What's your SurfGF and how does it compare to your (Rec) GFHi?

[stuartv]

As I have observed, and @scubadada nicely confirms, your GF99 drops about 2% per minute at the safety stop.

So if you ascend and see a SurGF of, say, 84% when you really want to surface with 70% or less,
plan on a safety stop of
84-70 = 14% required change
14%/2 = 7 min stop

(But since you set your toy for GF 90/90, you didn't exceed NDL, so there's no "required" deco stop. All you have to do is make the nosey Divemaster think you're looking at fishies instead of doing a 7 min "lite deco" stop.)

If you did exceed your NDL and did have a short but mandatory deco stop, how would a nosey DM know anyway? You mean, just by looking over your shoulder to see your computer in the water? Once you get out, is there some way on a Shearwater to see if you had a mandatory deco stop on the previous dive (assuming you did any required stops, of course)?

 

[rsingler]

I've had DM's ask me why I was hanging around longer than three minutes at the cluster around the anchor line on some trips. "Were you doing deco!?" Had one particularly pesky dive leader on one trip who I basically told to back off after showing that I was in "Recreational" mode.
But they have the power, and all you can do is not use their boat on the next trip.

 

[scubadada]

Semantics

I am what my computers say I am. I dive two computers that run similar, but not identical, decompression algorithms. One runs DSAT and the other, Buhlmann ZH-L16C set at 80/95. If both my computers have remaining NDL, it is a no stop dive for me. Within the bounds of the computers, I could make a direct ascent to the surface. If one or both of the computers exceed NDL, it is a deco dive for me. I have a mandatory stop while ascending, to clear the obligation. If I blow off the stop, my VT3 would lock me out for 24 hours, the Teric would not, it would just inform me of my behavior.

I've been diving Oceanic computers, running DSAT, for a long time and many dives. I've only been diving a computer running Buhlmann for the last 5 years, about 850 dives. This was first a Dive Rite Nitek Q, then my Teric since May of 2019. On a first, clean dive, or after a long surface interval, especially if deeper, DSAT is almost always more liberal than Buhlmann. On a second or subsequent dive with shorter SIs, especially shallower, Buhlmann is often more liberal than DSAT.

This is the same dive I posted in #187, above What's your SurfGF and how does it compare to your (Rec) GFHi? This was a no stop dive on the Teric with 5 min of remaining NDL. This was the second dive of the day with a SI of 44 min. Especially the second half of the dive was reasonably shallow. On my VT3, this was a deco dive with a 5 min stop at 10 ft. After the stop was satisfied, I surfaced at a GF of 79.

So, this was a light deco dive, based on my Oceanic computer. The decision to reduce the surfacing GF further on a no stop dive is a separate one for me.

 

[Divin'Papaw]

If you did exceed your NDL and did have a short but mandatory deco stop, how would a nosey DM know anyway? You mean, just by looking over your shoulder to see your computer in the water? Once you get out, is there some way on a Shearwater to see if you had a mandatory deco stop on the previous dive (assuming you did any required stops, of course)?

That's not exactly the point. At least not my point. The boats I use (typically) have a no deco rule and a total runtime rule. By running a higher GFHi and then extended my "safety stop" a bit to get my SurfGF down below let's say 75-80% I can accurately and truthfully say that I fully complied with their rules. As long as I am on the surface by the time limit specified (runtime rule), the boat is happy and I'm happy. I've maximized my bottom time while also sticking to the rules of the boat.

 

[stuartv]

I've had DM's all my why I was hanging around longer than three minutes at the cluster around the anchor line on some trips. "Were you doing deco!?" Had one particularly pesky dive leader on one trip who I basically told to back off after showing that I was in "Recreational" mode.
But they have the power, and all you can do is not use their boat on the next trip.

"Why were you hanging around longer than 3 minutes?"

Because I like being extra conservative.

"Were you doing deco?"

Yes, a safety stop for 3 minutes is doing deco. Staying longer is still doing deco.

So, yeah, if those answers were not satisfactory for that boat, then I would probably not dive with that boat again. Do not try and rush me out of the water because you have some arbitrary rule. I will get out when I am satisfied that I have off-gassed sufficiently.

Since I use my SurfGF to determine when I ascend from my final stop to the surface, I would not really have any personal issue with changing my GF settings to 95/95 and then using my GF99 and SurfGF displays to regulate my bottom time and ascent - if that is what it took to make the boat happy regarding a "No Deco" rule.

 

[scubadada]

Don't get me wrong. nobody in Boynton, West Palm, or Jupiter has ever asked to see my computer. I have done up to 14 min of deco in Boynton, of course they knew I was in deco.

 

[stuartv]

The only time I have ever seen boat crew ask to see someone's computer is if, either, the diver got out of the water and the crew heard their computer beeping, or if the diver got out of the water and was overheard to say something like "I don't know is going on with my computer. It was showing something really weird that I didn't understand."

But, I confess to not having been on TOO many boats with a lot of new(-ish) divers. Living in northern VA when I started diving, I progressed fairly quickly to diving from boats off North Carolina, where the minimum qualifications are at least 25 dives and AOW preferred. Still seen a few there in NC that got out with computers beeping, though.

 

[scubadada]

I dive with new divers all the time in SE FL. I have told this story many times. Why does my computer not seem to be working normally? Answer, because you are in violation gauge mode from missing a deco stop. This usually occurs with one of RGBM computers, Cressi, Mares, or Suunto, but also happens with PZ+. After looking at me like I am an alien, they usually realize that they have violated the parameters of their computer. I would like think that they learned something, but I'm never sure

 

[dmaziuk]

I completely disagree. Everyone's physiology is different. I.e. personal. The GF that works for one person does not necessarily work for another. When you dive enough, you can start to develop your own database of what works for you.

Yeah, yeah, but you forgot to include the context:

I get that its very personal and kind of trial and error, but for a typical rec diver what range should one be looking at? For example, would anywhere from 80% and lower be fine and considered "safe"?

-- and nobody in their right mind is going to tell you that "anywhere below X is safe for you personally" based on the value of X. There is nothing personal in the algorithm and the whole point of gradient factors was to let individual diver do what you describe. But you knew that.

 

[Wibble]

If you are at your max depth, it WILL be 0. Your tissue tension has to be higher than ambient pressure for GF99 to have any meaning.

(I said "can be 0" because you may ascend and descend whilst on the bottom phase which will affect the GF99)