Another Tables vs. Computers Thread

[MikeFerrara]

Maybe the traditional training (with tables) is flawed? Perhaps we are wasting our time and theirs by training them to use tools that they have no use or patience for?

Personally, I think that traditional scuba training has plenty of flaws. However, many divers do still have a use for tables until some agency or instructor decides that they don't and stops teaching them to use them.

Let's face it, with the advent of online academics, my role as an instructor is more of a "coach" than a "professor". In that respect, I can concentrate on producing competent divers IN THE WATER rather than being a sage on the stage in regards to their academic training. Personally, I would rather spend more time in the water and less in the class.

A couple of things. first, even before online anything, a person could go into a good book store and buy about any text they wanted and teach themself about anything they might want to learn. Now lots of that is available online but how does that change things other than saving one a drive to the store?

Second, are you spending more time in the water because you needn't spend as much time in class? That question isn't directed so much at you specifically as it is dive training in general. Back when I was a PADI instructor, I attempted to discuss some concerns I had about course standards. those concerns were directly related to safety and my decission to approach the agency was directly inspired by several accident that happened locally.

The PADI folks presented two points. The first that the instructor was responsible for insuring that student skills were appropriate for the dive. ok but my point was that the standards didn't get them there. The second was that it was their HOPE that by improving learning materials they would enable instructors to spend more time in the water because they could spend less time in class. It doesn't work that way and I can clearly demonstrate that to any one who would like to spend a day on a field trip to go watch. Pool time and OW time represent different cost/time centers which do not necessarily change based on a reduction of necessary class time. Of course none of that addresses the specific material being presented either in the water or in the learning materials. I didn't so much get the impression that they disagreed with me. The impression was that they didn't know enough about diving to understand what I was talking about. We just didn't have a common frame of reference. For instance, to them the perfectly executed mask R&R is a comfortably kneeling diver who can calmly and smoothly demonstrate the skill. That a very different picture from what I have.

I approached IANTD with the same concerns because I was also an IANTD instructor. The answer that I recieved from them was that unfortunately they had to dumb down recreational training in order to compete with other agencies. I argued that we could do better without adding "much" time or cost. The person I talked to (I won't mention a name) asked me to present a write up of some of my ideas related to methods and standards which I did. I never got any feedback one way or the other.

I'm of the beliefe that the changes that we have seen and are seeing are only aimed at marketing concerns and have nothing at all to do with producing more competent divers. I am certainly NOT seeing the more competent divers that are supposedly being produced by all this extra in-water time. It's the same silty, divers bouncing off the bottom or reef mess that it's always been. Well, it's worse because there are more and more of them doing it...and they know less.

I'd actually like to be wrong in this and I look forward to the day when I can see an actual demonstration.

 

[MikeFerrara]

Many arguments here. I see something similar when we have a few folks do their first dives in our region after having taken their OW course in the warm, clear water. Your comment on diver competence is interesting. I suggest that this is certainly situational in nature. Someone who is only going to do their dives in a warm water environment is certainly not going to be competent in an environment where they have to wear thicker protection (or a drysuit). Yet, we have people returning from the Caribbean islands with a C-card and decide to join the local weekly group for a dive believing that the experience will be the same.

A change in environment can certainly complicate things. That's not all of it though. When I was teaching one of the things that I did was show classes a "good diver" video and a "bad diver" video. The purpose was just to let stuents see what diving could and/or often did look like. The bad diver video was video that a former student gave me after a tropical vacation. It was, I thought, a pretty typical resort boat full of divers and the video was professionally done. There were plenty of fantastic examples of just about everything that a diver shouldn't do...dangling equipment, divers bouncing off the bottom and the reef, kicking up the sand and the reef, head up-foot down trim with the diver never actually being neutral, not a single functional buddy team in the bunch (just a big pack of solo divers) and even a DM who tore up the coral to pull out an octopus so that divers could take turns playing with it.

I see things like that and get sick. I think some divers, never having seen anything different, just don't see anything out of the ordinary and they don't see a problem. Were any of those divers in danger? Not much as far as I can tell but any one of them might be if they put on a 1/4 inch 2 piece suit and tried that stuff around here. For starters, if they hadn't been over coral and heavy sand, they would have been in zero vis and, in fact, they did a fair job of silting even with that sand.

That video is pretty representative of what I've seen while diving on recreational boats and in many other such videos.

The legacy of the recreational dive industry...torn up reefs, stirred up lakes, destroyed habitat, a few injured folks and one or more agencies that may end up bigger than Microsoft.

The other day I caught part of a radio interview with an old time diver who has writen a book. I can't remember his name but I think he was one of JC's old bunch. Does any one know the diver or the book that I'm talking about. He really seemed in love with the sea and enthousiastic about sharing it but he stated that part of the purpose of the book was a warning. He has seen first hand what diving pressure has done to some of the popular dive sites over the years (he dived there before there was a dive industry) and he points out that there are more and more divers visiting those sites every year. Certainly I've read of the studies that claim that diver damage is insignificant but I've spent to much time in the water watching divers to believe it.

I'm not what you'd describe as a tree hugger but I do like a clean place to dive and they're getting harder and harder to find. My once loved local sites are out unless I can find a way to get there when they've been clear of divers for 24 hours or so.

 

[Kevrumbo]

now as an "answer" for your first link let me give you this one in return:
http://www.inspired-training.com/RGBM Really Good Bends Model.htm<snip>

[Off-Topic] An interesting but an extreme anecdotal account from an "Adventurer/Explorer" who IMO is the "Evel Knievel of Deep Diving". This Guru/Daredevil is doing stuff that 99.99% of Non-Commercial/Non-Military, Sport Technical Divers worldwide wouldn't even consider attempting. . .
(For Ellyat's wild take on DIR, see also: http://www.scubaboard.com/showthread.php?t=144113)

 

[Scuba]

Dive computers are not based upon tables. Tables are not based upon dive computers. Both are based upon the models.

There are models. Dive computers implement those models. If you are in compliance with the dive computer calculations, then you are in compliance with the model.

Dive tables are a simplified representation of those models, and if you dive in compliance with those tables, then you will be within the limits of the model.

The converse is NOT true. Since the dive tables are a simplified representation of the model, one can be within the model limits, but outside the table limits. Multilevel dives are a common, everyday example of where a dive within model limits can be well outside the limits of a square profile table.

This is a good explanation except for the last highlighted paragraph.

Since the simplication of the tables restrict it to represent maximum model limits, if you violate the model limits you violate the table limits. These are identical regarding NDL limits. Multilevel dives can not be appropriately applied to a table restricted to illustrate the model's limit at certain depths, spaced apart, thus the appearance of a time violation.

I know you are aware of this. We seem to be defining to a greater degree, which as far as I'm concerned - it's all good.

 

[lamont]

in order to adequately dive a computer i really think the diver needs to learn tables and some deco theory. they can survive by learning some rules, like not to follow the NDL curve up, and not to go into decompression on a recreational computer. to be fair there's also rules for tables, like square profiles and no reverse profiles, that also need explaining.

the basic problem is that the deco theory in OW classes is watered down to non-existant. i don't suggest that people need to be able to solve the differential equation for gas loading with a constant rate of ascent/descent on a test. i do think they need to be exposed to the concepts behind the rules over what they're doing and know that they're not arbitrary. if they turn around and completely forget the concepts and just accept that they need to follow the rules that's fine, but i think they should get exposed to it.

and since tables evolved into computers, i don't know how you can adequately teach computers without teaching them. if nothing else, you'll be missing historical context...

any book on numerical analysis still starts with newton's method, even though nobody is likely to ever actually use it...

 

[lamont]

There are models. Dive computers implement those models. If you are in compliance with the dive computer calculations, then you are in compliance with the model.

Actually, not so much. Ride the NDL curve up from deep to 30 feet and surface with only a 3 minute stop and I'll bet the DCS incidence on those profiles isn't so hot, even though you're in compliance with the calculations. Profiles like that are also not in any way suggested, allowed or were considered in the development of the haldanian physiological models which underly the tables.

And really to follow up on the post I just made, I think this is why you need to teach tables along with deco theory and computers. The deco theory was developed in order to generate tables for working dives which where typically square. That underlying physiological theory which worked for square profiles has been extended and used with considerable success in multilevel diving with computers (and with the analog wheel), but divers still need to understand when they could be abusing the crap out of their computer.

 

[Scuba]

I sort of see "learning tables first vs. learning computers first" as somewhat of a moot argument. One can argue forever about which is safer, which is more flexible, which is easier to use, and which is most needed for a basic understanding of deco models. There are just too many user variables to make much difference one way or the other in practical usage. Too many other aspects of the model omitted to make much difference either way. Specially when we consider their reason for being, to simplify safe dive limits and operational usage.

Either one is as useful on its own as a programming code for an automaton to operate fairly well, as long as he doesn't continually push the limits or falls through one of the cracks not accounted for, so to speak. Seems to work for most people at the rec level. Naturally, in order to increase safety, safely increase performance, and expand these operational limits, a more comprehensive understanding is necessary.

I don't think there is any going back though. Computers are simply a more encompassing tool which minimize user workload while maximizing operational limits under this minimal workload, compared to tables. They will only get better in the foreseeable future increasing safety for those who dive on auto mode. My 2 cents worth.

 

[Charlie99]

The converse is NOT true. Since the dive tables are a simplified representation of the model, one can be within the model limits, but outside the table limits. Multilevel dives are a common, everyday example of where a dive within model limits can be well outside the limits of a square profile table.

This is a good explanation except for the last highlighted paragraph.

Since the simplication of the tables restrict it to represent maximum model limits, if you violate the model limits you violate the table limits. These are identical regarding NDL limits. Multilevel dives can not be appropriately applied to a table restricted to illustrate the model's limit at certain depths, spaced apart, thus the appearance of a time violation.

While it is in some ways a subtle point, in other ways it is very important, and if you misread/misunderstood what I wrote, there are probably others readers missing the point also.

I agree that if you violate the model limits, then you violate the table limits.

However, the reverse is NOT true. I frequently dive profiles that violate the table limits but are well within the limits of the model. Multilevel dives with a maximum depth of 100', and a total dive time greater than 60 minutes are pretty common in my dive log. A dive profile like 10minutes@100', 10@70', 20@50', 20@ 40' would clearly be within the model limits and within the NDL of my computer.

OTOH, a 100', 60 minute dive is clearly beyond the limits of all air tables, and that is how that multilevel dive must be treated on square profile tables such as the PADI RDP, and the USN Tables and the derivatives used by NAUI, SSI, YMCA, and others.

 

[Charlie99]

There are models. Dive computers implement those models. If you are in compliance with the dive computer calculations, then you are in compliance with the model.

Actually, not so much. Ride the NDL curve up from deep to 30 feet and surface with only a 3 minute stop and I'll bet the DCS incidence on those profiles isn't so hot, even though you're in compliance with the calculations. Profiles like that are also not in any way suggested, allowed or were considered in the development of the haldanian physiological models which underly the tables.

I guess we will just have to agree to disagree on this. I simply stated that if you are in compliance with the dive computer calculations, then you are within the model limits. If you look into it a bit more, I suspect you will come to agree with me.

As for the profiles not being any suggested, allowed or considered in the the development of the haldanian phsysiological models, the "ride the NDL" curve is exactly the same thing that you would do when ascending from a dive with multiple required decompression stops. So although I do not have any direct knowledge whether such profiles were or were not considered during the development of the haldanian models, it would indeed be surprising if they weren't considered and allowed.

I do agree with your comments that riding the NDL isn't so hot an idea. I'm not saying that surfacing right at model limits is advised or wise, simply that the computer accurately reflects the model. This is why I typically surface with my Oceanic computer bargraph close to the yellow-to-green transition, which corresponds to a gradient factor around 80-85%.

If you look at what riding the NDL does to theoretical compartment loadings, you will see that initially at depth, a certain compartment will be nearing its limit (typically the one with halftime about 2/3 of the clean NDL for that depth). As you "ride the NDL" upward, the initial controlling compartment will move a small ways off of its limit, and a longer halftime compartment will replace it as the one closest to the compartment limit. This process will continue as you slowly ascend at 1 or 2 feet per minute. (Clearly, in this case, the slower ascent is NOT better. There is a limit to the "slower ascent is better" advice.). You will still be within the model limits, but compartments like the 60 minute halftime compartment will be close to their limits.

A 3 minute safety stop will not add much safety margin if you start that stop with a very long time constant compartment right at the limit.

A computer with a tissue loading bargraph display is a good learning tool. Dive a "ride the NDL" profile and you will find that it seemingly takes forever to get the bargraph back into the green.

 

[lamont]

I guess we will just have to agree to disagree on this. I simply stated that if you are in compliance with the dive computer calculations, then you are within the model limits. If you look into it a bit more, I suspect you will come to agree with me.

Nope, I tend to disagree. A better example is probably riding the NDL up from deep (100-120) up to 60 feet and then maxing it out at 80 feet and then 60 feet (30 feet probably was too shallow of an example). You'll have faster compartments which are much more loaded at 60 feet (they're offgassing from deeper) than you would have just dropping down to 60 feet and maxing out the NDL (they'd be fully loaded for 60 feet. If you follow it *all* the way up then you'll essentially deco out, but if you interrupt that dive in the middle of it then you will have tissues more loaded with gas than what a square profile gives you, and its not quite the same picture that the model was validated against. You'll have done, basically, 'deep stops' and may have offgassed the faster compartments compared to what they looked like at 100-120 feet and you may be at less risk of a type II hit, but I don't think its correct to state that you're within the "NDLs" there. The underlying tissue model wasn't validated against that kind of profile, and even though you may not be exceeding any M-values in any compartments, I'd be more careful with that loading than with a square profile dive to the NDLs at 60 feet.