Trimix with Nitrox comp?

[grazie42]

Ok, so I´ve just finished a "recreational trimix course".
During the course I did dives with my computer in both Nitrox and Gauge mode (a Suunto Vytec).

I did have a slate with planned stops and so on (not diving according to the computer).

My question is:
Do any of you use your non-trimix computers this way (ie in nitrox not gauge mode) and have you ever had problems doing it?

The reason for my question is that I have to wait 48 hrs after the dive before I can switch back to nitrox mode on my comp and thats something of a hassle when I might just do one trimix dive during a weekend and do the rest of the dives on nitrox or air...

 

[ninjamuzo]

Most computers will Error out when you do dives outside of their recommended profiles. Better to use gauge or get a Trimix computer.

Some of them get really annoying, beeping all the time in error.

 

[wedivebc]

Ok, so I´ve just finished a "recreational trimix course".
During the course I did dives with my computer in both Nitrox and Gauge mode (a Suunto Vytec).

I did have a slate with planned stops and so on (not diving according to the computer).

My question is:
Do any of you use your non-trimix computers this way (ie in nitrox not gauge mode) and have you ever had problems doing it?

The reason for my question is that I have to wait 48 hrs after the dive before I can switch back to nitrox mode on my comp and thats something of a hassle when I might just do one trimix dive during a weekend and do the rest of the dives on nitrox or air...

Actually I often do just that. I have a vytek that I take on dives using v-planner tables. So far to 250ft I have not gone beyond the vytek ceiling using the table.
I have not done multiple dives using this method though and would not do one dive on table then second dive on computer. That's like changing tables between dives. Too many variables.

cheers,

 

[gkndivebum]

Do any of you use your non-trimix computers this way (ie in nitrox not gauge mode) and have you ever had problems doing it?

Nope. He on/off gasses 2.7 times faster than N2. No nitrox-only computer is able
to properly model that scenario.

Either get a trimix capable computer, or use tables for trimix diving.

Personally I use tables for deep and/or dives requiring more than a few minutes of
mandatory decompression. I have an HS-Explorer that I use for more relaxed profiles,
including some trimix dives.

 

[grazie42]

Originally Posted by wedivebc I have not done multiple dives using this method though and would not do one dive on table then second dive on computer. That's like changing tables between dives.

But wouldnt doing the first dive according to tables/software, only with the comp in Nitrox mode, and then doing Nitrox dives "on the comp" be more conservative then just doing it according to tables (assuming you dont introduce extra margins yourself), as like gkndivebum said, He offgases faster.

Once again I´m not talking about doing trimix dives according to the Nitrox computer only having it in nitrox-mode during the dive for the convienience of being able to do the next dive (on Nitrox) in Nitrox-mode.

 

[wedivebc]

But wouldnt doing the first dive according to tables/software, only with the comp in Nitrox mode, and then doing Nitrox dives "on the comp" be more conservative then just doing it according to tables (assuming you dont introduce extra margins yourself), as like gkndivebum said, He offgases faster.

Once again I´m not talking about doing trimix dives according to the Nitrox computer only having it in nitrox-mode during the dive for the convienience of being able to do the next dive (on Nitrox) in Nitrox-mode.

Yes that is right that you offgas faster with he but you also ongas faster. That means certain tissue compartments may be more saturated than your nitrox computer would be tracking and so your si would not be accurate.
Bottom line, I'm with gkndivebum on this. Helium should not be screwed with. For what you paid for the vytek with transducer you could get a HS explorer that will allow you to set 10 different gasses.
If you are using the vytek as BT in nitrox mode, fine but you can't change mid dive series. It's just got too many variables.

cheers,

 

[Green_Manelishi]

Ok, so I´ve just finished a "recreational trimix course".
During the course I did dives with my computer in both Nitrox and Gauge mode (a Suunto Vytec).

He <> N2

Your instructor allowed you to do use that 'puter for
those dives?

 

[grazie42]

I did all the calculations both on software and according to tables.
I had a slate with all the decostops and run/stop time.
I only USED the comp as a depth and time gauge.
During a few of the dives I had the comp in Nitrox mode and during others in gauge mode.

I dont see a problem with using the comp in whatever mode I choose as long as it doesen´t "bend" as all I used/am planning to use it for during trimix dives is as a depth/time keeper.

My question was about whether I´d actually be likely to "bend" it if I do this in the future for reasons stated in my earlier posts.

Hope this clears up any confusion.

 

[Scuba_Steve]

Ok, so I´ve just finished a "recreational trimix course".
During the course I did dives with my computer in both Nitrox and Gauge mode (a Suunto Vytec).

I did have a slate with planned stops and so on (not diving according to the computer).

My question is:
Do any of you use your non-trimix computers this way (ie in nitrox not gauge mode) and have you ever had problems doing it?

The reason for my question is that I have to wait 48 hrs after the dive before I can switch back to nitrox mode on my comp and thats something of a hassle when I might just do one trimix dive during a weekend and do the rest of the dives on nitrox or air...

Hey Grazie42, thanks for asking the question, as it gave me an opportunity to think about something I never really thought about before!

I must first put forward the disclaimer that I am probably out of my tree, so don't believe me, but instead, seek out professional and properly trained instructors on the matter.

But here goes from where I sit.....

First of all, I dive a bottom timer, and an old Nitrox computer with no guage mode (Unless I "bend" it into gauge mode.) From there it still continues to work...in a type of guage mode only.

yeah yeah TomR, I'm still working on that B/Timer from you. Had DiveMistress not said anything in front of my wife, i would have got it on the sly from you Now I'm screwed until she forgets about it.....

OK.

I don't know what kind of Trimix diving you do, but here's the skinny from my very limitted trimix diving. I do however believe in it whole-heartedly, as I have the utmost faith in my training from Doppler, on this board, and at the same time, from how he taught his "tables"/decompression schedules, or whatever else you wish to call it.

If Doppler is cruising by, and he spots something I had said in err, by all means correct me!, please.

From my understanding, your issue shouldn't be all that difficult to understand and dive.

Lets break the problem down to it's simplest form.....

(I will detail as best as I can in my next post, but first let me compose it off-line to get it worded as accurately as I can, the first time).

 

[Scuba_Steve]

Lets assume the Trimix dive is followed by a Nitrox dive, and then possibly another Nitrox dive the next day.

Your problem, so you say, is tracking the Nitrogen loading, and calculating subsequent dives.

Doing the Trimix dives that we/I do, and using the Deco gas selection that I/we use, it has been shown, that one can do the identical dive, with approximately a 90minute surface interval. Of course I’m purposely not spelling out the mixes, and I do suggest proper training on the matter. We are also assuming that the first dive went well, gas switches etc went without a hitch, times were smack on, and you feel good about all facets of the dive.

**NOTE** I have NO IDEA if YOUR selection of Bottom mix and Deco mixes will work the same way.

So now we get to dive number 2 of the day. The Nitrox dive. Well, given the assumptions from above, including the proper selection of deco and bottom mixes, to keep in check our CNS tracking etc, we basically have a “wash” after the 90 min SI from the first dive.

What that means is, you could arguably go into this dive as if it was dive number one of the day. Now I should take a step back for a second.

I am on record here, over a year ago, in thinking that one needed a computer for multi-level, multi-dives days. I couldn’t fathom how a person could actually figure this voodoo math out with enough precision, to be SURE that he was staying within acceptable limits. I WAS WRONG. Being the curious type of guy that I am, I took some “advice” from TomR, Kevin Ripley, MHK, and a few others and started my personal quest to find the “key” to this no computer diving “thing”.

In short order, I figured it out (I think) by running a few scenarios, as I remember MHK doing them.

So the history behind this next step is, I can now feel confident enough, after practicing this “voodoo” math, to do multi-dive days without the use of a computer.

Let step forward again. Dive # 2. Treat it as dive number 1 of the day, given the above caveats. If you know, as I do now, how the Nitrox calcs are performed with no computer, then your problem is solved!!! As long as you have a B/Timer, you’re golden for dive # 2! No computer required.

Day #2, Dive # 1, then, ultimately falls into place. You have a B/Timer with a computer “stuck” in gauge mode. (I think that’s how you said your works, but I’m not sure) I know mine works that way, unless I pull the battery. (Which I don’t bother doing).
So you perform this dive calcs the same as Day # 1, Dive # 2.

Easy!

Again, check it out for yourself, ask the appropriate folks who know, and heck, borrow a computer that can do it all, and see how it works it out vs. the “voodoo” math above. I think you’d be pleasantly surprised at your accuracy.

After all, as Doppler says, decompression is part theory, part science, part alchemy and part luck! His best advice, DON’T TRY IT!

Regards

Steve

Hope this helps more than it confuses.

Awaiting the final mark, Doppler