Transome height

Discussion in 'Powerboats' started by SC1, May 12, 2006.

  1. SC1
    Joined: Jul 2003
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    Location: Sweden

    SC1 Senior Member

    Hi
    What should transome height be for an XL shaft outboard?
    Keel to engine support.
    transome angle is 14 degrees
     
  2. tom28571
    Joined: Dec 2001
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    Location: Oriental, NC

    tom28571 Senior Member

    The cavitation/ventilation plate on the lower unit should be approximately at the level of the hull bottom. Lower than the hull works fine but introduces more drag. Higher than the hull introduces a greater possibility of ventilating the prop in waves and turns.
     
  3. SC1
    Joined: Jul 2003
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    Location: Sweden

    SC1 Senior Member

    Thanks for respond but is there a standard height on L or XL shaft outboards and a standard height for transomes on production boats?
    What is the effect of performance between a L or XL on a particular same hull.
    In style a XL be high and looks more powerful but will it affect stability in turns?
    Cutout at transome be also smaller.
     

  4. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Short: 15" nominal.
    Long: 20" nominal.
    X-long: 25" nominal.
    Some bigger OBs also offer a 30" shaft.
    The motor shaft will actually be about 1" longer than nominal, from bracket to plate. The transom should be about nominal, measured vertically.
    Any given transom configuration will only work with one length. You can usually play with the mount height an inch or two to get things set up smoothly, but you can't use a short shaft engine on a long shaft transom. (If you mount too short a shaft, you will at best ventilate the prop and have no useable power; at worst, you will suck air into the coolant lines and blow the engine.) Too long a shaft will still run, but there will be a lot of extra drag and the boat will perform very poorly.
     
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