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Free diving, tank sharing fatality - Australia

Discussion in 'Accidents and Incidents' started by DandyDon, Jun 14, 2019.

  1. JackD342

    JackD342 Dive Shop

    # of Dives: 500 - 999
    Location: Highland Park, IL
    Man, I am dying to see something authoritative posted on this. I didn't get any good answers with a few Google searches, just some similar conflicting info and debate on some physics forums.

    Here is what my "gut" thinks might be the case:
    1. If you are floating freely in the water column, you will probably move with the wave in a circular motion that is greater at shallower depths than when deeper. At some depth that is probably calculable by someone who actually knows this stuff, that circular motion vanishes. Within that circular motion, your gauge would probably show you a variance of depth, but a variance that is less than the variance between the crest and the trough, and which diminishes if you actively move deeper.
    2. If you are somehow rigidly tethered to the bottom, perhaps on a mooring line, then I would think that the crest/trough variance would have a more direct effect on your depth gauge, but again in some predictable ratio that diminishes with depth.
    3. Even if holding firmly to a mooring line with a significant rise and fall above, I would expect the diver to still bob around, perhaps executing just the lower half of that circle motion that I described in bullet point #1, while trying not to dislocate a shoulder on the upper half of the circle. I think you would have to be held firmly in place on a completely rigid vertical line, such as a pole, in order to experience solely the effect of the wave variance, again diminishing with depth.
    So my gut is telling me that there probably is a pressure change, just not as much or as straightforward as you might think. And also that the riskiest related theoretical scenario would be to hold a deep breath, of compressed air, while bobbing around very close to the surface.
  2. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    I came up with the same results, not the explanatory picture that I was looking for. The link below may help, the math is hell, but the pictures may help, especially page 5 of 17.

    The depth of 1/2 the frequency of the wave seems to be the zone that the circular motion in the wave happens. In submarines we called it surface action, and depending on the sea state, it could affect a submarine pretty deep.

    It is like at a depth below this action, the pressure, and therefore the depth readings, seem to average out and remain stable, despite the waves on the surface.

    In any event, if one keeps an open airway there shouldn't be an issue.


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