Center Of Effort And Helm Balance On Kite Boats

Discussion in 'Boat Design' started by zstine, Mar 17, 2021.

  1. zstine
    Joined: Sep 2013
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    Location: New Jersey

    zstine Junior Member

    I'm interested in the community's thoughts on the helm balance of Kite boats. On a standard sailing rig, a little weather helm is desired. However, this condition on a Kite boat could result in the boat turning head to wind accidentally and the kite tow line would be over the stern of the boat... not where you want it.
    I would think some lee helm would be desired on a kite boat so it would turn down and follow the kite. Don Montague's Kai Project Kite Boat made several purpose built kite boats. In photos, it appears the kite tow line is well aft of the main strut/foil in a standard plane trifoil configuration, meaning they design weather helm into their kite boats. Any ideas why this is desired?
     
  2. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    Weather helm is not always a preferred condition, however, many ocean sailors like it as a safety feature in case of a man overboard. It also forces the rudder/keel foil underwater to reduce windage a little. In addition, the heeling introduced by wind forces and lift from rudders countering weather helm, can spill air in conditions where sudden gusts could otherwise put the sail in the water.

    For a kite boat, I think those conditions don't exist. A kite boat with weather helm would not stop by heading up into the wind. However, would you want your boat to turn broadside to the wind? That seems like it would potentially bring water aboard as the boat was pulled over.
    Giving the boat a lee helm might be OK. The bow would turn naturally toward the kite and the helm would have to fight that. Balance would be critical. If you were sailing DDW, no problem, just relax, if you were sailing on a reach, your helm is toward the wind and the foil of your keel counters heeling, but adds to leeway.

    With a weather helm, DDW might not be so awesome, but on a reach, you have more heel, but less leeway. Better for navigation, not as comfortable of a ride.

    These are my thoughts off the top of my head.

    A weather helm in a MOB, might lead to a fishtailing, or the rudder swinging hard over to one side and the boat would resist the kite's pull by trying to turn to one side, maybe leading to a taking on of water again. Balance seems critical
     
  3. BlueBell
    Joined: May 2017
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    BlueBell "Whatever..."

    Running the kite load-line through a stern barber-hauler pulley makes the weather helm adjustable to the point where I was actually able to steer the boat with it, no rudder.
    It necessitates a hauler on each side but they share the same pulley for the load line to run through.
    Not my idea, I stole it from a Kiwi!
     
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  4. zstine
    Joined: Sep 2013
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    zstine Junior Member

    That's a good idea. I have some issues with C.G. and crew location, since I'm designing a foiling boat. My original design had the kite connection aft and the barber-hauler pulling fwd, but then it would hit crew in the head. I may be able to move the kite connection fwd and barber-haul aft. Such an obvious mod but it didn't come to mind. thanks....

    Hey, BlueBell.. Can you comment on how sensitive the tow position is to rudder load? Like, does a few inches of barberhaul make the rudder go from balanced to over-loaded / rudder stall or do you have to move the barberhaul several feet for that? Obviously your rudder size matters, but it gives me a data point.
     
    Last edited: Mar 17, 2021
  5. BlueBell
    Joined: May 2017
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    BlueBell "Whatever..."

    Ya, a lot of variables in there to influence my response...
    But about 6" of barberhauler travel would produce a pretty good turn rate with no rudder (rudder up, out of the water).

    I wasn't interested in weather helm during these tests so I can't really comment.
    It was a through-together prototype, skin on frame, 17' x 1' stabilized monohull (tiny amas).
    A long slender hull, no planing, little rocker.

    A big variable is your centreboard size and performance characteristics.
    Are you hard fastening your load line or on a traveller?
     
  6. zstine
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    zstine Junior Member

    It's on a traveler to help get the center of effort down lower and help lift the lower ama... similar stabilized mono/trimaran with tiny amas setup.
     
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  7. BlueBell
    Joined: May 2017
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    BlueBell "Whatever..."

    Are you running your control lines through the traveller too?
    And through the barberhauler pulley as well?
     
  8. zstine
    Joined: Sep 2013
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    zstine Junior Member

    no, control will be done aloft. just a tension line run to the boat.
     
  9. BlueBell
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    BlueBell "Whatever..."

    Nice!
    Home-made control box or commercial?
     
  10. zstine
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    zstine Junior Member

    It will be home-made, but is not complete.
     

  11. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell "Whatever..."

    I was in touch with a Kiwi who claimed he was 6-months away from a functioning box.
    That was four years ago... I haven't heard from him.
     
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