Question Shearwater Petrel is Too Conservative

[Steve Lawson]

I plan my dives using V-Planner with VBM tables with a conservation level of +2, however, I notice a significant difference in that my Petrel is much more conservative, possible as much as 25 to 33%. I recently made a dive to 140' using both my Petrel and a friend's Perdix and found that after 15 minutes on the bottom, the deco between the Petrel and Perdix varied by 5 minutes, with my Petrel being the more conservative. My Petrel has V.72 and is set to VBM tables with a conservation level of +2. During the dive, the depths of both computers matched. Is there another setting or variable that can be changed? I wish to have some conservation on my dives, however, my Petrel appears to be far too conservative.

 

[boulderjohn]

First of all, I assume you mean VPM. Although you only talk about the settings on the Petrel, I further assume that both computers are running VPM with the same settings.

So if you had two different Shearwater computers running the same firmware and using the same settings giving different results, it sounds like a problem for Shearwater. There should be no difference between the two computers. You should contact Shearwater and get their input. You may end up doing the world a favor. Many years ago a friend of mine contacted Shearwater about a similar problem, and that led to them adding altitude to the computer. Then another friend and I contacted them when we were getting different results on an altitude dive, and they changed it so that the altitude settings returned to the last reading instead of sea level when they turned on through water contact.

I am not sure you will find a whole lot of people familiar with the Shearwater VPM software. I think this is the first question about it I have seen on ScubaBoard. Most people use the standard Buhlmann algorithm.

 

[Steve Lawson]

First of all, I assume you mean VPM. Although you only talk about the settings on the Petrel, I further assume that both computers are running VPM with the same settings.

So if you had two different Shearwater computers running the same firmware and using the same settings giving different results, it sounds like a problem for Shearwater. There should be no difference between the two computers. You should contact Shearwater and get their input. You may end up doing the world a favor. Many years ago a friend of mine contacted Shearwater about a similar problem, and that led to them adding altitude to the computer. Then another friend and I contacted them when we were getting different results on an altitude dive, and they changed it so that the altitude settings returned to the last reading instead of sea level when they turned on through water contact.

I am not sure you will find a whole lot of people familiar with the Shearwater VPM software. I think this is the first question about it I have seen on ScubaBoard. Most people use the standard Buhlmann algorithm.

Thanks, John. Yes, typo on on the VPM. The firmware is different between the Petrel (V72) and Perdix (V97), however, the tables should be similar (if not identical) and both are running with +2 conservative mode. Interesting note about the altitude, a variable that could significantly add to the deco. I typically turn the computer on prior to going down, but sometimes it times out and turns on automatically. I have reached out to Shearwater and they're asking for the dive profiles. I can easily download the one from my Petrel, but I need to reach out to my friend to get the profile from his Perdix.

I was hoping it was something simple I could easily change. I have the original version of the Petrel without the compass and so want the compass, but hate to drop another $1k+ for a new computer.

 

[boulderjohn]

I typically turn the computer on prior to going down, but sometimes it times out and turns on automatically.

Same here. The problem is that you can set the computer perfectly and then have it turn off automatically before your get in the water. That's no problem now--it will assume you are at the same altitude you were at before it shut off. My point was that Shearwater added this feature because we contacted them with the problem, showing they are pretty darn responsive to such problems.

It sounds like there is a problem that only Shearwater can fix. They wrote the software for the VPM on their computers, and it should be the same on all of them, regardless of the model.

 

[tursiops]

Why use VPM?