transom repair

Discussion in 'Boatbuilding' started by cflood, Jul 30, 2007.

  1. cflood
    Joined: Jul 2007
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    Location: massachusetts

    cflood New Member

    I was hoping someone could give me some advice about repairing my transom.

    I own a 1968 crown line fiberglass 16'. The transom is rotting but it's not completly gone yet. I was considering using 3/4 cabnet grade plywood to put on as another layer to sure it up. I would re-fiberglass it and use stainless carriage bolts and washers to tie it all back in.

    My question is, would this work and would it be strong enough for a 30-50 hp outboard. I'm looking to repair it cheaply since I got the boat for free. It is my first boat and would appreciate any advice other than completly replacing the transom which I know would be a lot of money.
  2. charmc
    Joined: Jan 2007
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    Location: FL, USA

    charmc Senior Member

    Transom repair discussed before

    Try searching (upper right corner) for transom repair or transom replacement in the forums. There have been several discussions of cost effective techniques, including photos and links to photos of works in progress. Your best bet will probably be to cut and grind away the inner fiberglass and all of the rotted wood, but leaving the outer fiberglass transom intact. Then you can bond your replacement plywood to the inside surface of the fiberglass transom, reinforce and bond to the remainder of the hull, and glass in the whole thing. The earlier discussions include detailed instructions for each step of the work. You need to cut away all the rotted wood and replace it, rather than glassing something to reinforce it. The cost is more your time, not much more materials cost, but it's imperative to do it right. Rot is an attack on wood by microorganisms; it will continue and spread to other areas unless the affected wood is removed. I think 3/4" will be sufficient for a 16' outboard, but check with the people who have done this before.

    Good luck with your project!
    1 person likes this.
  3. jigerbetter
    Joined: Jul 2007
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    Location: tn.

    jigerbetter New Member

    good advice

    I think charmc gave you good advice.
    to do correctly is pretty technical good luck !!!!!
  4. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    I have a 15 1/2' tri-hull i bought in '93. I assume the transom was rotted then because it had aluminum plates on it. I know it's rotted now as I occasionally have to knock fungoidal mushroom growths off of it. I've always had a 40 hp Yamaha on it and have never had any worries about the safety of it, but possibly I'm just being stupid. The plates are 22" wide, the outside one being 15" tall and the inside one 6" tall, being shorter because of the splashwell. They both have a 1 1/2" lip bent in at the top, so at the top of the transom they sit on top of each other and form a double layer. The thickness is over 1/8 but less than 3/16", whatever gauge that might be. The top motor mount bolts bolt the two plates together, sandwich like, and below the splashwell the lower motor bolts just have big washers on the inside. Another chunk of plate or a piece of angle would have been allright, too. Around the edge small screws hold them generally in place.
  5. Catsailor
    Joined: Jul 2007
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    Location: Sydney, Australia

    Catsailor Boatbuilder & sailor

    See "hull & deck" on the website There are articles and pictures of repairs. Charmc is right - cut out all of the rot area, then bond in either a foam or ply patch, glass over the lot, fill and fair it. If you work carefully and systematically, the result will be stronger than the original boat and completely invisible



    Attached Files:

  6. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Outboard powered small craft, have pretty much accepted a transom thickness standard as 1 1/2", which typically is two layers of 3/4" plywood, bonded to the hull shell. Cabinet grade plywood will not do (panel construction issues) and likely will not have WBP adhesive also, which makes this a very poor choice for a transom. There are a number of ways you can approach this problem and many previous threads have covered the subjects involved well.
  7. Loveofsea
    Joined: Jan 2007
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    Location: Southern California

    Loveofsea New Member

    don't ever use anything but marine plywood in a boat--

    because the original manufacturer didn't use marine grade wood is exactly why you are having to replace the existing wood...
  8. Catsailor
    Joined: Jul 2007
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    Location: Sydney, Australia

    Catsailor Boatbuilder & sailor

    Sorry to disagree, but the only difference between "marine" and "construction-grade exterior" ply is the face veneers. The thing to look for is the bonding - namely boilproof - specifically Moisture Resistant Waterproof Structural Panel "technical" grade or at worst - Type I

    If you are going to glass over it, why pay the extra money for expensive face veneers?
  9. boatman2
    Joined: Dec 2008
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    Location: custat ohio

    boatman2 New Member

    Check into seacast. It works.

  10. thill
    Joined: Mar 2007
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    Location: Virginia, USA

    thill Junior Member

    If you are going to plywood and epoxy, make sure to get the right materials and do your research, so you do it right, and don't just waste your money.

    Seacast might work well for you, but again, you must use the proper materials, and follow the instructions. Don't skimp on the glass, as that's where the majority of strength is.

    Either way, make sure to get ALL the rot out before attempting to repair.

    Best wishes!

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