Deco Or No Deco? What Happened With My Two Computers???

[TracyN]

I am a little confused by what happened today. I went on a three tank dive with an average depth of 80-90 feet. I recently bought a Nitek Duo computer and this was my first time using it. I also had my Oceanic VEO 1.0 as a back up. I noticed that each computer has a different NDL limit for the same depth with the Nitek giving me less than the VEO. The Nitek uses the Buhlman ZH-L16 algorithm and the Veo uses DSAT.

I was on my third dive and the Nitek said I had 9 minutes of deco to complete at 10 ft but my Oceanic said I had none. Apparently the Nitek does not off gas and count down if you don't stay at exactly 10 feet once in deco mode. Not easy to do on a drift dive in not so calm seas. Long story short, I decided to go with what my Oceanic said and I ended up "bending" my Nitek. Did I truly go into deco and blow a deco stop or is it just a technicality between the computers?

 

[Pullmyfinger]

There are differences between the Oceanic and Dive Rite computers. I used to have an Aeris/Oceanic computer, and currently have a Dive Rite Duo.

The differences can be even greater, depending on what level of conservatism you set your Dive Rite to....it has 3 settings.

That would account for the differences.

I would suggest using one of your computers as a computer, and set the other one to gauge mode.
You'll eventually get a feel for the Dive Rite vs. the Oceanic.
They will both always be a little (or a lot) different from one another.

-Mitch

 

[TSandM]

Tracy, what you got confronted with is the first step beyond rote learning in scuba . . . you found out that decompression is not a science, but an art. Nobody really knows what is going on with nitrogen dynamics inside the body during a dive. We use very simple mathematical models to try to create parameters that are safe -- but the models require assumptions, and nobody knows for sure that the values on those assumptions should be. Different values chosen to start result in very different outputs; thus your two computers, which can't agree on whether you are getting an advantage or a penalty during any specific period of your ascent.

This is one of the reasons that it is difficult to dive in a group, when people are using different computers, because they will not necessarily agree at all on what is allowed and what is not.

"Deco" is not a bright line -- it is a fuzzy area, and it is best not to do much diving in that range, unless you have the gas and the diving skills to allow plenty of properly shaped ascent time -- and the education to realize that, the closer you get to whatever the "mandatory deco" threshold is, the more risk you run if you have to surface early.

 

[TracyN]

There are differences between the Oceanic and Dive Rite computers. I used to have an Aeris/Oceanic computer, and currently have a Dive Rite Duo.

The differences can be even greater, depending on what level of conservatism you set your Dive Rite to....it has 3 settings.

That would account for the differences.


I would suggest using one of your computers as a computer, and set the other one to gauge mode.
You'll eventually get a feel for the Dive Rite vs. the Oceanic.
They will both always be a little (or a lot) different from one another.

-Mitch

I have the setting set to 0 wich is the least conservative out of the other settings. My oceanic doesn't have gauge mode so until I start doing deco diving I will have to use the Nitek as the guage mode computer. Thanks for your help

 

[Centrals]

Did I truly go into deco and blow a deco stop or is it just a technicality between the computers?

Anything is possible!!!!
I would clear the computer first if possible. I do not like to "bend" my computer because it stays lock up for 24hrs as well as beeping for awful long time. Battery is expensive to replace for Aladin
I might fire my smb and clip the computer on the line at 5m and surface. Pick them up few minutes later.
I never had any experience of diving with two different computers at the same time.

 

[gsk3]

I had a similar situation with the Duo:
http://www.scubaboard.com/forums/dir/359164-i-finally-get-gauges-why-they-make-sense.html

It's not that it's conservative (I dive very conservative profiles) it's that it doesn't deal with your profile in sensible ways. Deco time accumulates until you hit exactly the foot stop that it wants. 11ft will not do it for a 10ft stop, nor will 21ft work for a 20ft stop.

 

[DevonDiver]

I am a little confused by what happened today. I went on a three tank dive with an average depth of 80-90 feet. I recently bought a Nitek Duo computer and this was my first time using it. I also had my Oceanic VEO 1.0 as a back up. I noticed that each computer has a different NDL limit for the same depth with the Nitek giving me less than the VEO. The Nitek uses the Buhlman ZH-L16 algorithm and the Veo uses DSAT.

I was on my third dive and the Nitek said I had 9 minutes of deco to complete at 10 ft but my Oceanic said I had none. Apparently the Nitek does not off gas and count down if you don't stay at exactly 10 feet once in deco mode. Not easy to do on a drift dive in not so calm seas. Long story short, I decided to go with what my Oceanic said and I ended up "bending" my Nitek. Did I truly go into deco and blow a deco stop or is it just a technicality between the computers?

Variation in computers doesn't surprise me.

I do notice though, that you probably shouldn't be going into deco, or near-deco, situations

I am guessing you opted to follow the profile indicated by the least conservative computer? Just be aware, as others have said, that deco is a 'grey area'... and that your profile/dive was obviously well into that area. Personally, I wouldn't go close to that situation without a level of certainty that I could complete the requisite stops.

I would clear the computer first if possible....I might fire my smb and clip the computer on the line at 5m and surface. Pick them up few minutes later.

If your sole purpose was to save on some battery life, then fine. If you were trying to keep your computer from getting bent - thus enabling further diving in the near future - then that is a very imprudent action to take, especially for a qualified technical diver who should know better.

Computers lock for a reason.... in the same way that tables advise periods out of the water.... for missed deco.

 

[waterpirate]

The original poster of this eludes me but I think it summs up the situation.

decompression schedules/computers

measured with a micrometer

written in chalk

cut with an axe

Eric

 

[redacted]

If you are going to dive with a primary and a backup computer, the more conservative computer should be your primary. And you should follow it until it fails or just does not make good sense. I don't see much advantage of putting one in a gauge mode if you are computer diving. If you are depending on your computer for gas loading status, you are SOL or need to revert to tables (which you can do without a BU computer if you are monitoring your primary closely.

You busted a deco obligation. Very low risk if you trust your backup but still you might want to resolve what went wrong before pushing it again.

 

[JamesK]

My Nitek Duo's are more conservative then my OMS EaNX. I have dove with both just to see the differences. I like that the Nitek makes me hold at exactly 20 feet to count off the deco or safety stop built up. Even in rough seas it can be done, it just takes practice.

Personally, I always make sure both my computers are clear before I get out of the water. Be they the Duo's the OMS, or now the Nitek Q. Extra shallow time is not going to hurt.