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Replace on add on to transom . . .

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  • Replace on add on to transom . . .

    I'm working on a 1962 Glasspar Ventura; a 21' Cabin cruiser and I'm considering what to do with the transom.

    It was originally an outboard but I'm converting it to an I/O. The transom seems real strong and does not have any rot visibly showing. The only problems I see is the plywood is slightly depressed where the old outboard mounting bolts were.

    I know I need to add on to the outer fiberglass which is not a problem. The question is should I just add on to the plywood core or replace the entire core? It was obviously a longshaft configuration and the outdrive will be mounted well below the top of the existing transom.


  • #2
    Re: Replace on add on to transom . . .

    hi......the work you are about to do is not difficult....but it is something that you only want to do once. so do it right.

    remove the old transom......
    make the new transom go all the way to the top.
    glass it and gellcoat it.

    you will have to tear the deck out in the motor compartment and build motor mounts and re inforce everything any how.....so while you are in there make a proper transom.

    make sure you have a donor boat, because the transom plates and bell are worth big bux.
    choose your motor drive package carefully.

    when you are cutting the drive hole....make sure you follow the mafucturers instructions on crank shaft center line properly....or the boat wont handle right or it will porpus
    The Hull Extension Thread
    great info on all aspects on boat building with detailed information.


    IN MEMORY OF Our friend SpinnerBait_Nut LESTER WRIGHT July 31, 1953 - Nov 26, 2008 RIP

    IN MEMORY OF Our friend Tashasdaddy Robert (bob) Griffis. October 27, 1948
    November 29 2010 RIP


    • #3
      Re: Replace or add on to transom . . .

      oops!, thanks for the advice.

      I've already picked up a Chrysler 318 that is a fresh rebuild with all the boat hardware such as fresh water cooling, manifolds and such.

      I have a person that is getting me the appropriate Volvo 280 and bell housing that was available with that motor.

      I guess you are right, if I'm going through all that trouble, I should just do it all correctly.

      My big question is this: If i remove the inner fiberglass skin and leave the outer in place, how do I get the outer skin to hold its slightly curved shape and how do I get the new plywood to conform to that slight curve?



      • #4
        Re: Replace on add on to transom . . .

        If you're going to all the trouble to do it right, why put in a Chrysler 318? The Chevy 350s are much more common marine motors, have more power, and are much easier to get parts for?
        Sea Ray SRV-210 - Winter refit
        75-85 foot displacement hull trawler - gleam in my eye


        • #5
          Re: Replace on add on to transom . . .

          erikgreen, I thought about that but I have two of the 318's . . . on is a good running pull and the other is straight from the rebuild shop and has never been installed. Plus, a boat salvage guy near me has several more if I need them


          • #6
            Re: Replace on add on to transom . . .

            So I know that I can't steam plywood but how do I get the plywood to get that "curve" from left to right?


            • #7
              Re: Replace on add on to transom . . .

              Use multiple thin layers of plywood and bend them into place on a form or in the transom one at a time.

              Depending on the curve, 1/4" ply should be able to be bent into place without a problem. Glue the layers one at a time into place until you have the thickness you want.

              Or alternatively, you can make slit cuts in the back side of the panels for the transom... vertical slits about one every 2 inches all the way across should let you bend the panel into place. Then once it's in, fill the slits with resin putty and put in the next layer. Fill the slits on the top layer before covering with glass.

              Sea Ray SRV-210 - Winter refit
              75-85 foot displacement hull trawler - gleam in my eye


              • #8
                Re: Replace on add on to transom . . .

                You use 1/4" ply and laminated it to the curve. 6 piece will give you about a 2" finished transom counting the outer and inner skin.
                This guy did it this way but you can make it all one piece if you laminate 1/4 " His bracing for it is spot on though.


                I'm just sayin...
                1961 Lonestar Flamingo - SPLASHED...Kinda!!
                Fabricating Decks, Stringers, and Transoms
                Paint Your Boat with Tractor Paint...Say What!!!


                • #9
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                  Re: Replace on add on to transom . . .

                  Are you sure the transom is supposed to have a curve, it sounds like the wood is compressing at the bolts .
                  See FAQ Files.

                  Get the genuine factory service manual.