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"Advanced Divers Only..."

Discussion in 'Advanced Scuba Discussions' started by GameChanger, Jan 9, 2021.

  1. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO
    26,833
    19,708
    113
    I don't know to whom you are responding with this question. I scrolled back through the thread and realized it may have been me. If so, I was not very clear. An AOW deep dive has to be at least 60 feet deep. I do know that there are some shops that will weezle that depth using tables and altitude adjustments. Here is how it could be done where I live in the Denver area (5280 feet). Follow these steps closely to see how it works.
    1. The diver goes to 41 feet for 30 minutes at Aurora Reservoir, just outside Denver (5280 feet elevation).
    2. Using tables, that is rounded up to 50 feet.
    3. To adjust for altitude, use a Theoretical depth at Altitude table.
    4. Go to the 50 foot row and move across to Denver's altitude (5,280 feet), which is rounded up to 6,000 feet.
    5. The value there is 62 feet, so PRESTO!, that 41 foot dive is now a 62 foot dive and valid for AOW.
    6. But wait! There's more! Theoretical depth is used for planning decompression for dives; i.e., finding your pressure groups. That means that 62 foot theoretical depth is rounded up to 70 feet when you log your dives if you are using tables. That means our AOW student will log that 41 foot dive as a 70 foot dive.
    IMO, this is, of course, totally bogus. I have never seen it done that way, but I have been assured that many people do it that way.

    That 6 step process shows the absurdity of using tables at altitude like that, because what I showed is indeed what you would do to calculate pressure groups for decompression.
    • Let's say that the 41 minute dive went for 30 minutes.Using the process described above, the student would be in pressure group O--pretty serious nitrogen loading. If the dive to 41 feet were repeated after a 45 minute surface interval, that calculated nitrogen loading would limit the student to a 22 minute dive.
    • If the student had only gone to 40 feet, there would have been no rounding up originally, and the theoretical depth would have been 50 feet--again no need to round. The students would be in pressure group I. If the dive to 40 feet were repeated after a 45 minute surface interval, that calculated nitrogen loading would limit the student to a 63 minute dive.
     
  2. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO
    26,833
    19,708
    113
    Making this part of the AOW course has proven to be problematic, because the signs are so hard to detect for most people. PADI used to include solving a problem of some sort on the surface and then doing it again at depth on the theory that students would see how much longer it took them to do it at depth. The problem was that this usually did not happen. In fact, in my experience, students usually did better at depth, probably because they had had some practice on the surface. This led to them learning that narcosis is no big deal. PADI has dropped that requirement.

    One of the problems with narcosis, in my experience, is that for most people, they cannot tell they ae narced unless something happens that makes it obvious, and usually nothing does. You are actually narced, but your narcosis keeps you from realizing it. I have never felt any effects of narcosis, despite knowing that I am likely narced to some degree on lots of dives. There have been exactly two times that I have clearly realized I was narced, and both times it was because something happened that made me realize I was being stupid, but if the things that had made me realize I was stupid had not occurred, I would have ended the dive with no indication of narcosis. One of those two events happened at only 100 feet, which does not give me a lot of confidence in the "keep equivalent narcotic depth to 100 feet and you'll be OK" theory.

    I have never had an AOW student show signs or feel symptoms of narcosis on an AOW deep dive, and I always get them as close to 100 feet (course standard limit) as I can. In the Deep Diver course, I have never had a student show signs or feel symptoms of narcosis, and I always get them to 130 feet.
     
    Esprise Me and drrich2 like this.
  3. Coztick

    Coztick Manta Ray

    # of Dives: 50 - 99
    Location: calgary
    584
    361
    63
    So 41ft. becomes 70ft in the log? Wow.
    I had thought the main point of the deep dive was to actually expose the diver to a depth of aprox. 100ft.
    Thanks for the breakdown of the justification. I suppose if 99% of students don't notice any narcosis, the gas consumption becomes the main takeaway...
     
  4. Carlos Danger

    Carlos Danger Manta Ray

    682
    163
    43
    In Aldora's case Advanced=Vetted,

    I have done their Adventure 3-tank dive trip maybe 8 times, and you do not need to be AOW certified. But what you will need is a Nitrox cert and vetting/recommendation from a DM that you are a good diver and less likely to be a liability waiting to happen. If you are comfortable diving spots like Barracuda, San Juan, Maracaibo, etc., you should be fine. I think it is important to keep in mind that the logistics of supporting dive-related incidents in the Northern areas are more problematic, which is why each diver is required to carry a recue GPS transmitter. Some of the dives can involve substantial current in deep open ocean, and with no land or other boats/people in sight anywhere.

    This trip is usually a blast; in-fact the shark caves are probably some of my favorite dives I've done anywhere. But it can also sometimes be a long and demanding day out, and the conditions can be unpredictable. Adlora are simply trying to do their due diligence as best they can and keep safety first.


    Hope this is helpful.
     
    eleniel, GameChanger, drrich2 and 3 others like this.
  5. shurite7

    shurite7 Dive Shop

    # of Dives: 1,000 - 2,499
    Location: In transit
    1,067
    470
    83
    Recognizing narcosis can be a challenge. I agree with others above that most people will not know they are narced. How I learned to recognize it was via my tech course where I had to go to 160 feet on air. I swore to my instructor I wasn’t narced; my buddy said he wasn’t narced either. The next day we went deep on trimix and wow, what a difference. I don’t always notice narcosis, especially when diving in warm clear tropical waters. As my tech instructor stated “everyone gets narced whether they realize it or not”.

    Sadly, I’ve witnessed instructors using the 61 feet standard to meet the requirement. I prefer to get my students to 95 feet. The students have always stated, after the dive, they didn’t feel narced.

    @boulderjohn, I too have noticed people fudging the depth equivalent while diving at high elevations in MT. What I’ve learned is, many people don’t understand what the depth equivalents are for with most believing they went to such an equivalent depth at sea level rather than using it for NDL. When I first learned about diving at elevation I was misinformed how to work out the details. After doing my own research I have since learned I was taught incorrectly.
     
    ginti likes this.
  6. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO
    26,833
    19,708
    113
    I moved from one dive shop to another a number of years ago, and when I did, the new shop gave all OW students planning to do their OW checkout dives locally a full page explanation on issues related to diving at altitude. It was a standard blurb they had been using for many years, and as far as I know, they are using it now. It is all based on tables, and, of course, they are using computers now, so no one pays attention to it. It is pretty much all wrong. I never said anything because at the depths we were diving for those courses, it did not matter.
     
  7. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO
    26,833
    19,708
    113
    On my first day of TDI trimix instruction, I was diving trimix and my instructor was diving air. He had us trade primary regulators for several minutes so I could feel the difference. I couldn't feel a bit of difference.
     
  8. shurite7

    shurite7 Dive Shop

    # of Dives: 1,000 - 2,499
    Location: In transit
    1,067
    470
    83
    In MT I rarely came across anyone who took diving at high elevation seriously. The only person who did lived in Cody, WY and dived quite a bit in Yellowstone Lake and a lake near Cody that was at an elevation of 9500 feet. I spent time at his place diving Yellowstone, so I decided to conduct research and learn about high elevation diving. Most people who dive locally dive shallow in Flathead that is only at an elevation of 3000 feet, so it really doesn’t matter much, as you noted.
     
  9. shurite7

    shurite7 Dive Shop

    # of Dives: 1,000 - 2,499
    Location: In transit
    1,067
    470
    83
    Hm, I too did TDI and thought the first (and second) deep dive had to be on air. I still remember my first deep air dive and still don’t remember being narced. The second dive on air I was more conscious and aware, and noticed it. I also notice a difference between diving deep on air in cold murky mountain lakes vs warm clear tropical waters. In the former I can usually recognize when I am narced, the later is not as easy.
     
  10. GameChanger

    GameChanger ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Frisco, TX USA
    306
    256
    63
    My first dive at Barracuda was an absolute E-Ticket thrill ride!
    I was on a boat with a bunch of experienced recreational divers and an awesome DM who held a very detailed pre-dive briefing. He laid down a few non-negotiable rules.
    1. No camera gear
    2. Must have DSMB (and know how to deploy it)
    3. Descend as a group. No exceptions. It was all of us successfully descending together or call the dive.
    4. Do not pass him in the group lead. He will call the dive if we shotgun by him in the lead.
    5. We ascend together. No exceptions, regardless of how much gas you have. We will all start to ascend together as a group with the 1st person at 1k psi.

    As soon as we all successfully descended to 90 ft , the extremely strong current took over and off we went! I never felt like I was in any danger though, and we all (8 of us) did a great job staying together. We hit a westerly outdraft at one of the small valleys along the wall and my dive-buddy son got caught in it. He did not panic and he was able to slowly get out of it by continuing to fin north. He was not hugging the wall like I was, and that is why the outdraft got him.

    It was about a 50 min dive, with a max depth of 93 ft and avg depth of 61 ft. I had about 1200 psi of air when the DM signaled to surface as a group.

    We did Punta Sur the day before and I think Barracuda is a more challenging dive site.
     
    drrich2 likes this.

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