Shearwater Tern and Tern TX

[stuartv]

I now have 18 hrs underwater with the Tern. I had a Zoop before, so my comparison reference is only that. Short version - I like the Tern a lot.

AI is the bomb, I really liked losing a hose and not looking in 2 places for data. Pairing is immediate and the 2 devices never became unpaired in 18 uw hours.

With the type of transmitter Shearwater (and several others) uses, there is not really "pairing". The transmitter has no clue about anything outside itself. I.e. it does not know anything about any computer that is receiving data from it - or if there is even a computer listening to it. The computer is set to listen for that particular serial number (of that transmitter) and that's it.

As long as the computer doesn't lose/forget that serial number (of the transmitter), then it will always "hear" the transmissions from that transmitter and show you the corresponding tank pressure. Unless something breaks, of course. E.g. the AI antenna in the Tern breaks, or something.

The only way the "pairing" should ever be lost is if the computer undergoes a total factory reset. Or you manually change or delete the serial number in the Tern, of course.

I didn't realize how basically NO off gassing occurs until about 15' and even then, most is above 11'. That data got me studying up, so that's a good thing.

Very cool that it got you more interested. It is REALLY good to be very aware of how much faster off-gassing occurs in that last 10 - 15 feet of your ascent, versus all the prior ascent time.

But, just for the record, if you're on the bottom for just about any amount of time, then there is off-gassing happening from the moment you start up. It just happens a lot more slowly (in much simplified terms) when the tissue pressure is really close to the ambient pressure.

Off-gassing happens more rapidly as the difference in pressure between where you "were" and where you "are" gets bigger. If you go from 60' to 55', very little off-gassing happens. I.e. it is slow. That is because ambient pressure only changed from 2.82 ATA to 2.67 ATA. That's roughly a 5% decrease. If you go from 15' to 10', then it's 1.45 ATA to 1.30. Roughly a 10% decrease.

And when you go from 10' to the surface, that is 1.30 to 1.0 - a 23% decrease! Off-gassing happens SO much more quickly in that last 10'!

 

[stuartv]

Depending on the dive log software you use, you may also do this to record the actual location. I've been using Subsurface for a while. They used to allow direct logging of phone GPS location, but as Apple (maybe also Google) updated the requirements for using the phone GPS location, this was disabled.

However, you can still save that info into the log if still on site. If using an iPhone, just open the Compass app. It will also give you GPS coordinates. Hold on the coordinates and you'll get an option to copy, which can then be pasted into the location info with Subsurface mobile. I don't use the Shearwater Cloud app for logging, but it appears that only allows you to save the name.

Thanks for sharing your thoughts on it. As expected, it's another great computer from Shearwater. Glad you like it, and enjoy your upcoming dives.

I try to remember to take a picture with my phone when I'm at the dive site.

Then I add the picture to the dive in my Subsurface log. Subsurface automatically grabs the geolocation data from the picture to set the GPS coordinates of the dive site.

 

[OMyMyOHellYes]

Off-gassing happens more rapidly as the difference in pressure between where you "were" and where you "are" gets bigger. If you go from 60' to 55', very little off-gassing happens. I.e. it is slow. That is because ambient pressure only changed from 2.82 ATA to 2.67 ATA. That's roughly a 5% decrease. If you go from 15' to 10', then it's 1.45 ATA to 1.30. Roughly a 10% decrease.

And when you go from 10' to the surface, that is 1.30 to 1.0 - a 23% decrease! Off-gassing happens SO much more quickly in that last 10'!

Offgassing? Quickly?

Usually after four street tacos, a tortilla or two filled with frijoles, and a half dozen cervezas. Offgas quite forcefully sometime after that or the next morning.

 

[Belzelbub]

I try to remember to take a picture with my phone when I'm at the dive site.

Then I add the picture to the dive in my Subsurface log. Subsurface automatically grabs the geolocation data from the picture to set the GPS coordinates of the dive site.

Aah. Yeah, that’s even easier. I don’t usually add pictures to my dive log. There’s usually a video that is dated for easy reference. I knew you could add pictures, but for some reason, it didn’t dawn on me that it would associate the gps data as well.

For me, though it’s now mostly moot. My primary is the Perdix and I now just download that to my phone. Backup is a Garmin, and that profile just magically appears in my Garmin log. When I get home, I add the Garmin dives to Subsurface and the GPS coordinates and backup profile are added to the dive.

 

[stuartv]

Aah. Yeah, that’s even easier. I don’t usually add pictures to my dive log. There’s usually a video that is dated for easy reference. I knew you could add pictures, but for some reason, it didn’t dawn on me that it would associate the gps data as well.

For me, though it’s now mostly moot. My primary is the Perdix and I now just download that to my phone. Backup is a Garmin, and that profile just magically appears in my Garmin log. When I get home, I add the Garmin dives to Subsurface and the GPS coordinates and backup profile are added to the dive.

I don't really add pictures to my log, per se. The pic I take for this is usually of nothing. It's just to capture the GPS coordinates.

Anyway... you've got a system that works for you. Maybe this will help someone else. I do think it's better than using the Compass app to copy and paste the coordinates.

My problem is that when I'm on a boat, I have usually put my phone in a drybag somewhere and I often forget to get it out when the boat is actually at the dive site.

 

[mattfish]

Also, one other difference that might be significant. Terns have "Toughened Glass" while the Teric has "Sapphire." So, the Tern might be a bit less resistant to scratches on the face. No clue if that will actually have an effect in the real world, though.

The glass on the Tern is definitely more susceptible to scratches than the sapphire lens (and raised bezel) on the Teric. My wife's Tern already has a big scratch on the screen, whereas my Teric doesn't have even a little mark on the screen (the bezel has some good nicks in it though).

EDIT:
I will have to check if her Tern has a screen protector on it or not. If it does, that's an easy fix to get rid of the scratch.

 

[Ukmc]

With the type of transmitter Shearwater (and several others) uses, there is not really "pairing". The transmitter has no clue about anything outside itself. I.e. it does not know anything about any computer that is receiving data from it - or if there is even a computer listening to it. The computer is set to listen for that particular serial number (of that transmitter) and that's it.

As long as the computer doesn't lose/forget that serial number (of the transmitter), then it will always "hear" the transmissions from that transmitter and show you the corresponding tank pressure. Unless something breaks, of course. E.g. the AI antenna in the Tern breaks, or something.

The only way the "pairing" should ever be lost is if the computer undergoes a total factory reset. Or you manually change or delete the serial number in the Tern, of course.



Very cool that it got you more interested. It is REALLY good to be very aware of how much faster off-gassing occurs in that last 10 - 15 feet of your ascent, versus all the prior ascent time.

But, just for the record, if you're on the bottom for just about any amount of time, then there is off-gassing happening from the moment you start up. It just happens a lot more slowly (in much simplified terms) when the tissue pressure is really close to the ambient pressure.

Off-gassing happens more rapidly as the difference in pressure between where you "were" and where you "are" gets bigger. If you go from 60' to 55', very little off-gassing happens. I.e. it is slow. That is because ambient pressure only changed from 2.82 ATA to 2.67 ATA. That's roughly a 5% decrease. If you go from 15' to 10', then it's 1.45 ATA to 1.30. Roughly a 10% decrease.

And when you go from 10' to the surface, that is 1.30 to 1.0 - a 23% decrease! Off-gassing happens SO much more quickly in that last 10'!

This is really oversimplified and a bit not true. While math is probably correct on the pressure drop, “off-gassing” continues for quite some time once on a surface - not all at once. Also taking slow tissues into account, moving from 60 to 55 may start off-gassing some but still on-gassing most tissues, unless those compartments are saturated.

 

[Deezer-D]

The glass on the Tern is definitely more susceptible to scratches than the sapphire lens (and raised bezel) on the Teric. My wife's Tern already has a big scratch on the screen, whereas my Teric doesn't have even a little mark on the screen (the bezel has some good nicks in it though).

EDIT:
I will have to check if her Tern has a screen protector on it or not. If it does, that's an easy fix to get rid of the scratch.

Sticker on the screen when new says - This dive computer comes with a screen protector pre-installed

 

[stuartv]

This is really oversimplified and a bit not true. While math is probably correct on the pressure drop, “off-gassing” continues for quite some time once on a surface - not all at once. Also taking slow tissues into account, moving from 60 to 55 may start off-gassing some but still on-gassing most tissues, unless those compartments are saturated.

"probably" correct. LOL!

I don't see anything in your post that conflicts with anything I said. I said "much simplified". You said "oversimplified". Potato, potato. I don't think I simplified it TOO much (as "over" implies). I think I simplified it just right for the purpose of my post. But, you are welcome to your own opinion on that.

You are never completely saturated in all compartments on a recreational dive. So, yes, you are still on-gassing in the slowest compartment(s) during your entire bottom time and a lot (most, I think) of your ascent.

The half-time of the slowest compartment is 635 minutes. If you stayed at 132'/40m for 15 minutes, you're still nowhere NEAR even being half way to saturated in that compartment. You will still be on-gassing in that compartment almost all the way to the surface. (I say without doing the math, as it's not linear and I'm too lazy)

So, what does that have to do with the price of tea in China? Nothing. We don't really care about on-gassing except as it contributes to longer required time to decompress safely. What we *care* about is controlling the rate of off-gassing - which is a moot subject for compartments that are on-gassing.

Your MOST rapid off-gassing happens once you're on the surface. Assuming you're comparing to breathing actual air while in the water. That should all be pretty obvious. And it does not change the fact that the most rapid off-gassing in the water happens in the last 10'. And thus, the last 10' is where we should be the most careful and making the slowest part of our ascent (conditions permitting, of course).

 

[scubadada]

...And it does not change the fact that the most rapid off-gassing in the water happens in the last 10'. And thus, the last 10' is where we should be the most careful and making the slowest part of our ascent (conditions permitting, of course).

GF99 shown in orange. 1% on ascent until 40 ft. 41% at the start and 25% at the end of the safety stop. 73% at the surface. Final ascent over 1 min.