Dinghy wooden transom repair

Discussion in 'Boatbuilding' started by andrei_0, Feb 27, 2017.

  1. andrei_0
    Joined: Feb 2017
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    Location: Romania

    andrei_0 New Member

    Hi guys, I just picked up an old dinghy from a friend's garage. The boat is old and was stored in pretty bad conditions. It needs some patching up and some valve replacement, but that I can handle. I need some advice regarding how to proceed with repairing the transom. It's made of laminated plywood with a wooded core. The plywood has split from the wood, the wood has started to decay in some places, but to me it doesn't look so bad. I don't think I can handle replacing the transom on my own and would consider this as a last option. Where I live there's no place I can take the boat to have it professionally repaired, so I have to somehow manage it on my own.

    I attached some pics of the transom, I was thinking to scrape between the plywood and wooden core and take out as much decayed wood, dirt and other debris, then fill in between the plywood and wood with epoxy, clamp together tightly and pray for the best. Any kind of advice is appreciated, thanks a lot!
     

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

    PAR Yacht Designer/Builder

    Welcome to the forum.

    You have a poorly repaired transom there. I don't think it's original and the plywood skins over solid wood, is of very poor quality and a bad engineering approuch.

    I wouldn't try to save any of the transom. It's just not worth the bother and effort. Get some real marine plywood and make the whole transom from it, no solid wood core.

    If the outboard will be smaller than 15 HP, you can get away with a 1" (25 mm) thick transom. If you plan on a bigger engine use a 1.5" (38 mm) thick transom. Two pieces of 1/2" (13 mm) plywood, glued together or 2 pieces of 3/4" (19) if you need a thicker transom.

    The key to transoms is the veneer count. The stuff you have there is 3 veneers and the least desirable you can get. If you have no choice because of availability, use thinner sheets and double or triple it up. For example, if you use real marine plywood, a 1/2" sheet will have a minimum of 5 veneers per sheet, so two layers is 10 veneers with an extra glue line. If you can't get the good stuff, use 4 layers of 1/4" (6 mm) plywood, instead of two layers of 1/2". This will give you enough veneers to make the transom strong and stiff. The same is true if needing a thicker transom. 4 layers of 3/8" (9 mm) plywood will make a nice 1.5" (38 mm) thick transom.

    Yeah, this is extra cost and trouble, but the transom takes quite a beating with a heavy motor on it, trying its best to twist it off the boat, so consider what it's job is, before you look to cut corners on costs or materials.
     
  3. andrei_0
    Joined: Feb 2017
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    Location: Romania

    andrei_0 New Member

    Whoa, what a detailed answer, this helps a lot! The main reason for trying to get away with replacing the transom is that I have no idea how to do this :)

    For now I will not install an internal combustion engine because on the nearby lakes where I plan on taking the boat only electric engines are allowed. It will be a struggle, but I have to start somewhere. Of course, I'd love to have a decent engine someday, so if I invest the time in replacing the darn transom, I'd do it properly :)

    Then there is a problem with finding the right plywood. I live in a place that's far away from the sea, so I doubt i'll find any "marine" rated plywood. I can get beech plywood that's rated for outdoor use in several thicknesses, for example a 15mm piece of plywood has 7 layers, 18mm has 9 layers. Would that work? If not, what exactly makes plywood "marine", maybe I can find something similar. What should I use for bonding the pieces together and for "painting" on the finished piece? Epoxy? Something else?

    And then there is the question of how to unglue the hypalon and then glueing it back on the new transom and what kind of products to use for this.
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The main concern is the glue. You can test it by boiling a piece of plywood for four hours. If it does not delaminate , the glue is WBP. Also, check for voids in the inner cores.
     

  5. andrei_0
    Joined: Feb 2017
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    Location: Romania

    andrei_0 New Member

    The plywood is conformant to some EU standard that involves testing by boiling it in hot water. Checking for voids... is there a way to do that besides cutting it to actually see the voids?
     
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