Rudder foils

Discussion in 'Hydrodynamics and Aerodynamics' started by cat nap2, Jun 25, 2016.

  1. cat nap2
    Joined: Nov 2015
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    Location: Orange,Ct

    cat nap2 Junior Member

    I have a medium weight cruising cat. 37ftx 20ftx2ft 9500lb cruising wt. The stern tends to squat a little when sailing at cruising speed (6-10 knots+-)
    The question is would adding foils say 2ft wide or so to each rudder help reduce the squat at this speed range.
    If so are there any suggestions for the foil shape ??
     
  2. Gary Baigent
    Joined: Jul 2005
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    Location: auckland nz

    Gary Baigent Senior Member

    Arse dragging is SO annoying. And can be rectified so easily with just about any shaped inverted T setup on rudder. Here's what I use on Frog - which is proportionately the same as on my other larger 8.5 metre (second image) tri foiler. My lifting sections are asymmetric and set at zero degrees angle of attack.
     

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  3. Jim Caldwell
    Joined: Aug 2013
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    Location: Cleveland, Ohio

    Jim Caldwell Senior Member

    Moving weight forward might be easier.
     
  4. Gary Baigent
    Joined: Jul 2005
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    Location: auckland nz

    Gary Baigent Senior Member

    You mean reduce weight don't you?
    But this is a cruising/overweight? multihull question.
    Re-ballasting/shifting weight forward just sticks the nose down.
    Ever sailed/tacked a bow down multihull?
    There is no easy answer ... except rudder foils will lift the arse up.
     

  5. Jim Caldwell
    Joined: Aug 2013
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    Location: Cleveland, Ohio

    Jim Caldwell Senior Member

    I agree there is no easy answer.
    Yes, I have sailed a Cruising cat bow down as an experiment to see if it helped.
    It got the transoms out and added .2 of a nt at 7 kt's boat speed.
    Tacking was slightly slower.
     
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