Shearwater Perdix AI

[scubadada]

Thank you for explaining the definition of GTR. I agree with Stuart that there is no reason not to account for deco obligation and safety stop. It appears to be a lazy implementation of GTR. My old Galileo accounts for the stops as well as for a variable ascent rate. Perhaps Shearwater can learn from Uwatec on the implementation of GTR.

I'm also disappointed in the Shearwater implementation of GTR. Oceanic ATR includes safety stops or deco and is quite accurate. The end pressure alarm will activate whenever the active cylinder (in this case 1, 2, or 3) hits the set point. Here is the description of ATR from my 2010 VT3. I have sent this to Shearwater to consider as an improvement to the Perdix AI

 

[scubadada]

Hi Stuartv,

In handling multi-tank GTR, there are a lot of complexities. The killer for us though, was simply the need to properly setup tank size for each tank.

In the 1 tank situation, the GTR can simply be based on SAC, which is a measure of the rate of change of pressure. For this, the tank size is unknown and doesn't matter. However, the SAC isn't transferable to to another tank, which may be of a different size.

So to handle 2 or more tanks, the GTR must be based on RMV. Calculating this requires having proper information on tank sizes. In the imperial system this requires entering both capacity (e.g. 80 Cuft) and rated pressure (e.g. 3000 PSI) correctly. In the metric system only the tank size in liters (e.g. 10 L) needs to be entered. Technically, the calculations are simple, as was the user interface to enter the information. However, in practice, it is too easy to forget to change this, resulting in incorrect GTR values.

There are other drawbacks to multi-tank as well. Having to associate transmitters to gases is a pain and easy to make mistakes or forget as well. Also, covering situations where multiple tanks are used for the same breathing mixture adds additional complexity.

We feel that the solution we are launching with is a good solid starting point. The main utility of AI is having the pressure available at a glance on the wrist. Logging of pressures for post-dive analysis is also useful. Features like the GTR and real-time SAC are nice, but our current opinion is they best suited for single-tank, no-stop diving.

We are paying attention to comments and feedback, and may make changes as long as we feel adequate usability can be maintained.

Best regards,
Tyler Coen
Shearwater Research

To make this easier, at least at 1st, the GTR could simply be based on the active tank being used, then SAC would work fine. Including a safety stop or deco in the calculation should be a high priority. See my post with the description of Oceanic ATR

 

[Joneill]

Some of us are just happy to be able to now also see our tank pressure on our wrist along with other dive info on a SW computer versus needing to check the computer and the SPG...

 

[kelemvor]

I'm also disappointed in the Shearwater implementation of GTR. Oceanic ATR includes safety stops or deco and is quite accurate. The end pressure alarm will activate whenever the active cylinder (in this case 1, 2, or 3) hits the set point. Here is the description of ATR from my 2010 VT3. I have sent this to Shearwater to consider as an improvement to the Perdix AI

Scubapro's implementation is a little different. The manual doesn't indicate it accounts for optional safety stops, but does indicate it accounts for mandatory deco stops. It would be nice if they'd make the inclusion of a safety stop an option. I sure wish burger king was tastier, because I do like to have it my way.

RBT:
The RBT (remainingbottom time) is the time you can spend at the current depth and still have enough gas supply to make a safe ascent and reach the surface with the tank reserve. The RBT calculation is based on your current breathing rate, accounts for any existing and upcoming decompression obligation and for any temperature gradient in the water. It assumes an ascent at the ideal ascent rate (defined in section 3.2.1). When the RBT reaches 0 minutes, it means that Galileo has computed that if you start your ascent now and ascend at the ideal ascent rate, you will arrive at the surface with just the tank reserve, and any further delay increases the risk that you run out of gas supply before reaching the surface.

NOTE:
- Galileo needs approximately 2 minutes to analyze your breathing pattern, thus the RBT is not displayed during these first 2 minutes.
- When you are close to the depth of the deepest mandatory decompression stop, the RBT indicates the time you can stay at that depth before reaching the tank reserve

I've never used Galileo for a dive involving mandatory deco. Even though I said I'd prefer a dc to include safety stops, a little thinking about my diving tells me that shearwater's sentiment is correct. I'm a gas hog, and I use so little gas on a safety stop I never noticed that ss was not included in RBT (aka atr, gtr) calculation. I always find myself on the boat with more than just my reserve pressure.

 

[scubadada]

My VT3 is still working perfectly and I'm diving a Nitek Q as backup, to Iearn about Buhlmann ZHL-16C. By the time I need a new computer, the bugs will be worked out of the Perdix AI. I don't need many of the advanced features, but would like the GTR fixed. Who knows, I may even have other choices for a good AI computer running Buhlmann with GFs by the time I need it

 

[BoltSnap]

Some of us are just happy to be able to now also see our tank pressure on our wrist along with other dive info on a SW computer versus needing to check the computer and the SPG...

What is happier and more exciting is to see the anti-AI puritans are ALL quiet and not a sound from them. This is so funny.

 

[Lorenzoid]

What is happier and more exciting is to see the anti-AI puritans are ALL quiet and not a sound from them. This is so funny.

I suppose it's because Shearwater (at least for now) still offers a non-AI version of the Perdix and Petrel 2 to satisfy those types of people.

 

[CarcharodonCarcharias]

I get a chuckle out of the "I just bought the prior one, I want an upgrade at the manufacturer's expense".....

I remember buying my Pertel1, and within a month, the Petrel2 was out (integral compass for those with a short memory). Sure, I'd have loved to have one that could do that, but I don't blame SW or the retailer, nor did I expect any opportunity for upgrading on their dime..

Looks like I may now be able to get either a Petrel2 or the Pedrix at a "discount".

They're the diving millenials?

 

[kelemvor]

I suppose it's because Shearwater (at least for now) still offers a non-AI version of the Perdix and Petrel 2 to satisfy those types of people.

I'm curious if the firmwares will be the same between AI and non AI computers. I'm sure maintenance would be easier if they don't have a separate branch. We'll probably never know.

 

[Wah]

I was hoping for a Perdix with AI, but couldn't wait and ended up buying a used VT4.1 less than a year ago. It works fine and does what I need it to do, so I'm going to hold off. This does look like the perfect DC, though... If I had know, I would have waited. Oh well.