble seed and ascent rate managment rather than offgassing.

It's a fascinating and important topic, no question, but I'm afraid this is turning into a hijack of the OP (Cobra for Deco?). There are lots of "deep stop" discussions here--this one in particular has lots of external references.

-Bryan