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20" shaft on a 15" transom? Is this possible?

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  • 20" shaft on a 15" transom? Is this possible?

    hello - if this has already been answered somewhere, please just direct me to the answer (I couldn't find it!).

    I have a 14' fiberglass skiff w/ 15" transom, and I'm looking for an outboard. Unfortunately the only ones I can find are 20".

    Should I hold off on buying a 20" for a 15"? Is there a way to accommodate a 20" shaft on a 15" transom?

    Thanks for the help
    "More Motor Than Boat!"

    1983 Sears Gamefisher 14'
    2012 Tohatsu 20hp


  • #2
    Re: 20" shaft on a 15" transom? Is this possible?

    I have a long shaft 15hp Evinrude, and I used a Mini Jacker jack plate and some 2 peices of aluminum square tubing to get the extra few inches of lift. If you dont want the setback, you can just take the transom wood and build it up 5 inches.

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    • #3
      Re: 20" shaft on a 15" transom? Is this possible?

      Excellent; thanks.


      Originally posted by Kobie View Post
      I have a long shaft 15hp Evinrude, and I used a Mini Jacker jack plate and some 2 peices of aluminum square tubing to get the extra few inches of lift. If you dont want the setback, you can just take the transom wood and build it up 5 inches.
      "More Motor Than Boat!"

      1983 Sears Gamefisher 14'
      2012 Tohatsu 20hp

      Comment



      • #4
        Re: 20" shaft on a 15" transom? Is this possible?

        The link below is plans for a jack plate. Let us know what you do. Good luck!

        http://www.dillon-racing.com/jackplate/index.htm
        Old geezer who never worked a day as a professional in the marine industry but has been fooling with outboard motors for 55+ years!

        Comment



        • #5
          Re: 20" shaft on a 15" transom? Is this possible?

          Good advice so far. You can run a long shaft motor on a 15-inch transom, but the trade off is less speed and quirky handling. You'll have more drag to overcome because you have more motor leg in the water. I've read posts from others on this board who talk about transom walking...where the outboard is under more stress in quick turns...which can try to leverage the motor loose on the transom. There are a couple of ways to raise a long shaft motor on a short transom...including homemade and factory jackplates and shimming the motor up a bit at the transom. Some outboards are manufactured/designed so you can retrofit the leg length...add an extension to make it a long shaft, or pull the factory extension off to make it a short shaft. There are also several posts/threads on the Iboats forum about making the change. Good luck.

          Comment



          • #6
            Re: 20" shaft on a 15" transom? Is this possible?

            Thanks for the help! I should be able to find a 15" motor eventually. But now I know that it's possible (and not too difficult) to use a 20" if I really had to.
            "More Motor Than Boat!"

            1983 Sears Gamefisher 14'
            2012 Tohatsu 20hp

            Comment



            • #7
              Re: 20" shaft on a 15" transom? Is this possible?

              I'm running a 25 inch shaft 150 Mercury on a 20 inch transom with a jack plate all the way up, but on a smaller boat I would find a 15 inch short shaft.
              1974 Wellcraft V-20 CC Steplift/ 1999 150 HP Mercury Bluewater http://www.wellcraftv20.com/gallery/album115
              1975 Wellcraft V-17 CC Steplift
              My CW site www.enfieldwargraves.smugmug.com
              My book I authored http://www.blurb.com/books/1137672

              Comment



              • #8
                Re: 20" shaft on a 15" transom? Is this possible?

                I suspect that, in most cases, the answer would be, as tmcalavy said, less speed and quirky handling.

                However, I ran a 1984, 20", 25 horse Johnson on a 1957, 14', aluminum, Lonestar King Commander with a 15" transom for quite some time and it performed just fine. Didn't appear to operate much, if any, differently from the short shaft, 25 Horse, Johnson that it replaced. We used both motors at different times for 15 to 25 mile trips on a Mexican lake sometimes running flat out for several miles before throttling back. Also operated in all kinds of wind and wave conditions with no problems.

                This was back in the 80's so I've forgotten some of the details but I do remember that at one time we shimmed the motor up an inch or so with a length of wood secured to the top of the transom.

                Later on both boat and motor went to my son and he did build up the transom to the proper height. He is still running both boat and motor.
                Las Cruces, New Mexico

                Comment



                • #9
                  Re: 20" shaft on a 15" transom? Is this possible?

                  The handling can get quirky at higher speeds doing tight turns...not my cup of tea as I mostly fish and just cruise around, but this has been noted by others on the board. As noted, matching the transom depth to the outboard leg length gets you the best performance.

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