1973 I/o transom replacement

Discussion in 'Restoration Projects & Questions' started by Ian D, Jun 9, 2017.

  1. Ian D

    Ian D Hydrodyner

    Joined:
    Jun 9, 2017
    Messages:
    12
    Boat Model and Year:
    1973 18 I/o
    image.jpg Here's a long story

    I have a 1973 Hydrodyne 18 with the 888 mercruiser I/o drive and 302 ford engine. I have had the boat for several years. I got it from my uncle, it was the first boat I ever skied behind. He took it somewhere in pewaukee an had a floor put in it sometime in the 90s. He said 10 years but I think it was more like 20. It had been sitting for a number of years after the outdrive broke. I got it going again and used it with only occasional minor repairs. Shift cable, points tune up, etc. for 3 years. I used it a lot in my ownership of it.

    Earlier this week I took a screw out of the transom and about 1 gallon of stinky swamp water came out. I took out the engine and mercruiser transom parts yesterday. My transom is soaked. I checked the core in 2 places near the transom and found dry wood. Same story with the engine mount stringers dry sawdust.

    I would like to replace just the transom. My plan is to use aa grade plywood and poly resin. I really don't want to take the top off. I don't intend to do a restoration just get it back to sea(river)worthy status.

    Is it possible to build up the transom in 2 pieces for the first layer then 3 for the second so I can leave the top on and just slide them in from the engine cutout? The joints would be staggered. Any other suggestions or input is appreciated.

    Here's a few pics. I think the engine cowl is the coolest part of the boat.
     

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  2. tj309

    tj309 Composite Specialist

    Joined:
    Jul 19, 2010
    Messages:
    399
    Location:
    LA (lower Alabama)
    Boat Model and Year:
    1972 18' Hydrodyne
    Ski Team:
    Former Hodag Water shows
    it's tough to do it right without removing the deck/top. But I think it is possible. Get all the wood out from the transom. If possible stand the boat up with the bow pointing to the sky. Then laminate plywood and fiberglass layers for the new transom. Pay particular attention to tying your new work into the original structure like the sides and bottom and top with fiberglass cloth. tie it into the stringers too.
     
  3. Ian D

    Ian D Hydrodyner

    Joined:
    Jun 9, 2017
    Messages:
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    Boat Model and Year:
    1973 18 I/o
    So I have most of the wood out. Not a fun job. It apears that the rear plywood sheet went down all the way to the hull and the forward sheet sat on the glass that encased the core. I have gone down to the hull the full thickness of transom. The core wood was dry and had the grain going vertical. Is that the later building style?
    What is the best way to glue the 2 layers together? I am going to be doing that at the same time I glass them to the skin. I plan to bolt a 2x12 to the back through the holes for the tie down hooks the clamp through the I/ o hole when I install the new wood.
     
  4. tj309

    tj309 Composite Specialist

    Joined:
    Jul 19, 2010
    Messages:
    399
    Location:
    LA (lower Alabama)
    Boat Model and Year:
    1972 18' Hydrodyne
    Ski Team:
    Former Hodag Water shows
    I don't understand what you plan to do with the 2 x 12's. Are you adding additional knees? Laminated layers of plywood would be better.
     
    Last edited: Jun 12, 2017
  5. Ian D

    Ian D Hydrodyner

    Joined:
    Jun 9, 2017
    Messages:
    12
    Boat Model and Year:
    1973 18 I/o
    i was planning on using a 2x12 on the outside to clamp and temporarily bolt the inner plywood to during layup. What is the best way glue the two layers together? I will be assembling them in the boat at the same time I install the transom. Can I use just resin to glue them together?
     
  6. tj309

    tj309 Composite Specialist

    Joined:
    Jul 19, 2010
    Messages:
    399
    Location:
    LA (lower Alabama)
    Boat Model and Year:
    1972 18' Hydrodyne
    Ski Team:
    Former Hodag Water shows
    2 x 12's as clamps is a great idea. Use resin and cloth between layers
     
  7. Ian D

    Ian D Hydrodyner

    Joined:
    Jun 9, 2017
    Messages:
    12
    Boat Model and Year:
    1973 18 I/o
    I found this placard somewhere in there. Is it of any significance?

    I'm done grinding out the old wood, sanding the glass and will be making the new wood transom pieces soon. The foam templates go in ok so my plan to leave the top deck alone might be ok.

    Is there much of a benefit to epoxy over vynilester or polyester resin? Since I'm installing the transom in pieces would one resin be significantly better?
     

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  8. tj309

    tj309 Composite Specialist

    Joined:
    Jul 19, 2010
    Messages:
    399
    Location:
    LA (lower Alabama)
    Boat Model and Year:
    1972 18' Hydrodyne
    Ski Team:
    Former Hodag Water shows
    How many layers of plywood are you planning on using in the transom? Doing it in pieces and not one solid layer upon layer will be significantly weaker.
     
  9. Ian D

    Ian D Hydrodyner

    Joined:
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    Messages:
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    Boat Model and Year:
    1973 18 I/o
    2 layers of 3/4
     
  10. tj309

    tj309 Composite Specialist

    Joined:
    Jul 19, 2010
    Messages:
    399
    Location:
    LA (lower Alabama)
    Boat Model and Year:
    1972 18' Hydrodyne
    Ski Team:
    Former Hodag Water shows
    Not enough. 3 layers minimum. Factory transoms were 2". Make sure the layers span the entire width and stagger the horizontal seams.
     
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