what do you think would happen if...

Discussion in 'Boat Design' started by Frosty, Oct 22, 2011.

  1. Frosty

    Frosty Previous Member

    What would happen if you put the rudders of a power catamaran in front of the prop?
     
  2. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    You would loose some of the effectiveness of the rudder, the higher velocity of the prop wash onto the rudder makes them work more efficiently.....but you knew that....
     
  3. Frosty

    Frosty Previous Member

    Yes I did but is that all. So with a power cat and monouvering at slow speeds with engines the rudders can be in front and to the side a bit.

    You think nothing would happen but a lack of manuvarability. Ive never seen it before,--Have you?

    I dont know every thing and need some one to bounce some ideas with, there no one down the pub!!.
     
  4. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    Would be better in reverse ...why not a rudder with 66% behind the prop and 34% in front.....piviot hole directly above the prop..prop runs in a slot in the rudder .....

    Well this is a Frosty question.......
     
  5. Frosty

    Frosty Previous Member

    Cant do that Piston, its a suface drive so the bit in front would not be in the water or it would hit the shaft. Any way tried that, the rudder could not be moved far enough away and it vibrated too much.

    The idea is to put a spade infront of the prop and to the side. Does anyone think that wont work Ok.
    I manuvoure with engines anyway.
     
  6. river runner
    Joined: Jul 2011
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    river runner baker

    What you really need is force vectoring. Props that turn or a nozzle that turns. You could possibly elliminate the rudder alltogether, lowering drag. I'm not a power boat guy, so if they already have that, sorry for my ignorance.
     
  7. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    sorry frosty missed the surface drive bit ...glad to see you are with us and on form.
     
  8. yipster
    Joined: Oct 2002
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    yipster designer

    question made me think of if-than and other computer commands from the past
    guess a lot is possible but results usually depend a lot on how well its done
    about having the -surface- prop in a rudder think sonny levi where you allready made some for-next thinkings ;)
     

  9. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    There will be a huge difference in the torque on the rudder when the props are reversed. With 80% of the rudder on the far side of the rudder shaft, not so bad; with 80% on the near side, it can get out of hand. I'm thinking largish slow speed rudders. That and the fact there is usually a lot more twist in the slipsteam in reverse due to lower efficiency. For high speed craft it may be less of a problem. It does let you put some twist into the prop's supply stream and that has the potential to bump efficiency a skosh. If you turn the rudders at speed (crash maneuver) the props can suck. I reckon I'd rather it be well to the side than in front. I've had sailboats set up all three ways. Some experiments may be required to get the prop walk you want.

    A crash stop with forward rudders can be an exercise in statisical probability with the prop wash cancelling rudder or reversing it just when you need your instincts to save your bacon.
     
    Last edited: Oct 22, 2011
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