Transom Repair Question

[David McCollum]

I have a 1950 Matthews with the transom half removed (the lower half). I was making frame repairs, and now the time has come to put the transom back together. Original construction was a double layer, the inner part being half inch plywood, and the the outer layer 9/16" mahogany planks. The plywood didn't seem to hold up well, so I was thinking of using white oak planks as the inner layer, with new mahogany for the outer layer, seams staggered.

How would you treat these mating surfaces? I think I should paint with red lead at the very least, but is there something additional I should put between the layers, some form of bedding compound?

Thanks for your advice.

[Stephen Hutchins]

Mahogany on both layers glued with epoxy would be better.

[Bob Cleek]

What Steve said. You don't want to put two different types of wood with different movement characteristics together like that. Also, if you are using epoxy, you can laminate the whole thing with 1/4" strips and make your own "plywood." No need to struggle with thick planking at all.

[Venchka]

Originally posted by Bob Cleek:
... Also, if you are using epoxy, you can laminate the whole thing with 1/4" strips and make your own "plywood." No need to struggle with thick planking at all.Alternating the layers horizontal and vertical. Throw in a couple diagonal layers if you use enough layers. An odd number is best.

Wayne
In the Swamp. :D

[wyndham]

Bob and Wayne are both right but I would stick with the original builders intent. If you laminate white Oak and mahogany the differences in the rates of expansion are going to tear the whole thing to pieces pretty quickly.
Why not replace the plywood inner layer with new marine ply and laminate mahogany planking with epoxy and screws to it?
Saturate the edges of the ply with CPES and follow with unthickened epoxy. Prime both faces with CPES and laminate with Mahogany. Finish as you intend the rest of the boat.

[Bob Cleek]

What Wyndham said, too. It's really up to you. A decent marine plywood, well sealed on the edges with epoxy, ought to do the trick for you as well.

[RiverRat]

First off, that plywood aint original construction. Double planked Matthews had a cedar inner planking 3/8 thick with 5/16 inch mahogany outer planking. The inner layer was varnished and then the mahogany was bedded in the wet varnish.

Do not use oak. Red white. Live or chestnut. Use ply and seal with west system. Use MDO if the budget is tight. Use 2 layers of 1/4 fir and epoxy them together if you want to make a more radical radious. Hell, you could even steam bend the 3/4 ply if you wanted. Bet you didn't know you could steam bend plywood.

[ 06-24-2005, 05:56 PM: Message edited by: RiverRat ]