IO to Outboard

Discussion in 'Outboards' started by slow fred, Aug 21, 2015.

  1. slow fred
    Joined: Feb 2011
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    Location: florida

    slow fred Junior Member

    1984 22' StarCraft aluminum cabin cruiser with a 140hp Mercruiser. I would like to install a outboard bracket with a 125 to 150 HP 4 Stroke outboard. What problems, if any, will this create? Being cost effective is not a problem.
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Weight distribution will be the biggest issue, followed by a potential need for additional volume aft to support the outboard. This last concern can be handled with a well done bracket. The first will require some playing around to get the CG where it needs to be. The first thing to do is find the CG.

    On your boat, the easiest thing is to remove it from the trailer and place it on a length of pipe, balancing the chines, so it doesn't flop over. Move the pipe back and forth, until it all but balances front to back. Mark this on the rail and this is where the CG is currently. With the bracket made and outboard hung, balance the boat again, with the pipe in the same location as marked and shift weights (batteries, tanks, etc.) as necessary to get the CG back where it was. If you have to error, do so on the too far aft side, but try to get it close.
     
  3. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    1. Make sure the o/b has the same prop blade Area as the existing I/o prop.
    Just finished working with a fellow on a 25' Bertram repower: replaced 2 inboards (engines amidships) to 2 x 300 Hp mercury Verado on an Armstrong pod/bracket(which has some buoyancy). LCG a bit more aft (increased stern trim ) but quite acceptable.boat handles like a dream, tops out around 60 mph. Owner very happy
     
  4. slow fred
    Joined: Feb 2011
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    Location: florida

    slow fred Junior Member

    Thanks for the info. The boat will be used for long distance cruising on inland US waterways. Speed is not an issue but, quiet sound is what I am looking for.
     
  5. JJO
    Joined: May 2014
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    Location: SE. Michigan

    JJO Junior Member

    21' 73 holiday

    I am thinking i am going to do the same with my 73 starcraft holiday. What shaft length OB will you go with?

    I have read some threads warning about going with 20 inch shafts. I'm not sure if it is a valid concern... My thoughts are if the bracket is positioned correctly this should not be a problem.

    I plan to fab my own bracket with float chamber.

    I did not do the CG activity PAR suggest before pulling the IO, didn't shift directions to change propulsion until recently, is the reason for that.

    Pulled the io awhile ago.

    Good luck with your project.
     

  6. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Don't go with 20" shafts, 25"s minimum.

    Using a bracket that provides some flotation works very well, then just move stuff around until it's right
     
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