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

[boulderjohn]

A number of years ago I did a week of liveaboard diving in Truk Lagoon. I was using a Suunto, and my buddy was using an Oceanic. By the end of that week the differences were ridiculous. He was calling me Captain Deco. I once used a Nitek He on a dive with a friend who was using a Liquivision X-1. The difference was even more ridiculous, and I never used the Nitek out of gauge mode again.

Is one more "right" than the other? Is more conservative always better? If so, then isn't staying in bed instead of diving the best move? The purpose of a deco algorithm is not just to keep you safe, it is to keep you safe and also have reasonable dive times and surface intervals. The trick is finding the best balance between the two conflicting goals. You have to decide which makes the most sense to you and use it.

 

[TracyN]

My Oceanic has been my trustworthy little computer since I started diving. When I saw that my Nitek was going into deco but my Oceanic wasn't I decided to go with the VEO since it was what I was used to. When my buddy and I started our ascent which took us about 10 min to go from 86 feet to the surface I had 5min NDL left and he told me that he had about 10 min left. We waited and waited for my Nitek to clear and it wasn't going to do it so we surfaced.

 

[fisheater]

This shows the wisdom of that "ancient" saying: "He who has a watch always knows what time it is. He who has two watches is never sure."


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[Dive Bug Bit Me]

I sometimes dive an Oceanic Veo with the DSAT algorithm. It hasn't bent me yet, so that is good. I find it very aggressive against all my buddies' computers. I guess its just a case of not all computer algorithms are the same. (Which Mark Powell explains in "Deco for Divers" if you are really keen on digging deeper)

My reaction - I don't dive my Veo to the NDL limit. I also know that my Suunto and NHeO are less aggressive and will push them closer to their limits.

Also FYI, I have seen a tech diver take down two NHeO computers strapped to the same arm. He came up with 11 minutes difference in deco obligation on them. Next dive, the computers reversed and the other one now had 5 mins more deco obligation. As TS&M said, sometimes deco and NDL are more art than science.

We waited and waited for my Nitek to clear and it wasn't going to do it so we surfaced.

In your case, you were diving two computers and the one you trusted was not in deco so you were fine.
As and aside, that experience with your Nitek is why you want deco training before you put youself into true deco. You need to have more gas than deco obligation. Also, you need to be reasonably spot on with your stops, else the deco clears sloooooowly.

 

[ajduplessis]

Interesting how most divers always pick the bigger NDL time if 2 DC's give different times for the same dive

Nothing is considered, one look at the DC and life is fine. Generally divers trust computer blindly.

 

[Dive Bug Bit Me]

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

You were able to surface without bending, so technically no you were not in deco. Practically were you one second from bending or one hour from bending? You don't know, maybe you just got lucky on the day. What your computers were telling you is that you were close to the line. Clearly you did not have further obligatory deco when you surfaced. Personally I would play it safe and keep away from the deco line because a number of random factors including dehydration, fatigue, temperature and who knows what else could combine to make you more susceptible to bending on any dive.

 

[flots am]

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.

A person with two watches never knows what time it is.

For recreational diving, you need to pick one computer and trust it, and use it and have a plan for what to do if it fails, which in the case of recreational diving, would be for you to end the dive.

For technical (deco) diving, you would typically print out a dive plan using something like vPlanner (or tables if you're old-school) and use a depth gauge and a bottom timer/watch, and have a contingency plan for a failed watch or gauge. A printed dive plan is unlikely to fail.

I'm not sure where the "backup computer" thing came from, since it only adds confusion and uncertainty and is completely unnecessary for recreational diving. They seem to have become more popular over the past few years.

flots.

 

[Jim Lapenta]

This is why I plan all dives using tables, try to dive square profiles as much as possible, and advise students to do the same. And this is based on my own experience of when I first got a computer and did what many new divers do. I flew the computer right up to the yellow believing I was safe and continuing to do that for a while until I really started educating myself. Even diving using the most consvervative computer is no guarantee that you are ok. It's why I don't recommend computers for new divers. Tables give more than enough time for the avg recreational diver. Save the comps for when you get better at buoyancy control and judgment. Cause if you go tech you'll start with tables any way.

 

[TracyN]

A person with two watches never knows what time it is.

For recreational diving, you need to pick one computer and trust it, and use it and have a plan for what to do if it fails, which in the case of recreational diving, would be for you to end the dive.

For technical (deco) diving, you would typically print out a dive plan using something like vPlanner (or tables if you're old-school) and use a depth gauge and a bottom timer/watch, and have a contingency plan for a failed watch or gauge. A printed dive plan is unlikely to fail.

I'm not sure where the "backup computer" thing came from, since it only adds confusion and uncertainty and is completely unnecessary for recreational diving. They seem to have become more popular over the past few years.

flots.

Why the back up computer? There was a method to my madness. I had just purchased this computer and prior to this use it had been in storage for 5 years. While there was no indication of low battery or other malfunction I wanted to have my trusty computer with me just in case something went wrong with the Nitek. Five years is a long time not to use a computer. Plus I wanted to compare the two computers.

 

[DiveNav]

What the dive computer(s) says ..... it doesn't matter!

What really matters is the PROFILE of your dive and how you analyze it.

As other people said, different computers will give you different results for the same dive profile. At the end of the day, it is up to you to decide how aggressive - or how conservative - you want to dive.

Send me your profile so we can take a look at it with divePAL.

Alberto (aka eDiver)