26% O2 to equal DSAT computer?

[carltona]

I recently heard that in order to get an Aqualung i450 to match a computer using DSAT, set the i450 to 26% nitrox and it will be very similar to the DSAT. I am going to try it, I have both computers. The reason is that when two divers are doing a deeper wreck on air, and one that has the more conservative i450 will have much less bottom time before deco. Thoughts on the concept? Is there a "safe" way to make a Z+ algorithim more forgiving to match profiles with DSAT computers?

 

[scubadada]

There have been many threads on SB that have mentioned faking out one's computer. I think it is a bad idea. Would have been better for the person with the i450 to have bought an Oceanic OCi. You cannot make a conservative computer more liberal.

 

[tbone1004]

do NOT adjust the fO2 to alter conservatism. If you don't like the algorithm on your computer, sell it and get a different one.

 

[KenGordon]

Very simplified, dive computers work on a couple of numbers. One is how much n2 is dissolved and the other is the limit on how much dissolved n2 there can be at a given depth. Conservatism is controlled by reducing the limit allowed.

By changing the fo2 you will change the rate at which the n2 seems to be going into solution. This sounds like a convincing way to make the computer less conservative. However you are also changing how fast it thinks it comes out of solution. So not only will it let you stay down longer, it will let you come up faster. This means that a dive which starts deep and goes shallow will get a double effect, longer NDLs due to slower on gassing, and then disproportionately longer again due to faster offgassing when you get shallow, this is the double benefit of diving Nitrox. But you will be diving air. While this scheme may look like it is equivalent to DSAT for a square dive there's is no telling what it will be like on an actual dive.

If you feel limited by your computer, I suggest diving actual nitrox or learning to do the stops.

 

[fmerkel]

That's one of the more understandable explanations I've read. Thanks.

 

[Centrals]

The usual recommendation for diving on two computers with different algorithm is to follow the conservative one.
I have heard suggestion on diving with nitrox but set the computer to air for added safety(N2 intake) but never the other way around.
Since the OP has two computers it might be worth a try to satisfy his curiosity. But don't blame me if his DSAT computer fails on the dive and he needs his wrongly set computer to bail him out.

As already suggested, get another DSAT computer. Only a fool will try to fool a computer, nothing to win.

 

[TMHeimer]

Sorry. As a "retired" divemaster who only assisted with courses, I have to ask. 26% O2? What kind of diving are you doing that would mean 26% is better than Air. Admit, I'm still in many ways a simpleton.

 

[Bob DBF]

Sorry. As a "retired" divemaster who only assisted with courses, I have to ask. 26% O2? What kind of diving are you doing that would mean 26% is better than Air. Admit, I'm still in many ways a simpleton.

He is not using 26%, he is setting one computer to 26% to try to match another computers algorithm. Personally I'd just pick a computer and dive.


Bob

 

[rjack321]

I recently heard that in order to get an Aqualung i450 to match a computer using DSAT, set the i450 to 26% nitrox and it will be very similar to the DSAT. I am going to try it, I have both computers. The reason is that when two divers are doing a deeper wreck on air, and one that has the more conservative i450 will have much less bottom time before deco. Thoughts on the concept? Is there a "safe" way to make a Z+ algorithim more forgiving to match profiles with DSAT computers?

I find it hard to believe that on the first dive of the day two computers regardless of algorithm diverge that much - unless you have set one on some arbitrary conservative setting and the other is not. Repetitive dives is another matter.

Rather than diving the most generous limits why not dive the more conservative of the two? Why even carry the i450 if you are just fooling it?

 

[RainPilot]

My personal practice is to NEVER lie to the computer. If there is a conservancy setting etc etc, then by all means but no lies.

Computers are GIGO machines, Garbage In Garbage Out. Changing the FO2 to get longer dives is a recipe for trouble. Im not even in favour of diving nitrox with the DC set to air, even though it will lead to very conservative dives. There is a lot of calculating going on, especially over multi day multi level multi gas diving, thats why we are using a DC in the first place.

if you dive air but set 26%, then your next dive you are using 32% will you then set 37% or 32% or have any idea of what your inert loading status is?

If your DC is not working for you, then get a different one with a different algorithm by all means but no lying for me.