Want to gain a few knots

Discussion in 'Inboards' started by Three Ts, Nov 18, 2011.

  1. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Will, I can't really blame your wife . . .
     
  2. cyclops2
    Joined: Sep 2010
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    cyclops2 Senior Member

    Assume the worst.

    The WOT is at 120% of maximum rpms. You are cheap & do not want to change the shaft length.:)


    You must stop eroding the the bottom. Contact ALL the prop companies. 1 of them MAY have a multiblade prop to get you the 15% to 20% prop to hull clearence you need. A GOOD & LARGE prop shop MAY loan you a prop that is far better then a ruined, turned down, piece of junk.

    You MUST be sure your tachometer is ACCURATE before doing anything. Tach errors are just wasting time & money
     
  3. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Another possible solution, is twin rudders. Not a cheap or easy conversion, but then you could extend prop shaft.
     
  4. cyclops2
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    cyclops2 Senior Member

    He can extend the shaft. Has the room.

    Twin rudders on a single prop is a total loss of docking control unfortunatly. You lose all angled thrust from the prop in foward.
     
  5. Yobarnacle
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    Yobarnacle Senior Member holding true course

    I have more than 10,000 days at sea. I have been a deep sea tug captain more than 30 years. I am accustomed to handling not just one vessel, but multiple vessels at once. I have had as many as four pieces of equipment on tow at same time. Boat handling? I suspect there is little that I don't know on that subject. Twin rudders don't have to be widely separated but can be in the single prop stream and yet far enough apart to allow the prop on a tail shaft to extend further aft. ;P
     
  6. cyclops2
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    cyclops2 Senior Member

    Why would he go to 2 rudders & still have the prop where it is ?

    Worst case is move the 1 rudder farther back, use a longer shaft to allow any normal sized prop with normal prop to hull clearence. Would also lenghthen the rudder control rod / shaft.
    Twin rudders should run up a tab for designing 2 correctly sized rudders, posts bracing & new connecting linkage. The force to move them may increase steering effort also.
     
  7. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    If i read this right you are over reving to 120% so is that 6000 rpm instead of 5000 ?
    Like I said earlier 170 hp and 17 p does not match.....you need about a 21 pitch to pull the revs down about 800 rpm ...So stop fiddleing about with prop clearance and rudders and go get another prop. You have such a huge mismatch with your prop pitch that you will gain more than "a few knots" requested. Everything with your prop set up does not have to be perfect and ideal for you to be happy.
     
  8. cyclops2
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    cyclops2 Senior Member

    Well put pistnbroke.

    At my age, I ramble too much.

    Rich
     

  9. Three Ts
    Joined: May 2011
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    Three Ts Junior Member

    Thanks to all. I was even able to get some feedback separately from family of the original manufacturer of the boat on ideas. I still haven't been able to splash the boat, and probably won't be able to do so for another two weeks. Once I do, I will have a true benchmark to work from. By the way Pistnbroke, I've been to Noosa a couple of times, most recently about 3 years ago while visiting old friends in Mooloolaba and Coloundra. I sure wouldn't mind living there - great place!
     
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