Loading ...
Sorry, an error occurred while loading the content.

Leeboards

Expand Messages
  • prairiedog2332
    Came across this posting I saved - not sure if it was ever re-posted here. From John Welsford and it might be worthy to consider and discuss. I have much
    Message 1 of 81 , Jun 20, 2013
    • 0 Attachment
      Came across this posting I saved - not sure if it was ever re-posted here. From John Welsford and it might be worthy to consider and discuss. I have much respect for his writings.


      For the likes of a leeboard, a streamlined flat plate is going to be as good a performer as anything else. Make the leading edge a nice 30 deg ellipse about 50% of the plate thickness, bring that to full thickness at about 20% chord, flat plate back to 60% then taper to the trailing edge which should have a square "back" of about 4mm.

      Note that NACA foils were developed back 80 years or so ago, they were developed for use in a compressible medium ( air) rather than an incompressible medium (water) and while they do work pretty well, science and hydrology have moved on a long way since then and you won't find professional designers using them.

      They do have the advantage of being easy to reproduce and tolerant of mistakes in shaping so suit the amateur builder. But they do not justify the mythology that has built up around them. - John Welsford

      Nels
    • 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
      • 0 Attachment
        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.
        >

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




        [Non-text portions of this message have been removed]
      Your message has been successfully submitted and would be delivered to recipients shortly.