Question Shearwater Teric (GF40/85) goes into DECO on first dive (max depth 25.9m, avg depth 17.6, duration 48mins)

[dflaher]

Your Teric and your wife's Apple Watch are running the same GF high 85, generally considered moderate in the spectrum from conservative to liberal. The NDL is entirely controlled by the GF high. I would expect the two computers to behave identically, or nearly so. I would imagine that your wife stayed enough above you on the dive that she avoided entering deco.

@scubadada - That was my first thought about why the AWU did not go into deco, while the OP's did. But...could it be because the two computers are running different algorithms (no idea what algo the AWU runs), even though both computers had the same GF High?

 

[tridacna]

@scubadada - That was my first thought about why the AWU did not go into deco, while the OP's did. But...could it be because the two computers are running different algorithms (no idea what algo the AWU runs), even though both computers had the same GF High?

AWU runs the unmodified Bühlmann ZHL-16C algorithm.

 

[scubadada]

@scubadada - That was my first thought about why the AWU did not go into deco, while the OP's did. But...could it be because the two computers are running different algorithms (no idea what algo the AWU runs), even though both computers had the same GF High?

@tridacna just beat me to it. Oceanic+ runs Buhlmann ZH-L16C with GF. It has 3 presets and custom GFs. Preset 0 is 70/85, mentioned by @Divedeeplastlong as being used by his wife.

 

[tursiops]

@tridacna just beat me to it. Oceanic+ runs Buhlmann ZH-L16C with GF. It has 3 presets and custom GFs. Preset 0 is 70/85, mentioned by @Divedeeplastlong as being used by his wife.

His wife was wanting to get to the surface. There is a good chance she was not only diving shallower than the OP, but especially that she started up sooner, and got shallower faster.
Getting away from depth sooner will do a lot to back off from deco.

ADDED: Lots of questions could be resolved by showing both of their dive profiles and some Cloud details of his, like SurfGF.

 

[scubadada]

His wife was wanting to get to the surface. There is a good chance she was not only diving shallower than the OP, but especially that she started up sooner, and got shallower faster.
Getting away from depth sooner will do a lot to back off from deco.

ADDED: Lots of questions could be resolved by showing both of their dive profiles and some Cloud details of his, like SurfGF.

It is unfortunate that SurfGF is not included in the display of the Shearwater Cloud graph. It would be nicely complimentary to GF99, that is displayed.

I have recommended the addition of SurfGF to Shearwater on a couple of occasions. They acknowledge the value of my request and tell me it is under consideration. Perhaps if others also submit the request?

@rsingler manually created a graph that included both SurfGF and GF99. It is very interesting. SurfGF is shown on the yellow line and GF99 on the orange line. This was a deco dive. Of course, the 2 lines meet nicely upon surfacing.

 

[tursiops]

His wife was wanting to get to the surface. There is a good chance she was not only diving shallower than the OP, but especially that she started up sooner, and got shallower faster.
Getting away from depth sooner will do a lot to back off from deco.

Some numbers, using MultiDeco.
Assumed: air, max depth 70 ft, BT 40 mins, GF 40/85.
Nominal deco is 0:20 min at 30 ft, 1:00 at 20 ft, 4:00 at 10 ft. Total deco is 5:20 mins.

+10% depth change increases total deco by 69%​

-10% depth change decreases deco by 77%.​

​

+10 BT increases total deco by 19%​

-10% BT decreases total deco by 54%​

​

ADDED: in round numbers, 10% depth change is twice as important to total deco as is 10 BT change.​

​

FYI, if the GF had been 70/85, total deco would have been 4:30 min, all at 10 ft, a decrease of 18%.

 

[lowwall]

I have very limited knowledge on GF and what GF I should set.

Should I change my teric GF to 70/85 to match my wife’s AWU so we both will have similar NDL/DECO?

When you are looking at gradient factors, the second number is what sets the conservatism level for NDL dives. The first number only comes into play if you go into deco. It controls the depth and time of your deco stops, with lower numbers requiring deeper initial stops.

Since both you and your wife are using 85 as the second number, your no deco limits will be the same if you are diving identical profiles.

But....

Some numbers, using MultiDeco.
Assumed: air, max depth 70 ft, BT 40 mins, GF 40/85.
Nominal deco is 0:20 min at 30 ft, 1:00 at 20 ft, 4:00 at 10 ft. Total deco is 5:20 mins.

+10% depth change increases total deco by 69%​

-10% depth change decreases deco by 77%.​

​

+10 BT increases total deco by 19%​

-10% BT decreases total deco by 54%​

​

ADDED: in round numbers, 10% depth change is twice as important to total deco as is 10 BT change.​

​

FYI, if the GF had been 70/85, total deco would have been 4:30 min, all at 10 ft, a decrease of 18%.

Two people never dive identical profiles. What this post illustrates is that being a little deeper than your buddy on average can make big difference in required deco time. The same holds true for allowed no deco time.

This goes double for the DMs profile versus yours. You aren't that close to the DM, so it's difficult to match exactly what they are doing.

That's why it is essential that you monitor your own NDL time.

 

[Divedeeplastlong]

Your Teric and your wife's Apple Watch are running the same GF high 85, generally considered moderate in the spectrum from conservative to liberal. The NDL is entirely controlled by the GF high. I would expect the two computers to behave identically, or nearly so. I would imagine that your wife stayed enough above you on the dive that she avoided entering deco.

Do you recall how much deco time you had and what it was when you surfaced? If not, you can find that and other interesting information from the Shearwater Cloud log. In addition to your deco data, you might want to check your end surface GF. As you surfaced in deco, I would imagine that your surfacing GF was a little in excess of 85

Best of luck in your future diving

Yes, you were almost spot on. My dive ended with Surface GF of 84.

Thank you all so much for your response. It has really broadened my understanding of GF.

Attached is my wife’s AWU dive graph (both depth and no deco graph)

 

[Divedeeplastlong]

Thank you all for your response and sharing. I’m really thankful for this forum and for everyone’s helpful replies and advice.

I have another question, with me ending the dive with Surface GF of 84%. Would it be safe for me to dive again? If yes after a surface interval of how long.

Thank you all in advance.

 

[Divedeeplastlong]

Well a personal take, how I would carry on and interpret it. But I am not a professional, nor a medical doctor, neither did I analyze it fully. So its just an opinion, nothing to rely or reference on!

Usually with a healthy body, clean and slow ascent with doing a more or less safety stop there should be no issue even for the most possible aggressive setting. That is statistically speaking, if you do not or marginally violate the obligations. In the end all deco calculations are with lots of statistical and empirical data. Older computers have been much more aggressive... I set my computer a bit more conservative and follow it.
If you are more conservative on the settings and "violate" these obligations, you may have been very well within the limit of a more aggressive settings.
According to the Padi Table its 29min NDL at 25m. So depending on the profile its probably at the edge of a deco dive.
So from what I see you are most probably fine, especially, if you feel ok.
I would be more interested, why your wifes computer did not show a deco - or did it already clear on the ascend and you just did not notice? Maybe also because of the profile it was just on the verge and you have been a bit deeper as she was, and then because of the profile it did clear.

You could check your profile with subsurface and see if that corresponds, and also compare the profile of your wifea data, if you want to be sure. But I would say the computer was right.
.

However: Please follow the information on your computer, if possible. As far as I understood there was a dive guide who could perfectly well ascend with your wife and you could have stayed liked 2-3 more minutes down (well yeah ok you would have been alone ... trading risks..)

Thank you for your in depth sharing and advice!

Pls find my wife’s AWU depth graph and no deco graph for the dive attached.