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Re: Rescue Minor trim with speed

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  • liokai2002
    ... at ... seabright- ... Hello Ron, think you are right. It might be the negative deadrise which gains power with increasing speed. When a sailboat with a
    Message 1 of 3 , Jan 18, 2005
      --- In AtkinBoats@yahoogroups.com, "ronschwiesow" <nanron62@m...>
      wrote:
      >
      > Robb White in his very interesting writeup on the Rescue Minor
      > (http://www.robbwhite.com/rescue.minor.html) notes that at 10.5 kt
      > the stem runs above the water, at 12.5 kt the forefoot is exactly
      at
      > the surface, and at 15.5 kt (about 17.8 statute MPH) it is about an
      > inch and a half immersed.
      >
      > Can anyone explain why this is so? Is it lift under the (negative
      > deadrise) tunnel stern from convergence of flow around the
      seabright-
      > skiff box deadwood? If we can understand the change in trim with
      > speed, we may be able to tailor Atkin's outstanding hull design for
      > even more efficiency at slower displacement speeds.
      >
      > I second the motion for some tank testing of a tunnel-stern,
      > seabright skiff. Has this ever been done?
      >
      > Ron

      Hello Ron, think you are right. It might be the negative deadrise
      which gains power with increasing speed. When a sailboat with a
      convex hull accelerates in a gust, the bow wave and the stern wave
      increase and the "valley" between them gets deeper because there is
      suction (Bernoulli) caused by the convex hull (same with a similiar
      shaped motor boat). A deep Vee Motor boat reduces its wetted area
      with increasing speed and rises its nose running on the last third
      part of the hull. Only Atkins outstanding hull design is able to
      develop hydrodynamic lift in the rear part of the hull without
      increasing the resistance and keeping the good trim. This reminds me
      to the underside of an aircraft wing with a trim flap at the end
      (outboard wing assy ? ). Might be that there is analogy. Regards,
      Manfred
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