Playing with V-planner

[jbd]

I'm not certified for trimix or decompression diving but hope to move in that direction next year. I've been playing around with V-planner and have a question.

I put in a dive to 150 feet for 40 minutes on air and got the dive plan. As I expected there was considerable decompression time.

I put in the same profile but changed the gas by entering 50% for the helium. I kept the O2 at 21%. As expected I saw the change in END, but what I didn't expect was that there was even more decompression time.

I used a 48 hour surface interval.

I would have thought that by using a trimix the deco time would have gone down.

Can anyone explain why it didn't?

[Genesis]

actually INCREASES decompression time on many profiles.

Whether it decreases or increases it depends on the profile. If you look at V-planner and run a bunch of different profiles for both Trimix and Air (in regions where the PO2 of air is not a tox cocktail), ignoring the narcosis issue, you will find some where the Trimix deco is longer, some where the Air deco is longer, and some where there is very little difference between them.

Part of the issue is which tissue group (the "speed" of uptake and offgassing) is controlling your decompression. The critical factor is that no tissue group can go over its critical tension - if it does, you get bent.

The other thing that gets involved in this is counterdiffusion (e.g. you breathe a mix that has Helium in it, and have none in your body to start, it may diffuse in faster than Nitrogen diffuses out to "balance" with your tissue's existing inert gas loading) When you decompress, assuming you take a deco gas (or two) you will typically remove the Helium and go back to Nitrox (and possibly pure O2 at the 20' stop). In the case of pure O2 there is no counterdiffusion issue, but in the case of going to 50/50 Nitrox there can be, since you have removed the helium but have increased the nitrogen percentage.

Finally, realize that this is ALL theory, backed with reasonable science and trials, but NOT scientific "proof", since what you're doing here is running a mathematical model that approximates how your body tissues handle inert gas loads. That approximation is NOT exact.

[Bottomfeeder]

jbd once bubbled...
I'm not certified for trimix or decompression diving but hope to move in that direction next year. I've been playing around with V-planner and have a question.

And you're a "regulator" here?

If you can't figure this out by yourself (it's pretty simple math if you look a bit farther), you have no business here except as a lurker.

bot

[MikeFerrara]

Bottomfeeder once bubbled...


And you're a "regulator" here?

If you can't figure this out by yourself (it's pretty simple math if you look a bit farther), you have no business here except as a lurker.

bot

I have to disagree. What does being a technical diver have to do with regulating online discussions? Not everyone has any interest in technical diving and it stands to reason many of those don't spent the time reading the reams of material to gain an in depth understanding of the subject (if there is such a thing).

JBD,
I have some software that will display the status of individual campartments. With this you can change the profile and gasses and see the calculated effect on each compartment.
I also have some other stuff you could look at that'll make sense out of this pretty quickly. Next week when you come by we'll take a look if you have a few minutes.

[jbd]

I am a regulator on this website. That makes me no better nor any worse than anybody else on this planet. Being a regulator on this website certainly did not confer upon me the pocession of all knowledge of diving that there is.

I'm truly sorry that my lack of knowledge is so offensive to you. I do wonder if you are truly so much more superior than any of the rest of us since you have no apparent ability to share your knowledge with us.

Genesis thanks for the info and pointing me in a direction to look for more info. Mike I'd would appreciate the chance to look at that program next weekend.

[Aquamaniac]

Bottomfeeder once bubbled...


And you're a "regulator" here?

If you can't figure this out by yourself (it's pretty simple math if you look a bit farther), you have no business here except as a lurker.

bot

Bottomfeeder

If your going to make pointless, irrelevant comments, that make no sense, perhaps you are not even qualified to be a lurker.

[Doppler]

Bottomfeeder once bubbled...


And you're a "regulator" here?

If you can't figure this out by yourself (it's pretty simple math if you look a bit farther), you have no business here except as a lurker.

bot

Bottomfeeder: I'm sure you did not intend to be offensive with your post... perhaps you wrote it without giving too much thought to how it could be interpreted. Regulators are simply folks who've posted a lot of messages... it doesn't indicate any special knowledge or understanding.... Sorry JDB!!! :rolleyes:

Take care, dive safe

DD

[Doppler]

jbd once bubbled...
I'm not certified for trimix or decompression diving but hope to move in that direction next year. I've been playing around with V-planner and have a question.

I put in a dive to 150 feet for 40 minutes on air and got the dive plan. As I expected there was considerable decompression time.

I put in the same profile but changed the gas by entering 50% for the helium. I kept the O2 at 21%. As expected I saw the change in END, but what I didn't expect was that there was even more decompression time.

I used a 48 hour surface interval.

I would have thought that by using a trimix the deco time would have gone down.

Can anyone explain why it didn't?

Try the same profile, same time and same gases (mix and air) but now add standard deco gases to the equation.... 50/50 and 100%.

Now you'll see that your run times with mix are actually shorter! It's magic!!!!

Since this schedule models more closely an actual dive practice, in many practical applications, helium helps rather than hinders

DD