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General rudder endplate specs

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  • 10 Jul 2017 20:37
    Quote
    Reply # 4961823 on 4960082
    Anonymous member (Administrator)

    Scott.

    making a useful endplate for that rudder is not rocket science. Basically it is a fence to stop the waterflow from escaping under lower end. At the upper end there is no need for an endplate as the gap between the rudder and hull is narrow.  In addition, the water-flow that close to the hull is probably far from horizontal. Now I looked up 3-4 of Bolger's designs in his 'Boats with an open mind': The 'wingspan' of the endplates he designed, seems to vary between 35 and 65% of the chord. I guess, if it was my boat, that I would just make it in one piece from plywood (10-12mm) with leading edges cut back 45 degrees to keep ropes and kelp from catching it. I would just grind off antifouling etc. from the lower end of the rudder and fit the endplate with epoxy and light glassing.

    What about  trying an endplate with a wingspan at 50% of the chord? Cut out one in cardboard first and see how it looks on the boat...

    Arne

    Last modified: 11 Jul 2017 09:35 | Anonymous member (Administrator)
  • 10 Jul 2017 17:05
    Quote
    Message # 4960082
    Deleted user

    While I have her on the hard, I'm considering adding an endplate onto Moon River's rudder, mostly to prevent me being annoyed that I didn't when I finally get the rig on an discover a bit more weather helm than I'd have liked.

    While I've found over 2000 posts with words "rudder end plate" in 'em, I'm at a loss for general specs.  It may be that I just don't know how to do smart advanced searches.

    Moon River (née Mudita) has a vertical, non-balance skeg-hung rudder:



    What are the general rules of thumb?  What's the recommended width of the plate?  Is it a percentage of the rudder cord?  What about the plan view shape?  Is it just a scaled profile of the rudder cross section, assuming the rudder is a NACA foil?  Or do the trialing edges need to be swept back and extended aft of the rudder's trailing edge like typical aircraft winglets?  (I work tangentially with the Airbus A380, which just unveiled its new 5 meter long winglet design at the Paris Air Show.  I'm assuming something smaller should be sufficient on Moon River.)

    My Google searches have turned up a million opinions, but few solid design papers.

    And now.... here's Arne! (Hopefully).
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