first deco dive

[Cave Diver]

Depending on the deco algorithm used by your computer, the "one min at half max depth" may cause the computer to accrue more deco (or could clear it completely).

When running my VR3 (VPM-B algorithm) vs my Nitek Duo (Bulhmann) side by side....

I'd be clearing deco on my VR3 during a computer mandated "deep stop" and the Nitek Duo would be adding more deco. I'd get to the 20 foot stop, switch to O2, and the VR3 would clear me several minutes before the Duo did (because the VR3 counted the "deep stop" for decompression whereas the Duo counted it as additional time spent at depth).

I wound up bending the poo out of my poor Duo on one series of dives, and the VR3 was perfectly happy...bamamedic was also happy and unbent.

Yep, those were the two computers in my earlier example. Whenever I dive my VR-3, my Duo is in gauge mode.

To extrapolate on this, on the last trip one of my buddies was on with me, I was diving a recreational computer and he had a tech oriented computer. We incurred some planned deco on a dive and on the ascent, his forced a deep stop that mine totally did not like. As we did the stops his computer called for, his deco obligation was steadily decreasing, mine was increasing rapidly. It was no big deal as we had plenty of gas and out times still ran within the parameters of the plan, but it illustrated how vastly different computers can be. At one point, mine showed 30 minutes of additional deco over his, but most of that cleared as we hit our shallow stops. We finished up the last of the stops, played around in the shallows for a while, then made our exit.

Don't assume that just because you've only incurred a minute or two of deco that something can't hang you up and cause a rapid change in your circumstances.

 

[LanceLisenby]

So what is happening to ME at 40' after a 37 min look-see at 80'? Am I loading or off-gassing if im comfortably hanging by the anchor line.?

 

[bamamedic]

Yep, those were the two computers in my earlier example. Whenever I dive my VR-3, my Duo is in gauge mode.

Yeah...that's what I've been doing lately...works much better than hearing the Duo go "beep, beep, beep" for half my deco :cool2:

 

[Cave Diver]

So what is happening to ME at 40' after a 37 min look-see at 80'? Am I loading or off-gassing if im comfortably hanging by the anchor line.?

Running it through V-planner with 37 minutes spent on air at 80' I'm showing that your off gassing starts at 58' and you will incur 10 minutes of deco time in addition to your 3 minute safety stop.

So the rough answer is that you're off gassing. For a more exact answer we'd have to talk about slow compartments, fast compartments and halftimes.

 

[Mr Carcharodon]

So what is happening to ME at 40' after a 37 min look-see at 80'? Am I loading or off-gassing if im comfortably hanging by the anchor line.?

Well both of course. Your fast compartments, pretty much everything up to 12 minutes, is running close to saturation when you leave 80 fsw. So those start unloading the moment you start your ascent. But the slow compartments were never close to loaded, because your were not at 80 fsw long enough. So some of them will still be loading at 40 fsw. And the mid compartments are in between.

As you ascend your fast compartments off gas, and assuming you follow a reasonable ascent rate they will never run over their maximum allowable pressure. So what you have is some mid compartment controlling the ascent, at least if you run it on a computer. Tables have to make more assumptions which can sometimes lead to odd answers.

 

[Blackwood]

I still think 10' is probably a ceiling

Agreed, and I suspect that the depth, like the 'safety stop', is also programmed in (i.e. not generated by the computer's deco model). If the diver with a 10' ceiling on an 'NDL computer' were to stay at depth longer, I'm not sure it would ever generate a reasonable ascent profile. It may make the ceiling progressively deeper, or it may flash a big question mark and start displaying depth only.

They may be functional for dives where you mostly clear the deco by the time you reach the ceiling (divers who break NDL and ascend at 30fpm on a 60fpm model have likely experienced that), but for anything beyond NDL computers are clearly not the proper tool.

 

[dumpsterDiver]

Agreed, and I suspect that the depth, like the 'safety stop', is also programmed in (i.e. not generated by the computer's deco model). If the diver with a 10' ceiling on an 'NDL computer' were to stay at depth longer, I'm not sure it would ever generate a reasonable ascent profile. It may make the ceiling progressively deeper, or it may flash a big question mark and start displaying depth only.

They may be functional for dives where you mostly clear the deco by the time you reach the ceiling (divers who break NDL and ascend at 30fpm on a 60fpm model have likely experienced that), but for anything beyond NDL computers are clearly not the proper tool.

Is this some DIR brain wash material or what? I've done hundreds and hundreds of deco dives using a computer and many were for more than a few minutes of deco?

I had my computer to 225 pretty many times, 240 once and 287 ft (all on air) and the computers never gave me a question mark.

 

[Garth]

Wow! Recently?

 

[LanceLisenby]

Wow! The manual on my oceanic say's it won't freak out until 330' . That be a feature I won't be putting to the test!

 

[Cave Diver]

Wow! The manual on my oceanic say's it won't freak out until 330' . That be a feature I won't be putting to the test!

Is that a "freak out limit" where you fry the algorithm, or is that just the depth that the case is rated for and they don't recommend you exceed due to increasing chance of flooding the computer?