Computers & DIR

[StSomewhere]

Honestly, how many non-instructors with over 100 dives do you know that dive computers, but can still work a set of tables. Deco tables are becoming a lost art... and this coming from a former SDI instructor.

I have had my Buhlmann NDL EAN32 table basically memorized for some time. Its not that difficult, in fact if you stick to one standard gas and some reasonable parameters like minimum 1 hour SIs its very straight forward. Ratio deco is probably just a extension of that principle, basic parameters and knowing how to adjust for minor differences.

Besides, I find I'm a lot more attuned to my profile when *I'm* the one who's responsible for knowing it.

But I also believe that physics equations are alot easier with a calculator... Plan your dive, dive your plan.

Dunno. Like others have said, whoever programmed my dive computer has their own version of dive physics, like ascend at 30'/minute directly to 15' for 3 minutes. If I make the profile more conservative by starting stops at 1/2 max depth and ascending slower, the d*mned thing actually penalizes me. What good is it doing me if my computer calculates a poor algorithm, albiet very accurately?

 

[Snowbear]

Computers don't work in technical diving, BT's work for all diving. Its simple as that for me.

Hehe ... one of the guys in my Tech1 class found this out the hard way when he "bent" his Vyper into lockout mode. He then had a crash course in guage mode (the Vyper will still work as a guage if it's locked out ) Once the thing finally cleared, I showed him how to put in in guage mode on purpose.

After I took the DIRf class, it took me a few weeks and a lot of dives to learn to trust my own brain to keep track of the dives using my SPG and Vyper-as-a-bottom-timer. In that time, I learned that by doing so, I was getting longer bottom times and even longer run times than the computer was "giving" me. I learned how to adjust my shallow time if I ended up spending a bit more time deep to play with that octo or watch whatever critter interaction (like the octo killing the lingcod:11: ) or taking whatever picture I'm interested in getting at the time. Once learned, it's an incredibly simple system and is easily adapted to any multi level or "square profile" dive and is easily tweaked to be plenty "conservative" for any recreational dive whether I'm using air, EAN 32 or 30/30. It's slightly different for "extended range" dives on 21/35, but the ratio deco using EAN 50 by itself as a deco gas or with O2 is so close to how I figure out my recreational profiles that it's really not a big deal to figure it out. All this of course depends on my actually paying attention to and keeping track of the dive as it progresses (I use 5 minute increments and average the depth). Since I started doing that, I end the dives (and the dive days with multiple dives) feeling WAY better than I ever did by just making sure I stayed well within the Vyper's NDL limits. While I was learning the system, I kept another Suunto computer in my drysuit pocket to "check" myself during and after the dives. I found that if I checked the computer as I was starting my ascent, often I would be "violating" the computer's NDL limits. But when I would check later when I reached the 15-20' depth that most folks consider the "safety stop" that I now had "cleared" the computer to the point that it "said" I would have a whole bunch more dive time back.

 

[Jason B]

When you guys depth average, do you just average 2 depths?

In other words, say dive 10 minutes at 100 ft then ascend to 80ft for 10 minutes. That gives an avreage of 90ft. No problem.

Now let's say that you ascend to 60 ft for 10 minutes. Do you average that with the 90 ft (the average of the original 2 depths) or do you average 100, 80, and 60.

The two methods give different answer so I was wondering which way you do it. It seems it would be easier to do in the head with only 2 numbers, but not as accurate (in this case 5 ft difference which may not equate to much).

I've been trying this lately as my computer will show the average depth at the end of the dive. I do find that I'm usually pretty darn close so it doesn't seem to be that hard of a concept to apply.

Any insight appreciated.

 

[lamont]

When you guys depth average, do you just average 2 depths?

In other words, say dive 10 minutes at 100 ft then ascend to 80ft for 10 minutes. That gives an avreage of 90ft. No problem.

Now let's say that you ascend to 60 ft for 10 minutes. Do you average that with the 90 ft (the average of the original 2 depths) or do you average 100, 80, and 60.

The two methods give different answer so I was wondering which way you do it. It seems it would be easier to do in the head with only 2 numbers, but not as accurate (in this case 5 ft difference which may not equate to much).

I've been trying this lately as my computer will show the average depth at the end of the dive. I do find that I'm usually pretty darn close so it doesn't seem to be that hard of a concept to apply.

Any insight appreciated.

10 mins @ 100, 10 mins @ 80, 10 mins @ 60 I'd call 20 mins @ 90 and the 60 foot time isn't shallow enough for deco and isn't long enough for gas loading.

10 mins @ 80, 10 mins @ 100, 10 mins @ 60 I'd call 20 mins @ 100 because of the reverse profile.

on air, 10 mins @ 100, 10 mins @ 80, 20 mins @ 60 is getting too close to riding the NDL curve for me and is where I'd move up (basically, 20 mins @ 90 for the deep portion, and I'd double the time deeper for 40 mins and add that to the 20 mins @ 60 to get 60 mins @ 60 -- a computer would probably get you longer at 60, but that's okay by me...)

 

[lamont]

The "lazy" argument certainly has merit to it but in my mind it isn't the dispositive issue. My broader concern is more along the lines of divers accepting what the computer calculates as gospel, coupled with the notion that as a result of using a computer divers need not learn about decompression theory, I mean, afterall the computer is doing the work for you. This is essentially the grudge against computers, especially when you consider that more often then not the built "conservation" of the underlying algorithm mitigates any potential increases in bottom time. Many of the recreational computers build in a conservation mechanism into the algorithm to account for the contributory factors of DCS, ie; age, smokers, PFO's, obesity, poor physical fitness, lack of skill etc. etc. so a divers knowledge is often times limited because they've accepted as gospel that which an unknown algorithim computes.

Additional considerations include, but are not limited to, the ability to incorporate deep stops into the ascent rate strategy, slower ascent rates, better physical conditioning, non-smoking and so on.. In the absence of a complete understanding of the issues, all too many divers have a limited understanding of the artifical limitations imposed by many of the computer models, but yet perceive these "NDL limits" as the penultimate holy grail solution to decompression theory. Next time you come across one of the die hard computer fans simply ask them "what is an M-value", and "how does your computer compute it." Normally, after a blank stare and a period of silence, you'll hear why it isn't important for a diver to know those answers. At that point, walk away because your point has been made. Surely, some of the newer computer models have attempted to address some of the foregoing concerns, and in that regard they are doing a better job, but at the end of the day a strong knowledge of decompression theory coupled with your individual recognition of your own body's make-up will likely provide a more reliable predictor of YOUR own limits when juxtaposed against a product that is mass produced for a more global and variable marketplace.

Hope that helps.

Regards

I hear what you're saying, but you need to be careful with this argument when you're talking to propellerheads. I generated some quick ZHL-16B NDL tables from a perl script I wrote a month or so after my PADI BOW class after going through the documentation for my Suunto Vyper and wanting to know more about the stuff in there talking about tissue compartments and the deco model that it used.

The conservatism of the underlying algorithm, the punitive stuff that the algorithm does over and above the deco model, the bend-and-mend approach to deco ceilings, and the limitations and unforgivingness of the UI if you forget to plug in the correct mix are better arguments for propellerheads. If you go for the argument that the computer does the work for you, you risk being filed away in the "technophobe" folder in their head.

 

[fishb0y]

So being a lazy computer diver, does DIR-F actually cover using tables in this way? I like the idea behind actually using your head instead of plugging in your deepest depth number. If everything you guys say is true, I'm having a harder time putting down DIR (but don't think I won't try!)

 

[JeffG]

So being a lazy computer diver, does DIR-F actually cover using tables in this way? I like the idea behind actually using your head instead of plugging in your deepest depth number. If everything you guys say is true, I'm having a harder time putting down DIR (but don't think I won't try!)

Yes. But if the divers in the class do not make it a priority to talk about it, it could be covered very quickly and the knowledge may not sink in.

 

[MHK]

I hear what you're saying, but you need to be careful with this argument when you're talking to propellerheads.

If you go for the argument that the computer does the work for you, you risk being filed away in the "technophobe" folder in their head.

Lamont,

Here's a point to consider, no one in the DIR camp should be "trying to win arguments", whether it be against propellerheads, or otherwise. One of the fundamental misconceptions I see all too often is the subtle idea that we should be trying to convince people of anything. My approach has long ago shifted to the approach along the lines of: this is how, and why, we do what we do, if you are interested in learning more about it, I'm happy to help. If you are more interested in debating minutae on the interenet I have better things to do with my time.

I'd prefer more DIR advocates advance that approach, we don't need to convince anyone of anything. We do what we do, and we're happy to help anyone that wants to learn more about it. The days of trying to convert the masses are long gone and if someone is arguing for the sake of being a contrarian, then our efforts and our time are better spent avoiding those kind of discussions.

Just my thoughts..

Regards,

 

[fishb0y]

Yes. But if the divers in the class do not make it a priority to talk about it, it could be covered very quickly and the knowledge may not sink in.

Thanks... as I get closer to my class, I'll see what else people wish was covered more in the class.

 

[MHK]

Thanks... as I get closer to my class, I'll see what else people wish was covered more in the class.

It is important to remember that we try to keep the class as fluid as possible, and we try to tailor the class towards the students desire(s). We have a set of objectives that we need to cover, but we have a wide breath of latitude in terms of adding additional subjects to each class. GUE standards actually encourage their instructor core to exceed minimum standards, so each instructor is free to add as s/he sees fit.

I normally open my lectures by saying that this class is "yours" so if there is anything in particular you'd like me to cover please let me know and I make a point of covering that point in greater detail.

Talk to your instructor and I'm sure s/he'll will be glad to help.

Regards,