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Re: [Michalak] Re: Leeboards

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  • Andres Espino
    In many small home built boats I have seen rudders and centerboards and leeboards all being 3/4 plywood glassed over and no special fo rming rxcept slight
    Message 1 of 81 , Feb 20, 2013
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      In many small home built boats I have seen rudders and centerboards and leeboards all being 3/4 plywood glassed over and no special fo rming rxcept slight rounding of the edges to accomodate glassing.  My factory boat rudder is flat feathering toward the aft edge.

      Andrew




      ________________________________
      From: prairiedog2332 <nelsarv@...>
      To: Michalak@yahoogroups.com
      Sent: Tuesday, February 19, 2013 2:12 PM
      Subject: [Michalak] Re: Leeboards


       
      I have looked at many of Jim's and Phil's small boat designs and plans
      and have never seen one that called for fatter shaped foils either in
      boards of rudders. Also have never seen a small boat with them including
      canoe sailing rigs. They seem to recommend as thin as possible while
      still maintaining stiffness.

      I think it is of note that Jim calls for the trailing edge to be
      "squared off'' a bit by about 1/8" and not a feathered edge (Page 53 of
      his build book). He had a board that was chattering and could not get it
      to stop and got a mail from a builder to do that and it worked. Can't
      find where he shared that now - may have been in a newsletter many of
      which were lost.

      I am not suggesting one way is better than the other - just sharing
      information from what I understand and for what it is worth - which
      might not coincide with other's experience. I guess it could be tested
      using boards of each design and exchanging them and timing and recording
      the track with a GPS? Would probably be difficult to prove though as
      conditions change a lot over the time required.

      I am very dumb when it comes to how lift is created in a foil moving
      through water. But I think I understand how a flat surface resists
      getting pushed sideways by the force of the wind on a sail even when the
      boat is moving forward.

      And as Chuck has mentioned already it is the sail that is probably the
      most important if not the skill of the sailor.

      Nels


      --- In Michalak@yahoogroups.com, "JeffreyM"
      wrote:
      >
      > Remember that the foils we're talking about are
      practically flat anyway. So it's not about resistance while standing
      still, but "lift" when moving. A flat board and a foil shape both "fly"
      when moving, but a flat board stalls more easily.

      [Non-text portions of this message have been removed]




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    • Samantha Roberts
      Yes, you are using just the end of the ellipse to shape the leading edge. ________________________________ From: Anders Bjorklund
      Message 81 of 81 , Jun 21, 2013
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        Yes, you are using just the end of the ellipse to shape the leading edge.



        ________________________________
        From: Anders Bjorklund <andersbjorklund5@...>
        To: Michalak@yahoogroups.com
        Sent: Friday, June 21, 2013 8:08 PM
        Subject: Re: [Michalak] Leeboards



         
        I think I got it. Thanks. It looks like the tangent line back to the 20%
        chord would meet the ellipse VERY near its forward tip then. Interesting.

        Anders

        On Fri, Jun 21, 2013 at 2:10 PM, Samantha Roberts <
        samanthaeroberts@...> wrote:

        > A 30 deg ellipse is a circle viewed at 30 deg from the plane in which it
        > lies (if viewed at 90 deg, it appears as a full circle). This makes a 30
        > deg ellipse twice as long as it is wide. So if your plate thickness is 1",
        > the ellipse you need to draw is 1" long and 1/2" wide (50% of plate
        > thickness).
        >
        > Now draw a smooth curve that lies tangent to the ellipse and reaches full
        > thickness at 20% chord. Since John does not specify either this curve or
        > the one from 60% chord to the T.E., I assume he means that those shapes are
        > not critical. On the general principle of not trying to make water flow
        > around sharp corners, I would make those two curves come smoothly into the
        > flat section from 20% to 60% chord, but I am not sure how important that
        > might be.
        >

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