vr3 or shearwater pursuit

[DANM]

good point

 

[battles2a5]

The problem with this, is very few people know enough to start messing with their gradient factors. I consider myself an accomplished diver, and I don't have nearly the amount of knowledge needed in decompression theory to mess with these. My hammerhead electronics have user-adjustable GF's and I don't screw with it. My deco is done on the X1.

Well, if I've learned anything in technical diving it is that nobody knows everything and you have to figure out what works for you. I think if you understand the fundamentals on the neo-Haldanean models you can work with Gradient Factors; the lower gradient determines the depth of the first stop (and helps define the curve thereafter) and the upper gradient essentially determines how aggresive the deco will be (the higher the gradient, the closer you will be to the m-value of the controlling compartment upon surfacing). I think the standard Shearwater gradients are 30/85. This produces a profile roughly similar to VPM-B at conservative level 2 (at the least the profiles I was playing with in the 200-220fsw range. 10/90 is closer to VPM w/ nominal conservatism.

Back to my first point, I think everyone needs to figure out what type of profile works best with your physiology and work from there. GF's give you that flexibility. To my limited mental capacity, this is much simpler than messing w/ critical bubble nuclei and the other variables in VPM (way beyond my understanding). But If I'm diving the standard 30/85 and get some niggles, I can dial back one of the gradients (for deeper stops or lower surfacing pressure). Conversely, if I am getting good results with the those gradients you can see how you react to a more aggressive profile. You can also cut quicker bail-out tables or "s*** hit the fan" tables to get the most deco out of the gas you are carrying with aggressive gradients that theoretically won't bend you into a pretzel.

That's my take on it anyway. At my level of experience I cannot call myself an accomplished diver, but having this sort of flexibility was a really neat feature for me. Shearwater actually has some really good literature on this on their site. There is gradient factor overview in the actual manual and a lot of good articles on related subjects.

Shearwater Research Inc. - Computers for Diving

 

[DANM]

thanks for your input i do apreciate it, i'm still compiling info. then like you said i will make my own educated decision. Dan

 

[Tienuts]

Well, if I've learned anything in technical diving it is that nobody knows everything and you have to figure out what works for you. I think if you understand the fundamentals on the neo-Haldanean models you can work with Gradient Factors; the lower gradient determines the depth of the first stop (and helps define the curve thereafter) and the upper gradient essentially determines how aggresive the deco will be (the higher the gradient, the closer you will be to the m-value of the controlling compartment upon surfacing). I think the standard Shearwater gradients are 30/85. This produces a profile roughly similar to VPM-B at conservative level 2 (at the least the profiles I was playing with in the 200-220fsw range. 10/90 is closer to VPM w/ nominal conservatism.

Back to my first point, I think everyone needs to figure out what type of profile works best with your physiology and work from there. GF's give you that flexibility. To my limited mental capacity, this is much simpler than messing w/ critical bubble nuclei and the other variables in VPM (way beyond my understanding). But If I'm diving the standard 30/85 and get some niggles, I can dial back one of the gradients (for deeper stops or lower surfacing pressure). Conversely, if I am getting good results with the those gradients you can see how you react to a more aggressive profile. You can also cut quicker bail-out tables or "s*** hit the fan" tables to get the most deco out of the gas you are carrying with aggressive gradients that theoretically won't bend you into a pretzel.

That's my take on it anyway. At my level of experience I cannot call myself an accomplished diver, but having this sort of flexibility was a really neat feature for me. Shearwater actually has some really good literature on this on their site. There is gradient factor overview in the actual manual and a lot of good articles on related subjects.

Shearwater Research Inc. - Computers for Diving

Thanks, I understand what Gradient Factors are, and what the ratios mean. Yes you can play with the GF and say, well I feel better at the end of the dive on 25/85 than I did on 10/90. But I can also do the same on VPM by adjusting my conservatism level. I completely understand you can change the "curve" of your decompression. But how do you know which curve works best for your body?

You speak about getting niggles, and dialing back the GF for deeper stops. Well that will only work if your niggles are a result of a faster tissue compartment. How do you know which compartment is causing your symptoms? Using this theory, if your niggles were the result of a shallow compartment, adding deeper stops would only make the problem worse. At least that's how I interpret it. The problem is I don't know for sure, and I suspect most don't.

GF is popular in the circle I dive with, as it is used on the Optima handsets. I know a few optima divers who love GF, and talk about shearwater cause of their GF. And I'm not knocking it. It's just when you ask them "why do you like GF over VPM?" they really don't have a substantial answer - they just do. Usually for the same reasons you listed above. If that's what makes you happy go nuts - I could care less.

I have read the articles, and both sides of the coin seem to be in play here. The fact is most of us do not have PHD's in decompression theory, and for the layperson, it's probably irrelevant whether or not their computer uses GF, RGBM, VPM, or the ABC song from Sesame Street. There are many other features to consider when buying a computer.

 

[battles2a5]

In the case of niggles, or just feeling bad, I said I can dial back ONE of the gradients, not just the low one. If you dial back the low, and it gets worse, go back to what you were running before and dial back the high. With VPM, the conservatism is spread across the entire profile whereas with GF you can adjust different parts of the profile. So if you are doing a deep dive w/ a short bottom time you can plan a different curve than you would with a dive that where you are loading slower compartments for a longer duration (say 100-110 ft for 60-70min which is a typical NC wreck diving profile). To me, that's pretty neat. I have nothing against VPM, I have been planning most of my dives w/ V-planner and I love it. I just think GF is a bit more flexible and I like being able to dial in the profile to what works for me

 

[Tienuts]

In the case of niggles, or just feeling bad, I said I can dial back ONE of the gradients, not just the low one. If you dial back the low, and it gets worse, go back to what you were running before and dial back the high. With VPM, the conservatism is spread across the entire profile whereas with GF you can adjust different parts of the profile. So if you are doing a deep dive w/ a short bottom time you can plan a different curve than you would with a dive that where you are loading slower compartments for a longer duration (say 100-110 ft for 60-70min which is a typical NC wreck diving profile). To me, that's pretty neat. I have nothing against VPM, I have been planning most of my dives w/ V-planner and I love it. I just think GF is a bit more flexible and I like being able to dial in the profile to what works for me

I completely agree with everything you say here. My question, which leads back to my original post, is how do you know what curve works best for off gassing? Many people say what you post - you can adjust the curve of the deco schedule. I get it. How do you know that by adjusting this curve - your making a better profile for yourself? You really don't. You just just as easily be making a deco profile that is more stressful to your body, and off-gasses less efficiently. Unless you understand all these tissue models, and how they work with your body, you're really just throwing a dart in the dark.

I'm not knocking GF either - in fact I used it exclusively before I bought my X1, as that's what my Hammerheads had in them. However in the Hammerhead, there are 4 or 5 pre-set Gradient Factors built in that the user can adjust. Setting #1 is 10/100, and it goes down from there. I use mine on #3, which is 25/85, and that seems to work great. There is also a "custom user setting" where you can put whatever you want in there, and even in the manual, it tells you - if you don't have a doctorate in GF, then don't mess with the custom setting.

 

[Tomeck]

Is VR3 or Shearwater more precise for the depth?

 

[chasv]

If your still looking to buy a VR3, I have one, less than a year old, listed on ebay at this time. I am awaiting delivery of my Shearwater Pursuit, which hopefully will arrive this week.

 

[Tomeck]

The VR3 is nice, but unnecessarily complex.

Consider the X1. Much better computer - easy to use. Liquivision X1 Dive Computer

Why Liquivision X1 is much better computer?

 

[Curt McNamee]

Is VR3 or Shearwater more precise for the depth?

The Shearwater Pursuit just passed some very tough CE testing and is now being offered as part of OEM with 3 different rebreather manufacturers.

I would say that the depth precision for the Shearwater must have proven itself out to get through the testing.