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Impossibly hard scuba diving questions please

Discussion in 'Research and Development' started by diverdown13, Sep 3, 2006.

  1. wreckchick

    wreckchick Scubavangelist

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    bp/w vs. jacket vs. back-inflate

    R
     
  2. Walter

    Walter Instructor, Scuba

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    Poor kid. I thought you wanted to research them.

    Covered here.

    Dick Rutowski

    1. of or pertaining to a benthos.
    2. of or pertaining to a benthon.

    B

    YMCA

    Frankie Wingert of the YMCA SCUBA Program

    Whale Shark - Pigmy Shark

    1. A coastal region; a shore.
    2. The region or zone between the limits of high and low tides.

    1. Botany. attached by the base, or without any distinct projecting support, as a leaf issuing directly from the stem.
    2. Zoology. permanently attached; not freely moving.

    Nothing. It's not a feature, it's a bug.

    I'm leaving the rest for you.
     
  3. oceandjinn

    oceandjinn Angel Fish

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    Ok why is it that if you go to a padi store they say SSI is outdated or NAUI is nonexistent from next year or any variation of the three. And secondly can you buy THE WHEEL anywhere with instructions and is it better than a dive computer and why?
     
  4. oceandjinn

    oceandjinn Angel Fish

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    By the way the largest shark is my sisters baby.
     
  5. diverdown13

    diverdown13 Angel Fish

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    well, I actually did want too, but I ended up having a ton of great questions, and no good answers, and then I got all backed up, got a buch of different answers for certain questions and eventually gave up.
    thanks for the answers!!!!
     
  6. miketsp

    miketsp Solo Diver

    # of Dives: 500 - 999
    Location: São Paulo, Brazil
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    Ok here are mine...

     
  7. The Chairman

    The Chairman Chairman of the Board

    # of Dives: I just don't log dives
    Location: Cave Country!
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    Mike... the weight of the anchor and rope had ALREADY been displaced by the appropriate amount of water while IN the boat. There has been no change of combined density.
     
  8. knotical

    knotical perpetual student

    # of Dives: 1,000 - 2,499
    Location: Ka'u
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    Correct, but once the anchor is in the water, it displaces less than its weight.
    Think what happens when you add air to a lift bag to recover the anchor and get it back on the boat.
     
  9. knotical

    knotical perpetual student

    # of Dives: 1,000 - 2,499
    Location: Ka'u
    5,748
    826
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    Find the atmospheric pressure at altitude, and add sufficient oxygen to the breathing gas to reduce the nitrogen fraction proportionally.

    O2% = 1 - 0.79Pa

    Where O2% is the Oxygen content of EANx expressed as a decimal.
    And Pa is the atmospheric pressure at altitude, in atm.

    Example: at 4000 feet elevation, the atmospheric pressure is 0.8637, which can be offset approximately by EANx32.

    Caveat: This is theoretical. There are divers who use this technique to dive at altitude with sea-level air tables or computers, but I don’t know if any agency teaches it. Before anyone even considers diving this way, they should be at least Nitrox certified and keenly aware of the serious risks associated with elevated oxygen partial pressures.


    Simplified derivation:

    Altitude theoretical depth = (D + 33)/Pa – 33
    Where Pa is the atmospheric pressure (in atm.) at altitude.
    And D is the actual depth

    Nitrox theoretical depth = N(D + 33) – 33
    Where N is the ratio of nitrogen in the Nitrox to nitrogen in air, which could also be: (1-O2%)/0.79

    Assume some depth D1 and apply first the altitude formula, and then the Nitrox formula. For the effects to cancel, we should end up at D1 again, or:

    N((D1 + 33)/Pa – 33 + 33) – 33 = D1
    (We just substituted “(D1 + 33)/Pa – 33” for D in the Nitrox formula, and set it equal to D1)

    This reduces to:
    N((D1 + 33)/Pa) = (D1 + 33), or: N/Pa = 1

    As mentioned above, N is (1-O2%)/0.79, we can substitute and rearrange to get:
    O2% = 1 - 0.79Pa


    n.b. You can find atmospheric pressure (Pa) at various altitudes either from tables or from:
    Pa = (1 – H*6.87535E-6)E5.2561
    Where H = Altitude in feet
    And E means: “raise to the power of”
     
  10. miketsp

    miketsp Solo Diver

    # of Dives: 500 - 999
    Location: São Paulo, Brazil
    3,493
    139
    63
    Thank you knotical.

    NetDoc, if you have a problem visualising the problem with the anchor, try imagining a boat that weighs nothing. While the anchor is in it the boat will displace a lot of water whose weight is equivalent to the anchor. Once the anchor is in the water, the boat will just sit on the surface displacing nothing, while the anchor only displaces its own (small) volume.
    The water level will drop wrt the shoreline.

    Then as knotical suggests, add a lift bag to the anchor, fill it until the anchor is neutral and you've displaced water which will make the water level rise back up to the original shoreline.
     

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