rudder end plates

Discussion in 'Boat Design' started by robwilk37, Dec 22, 2014.

  1. robwilk37
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    robwilk37 Senior Member

    ive not seen one, just wondering if a small plate or fence at the top or the bottom of a sailboats rudder would help to keep the flow parallel? or is the drag penalty from the vertical motion of the boat greater?
  2. Richard Woods
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    Richard Woods Woods Designs

  3. PAR
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    PAR Yacht Designer/Builder

    A number of designers have employed fences and end plates. Effectively makes the rudder blade think it's deeper than it actually is.
  4. frank smith
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    frank smith Senior Member

    Do they serve a similar function of a wing tip?
  5. Eric Sponberg
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    Eric Sponberg Senior Member

    Basically, yes. A fence at the tip on the bottom will prevent cross-flow off the tip, and thereby minimize the tip vortex. The smaller the tip vortex, the less the induced drag. A fence at the top near the waterline will help prevent ventilation--the sucking of air down from the surface. This is the same beneficial effect that a cavitation plate serves on an outboard motor just above the propeller.

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    FAST FRED Senior Member

    On slow boats that have too small rudders , yet need to manuver I have seen SS angle bolted to the trailing edge of the rudder.

    Some lay it flat so the angle is 90 deg to the rudder surface, others bolt it on so the metal forms a diamond , at the trailing edge.

    My boat could use some help at dock manuvering speeds , anyone know which configuration works best???
  7. Petros
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    Petros Senior Member

    it would be most efficient just to make the rudder deeper, or higher aspect ratio. the end plate effect makes the flow behave like a deeper higher aspect ratio rudder, but you have the added drag of the plate surface area and the interference drag at the intersection. It would be effective, despite the drag penalty if you require a limited draft, and or to reduce the stress at the pintle hindge if you could did install a deeper rudder.

    a surface plate is can also reduce surface interference effects, and ventilation as already noted. but that would only be useful if you assume the rudder is always perpendicular to the surface, which is not the case with a mono-hull sailboat.

  8. Mark Fisher
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    Mark Fisher Junior Member

    An end plate is an excellent method to improve steering effectiveness in a shallow draft boat. Here in the Chesapeake, the average depth is 15 feet for the entire bay, and there is a LOT of territory that is open if your draft is slight. Here's Sanderling (that's NOT me!):

    I put that rudder on. It replaced a much larger swing rudder that got wrung off when backing down (oops). The new rudder has more turning effectiveness.

    Bolger uses it on a lot of his shoal draft boats.
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