Diver Training: How much is enough?

[ElGaucho]

Actually PADI materials including the RDP still talk about 60 fpm .... Believe it or not!

 

[boulderjohn]

Actually PADI materials including the RDP still talk about 60 fpm .... Believe it or not!

That is correct, and if you give it a moment's thought, you will realize why it has to be that way.

The PADI RDP was developed after very thorough, peer-reviewed research. Divers did thousands of dives and were studied using Doppler bubble imaging. All the numbers in that table are based on the results of that study.

When that study as conducted, 60 FPM was the time-honored ascent rate, and that was what was used throughout the study. That means that every number on the RDP is based on the assumption that the diver will ascend at the end of the identified bottom time at a rate of 60 FPM. If the diver ascends at a different rate, then the numbers are no longer valid.

More recent research says that 30 FPM is a safer ascent rate, but if you ascend at that rate, you should leave the bottom sooner than indicated on the RDP because of your slower ascent. For PADI to change to 30 FPM, they would have to redo the study. And they don't have to. Their study showed that diving within the parameters of the RDP, ascending at 60 FPM, is extremely safe. The studies that showed that 30 FPM is better also showed that 60 FPM is very safe, just not as safe as 30 FPM. Those studies also showed that doing a safety stop was more valuable than either ascent rate.

---------- Post added January 13th, 2013 at 04:26 PM ----------

Actually Wayne, since we're on the topic of yo-yo diving (or zig-zag profiles), do you have any recollection regarding how the advice to avoid those things got raised to the status of "best practice"?

For what it is worth, I just did a search of the Rubicon Foundation archives and could find no studies. I know that Bruce Weinke theorized along those lines (but actually related to multiple dives, not multiple ascents in one dive) back when the workshop on reverse profiles was held, but he was talking about very deep diving, when bubbles formed on the first dive would be significantly compressed on the second very deep dive. That is why the workshop retained the recommendation against reverse profiles in the case of technical dives, but not recreational dives.

George Irvine made a warning about bounce dives a couple decades ago, but he was again talking about new dives after very deep dives. Additionally, if you read what he wrote, you will see that he makes a number of assertions related to the science that are debatable.

As for yo yo diving messing you up, just read BoulderJohn's post.

Are you saying that my post was messed up as a result of my having done yo yo dives? I don't believe I said anything about yo yo diving in my post.

I don't promote yo-yo or bounce diving. You are the only instructor I know who does and without any support for the practice.

This is a deceptive response.

I sense that your reference to this earlier in the thread was to the debate on your agency's refusal to do CESAs in OW instruction because it believes doing repeated ascents as a part of the instructional process is bad for the instructor and promotes dangerous diving to students.

No one wants to do yo yo diving. No one promotes it. I don't think Wayne promotes it. The question that was asked was not whether we should all go out and do yo yo dives. The question was whether or not there was any research saying that such a dive is inherently dangerous. As I indicated above, if there is any such research, I don't know of it. You have been asked to provide such research, and you have not done so.

I don't promote that kind of diving in any way, and I don't know any instructor who does, including Wayne. On the other hand, I don't know of any research saying it will harm me to conduct those exercises during OW instruction in shallow water, and I am quite sure students can tell the difference between what I do while supervising a CESA and what they should do during a dive.

 

[RTee]

Likewise

 

[The Chairman]

Are you saying that my post was messed up as a result of my having done yo yo dives? I don't believe I said anything about yo yo diving in my post.
This is a deceptive response.

Any multi level diving adds problems to a dive, especially if you aren't using a PDC. If it can happen here, then popping to the surface over and over again is problematical.

No one wants to do yo yo diving. No one promotes it.

On this we disagree. Students emulate their mentors. It's only natural. You're a role model and they want to dive just like you do. Whether it's kneeling, bouncing up and down like a yo yo or not doing a full safety check before you dive, they notice. Monkey see, monkey do and the younger they are, the less able they are to differentiate.

If you do anything in front of your students, you are promoting the practice. John, I am sure that there are many, many doctoral dissertations on this subject matter. Just a Googling of "student imitates teacher" brings up a litany of references on the subject. In fact, my instructional method is based on getting my students to imitate how I dive. I bet yours is too.

 

[DaleC]

I liked this post but wanted to address two points made

2. Mark Powell wrote an excellent book, Deco for Divers, which will tell you anything you could want to know about decompression theory. Bruce Weinke's Technical Diving in Depth tells you much more than you would ever want to know about decompression theory, assuming you have the calculus skills to understand it. Neither book tells you how to use tables.
3. ...that computers could not be trusted, that they should rely upon the computers between their ears instead. They were taught to estimate average depth and plan their ascent accordingly.

2. I'm pretty sure Mark and Bruce both know how to read tables and they probably assume anyone reading the books do too. Delving into deco theory while thinking being able to read tables burdensome would seem to be oxymoronic.

3. Something I have noted myself in the past. Thinking that the human mind doing math and guesstimating depth averages underwater would be more accurate or reliable than a computer is not right. If computer error is a concern, using two , or using a computer to back up mental calculations would seem to be the answer.

 

[boulderjohn]

2. I'm pretty sure Mark and Bruce both know how to read tables and they probably assume anyone reading the books do too. Delving into deco theory while thinking being able to read tables burdensome would seem to be oxymoronic.

I know they know how to use tables. They also know that there is a difference between teaching deco theory and using the tables. Some people seem to think that you can't teach deco theory without teaching the tables. They showed that you can. Deco theory would be deco theory if no one had ever invented tables and had instead found a different way to deal with it.

 

[yojace]

One of the best divers I've ever met told me that a card is simply a certification that you are ready to begin learning. From that point it's every divers responsibility to practice, practice, practice - strive for perfection knowing you will never get there. After so many years and thousands of dives she still regularly practices buoyancy skills. She also told me to practice one skill till I've got it down before moving on to the next skill. Perhaps that should be the last thing students are told as they get their C-card.

I know this forum is about diving. As a 4th degree black belt and certified martial arts instructor with 40 years experience, I've learned that reaching first degree black belt does not an expert make - to the contrary, it only means one has mastered the basics, and is then ready to begin learning to become a competent martial artist. One must continue to train, and specializing on one skill at a time for many hours and many years usually results in mastery of that skill. Usually 3rd or 4th degree and above denotes mastery level. That typically takes a minimum of 10 years of dedicated study and practice.

I have dived with divers who at night left their group and joined mine, rammed me into coral, knocked lenses off my camera, dropped items and went off by themselves to look for them, and instructors/divemasters who took me to 140 feet without checking to see if I was qualified at that level (I was). On one occasion I brought a newly certified friend on a dive in Fiji and explained to her and her divemaster that she was not to descend below 60 feet. I had a separate dive guide/divemaster and we agreed that only the two of us would descend lower. At 70 feet I was surprised to see my friend led by her divemaster level with us, and my friend was displaying signs of severe ear trauma. My divemaster reached for her BC and tried to take her further down until I interjected, loosened his grip on her BC and made a safe ascent with her, despite both divemasters objections. She was crying with pain upon surfacing and required a trip to emergency. I reported the events to the dive operator owner who dismissed it, saying "sometimes people just have problems descending", thus defending his divemasters actions.

In diving, I have seen all levels of competency and incompetency, from divers to divemasters to dive operations personnel including managers. In martial arts, I have seen the same. Keeping my awareness has led me to many successful martial arts tournament results and studio operations, as well as many successful dives with groups in spite of the unsafe, unsavory or unqualified actions of others. I agree with Kharon. 1st degree black belt is or the equivalent is only an invitation that one is qualified to begin learning to be a proficient martial artist. Open water certification or the equivalent is only an invitation that one is qualified to begin learning to be a good diver. I hope to one day achieve that status. Until then, I will keep reaching for it.

 

[TMHeimer]

boulderjohn, I follow what you're saying. Can you explain exactly why (re the offgassing) you should begin ascent sooner if going 30'/minute as opposed to 60' using the PADI RDP? I have an idea why, but not positive.

 

[boulderjohn]

boulderjohn, I follow what you're saying. Can you explain exactly why (re the offgassing) you should begin ascent sooner if going 30'/minute as opposed to 60' using the PADI RDP? I have an idea why, but not positive.

Because you are at depth and on-gassing a little longer.

Remember that you have different tissues with different half-times. As you ascend, some tissues are on-gassing while some tissues are off-gassing. Think of it in the extreme--if you ascend from 100 feet at 1 foot per minute, then you are going to be on-gassing much more than you are off-gassing; it is like you are not ascending.

In the actual case described, the difference is very slight, and I frankly would not worry about it.

 

[TMHeimer]

Thanks. That's pretty much what I figured.