PADI tables finally going away?

[notivago]

I read your response as carefully as I could, trying my best to understand your points. I think we have a problem in that English is not your first language, so perhaps you are not phrasing your responses to best advantage.

It seems I am certainly not.

I have finally decided that, to put it as politely as I can, you are drawing conclusions based upon an incomplete understanding of the theory behind ascent rates and decompression.

On the other hand, that is not true. While I am bad at expressing myself in foreign languages, I can understand it very well, indeed I read far more stuff in English than I do in my own language, all the documentation for my profession is in English(I am a programmer), most fantasy books, sci-fi, RPG and so on are written in english as wikipedia is most complete in English, so I always prefer reading in English when possible. I read from 12 to 20 books a year in English from Tolkien to Star War, not including tech stuff.

I can guarantee you that in most cases, if I read something, I understand it. Specially when the matter is not that complicated, as it is the case.

To put it bluntly, I don't think you understood what you wrote about in your response. It really doesn't make sense to me. You are presenting opinions here that I have never seen presented anywhere, and I have done a lot of reading on this subject.

Let me try to clarify then, I think the best way here being quoting the Suunto paper. Forget a second about the NDL time mark, I am talking about ascension here, or rather, Suunto is:

Traditionally, since Haldane’s 1908 tables, decompression stops have always been deployed in fixed steps such as 15m, 12m, 9m, 6m and 3m. This practical method was introduced before the advent of dive computers. However, when ascending, a diver actually decompresses in a series of more gradual mini-steps, effectively creating a smooth decompression curve.

As you can see, according to the Suunto model, ascend do differ from the traditional way, thus two buddies with Suunto and other model would have to ascend in different ways as gradual ascension and fixed step ascension can't be reconciled as there is no way to ascertain which one is the 'most conservative'.

As you said at the end of your post, you are still pretty early in your education in these matters.

And yet I am noticing stuff that people with years of experience never noticed. That is called a fresh point of view.

Some of the people who have been disagreeing with you have a lot of experience and have done a lot of studying of decompression theory.They have gone well beyond the baby steps you say you are taking.

Maybe they have strode with too large steps and missed a few things, maybe they didn't go back often enough to review what they think they know.

With that in mind, I have to have a great deal of admiration for your self confidence. If I were early in my understanding of a complex theory, and if people who really knew a lot about it were telling me I was completely wrong about what I understood, I would not have the courage to tell them that they were wrong and I was right. You obviously have more confidence in yourself than I would have ever had at that stage in my learning.

That is not courage, I simply do not care being wrong and I am not prone to Authority fallacy, I always challenge authority, always put Ideas to proof, that brings better and faster knowledge than anything.

Take a look at this video, it summarizes much of what I did my entire life:
Noreena Hertz: How to use experts -- and when not to | Video on TED.com

On the other hand, if you ever want to progress beyond baby steps, it might be wise to listen to people who have gone beyond those steps rather than lecture them about why they are wrong about everything.

I do listen, but listening does not equate to take to heart something without criticizing it. I listen, I examine the info, I look for flaws, I try to make people to justify it and throw out what does not make sense still. I'd rather do this here than learn the hard way in the water where I can die.

I can only die by being wrong if I do not correct myself, and I can only do that challenging established knowledge.

 

[dmoore19]

I HAD a Suunto Cobra 3. As I recall in the set up of the computer one can disengage "deep stops" if desired. I don't have it any longer so I don't have the manual to look at.

 

[Blackwood]

And yet I am noticing stuff that people with years of experience never noticed.

You are drawing a conclusion that experience would show to be incorrect (namely that an RGBM diver and a Buhlmann diver must separate on ascent).

Within the paradigm of no-stop diving (recall that we are discussing PADI's basic training here), that is simply not true.

RGBM may prescribe a deep stop. So both divers will stop. It's NDB.

 

[Paladin]

Brendon, you're reading too fast. If you go back to my post, you will see that I'm not saying that my views are those three I listed at the top, but instead that this is my analysis of the responses of those posters who advocate strongly that tables must be taught. Therefore, a lot of your response to my post is way off target, to put it nicely.

As to your last paragraph, just go run the numbers, and you'll see that what I'm saying has merit and is not, as you claim "ridiculous." Let me illustrate it for you:

If a diver has done, for example, a multilevel dive to a maximum depth of 80 fsw without coming anywhere near the NDL as indicated by his dive computer, and then 35 minutes into the dive his computer dies, according to the PADI table (since this thread concerns PADI tables) he has already exceeded the 30 minute NDL for that dive, and furthermore, since he has exceeded the NDL by "only" 5 minutes, he must perform an 8-minute deco stop before surfacing and then stay out of the water for 6 hours. I don't know how the charters run where you dive, but here, if a diver has to stay out for at least 6 hours, the diver misses the next dive (yes, even if it is a dive to a 40-60 foot reef), and most likely all subsequent dives on that day.

Now, let's take it a little further and say that the diver's computer fails on the second dive of a three-tank trip. The first dive was to a maximum depth of 80 fsw for 30 minutes (to keep things within the NDL), and that he then ends up in pressure group R. After a standard 1 hour SI, he's now in F. His next dive has a max depth of 70 fsw, and he starts out with an RNT of 16 minutes. Then, curses, his computer fails when he's 35 minutes into the dive. Yikes! He's now a whopping 11 minutes over his NDL, and table rules require a 15 minute deco stop plus 24 hours out of the water. That's not just the next dive scratched today, but tomorrow's dives too!

The only conceivable way in these kinds of scenarios--which are actually quite benign dives here where I work--to avoid this outcome while using PADI tables would be to perform an average depth calculation and apply that to finding a pressure group. This is why I said that the third category of reasons, not wanting to miss a dive and therefore planning with a table after a computer failure, is not workable in many, many instances, and in fact would not be workable in the vast majority of dives we do here.

I generally use the US Navy tables which allow for 40 minutes at 80 ft. So does the 120 rule (which is based on the Navy tables). But even ignoring that, your arguments against switching to tables after a computer failure actually reinforce my view on the whole thing: Learn the tables and forget the computers. No computer to fail = no lost dives. I have a computer and I keep it in gauge mode. It makes an acceptable backup to my watch and depth gauge.

 

[ekremer]

I cannot believe that this thread is still going on after 1100 posts. I also cannot believe how strongly some of you cling to the tables.

Yes tables are great, and I still carry mine, but lets be honest that is not how divers dive. And at the end of the day, your average open water student wants to learn how to dive. She does not care about deco theory, as long as she doesn’t get sick.
And at the end of the day in practical diving, there is no difference between tables and a dive computer. They are both representations of deco theory that are simple enough for a lay-person to use.

Lets look at some of the normal dives I do, and I assume they are pretty standard for your average OW/AOW diver.


From what I witness, dive tables are not really that important from how a normal recreational dive goes.
Case 1) Charter dive boat.
Step 1 Dive untill A) air runs out or B) NDL runs out.
Step 2, surface and wait until the captain kicks you off the boat again.
Step 3, repeat step one until out of tanks.

This is the most common type of vacation dives. The reality here is all the important planning gets done by the crew. you don't have a lot of say in a shallower or deeper dive, so you plan the dive given. For this dive, the computer is perfect, and after a couple dozen of these you realize the pattern. Dive to 60 -90 feet for 20-40 minutes. wait 1 hour and then do another shallower dive for another 20-50 minutes. This kind of dive is really easy to spot problems with your computer, as it is always about the same.

Case 2) Private Boat.
This is where the divers themselves get to choose a spot and do the dive. This is my favorite type of diving
Step 1) find a location, (usually for us it is between 70 and 130 feet.)
Step 2) Dive till either A) gas or B) NDL runs out.
Step 3) return to boat and fish. and figure out your next location. (Usually for us it is between 30 and 60 feet. ) Here I will go into my computers plan mode, and figure out what surface interval I need to get me close to finishing my next tank, This is where we could do the same thing in the tables, and I do on occasion to keep my skills sharp.
step 4) repeat step 1 until out of tanks.

For this scenario, Planning on a table, and planning on a computer is exactly the same. And experience can tell us if there is an issue with the computer, or a typo on the tables. no advantage to tables here.

Case 3) The shore dive.
I admit I don't do a lot of these, but in my little experience the only part of the planning you control once the site is chosen is surface interval.
This one has the added complication that fills are easy so you can have many dives here. But once again, I don't see any difference in practical use. It is still the same 4 steps.
Step 1) Find a location.
Step 2) Dive till either A) gas runs out or B) NDL runs out.
Step 3) return to shore and wait until NDL is close to gas time, or until you get bored.
Step 4) Go to step 2 until out of tanks.

 

[TMHeimer]

And at the end of the day in practical diving, there is no difference between tables and a dive computer. They are both representations of deco theory that are simple enough for a lay-person to use.


I like that.

 

[notivago]

I think you are worrying about the theory more that what will actually happen. I dive all the time with someone using a Suunto, Yes the model is different. Yes the accent profile effect is a bit different. But because the bottom time is slightly less with the Suunto, the effect is that, if you follow the more conservative Suunto, is you both end up very close to each other. In several hundred dives, have not seen any issue.

But, is it always so? In the particular case of your Suunto and your buddy computer that is true, but what garantees that there is no instance in which your suunto would give you less conservative measures? Can you vouch for all the possibilities? For all computer combinations in all dive conditions? Maybe really there is never a huge gap. Then again, maybe there are.

Regarding who is right in this, Suunto would get my vote, as they are attempting to reduce the formation of micro bubbles (which are most likely not that huge of a concern, except that you have to have micro bubbles before you go to getting really bad big bubbles). Theirs is based on actual testing, not some guess as to what was best.

I myself liked Suunto theory and but there is no objective way of choosing which one is being more conservative.

You do raise a very interesting issue though....involving teaching tables...it tends to accidentally teach a dogma, rather than an ever changing science. I don't think that was intended, but teaching hard numbers tends to produce that effect in a lot of people. (note: I was taught the classic 60 ft = 60 minutes, and 60 ft per minute maximum ascent rate, and not safety stop, should I still be using that today?)

That is the classic conflict between tradition and innovation. Tradition relies on time tried solutions that work, no matter how bad or inefficient, but if you stood too rigidly you become unable to adapt for changes, innovation gives you adaptive edge and can tune up processes, but too much too fast is more likely to kill you than benefit.

Tables are good for planing, are a cost effective way to redundancy in dives and a good tool to fall back if you for some reason do not have or want a computer for a dive.

 

[notivago]

The response to the first category of reasons that most appeals to me is something like, It's not necessary to understand how an internal combustion engine works in order to safely operate an automobile. Decompression theory is fascinating, but I think a general understanding of it is sufficient for open water students, and further, I think the same level of understanding is needed whether learning to plan dives with tables or with a computer. For those who want more, there are books like Deco for Divers that lay the theory out in non-technical terms without any reference to dive tables.

False analogy, a better analogy would be: knowing what happens to you if you crash with a car at an wall(Bends) to choose among using brakes(Computers) or not speeding and keeping to the street(Tables).

The response to the second category of reasons that most appeals to me is that we should be teaching what students need. If we are teaching students who have limited or no access to dive computers, then of course we need to teach tables, but if we are teaching students who already own/plan to purchase dive computers or who intend to rent computers for their dives, I see no reason to force them to study table use. We should be teaching what students need and are most likely to use, not what some well-intentioned but misguided it's-important-in-principle view mandates.

The reason I see is there is no damage in having knowledge.

In response to the third category of reasons, this is where it gets really muddy. Assuming a dive computer fails during a multi-level dive and assuming there is a set of tables accessible to the diver, and assuming the diver has the data from the previous dive(s), yes, s/he could try to plan a subsequent dive using the tables. However, in my experience here, many, if not most, of our multi-level dives that are perfectly okay on a computer violate the NDL on a table. This violation will prevent the diver from doing any subsequent dive anyway, if the table rules are adhered to. So even knowing how to use the tables won't help in most cases, unless the diver has conscientiously tracked average depth throughout the previous dive(s) and can use a rule of thumb, like the 120 rule, as a way to interpolate the data and apply it to planning the next dive according to the tables. For most people, diving is a recreational pursuit. As such it's not worth risking one's physical well-being just to avoid missing a dive. When a computer fails, just sit the next dive or two out. It's the prudent thing to do in the same way that skipping a dive day when you're congested rather than stuffing yourself with decongestants is the prudent thing to do. Yes, some people will try to dive anyway by self-medicating when they've got a cold, and some people will try to do a dive using another means of dive planning after a computer failure. But just because some people do it does not make it advisable.

The following dives would become a guessing game. I would sit out and wait for the following day.

 

[Blackwood]

False analogy, a better analogy would be: knowing what happens to you if you crash with a car at an wall(Bends) to choose among using brakes(Computers) or not speeding and keeping to the street(Tables).

Seriously?

While his analogy isn't quite apt (since a table isn't the 'engine' driving modern the PDC), yours is absurd. It implicity suggests that a computer diver hasn't the ability to dive without recklessly approaching and breaking limits.

That clearly nonsense.

A computer diver is equally able as a table diver to 'keep to the streets', and moreover has active warnings in place.

The fact of the matter is, if a diver wishes to push and break limits, he will do so regardless of which tool he uses to plan and track decompression.

 

[TMHeimer]

A comparison:
With tables you watch your watch and SPG, making sure you don't exceed planned depth and time limit.
With computer you plan your dive(s) but you check your remaining allowable NDL.
Obviously the computer is very handy on multi level dives, especially such as 5 mins. at 100' and the rest at 50'.
Assuming you do all those things right there is only one other real difference--Though you should never go right to the
NDL, I guess it could happen, especially on a deep dive. So with tables you check the SPG for max depth--and you know that the worst it could be is if you spent the whole time at that depth and actually are at the limit. But it is likely that at least sometime was spent even a little shallower, giving you a small margin for error. The computer tells you your actual theoretical NDL, so if it says "0" bottom time left you ARE at the limit. You can be conservative and end the dive quite a few minutes before it would read "0". These are reasons why I always use both unless diving real shallow, then it's just the watch, etc.