VPM vs BUHLMAN

[nereas]

I haven't found that to be the case.

Buhlmann ... particularly as it's used with a Nitek He ... is not very helium-friendly at all. Nor does it give you credit for deep stops. Following a Buhlmann profile will have you doing almost all of your deco at 30 feet and above. When I owned a Nitek He, I bent the computer several times trying to "make" it fit deep stops into the VPM profile I was getting from V-planner ... even when padding the 20-foot stop by a few extra minutes.

Ratio deco uses deep stops ... starting at roughly 2 ATA above your deepest depth and every 10 feet thereafter up to the surface, with progressively longer stops as you get closer to the surface. In effect, ratio deco will have you deeper, for longer periods of time than Buhlmann. If you consider a bubble model, the latter will basically allow the bubble to form, and keep you at what's considered a "safe" depth until it dissipates. The former will bring you up slowly enough to prevent the bubble from forming in the first place.

VPM is somewhere in between ... when I run a VPM profile at a conservatism level of +2, it approximates ratio deco in certain depth ranges (180-220) with bottom times of 25 minutes or more. With shallower dives, or shorter run times, there seems to be more variance between the two, with VPM requiring less time on the deep stops and more time for the 30 and 20 foot stops. But overall run times are still similar.

When planning a dive, I use a modified version of ratio deco ... not because I think it's the best approach for everyone, but because it works for me. I'll look at V-Planner at +2, compare it to a standard ratio deco profile, and modify my stops a couple minutes here and there, depending on profile and conditions.

... Bob (Grateful Diver)

So Bob is telling you, Mr. Bottomtimer, that Buhlman is "more" conservative than VPM. With my V-Planner set at +3 I myself have found them to be about the same, however.

 

[MXGratefulDiver]

And remember... a few extra minutes looking at the plankton in the 10F/3M range covers many sins
Rick

Got that right ... we had that very discussion just a couple days ago at a team meeting where we got into some heated discussion over deco profiles.

I believe it was Ross Hemingway who authored a paper I once read that said something to the effect that "with deco, we're all lab rats" ...

... Bob (Grateful Diver)

 

[MXGratefulDiver]

So Bob is telling you, Mr. Bottomtimer, that Buhlman is "more" conservative than VPM. With my V-Planner set at +3 I myself have found them to be about the same, however.

No ... Bob is telling you that with Buhlmann, your deco profile will look quite different than with VPM.

VPM will have you coming up slower, and spending less time at 20 feet. Buhlmann will have you coming up faster, and spending more time at 20 feet.

You get to decide which suits your needs better ...

... Bob (Grateful Diver)

 

[BOTTOMTIMER]

Hi again to all of you.
Allthese you wrote are o.k for depths to 50m. Because deco on the fly is for the maximum depth of 55m. Nereas wrote that he has done dives to 75m. So he used He.
What is going on with this gas that goes to the tissues faster. Is it a good idea to do deep stops in dives up to 60m. I am saying this because i think that because helium goes faster in the tissues, it comes out the same fast. So do i decompress or isteel ceep gas in my tissues?

Sorry again for my English.

 

[Rick Inman]

VPM will have you coming up slower, and spending less time at 20 feet.

... which I prefer and then pad the 20' stop a bit too. I cut with V planner, but love having RD in my back pocket. I really try to track how I "feel" and adjust accordingly. The old navy table days of popping up from depth to 20' and hanging there for a couple of days worked, too (off-ing those nasty bubbles instead of stopping their formation), and keeping all this in mind - VPM, navy tables, RD - WAG-ing for age, cold, exertion, hydration, fitness, what my real profile was verses my planned one, how I've felt after other similar dives, and in general how I happen to feel at the time, is the fun of mixing science and art.

 

[MXGratefulDiver]

Hi again to all of you.
Allthese you wrote are o.k for depths to 50m. Because deco on the fly is for the maximum depth of 55m. Nereas wrote that he has done dives to 75m. So he used He.
What is going on with this gas that goes to the tissues faster. Is it a good idea to do deep stops in dives up to 60m. I am saying this because i think that because helium goes faster in the tissues, it comes out the same fast. So do i decompress or isteel ceep gas in my tissues?

Ratio deco ... or what you call deco on the fly ... was used successful in the Red Sea for a dive to 180 meters. I'm not sure where you got the information that the max depth for RD was 55 meters. That is certainly not the case. In fact, I find it more closely fits the VPM model in the 60-75 meter range than it does at shallower depths.

Yes, helium both ongasses and offgasses much faster than nitrogen ... which is why I think deep stops and slow ascents are increasingly important as the amount of helium in your mix increases.

Sorry again for my English.

No need to apologize ... your English is MUCH better than my Greek ...

... Bob (Grateful Diver)

 

[BOTTOMTIMER]

Thank you Mr NWGratefulDiver.
What is the difference between Ratio Deco & Deco on the Fly?
I have never heard about this dive you wrote me for. Who did it?

 

[MXGratefulDiver]

Thank you Mr NWGratefulDiver.
What is the difference between Ratio Deco & Deco on the Fly?
I have never heard about this dive you wrote me for. Who did it?

Ratio Deco and Deco on the Fly are two names for the same thing.

Here's a link to the 180m dive I referenced ... Red Sea Explorers - 180 meter Dive on Yolanda

... Bob (Grateful Diver)

 

[BOTTOMTIMER]

Thanks for this information NWGratefulDiver .
Buhlmann works purely on dissolved gas, and VPM does indeed calculate the size of a THEORETICAL bubble. In one sense, Buhlmann has 100 years of research behind it, and VPM is but a few years old!
Don 't you think that this is a nice reason to prefare Buhlmann?
I am just asking opinions.

 

[Rainer]

100 years of Buhlmanm as applied to what? Certainly not He dives.

In any case, your logic would seem to rule out all advances.