I finally get it (or, gauges and why they make sense)

[gsk3]

For repetitive diving, the nitek duo is pretty darn hard to "bend" doing ocean dives (not impossible, but not as easy as sloping cave dives). If it's showing deco I'd pay more attention or question my depth averaging.

This wasn't repetitive...only did one dive that day. I went through the computer log when I got home, and the dive profile was:
* 33 minutes at 60 feet
* 25 minutes at 50 feet
* Then started ascent (took almost exactly one minute getting to 30', spent 90 secs at 30', then ascended to 20' and stayed there for a long, long time)
There's some minor variation in depth in there but I rounded deeper rather than shallower.

Even without using depth averaging that's 60ft+58 mins=118, which is still under 120. With depth averaging it's more like 113. As a sanity check, PADI RDP gives 55 mins at 60', 80 mins at 50'. So it's in the right ballpark.

Computer was in SF2, which may have a lot to do with it.

 

[flots am]

So if I had to do it over again, would I still keep the computer in computer mode post-Fundies? Yes. I think I learned a lot by making the transition pretty slow, and at very least I needed the crutch for a little while. But I think I've reached the point where it's more of a net risk than a net benefit.

Comments/criticisms welcome, as always.
Ari

Not a criticisim at all, but just because your computer doesn't match up with your "on the fly" calculations doesn't mean that either is wrong. Or it could mean that both are wrong.

OTOH, your life will be easier if you just pick a horse and go with it. If you're using two different methods, it's entirely possible that you'll get to a point where there are really significant differences between what they both call for and you really won't have any way to decide "Which is right".

And if significant deco is involved, I trust vPlanner and a preprinted plan on a wrist slate, much more than a live computer or a rule of thumb. Computers have a terrible habit of crapping out at really inconvienient times and I trust a multi-compartment model and a pre-generated plan much more than something I can do in my head with a watch and a couple of numbers.

flots.

 

[gsk3]

Not a criticisim at all, but just because your computer doesn't match up with your "on the fly" calculations doesn't mean that either is wrong. Or it could mean that both are wrong.

I totally agree here. I didn't think the computer was wrong because it disagreed with the rule of 120. I thought it was...well, not wrong but old-skool...because nothing it was asking for made any sense in a bubble model world. I've read books and studied tables and even played around with deco algorithms in statistical software, but never quite had the same violent reaction to the idea of maximizing the gradient before. It just seemed like a silly thing to do to run up to 10 feet and hang there for awhile. That's partly intuition (which in this case can be completely discounted since I have no deco experience), and partly education. The computer is Buhlmann-based; not sure what gradient factors it uses but presumably they are such that it lets you get closer to the M-values than would generate deep stops.

OTOH, your life will be easier if you just pick a horse and go with it. If you're using two different methods, it's entirely possible that you'll get to a point where there are really significant differences between what they both call for and you really won't have any way to decide "Which is right".

That seems like it would be true for VPM vs. RGBM. There seem to be strong theoretical reasons to prefer both of the bubble models to non-bubble models. Of course, as a committed empiricist I remain open to the possibility that convincing theory is wrong. Maybe some day we'll see that study done :cool2:

And if significant deco is involved, I trust vPlanner and a preprinted plan on a wrist slate, much more than a live computer or a rule of thumb. Computers have a terrible habit of crapping out at really inconvienient times and I trust a multi-compartment model and a pre-generated plan much more than something I can do in my head with a watch and a couple of numbers.

This wasn't deco, but point taken. Still, a rule-of-thumb is but an algorithm, and an algorithm can be compared to what the multi-compartment models produce. I did exactly that before I ever used it, and was satisfied it's conservative enough (wildly so on shallow dives, because it's a linear equation trying to model a distinctly non-linear phenomenon).

 

[DiverLaura]

to reiterate what has been mentioned already... Computers have a place in recreational diving... when you start doing multiple days of recreational (minimum deco) multi-dive multi-level reef dives on vacation it isn't a bad thing to have in your took kit.

 

[gsk3]

to reiterate what has been mentioned already... Computers have a place in recreational diving... when you start doing multiple days of recreational (minimum deco) multi-dive multi-level reef dives on vacation it isn't a bad thing to have in your took kit.

Hi Laura,

I think for multiple days of rec diving I'd likely turn the computer back on, as I would once again hit the edge of the comfort zone. Unfortunately, such situations are a rarity in my life

I have it from good authority that the rule of 130 can be used indefinitely with proper MDL ascents as long as you've got 90 minutes of surface interval in between, and if you have less than 90 mins you just double the stops from 30 up. Being a trust-but-verify person, before I used that for repetitive diving I would have to have spent a looong time with V-planner, tables, and a big sheet of paper. :-D

Best,
Ari

 

[TSandM]

The place where I see a computer as still possibly being valuable is in caves where the profile has big up and down swings. Open water dives are generally pretty easy to depth average and even have just a gut level feeling for what you've done, but some cave profiles are totally squirrelly, and I think in those cases, I'd be happy for something which loves doing iterative calculations to backstop my mental record-keeping.

But if you ARE going to run a computer algorithm to back up your mental work, you need an algorithm that tracks with the rules you're using. Pure Buhlmann isn't going to do that, and neither is Buhlmann+RGBM kludge like Suunto uses.

Edited to add: I have done up to a week of repetitive diving using MDL tables and ascent strategies, and so far, so good. I just basically double the shallow stops from the second dive onward, and don't push limits. Interesting research shows that, on multi-day trips, DCS is more common at the beginning . . . not what you'd expect!

 

[lamont]

But if you ARE going to run a computer algorithm to back up your mental work, you need an algorithm that tracks with the rules you're using. Pure Buhlmann isn't going to do that, and neither is Buhlmann+RGBM kludge like Suunto uses.

Suuntos also have kludges like penalizing you for reverse profiles over and above what any dissolved gas or bubble model calls for, just because.

And if you piss them off (like diving 32% and forgetting to setting it to 21%) then they'll go into ! mode for days which just arbitrarily cuts NDLs down.

They do at least give you credit for time spent at intermediate depths offgassing your fast compartments.

It'd be nice to get a recreational computer / bottom timer that didn't have code written by lawyers.

 

[gsk3]

The place where I see a computer as still possibly being valuable is in caves where the profile has big up and down swings. Open water dives are generally pretty easy to depth average and even have just a gut level feeling for what you've done, but some cave profiles are totally squirrelly, and I think in those cases, I'd be happy for something which loves doing iterative calculations to backstop my mental record-keeping.

See earlier comment about caves ;-)

But if you ARE going to run a computer algorithm to back up your mental work, you need an algorithm that tracks with the rules you're using. Pure Buhlmann isn't going to do that, and neither is Buhlmann+RGBM kludge like Suunto uses.

Hopefully the price on dive computers that let you run your own software will come down eventually.

Edited to add: I have done up to a week of repetitive diving using MDL tables and ascent strategies, and so far, so good. I just basically double the shallow stops from the second dive onward, and don't push limits. Interesting research shows that, on multi-day trips, DCS is more common at the beginning . . . not what you'd expect!

Sounds like the same MDL strategy. Good to know someone else is using it, although I'm still playing around with V-Planner before I put it to the test.

I tend to just spend forever at the 20 and 10 foot stops anyway if my team consents. If you're diving decent gas management strategies, you've got the gas to burn, so why not use it. I'd rather be in the water than out of it, most days.

 

[gsk3]

Suuntos also have kludges like penalizing you for reverse profiles over and above what any dissolved gas or bubble model calls for, just because.

And if you piss them off (like diving 32% and forgetting to setting it to 21%) then they'll go into ! mode for days which just arbitrarily cuts NDLs down.

They do at least give you credit for time spent at intermediate depths offgassing your fast compartments.

It'd be nice to get a recreational computer / bottom timer that didn't have code written by lawyers.

I see I'm not the only one with computer rage!

 

[DiverLaura]

90 min of surface interval is easier said than done... i just looked at my Maui trip dive log and the longest surface interval I had on the boat was about 1:08. that was even stopping to look at a rainbow on the way back from Molikini to Red Hill. I was also the last person in because i had camera so some people had easily 5-10 min shorter SI. I don't think that the boat we were on was unusual with regards to the 1hr SI schedule...

Hi Laura,

I think for multiple days of rec diving I'd likely turn the computer back on, as I would once again hit the edge of the comfort zone. Unfortunately, such situations are a rarity in my life

I have it from good authority that the rule of 130 can be used indefinitely with proper MDL ascents as long as you've got 90 minutes of surface interval in between, and if you have less than 90 mins you just double the stops from 30 up. Being a trust-but-verify person, before I used that for repetitive diving I would have to have spent a looong time with V-planner, tables, and a big sheet of paper. :-D

Best,
Ari