Shearwater Peregrine

[Hoag]

So, I run my Teric at an end pressure of 560 psi, to take he SS into consideration. For what it's worth, my Teric GTR seems low at the beginning of the dive, more accurate at the end. I have not figured this out yet.

There may be a very simple answer to this which you probably already know and are taking into account, but which might help others. Do you often dive in water that is a lower temperature than the air, or do your tanks sit in the sun before you jump into the water?

If either of these is the case, then is the very early part of the dive, the pressure in the tank will drop rapidly at first. The computer doesn't "know" that the change in pressure is due to a change in temperature, it only "knows" that the pressure changed and it will calculate a GTR based on an extrapolation of that change (giving a very short GTR for the first few minutes). As your dive progresses, the rate of change in the tank's pressure becomes more dependent on what you are consuming and less dependent on a now stabilized temperature.

Sorry if this is obvious to you but it might help someone who is new to AI Computers.

 

[scubadada]

There may be a very simple answer to this which you probably already know and are taking into account, but which might help others. Do you often dive in water that is a lower temperature than the air, or do your tanks sit in the sun before you jump into the water?

If either of these is the case, then is the very early part of the dive, the pressure in the tank will drop rapidly at first. The computer doesn't "know" that the change in pressure is due to a change in temperature, it only "knows" that the pressure changed and it will calculate a GTR based on an extrapolation of that change (giving a very short GTR for the first few minutes). As your dive progresses, the rate of change in the tank's pressure becomes more dependent on what you are consuming and less dependent on a now stabilized temperature.

Sorry if this is obvious to you but it might help someone who is new to AI Computers.

Thanks @Hoag

I appreciate your comment. You may have misread my post. Why would this phenomena affect the Shearwater, but not the Oceanic computer, both running off the same transmitter with the same cylinder pressures? I intend on gathering more data on this phenomena, my wetnotes are ready. I will eventually post an update.

 

[Hoag]

Thanks @Hoag

I appreciate your comment. You may have misread my post. Why would this phenomena affect the Shearwater, but not the Oceanic computer, both running off the same transmitter with the same cylinder pressures? I intend on gathering more data on this phenomena, my wetnotes are ready. I will eventually post an update.

Sorry 'bout that. When I saw it was you, I was pretty sure I had oversimplified it but I decided to let my comment stand because it might be helpful to someone just moving up to an AI Computer.

FWIW, I noticed it on Oceanic computers as well (a ProPlus2 & a ProPlus3). In the Caribbean with the tank in the sun and then jumping into the water and suddenly, I have 5 minutes GTR and I was only a couple minutes into the dive.

 

[ATJ]

For what it's worth, my Teric GTR seems low at the beginning of the dive, more accurate at the end. I have not figured this out yet.

I thought you already worked out because (as Shearwater state) they don't take the differences in compressibility of air into their calculations.

I could go on about Shearwater only calculating SAC, because they don't think divers could accurately enter their cylinder volume and working pressure, but I won't. The calculation using the tank factor is very easy.

Additionally, they don't calculate SAC or GTR for a second tank. If you dive with two tanks, the Perdix will calculate SAC and GTR for the first transmitter. When you switch to the second tank, SAC for the first transmitter slowly creeps to zero, and GTR increases. If you switch back to the first tank again, after a while it correctly calculates SAC and GTR. If it can do this for the first transmitter there's no reason they can't do it for the second. They have been asked to do it but refuse.

 

[scubadada]

I thought you already worked out because (as Shearwater state) they don't take the differences in compressibility of air into their calculations...

Thanks. I don't know that Oceanic takes this into consideration either. Their ATR calculation has been available since the late 1990s. I asked both Pelagic Pressure Systems/Aqua Lung and Oceanic/Huish this question. I never heard anything back from PPS/AL. The nice folks at Oceanic/Huish thought I was an alien asking about deviations from the ideal gas law. I only dive AL80s at around 3000 psi, the error is only around 3%, I believe the differences I've seen are more than that. I will have real data the next time I'm diving, December, I hope.

 

[turandot]

On the other hand, I absolutely love SurfGF. I use it all the time to help me decide when to surface from a dive close to NDL or light deco.

Could you explain the use of SurfGF in Shearwater computers? Thank you

 

[scubadada]

Hi @turnandot

The SurfGF tells you your GF if you were to instantaneously surface. I use it adjust my surfacing GF when I am at my safety stop following a dive close to NDL or to adjust my last stop after a deco dive. I generally surface at a GF less than my GF high. You may find this from the Shearwater website to be useful Evolution of Dive Planning - Shearwater Research

 

[Barnaby'sDad]

Got a few more dives in with my Peregrine. Still happy with it. Just curious...for anyone that’s tinkered with the menus to alter the display, can you post up a picture of what you settled on for information/display options?

I’d like to do this before my next outing. I’d just like to get an idea of what others have tried and liked or didn’t like compared to the factory default settings. Thank you.

 

[dmaziuk]

Could you explain the use of SurfGF in Shearwater computers? Thank you

Surfacing GF shows calculated gas loading in the leading tissue compartment relative to the model's maximum allowed value. Shearwaters can also show a heat map of all compartments, which IMO provides a much better view of the subject, but for some reason nobody's raving about that one whole Surfing GrapeFruit is the ScubaBoard's best thing since sliced bread.

 

[turandot]

Hi @turnandot

The SurfGF tells you your GF if you were to instantaneously surface. I use it adjust my surfacing GF when I am at my safety stop following a dive close to NDL or to adjust my last stop after a deco dive. I generally surface at a GF less than my GF high. You may find this from the Shearwater website to be useful Evolution of Dive Planning - Shearwater Research

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Thank you so much! A very interesting article!