Rudder end plates

Discussion in 'Boat Design' started by tschienque, Dec 28, 2004.

  1. tschienque
    Joined: Feb 2004
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    tschienque Junior Member

    I seem to recall some 15-20 years ago, Phil Bolger did some work on end plates for rudders.

    Any online references to this or similar works?

    I believe the initial impetus was that a lot of his designs rudders were basically flat (not foils) and this was a simple and effective way of improving rudder efficiency.

    Q1 Any veracity in the method or foils simply superior? Fullstop!

    Q2 Any suggested foil section shapes for rudders?

    Q3 Does skeg have to be part of overall foil or end plate?
  2. Eric Sponberg
    Joined: Dec 2001
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    Location: On board Corroboree

    Eric Sponberg Senior Member


    End plates do work, and some of the aerodynamicists on this forum may be able to tell you what shapes work and how big they should be that would be appropriate for a rudder or keel. You can see the variety of ideas on this topic by looking at the wingtips of jet airliners. I have seen a myriad of types, even two different ones on the same wing.

    Foil section shapes can be just about anything. Foil sections are much less critical than the planform shape. Section shapes have only to do with lift and low profile drag, but planform has a lot to do with lift and 3-D induced drag. The planform usually overrides the section shape in importance, so one should concentrate more on profile shape.

    Having said that, I like to use the LS(1) aerofoil because its maximum thickness occurs at the 40% chord position (instead of the NACA 0000 series 30% chord position) which makes for a stiffer and stronger section. Also, this aerofoil has a trailing edge in which each side is nearly parallel to the centerline which reduces wake interference from each side of the foil. This section can also be changed in overall thickness by changing the thickness/chord ratio.

    Yes, the skeg has to be part of the overall foil and end plate.

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