convert inboard to outboard

Discussion in 'Propulsion' started by James007, Nov 20, 2008.

  1. James007
    Joined: Nov 2008
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    James007 New Member

    I am able to pick up a Bayliner 32 for next to nothing. It has had an engine fire and the gas inboards are toast. I propose to repower with two Honda
    135's. The objectives: lighter weight, less complexity, easier maintenance, more room in the boat. I know--this idea is way, way outside the box. Any comments?
  2. KnottyBuoyz
    Joined: Jul 2006
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    KnottyBuoyz Provocateur & Raconteur

    That's a big boat. What style of Bayliner is it? You might want to consider an engine bracket attached to the transom for the outdrives.

    I don't know if they make them for such a large boat. Not going to be a cheap alteration and may require a custom made bracket.
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    FAST FRED Senior Member

    You may have out of trim problems with a couple of heavy outboards aft of the boat , and nothing where the 1000lb engines were.

  4. James007
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    James007 New Member

    The shift of weight aft is an important consideration I had not considered, though the lighter weight of the outboards placed further aft may tend to balance the whole thing. A not-too-complicated math problem. More importantly, how does one become a provocateur and raconteur....?
  5. marshmat
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    marshmat Senior Member

    Hi James,

    It looks like the Honda 135s are 225 kg / 500 lb each, if you believe Honda's brochures. So 450 kg or 1000 lb, and a bracket would be about two feet back from the transom... so a moment of 2.7 kN.m or 2000 relative to the transom, pulling the stern down.

    What were the original engines, and where in the boat were they? A 200-250 hp V8 with transmission might tip the scales at 350 kg or so, let's guess that they were 4 m (about 13 ft) forward of the transom, which would be a moment of 27.5 kN.m or 20300 pulling the bow down.

    Now, those numbers are just guesses, but they give you a feel for how big a shift in weight this would be. It's not difficult to draw up a little spreadsheet to calculate the weights and moments more accurately, and see just how far the centre of gravity will move. But removing a lot of weight from the middle, and adding a lot of weight at the stern, will certainly cause some difficulty when it comes to maintaining level trim.
  6. partgypsy
    Joined: Jan 2007
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    partgypsy Junior Member

    inboard to outboard

    I am weighing my options as to replace the useless inboards (one seized and one making terrible noises) on a 35' Chris (1974)I just bought.
    thinking that as I can pretty much only do hull speed in the local waters. I could get by with two outboards of less than 80 hp each. The weight issue could be taken care of by removing the aft-mounted fuel tanks (2x90 gallons) and building a recessed transom mount for the outboards. New fuel tanks would be mounted in the space occupied by the old engines.
    Saves money, saves fuel, less noise...
    But the idea starts falling apart when I factor in all the labor involved. In addition to the refabrication of the transom, there are a few other time-consuming issues.
    -Shafts, struts, rudders all need to be removed and faired.
    -Steering has to be re-engineered
    -Large trim tabs will likely be needed.
    -Instruments will need to be replaced
    -Will I be able to get insurance?
    -Will it have any resale value?
    -What if I did want to go on an extended cruise above 7 knots?

    Good rebuilt small blocks are not much more $ than good outboards. I really think that I would spend less time and be more satisfied by keeping the boat as it was built.

  7. Butch
    Joined: Jul 2018
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    Butch New Member

    Hello James,
    I am very interested in the outcome of you conversion. If you did do it is it for sale?
    please send picture to
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