Swing keel not vertical

Discussion in 'Boat Design' started by Terje Dahl, Nov 30, 2022.

  1. Terje Dahl
    Joined: Nov 2022
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    Terje Dahl Junior Member

    Why is it that all the weighted swing keels I see are never vertical when lowered?
    fully extended they maintain a swept-back angle of maybe 20-30 degrees.

    If such an angle were optimal, modern fixed keels would surely be angled back also. But they aren't.

    Surely, it isn't because no one can make a mechanism to pivot the keel 90 degrees.
    so what gives?!
     
  2. bajansailor
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    bajansailor Marine Surveyor

  3. Terje Dahl
    Joined: Nov 2022
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    Terje Dahl Junior Member

    Only the Southerly 480, and then a barely vertical leading edge. The rest all have the swept-back profile.
    Also, hardly what I would describe as a performance keel. Instead reminiscent of a shark's dorsal fin.
     
  4. philSweet
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    philSweet Senior Member

    Of coarse they are, if they are practical. A 45 degree leading edge is a great, practical fin angle whether fixed or pivoting. Stuff slides off it. Chain doesn't wrap up on it. Grounding is much more forgiving. The performance cost under professionally crewed conditions is tiny. Normal sailors couldn't tell the difference, and will probably do better overall with a more forgiving arrangement. Unless you have a seven figure sailing budget for the year, and dry store the boat after every use, use a 45 degree leading edge.
     
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  5. jehardiman
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    jehardiman Senior Member

    I have said this before....Do not confuse the angle of the leading edge with the sweep of the foil, what you are looking at is the leading edge rake. The sweep of the foil is measured at the 1/4 cord line and taper will effect the rake of the leading edge. The vast majority modern foils, fixed or swinging, have negative sweep (i.e. swept forward). So while my Catalina 22 keeps the keel swept back to minimize grounding damage, there are many more high-performance planning dinghys out there with near vertical centerboard/dagger boards with forward sweep to the foil, but a leading edge that rakes aft (i.e. the International 470).
     
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  6. Skyak
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    Skyak Senior Member

    I can't speak for others, but I know why I would avoid letting a swing keel drop to full vertical. "Up" on a boat varies at least 20 deg. (waves, acceleration, deceleration) so if your lift mechanism is not a solid, the keel would be free to swing. Many are lifted with a line to simplify the mechanical advantage. You don't want the keel gathering kinetic energy that will end up as an impact against the boat.
     
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  7. wet feet
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    wet feet Senior Member

    This thread reminds me of a saga involving a man in England who decided that his dinghy centreboard absolutely had to have a vertical leading edge. None of the other hundreds of boats in the class did,but that didn't bother him because he really, really wanted his to be vertical.The consequence of extending the top of the board to permit this became evident when the boat was rigged and a lot of very useful space was lost.He only actually sailed the boat once or twice and then sold it.
    Post #5 contains the relevant points and any questions about a specific design should probably be addressed to the designer as he will have had reasons for his choice.Among other things,an element of sweep will make it harder for strands of seaweed to come along for the ride.
     
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