Whats Wrong with VPM-B

[DwayneJ]

VR Technology went VGM, Atomic Aquatics Cobolt is using Reduced Gradient Bubble Model, Liquivision Xeo and Shearwater Predator are using tried and true Buhlmann ZHL 16.

Dwayne

 

[Kern]

What exactly is VGM anyway.

According to RonR, BRW doesn't think a fully iterative version of RGBM should be used for NDL dives to less than 46mt. So most of the people using the Cobalt won't be using RGBM. RGBM will apparently kick in sub 46mt, but I wonder what's the point of this in a recreational computer.

VPM B is available on the X1, & the DR5 from HeinrichsWeikamp in the near future. It may or may not become available on the Xeo. There has even been talk in the past of making it available on the Pursuit.

 

[rossh]

VR Technology went VGM, Atomic Aquatics Cobolt is using Reduced Gradient Bubble Model, Liquivision Xeo and Shearwater Predator are using tried and true Buhlmann ZHL 16.

Dwayne

Hi, When you look a little closer, things are very different.

Xeo, Shearwater, VGM - these all use GF applied to ZHL16. However the prime use of GF today is to make ZHL look and feel just like a bubble model. GF is used to try to emulate VPM-B.

In fact, no one actually uses real Buhlmann in its original ZHL-16 form anymore - its too fast and too risky. Every instance of Buhlmann is morphed in some way with GF or other methods to inflate the times. The end reslut is deeper stops to look and feel like VPM-B or similar deep stop planning methods. This would seems to be rather a backwards way of planning dives.

There is one valid reason GF is used in dive computers: GF is really simple to program and compute, so it saves on battery power and only needs a simple (cheaper) CPU. VPM-B is more complex and it takes more effort to make it run in dive computers.

Regards

 

[rjack321]

In fact, no one actually uses real Buhlmann in its original ZHL-16 form anymore - its too fast and too risky. Every instance of Buhlmann is morphed in some way with GF or other methods to inflate the times.

Which is another way of saying original ZHL is not accurate and aims too close to the "bent" side of the gray zone between feeling marvelous and bent like a pretzel.

The model without kludgy the gradient factor low driving it deeper & longer is just plain wrong. And for really long dives where people can exit the water with a GF high in the 115-125 range its wrong too. Given these realities, why Buhlmann is still preceived as the gold standard with terms like "tried and true" is baffling to me.

Its still got market share with the GF implementation, although thankfully that has declined over even just the past 5 yrs. Maybe people will start to realize that it was good for its time but GFs are just fudging a poor fitting model into reality.

 

[Shearwater]

We see the world differently. We think that there are some people who like VPM-B and some people who like GF.

We spend a lot of time and money going to scientific conferences on decompression. We listen to what the scientists have to say. And more importantly, we listen to the discussions to get a feel for beliefs that have consensus and those that are contentious. I think I can say with some certainty that the superiority of bubble models is not a widely held view in the research community.

If you want to know what is really going on, I suggest that you ignore the advocates of any algorithm and find out what the science is. Join the UHMS and read the semi-monthly "Undersea and Hyperbaric Medicine Journal."

Use the Rubicon Foundation website to search for the data.

Do anything but make your decompression decisions based on the opinions of people who are trying to get you to believe in the one true algorithm.

We believe that there is insufficient evidence to say for sure whether GF or VPMB is a better algorithm. Clearly people are using both algorithms and completing dives successfully.

If you think we are just trying to support GF, we recently hired one of the mathematicians that was heavily involved in VPM in the early days, and we will be releasing the Shearwater take on VPMB in our products within the next few months. We weren't planning on announcing it quite yet, but this seems like an appropriate time.

Bruce

 

[LiteHedded]

i pick whichever one is shorter. is that bad?

 

[rjack321]

i pick whichever one is shorter. is that bad?

So why not pick the longer one? Your water's downright balmy anyway :blinking:

 

[LiteHedded]

So why not pick the longer one? Your water's downright balmy anyway :blinking:

psh. I don't have all day

 

[rjack321]

psh. I don't have all day

Oooh date night, I get it

 

[Liquivision]

We see the world differently. We think that there are some people who like VPM-B and some people who like GF.

We spend a lot of time and money going to scientific conferences on decompression. We listen to what the scientists have to say. And more importantly, we listen to the discussions to get a feel for beliefs that have consensus and those that are contentious. I think I can say with some certainty that the superiority of bubble models is not a widely held view in the research community.

If you want to know what is really going on, I suggest that you ignore the advocates of any algorithm and find out what the science is. Join the UHMS and read the semi-monthly "Undersea and Hyperbaric Medicine Journal."

Use the Rubicon Foundation website to search for the data.

Do anything but make your decompression decisions based on the opinions of people who are trying to get you to believe in the one true algorithm.

We believe that there is insufficient evidence to say for sure whether GF or VPMB is a better algorithm. Clearly people are using both algorithms and completing dives successfully.

If you think we are just trying to support GF, we recently hired one of the mathematicians that was heavily involved in VPM in the early days, and we will be releasing the Shearwater take on VPMB in our products within the next few months. We weren't planning on announcing it quite yet, but this seems like an appropriate time.

Bruce

Excellent post Bruce.

Many people are using the various common algorithms and are completing dives safely. While it's not quite like the Ford versus Chevy debate, having the option to choose as a consumer is very nice.

-Doug
Liquivision Marketing & Sales Manager