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PADI open water max depth

Discussion in 'Basic Scuba Discussions' started by skinerd, Jan 18, 2006.

  1. GrierHPharmD

    GrierHPharmD Instructor, Scuba

    # of Dives: 200 - 499
    Location: Charlotte, NC
    2,212
    0
    36
    Gary,

    My comments above were just meant to clarify the standards and my own position with regard to children and deep diving. You and your daughter seem to have come to terms with your own way of doing things, and that's just fine. I only worry about standards violations when my own students are involved or when I see instructors grossly violating standards. Two feet of depth wouldn't be enough for me to worry about with a deep dive. I might question the instructor's judgement, but then again, I am very conservative when it comes to children and diving. As for peer-reviewed, blinded studies, I think we'll have to wait for a long, long time for those...

    ***************
    On the other subject (vomiting through a reg), all I can say is that I've vomited underwater a few times and I've always moved the reg to one side of my mouth and vomited into the water, not the reg. I know that many people disagree, and I teach PADI's position of vomiting through the reg, but I have had great success vomiting to one side, swishing with seawater, and then getting my next breath through that clean regulator.

    As for the issue of dragging the octo through the sand, I agree with you, Gary. That's why I donate my primary regulator and then breathe through my octo, which I keep on a bungee necklace. If you're interested in learning more about that technique, just do a search on Global Underwater Explorers (GUE) or Doing It Right (DIR). You'll find plenty of info and lots of discussion...

    Safe ascents,
    Grier
     
  2. tedtim

    tedtim Divemaster

    # of Dives: 500 - 999
    Location:
    1,372
    2
    0
    I agree http://www.scubaboard.com/showthread.php?p=1276801#post1276801

    How many of you have the National Geographic specialty card????
     
  3. Diveral

    Diveral Solo Diver

    # of Dives: 200 - 499
    Location: North Alabama USA
    648
    0
    0
    I think that the depth limits and concerns are more of a function of what currently passes as "dive training". While I am not the coelacanth that Rick is, my initial certification was the YMCA Scuba Diver in 1983/84. I took the course at the University as a PE credit. We used the Jeppesen Sport Diver Manuals I & II and had a 1 1/2 hr to 2 hr classroom session every week and a 1 1/2 hr to 2 hr pool session every week for a whole semester. So the class was very thorough and we spent a lot of time in the water. We learned the basic scuba stuff and then went to the advanced stuff like Equipment techniques, Specialized Equipment, Boat Diving, Navigation, Limited Visibility Diving, Diver Stress, Diver Rescue, Deep Diving (INCLUDING DECOMPRESSION).

    Notice a trend there? Most(all?) of those topics now are specialty courses. I did a lot of stuff in my first open water class that they don't cover now. I think they dumbed down the original material to get the prices and time committments down, and by the way now you need to take these "specialty classes" to learn the stuff we used to teach and to keep the dive instructors and the dive agencies employed.

    My second open water certification dive was to a depth of 98 feet. My third and fourth dives were boat dives on wrecks off of Panama City and we threw in a cavern dive at a Florida springs in there somewhere. I later took the PADI AOW and Rescue courses in 1985 and 1986. A couple of friends and I have decided that we are going to do PADI Master Diver together so we have signed up for a Nitrox class and will take the other specialty courses later. I am interested in contrasting the classes I will be taking against the classes I took in the early 80's.

    AL
     
  4. garyfotodiver

    garyfotodiver Solo Diver

    # of Dives: 200 - 499
    Location: Chicago, but dive in FL. Not true anymore, as I di
    1,308
    4
    0
    My own instructor usually dives with the configuration you describe. He does caves and ice, neither of which I have any interest in doing.

    During my recent classes, we spent a considerable amount of time discussing the differences in technique that are prevalent today. My children are learning today's philosophy, not that of 1970. I have to have an understanding today. That's why I sat with Sheryl when she watched the video, read the book, answered the section questions. We got two divers trained for the price of one!

    It is my dream that, with three diving daughters and if I can get my future sons-in-law to dive, eventually I'll get to charter the entire boat!

    Money well spent.
     
  5. RadRob

    RadRob Barracuda

    349
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    Most of what you said is true. However, the idea that they cut these things to get prices down is way off. In '97, prices to be OW certified were $99 compared to what they are around here now of $299. Specialty courses add anywhere from $99 - $169. So, while you paid less to get more training then, to get OW, Deep, Specialized Equip, Rescue, Navigation, Boat, and night diver courses these days it would cost $1155. So there is no way it is cheaper now. Those are the skills you learned in your one class. It now takes 7 classes just to get these.

    I definitely think they "dumbed it down." Most of these skills can be taught in one class, but they want more money. Go ahead and "put another dollar in." This statement has to have some meaning, wonder where they got it.

    I think the sport is suffering as a result. I think the prices are crazy. But people pay it, so supply and demand theories are proved right once again.

    <end rant>
     
  6. Skinsfan1311

    Skinsfan1311 Barracuda

    255
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    I'm glad that I'm not the only one to have noticed this.....
     
  7. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
    2,695
    1,162
    113
    My NAUI Pro Manual (the Instructor's manual from 1977) discusses deep diving:
    As I recall, the reason we used 60 feet for the cutoff was that the tables of the time were 60 feet for 60 minutes (which was from the 1975 US Navy Diving Tables, and really easy to remember), and it was very difficult for a diver to exceed this limit on a standard 71.2 cubic foot tank. My subsequent tables (1990) had 60 feet for 55 minutes.

    So that is the history. Divers now routinely buy 80 or 100 cubic foot tanks, and can readily get themselves into decompression problems.

    SeaRat
     
  8. Darnold9999

    Darnold9999 Solo Diver

    # of Dives: 500 - 999
    Location: Victoria BC Canada
    2,373
    499
    83
    John:

    Re; diving on a single steel 72 tank. I vividly recall a discussion with the instructor were he said it was virtually impossible to get bent on a single tank on a single dive in a day (1978). Possible, but you had to be trying i.e a dive where you went as long as possible at 60 feet, bounced down to 120 for 5 minutes and then back up using up the balance of your air would do it. (Really dumb idea BTW). But for any other type of check mark or square profile, unless you were very very good on air you couldn't stay down long enough to get bent. (Note that this was at the end of a very long class discussing and working out dives with the tables.)

    It seemed to me at the time that this was good design, kept people out of trouble. Now I wonder: Is that the reason that tank size seemed to have settled in the 70 to 80 cf size?
     
  9. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
    2,695
    1,162
    113
    Actually, the 71.2 cubic foot tank wasn't 71.2, because that was the capacity at 2475 psi with the 10% overfill on the + stamp. If you do the math, it's:

    71.2 ft3/2475 psi = X ft3/2250 psi

    X = 71.2 ft3 * 2250 psi / 2275 psi

    X = 64.7 ft3

    So we were usually diving with a 65 cubic foot capacity, and even with very good surface air consumption would limit you to less than the No-Decompression Limits. For instance, a surface air consumption rate of 0.4 cubic feet per minute gives us the ability on the surface to remain on the scuba tank for 162 minutes. (Fire_Diver on another thread says this is his SAC rate.)

    64.7 ft3 / 0.4 ft3/minute = 162 minutes

    At 33 feet, it's half that (2x the pressure), or 80 minutes. At 66 feet, it's 1/3 that, or 54 minutes, and this is to completely drain the tank.

    With the use of SPGs, we kept 500 psi in the tanks (with the J-valve we started to the surface at 300 psi, in the really old days). If you factor this into the equation, then you would have a very difficult time staying at 60 feet for 60 minutes. Here's the math on that:

    71.2 ft3/2475 psi = X ft3/(2250-500) psi

    X = 71.2 ft3 * 1750 psi / 2275 psi

    X = 50.3 ft3

    Again, at that 0.4 ft3/minute SAC rate, or 126 minutes on the surface, you have a very difficult time getting into decompression problems. But at 66 feet (three atmospheres absolute pressure), there is only 1/3 of that air available, or 42 minutes available (with the 500 psi "time to surface" using a SPG).

    Now, on the possibility that someone tried to get bent, your profile is possible, but very unlikely.

    Concerning the 80 ft3 aluminum tanks, the original ones were 71.2 at a 2475 psi rated pressure (compared to the 10% overfill available on a steel 71.2 tank, and were advertised by USD as a "real" 71.2 tank). But it had floatation problems, and they figured a better formula for tank weight at 3000 psi rating to buoyancy with the 80 ft3 tanks. At least, that's my take on the situation. I do think that they were trying to keep the single tank to a size, which would help keep divers out of decompression problems. If they wanted to get more air, there was always the double tank option (twin 72s or twin 80s), or even a triple tank (UDS-1 system at 105 cubic feet). I currently have twin 42s and twin 50, which I really like. But I rarely dive to depths where I can even come close to decompression problems.

    SeaRat
     
  10. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
    2,695
    1,162
    113
    As a former USAF Pararescueman, EMT Paramedic, and NAUI Instructor, I would never, ever vomit into my regulator. The risk of aspiration of vomitus is too great, and I feel that there is a high risk of regulator malfunction because of this. Remember, there are "chunks" in vomitus, and vomitus is very acid. Aspiration of vomitus is a life-threatening event, much more so than sea water. Vomitus can eat away lung tissue (ever heard of hydrochloric acid?). The "chunks" in vomitus (sorry to be so blunt here, but we must discuss it) can become lodged under the non-return valve, and allow sea water to come into the regulator. My feeling is that taking the regulator out of your mouth is not a life-threatening event; you should be as familiar with this, and clearing the regulator (that's why they put the "purge button" on single hose regulators in the first place), as you are with exchanging a regulator for a snorkel when face-down in the water. If you don't have these skills, you really should not be diving except perhaps in what we used to call a "resort course" where you have an instructor on your shoulder, and are no more than about 20 feet deep.

    SeaRat
     

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