Nitrox Question

[ianr33]

Perfect! Exactly where I was going . . .

It bothers me -- am I in the minority? -- that manufacturers are trying to make their product 'fix' us, the diver. I don't want my computer telling me lies. Is it really 'safer' for a computer to adopt its own settings?

I rely in my equipment to report status, period. I count on that piece of equipment to do calculations thousands of times faster than I am able. I do not like the idea that it would make up a number based on some programmer's best guess.

Get a Bottom Timer and learn Ratio Deco

 

[Laurie S.]

The Oc1 has a 50% Defaut feature where, unless you turn this feature off, 10 minutes after your first nitrox dive it will set to EAN50 automatically.

Page 87 of this manual...
http://www.oceanicworldwide.com/pdf/12-2761-r02 Eng.pdf

My guess is when you review the log the mix will be set to 50 and the max depth for that dive will be closer to 86.

You should be able to turn that feature off, just be sure to check your mix before every dive!

I remember seeing that default function and turning it off. But does it stay off after each dive?

 

[Laurie S.]

This has been really interesting and informative, thank you! Like I said, I'm a nitrox newbie and only the divemaster in Tahiti bothered going over everything in detail with me as a quick refresher. I didn't have my nitrox book with me, but I did have my tables and was looking at them while working with my computer.

My dive log shows that the first dive went to 107 feet for 44 minutes. The second dive went down to 93 feet where I saw those readings, and I know I ascended at least 20 feet after seeing the anomalous readings until I got a reading of 1.4. The total dive time was 54 minutes and the last half was coming up a reef so we had an extended safety stop drifting along.

It looks like my computer must have gone into the default mode. After the second dive, the computer read "FO2 50 and PO2 1.90." On the first dive, it read as "FO2 21 and PO2 0.89."

The surface interval was 1 hour, 10 minutes, so it looks like my computer reset into the safety default setting. Now I know to reenter the percentage at each dive.

 

[Cave Diver]

Laurie, do you know how to figure your MOD for the mix you're diving?

 

[rigdiver]

Or a Shearwater or VR computer.

Just an FYI, if you want a computer that doesn't reset after each dive, spend the $$ and buy a Liquidvision X1.

Mine stays set on whatever I used last, regardless of whether that was the last dive 10 minutes ago, or 2 weeks ago. As others have said, resetting the last mix is a safety feature. If you jumped in the water without checking the settings on your X1, you could be really screwed, depending on what you last dive/mix was.

Of course the X1 does a few other non-conventional things as well. It doesn't give you a 10-20' safety stop time on recreational dives (you have to be smart enough to watch the clock and note those run times if you are doing that), It doesn't beep at you or lock you out if you do something wrong, and if you F-up the mix, you can change it underwater and it just keeps right on ticking.

John

 

[Laurie S.]

Not manually, no, I need to re-read the course book again and practice. I do know how to set it on the computer and the first divemaster watched me go through it to make sure it was working. I wasn't expecting to be able to dive nitrox on this trip, but didn't want to pass up the chance. Everytime I've tried to dive it in San Carlos, Mexico where I normally dive, the compressor is broken. At least that's what they keep saying.

 

[Cave Diver]

Not manually, no, I need to re-read the course book again and practice. I do know how to set it on the computer and the first divemaster watched me go through it to make sure it was working. I wasn't expecting to be able to dive nitrox on this trip, but didn't want to pass up the chance. Everytime I've tried to dive it in San Carlos, Mexico where I normally dive, the compressor is broken. At least that's what they keep saying.

Take your target Po2 and divide by the fraction of nitrox you're using.

For example if you want to plan a 1.4 Po2 on 32% then

1.4/.32 = 4.375 Atmospheres.

Convert atmospheres to depth: 4.37 - 1 (for the surface atmosphere) = 3.37

3.37 x 33 (# of feet per Ata) = 111'

So on 32% your depth would be 111' with a 1.4 Po2.

 

[Laurie S.]

Thanks, I just wrote that down in my log book for reference in the future.

 

[Cave Diver]

No problem. It can be helpful to memorize the mod for some of the more common mixes like 32 and 36. Or any mix common where you dive.

 

[jester1226]

It bothers me -- am I in the minority? -- that manufacturers are trying to make their product 'fix' us, the diver. I don't want my computer telling me lies. Is it really 'safer' for a computer to adopt its own settings?

I rely in my equipment to report status, period. I count on that piece of equipment to do calculations thousands of times faster than I am able. I do not like the idea that it would make up a number based on some programmer's best guess.

If you do not set it with the correct information in the first place, what is the difference? In either case the computer will have the incorrect information or lies as you put it. You can't count on a piece of equipement YOU never set. How can it give you an accurate 'Report Status' if it was never given the correct information before you hit the water? Would you prefer the incorrect number being made up due to a lack of inputting the correct data, or any data at all? If you use the same blend all the time, turn the auto feature off, it is that easy.