VR3 -vs. V-Planner

[Phoenix]

Does anyone know which conservatism setting on V-Planner would run closest to a VR3?

Ian

[Mark Chase]

In these months Out of the blue mag there is a piece on the Britannic expedition where they were using VPM-B for the deep and intermediate stops and Buhlmann for the shallow stops. Apparently the VR3 ran within a couple of mines of the tables on the 125m dive.

The article mentioned that they felt the VPM-B shallow stops were QUOTE '' scarily fast in the latter stages.''

Buhlmann was used to pad the stops from 24m up and the end result was similar to the VR3

Reading between the lines the VPM-B model will probably cut a load of time off the VR3 shallow stops so is not best suited to gas plan the dive. Either use the VR3 or get Decoplanner

The divers used the saturation feature of the VR3 to calculate on gassing during the multi level dive (90 to 125m) and this information was used to decide on which set of deco tables to use on ascent.

Chalk up another one for the VR3



ATB

Mark Chase

[Andrew H]

Can we take it that the team had little confidence in either VPM-B or Buhlmann for the job? Nor the VR3 for that matter. Does it seem odd that the team would choose to run with software they were unhappy with? It seems that while everyone wants to be out of water as quickly as is safe, they don't all trust what the theory is telling them. Padding one algorythm with the other all seems very rule of thumb.

Andrew

[Mark Chase]

Originally Posted by Andrew H

Can we take it that the team had little confidence in either VPM-B or Buhlmann for the job? Nor the VR3 for that matter. Does it seem odd that the team would choose to run with software they were unhappy with? It seems that while everyone wants to be out of water as quickly as is safe, they don't all trust what the theory is telling them. Padding one algorythm with the other all seems very rule of thumb.

Andrew

If you did a 125m dive with 5 hours deco would you cover all the bases? I am damed sure I wouldent trust the VR3 on its own I would back it up with comparison tables.

Fact is most softwhere past 100m with any serious bottom time is working way outside its core data. The Buhlmann stops we all know are long and shallow get up quick with little consideration for Helium. The VPM-B is more into deep stops and longer intermediate stops and reducing the 6m hang. Remember that a few divers got bent on the early VPM short shallow stops so I would pad it out as well.

They used the tissue graph function on the VR3 to decide what profile to follow. The VR3 was not intended as the primary deco tool but it ended up within mins of their eventual deco which is a good advert don’t you think?

ATB

Mark Chase

[TX101]

Originally Posted by Mark Chase

In these months Out of the blue mag there is a piece on the Britannic expedition where they were using VPM-B for the deep and intermediate stops and Buhlmann for the shallow stops. Apparently the VR3 ran within a couple of mines of the tables on the 125m dive.

I thought the "B" in VPM-B Stood for "Buhlmann". ie. VPM-B is essentially what you are saying (VPM for deep, Buhlmann for shallow)

[Padowan]

Originally Posted by Mark Chase

The Buhlmann stops we all know are long and shallow get up quick with little consideration for Helium

Classis Buhlman is a bit of a bend-and-mend methodology, but if you apply Gradient Factors as well, you can vary the "ratio" of deep to shallow stops to "soften" the microbubble formation - this is what DecoPlanner uses, I'm pretty sure.

[wreckweasel]

Originally Posted by TX101

I thought the "B" in VPM-B Stood for "Buhlmann". ie. VPM-B is essentially what you are saying (VPM for deep, Buhlmann for shallow)

That would be technical and clever. In fact... VPM-a was the first one, which had a bad reception (people were beginning to feel a bit like goats), so they cut a more conservative version. version b.... VPM-B

Sometimes the obvious answer is too easy eh?

[Mark Chase]

Originally Posted by Padowan

Classis Buhlman is a bit of a bend-and-mend methodology, but if you apply Gradient Factors as well, you can vary the "ratio" of deep to shallow stops to "soften" the microbubble formation - this is what DecoPlanner uses, I'm pretty sure.

Correct and I like Decoplanner it has a system of conservatism that I can get my head around.

I don’t know why they chose to do it like that I am just quoting the stuff from the article and guessing.

ATB

Mark Chase

Zac LOL M8 nice one

[Andrew H]

Originally Posted by Mark Chase

If you did a 125m dive with 5 hours deco would you cover all the bases? I am damed sure I wouldent trust the VR3 on its own I would back it up with comparison tables.

Fact is most softwhere past 100m with any serious bottom time is working way outside its core data. The Buhlmann stops we all know are long and shallow get up quick with little consideration for Helium. The VPM-B is more into deep stops and longer intermediate stops and reducing the 6m hang. Remember that a few divers got bent on the early VPM short shallow stops so I would pad it out as well.

They used the tissue graph function on the VR3 to decide what profile to follow. The VR3 was not intended as the primary deco tool but it ended up within mins of their eventual deco which is a good advert don’t you think?

ATB

Mark Chase

Certainly see your point here. Good use for the VR3 too. I can't help think that if more people were prepared to dive strictly to (for instance) VPM-B on these extreme dives we would learn a lot more about the VPM model for extreme dives of this nature. I realise that this is a huge ask, but the empirical data from padded and combined table dives is a lot less usefull in the long run.

Which model does the VR3 run? It would be equally demonstrative of course if the dives were performed trusting the VR3 (or two!), which as you say was on the money anyway.

I did see a profile from WKPP which got the guys out several hours earlier than comparable charts, which must show clearly how overconservative some cut tables can become.

Andrew

[Narked@50]

Surely it's hard to get a full picture on this with so many variables in vplanner?

For instance, the conservativness can be set as described:

"Provides an adjustable safety margin for decompression calculations, cold or stress. Nominal sets critical radius to base values dependant on VPM model or depth of dive. Plus settings increase the N2/He critical radii settings. Most divers should start at +2, and adjust as required. Use +3 or +4 for repeat, cold, stress, etc. A Nominal setting is for fit people with a good deco track record."

Are we assuming this was set at 0?, would this dive not be stressfull and therfor merit a +2 or +3? Also, what kind of ascent rates did they use etc? I'm no expert, but it's a very big question which without the right info is surely just an educated guess? I won't even get started on individualy physical and medical characteristics, not that I could explain it, it would be too stressful for me to try, I'd have to set my PC to +5!!

James