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51940Re: water ballast vs lead, iron, etc

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  • graeme19121984
    Dec 1, 2006
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      Guy,

      at your "The Stiffness of an Advanced Sharpie" at
      http://faculty.valpo.edu/gvandegr/ there is this:


      "This axis of rotation ensures that the total area of this
      underwater section remains constant. Close inspection of the graph
      indicates that the rotation slightly increases the area under the
      waterline. Hence the rotation is accompanied by a slight lifting of
      the boat, which becomes important only at large angle, I believe."

      What lifts the boat? How is it lifted if it remains the same mass?
      (disregarding any lifting component of the forces on any sail)

      I can imagine wider hull sections aft coming into play as they are
      immersed (more) with increasing heel, and so perhaps lifting this
      represented midships cross section. If this is the case then the
      data set gained from only this representative cross section would be
      insufficient to construct a generally representative model.

      If this is not the case it would appear that, as the boat is not
      able to just arbitrarily "lift" by some unknown means, then the
      assumptions made from this represented cross section are somewhat
      erroneous and therefore any further calculations based on them are
      also going to be in error. My calculus skills are too rusty to
      comment on your derived equations, and the insights and intuitions
      gained, other than to raise the point that any initial error in
      assumptions may be compounded, perhaps more than trivially so.


      Graeme
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