Cat or Outrigger Sailboat Rudder Turn Ratio

Discussion in 'Multihulls' started by BobBill, May 9, 2014.

  1. BobBill
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    BobBill Senior Member

    Any point to idea of outboard rudder with slightly more angle of attack?
     
  2. pogo
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    pogo ingenious dilletante

    Geometrie or profile ?
     
  3. oldsailor7
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    oldsailor7 Senior Member

    Don't quite understand what you mean here. ?
    The AOA of the rudder is controlled by the helmsman.
    Are you meaning an angle of attack of the rudder when the helm is centred.
    If so then you are using the rudder as a complement to the leeway resistance of the dagger board, a common occurrence.
    On any sailboat if the rudder is centred and the boat is in trim----then the rudder will have an AOA equal to the boats lee way.
     
  4. BobBill
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    BobBill Senior Member

    Was topo brief, sorry. catamaran/outrigger with two rudders. Does it make sense to cam each so the outboard rudder on a tack has slightly more angle, to move it faster through its travel? Or, it is not worth the effort?

    Sort of like the inside of a phalanx pivots, as the outside takes many strides...
     
  5. oldsailor7
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    oldsailor7 Senior Member

    What is commonly done is the tillers are angled to obtain the effect you want.
     
  6. bruceb
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    bruceb Senior Member

    rudders

    most beach cats and several of the small twin rudder monohulls all use angled tillers. I haven't seen the big boats, but I expect they do too. It makes quite a difference.
    B
     
  7. oldsailor7
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    oldsailor7 Senior Member

    To expand on that, Cars, Planes and Catamarans share a common problem.
    The front wheels on a car, the Ailerons on a plane and the rudders on a Catamaran will all drag on the outside of a turn unless the AOA is reduced.
    This is done in a car by what is called Akerman steering, on a Plane by Aileron Differential, and on a Cat by angling in the steering arms of the rudder turning mechanism.(Akerman for Cats).
    In the early 1950s I had an Austin A90 electric convertable, a very swish car in it's time. It would wear out it's front tyres in 2000miles due to its poor steering geometry.
     

  8. BobBill
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    BobBill Senior Member

    Ahhh, the Ackerman magic work. Thanks. I forgot about that when applied to boats.

    Thanks. Much there. Tom Speer here has good information too, I just found. And Richard Woods and I will bet I find more...very grateful.
     
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