Fabricating a new transom for a 14 foot Cadillac aluminum boat

[khe]

The inner and outer wood has rotted away. There was a 3/4" piece of plywood on the inside of the aluminum and 1/2" on the outside based on the amount of exposed portion of the bolts.

I am going to fab up new transom pieces using exterior grade plywood and I initially thought about coating it with fiberglass resin but a friend suggested three coats of spar urethane. What would be the best coating to use? I don't want to spend a ton of money on this old boat but would like the new transom pieces to last.

Thanks.

 

[airshot]

Won't last very long with spar varnish, clean the aluminum real well to remove any corrosion. Easy to coat both sides of the new wood with an epoxy, some use water sealer like Thompsons for their replacements to save some money. Won't last as long but doesn't cost as much either !! Yours sounds fairly easy with wood on both sides of the aluminum transom. Just throwing out some ideas here, if the wood is easy to acess then a shorter life repair might be in order. Some transoms are enclosed wood inside the the aluminum covers and diffficult to access that wood...so a longer life treatment might be in order. On my jon boat the transom wood can be removed in about ten minutes, so why would I bother to spend countless hours creating a lifelong repair....if you get my drift....

 

[khe]

Won't last very long with spar varnish, clean the aluminum real well to remove any corrosion. Easy to coat both sides of the new wood with an epoxy, some use water sealer like Thompsons for their replacements to save some money. Won't last as long but doesn't cost as much either !! Yours sounds fairly easy with wood on both sides of the aluminum transom. Just throwing out some ideas here, if the wood is easy to acess then a shorter life repair might be in order. Some transoms are enclosed wood inside the the aluminum covers and diffficult to access that wood...so a longer life treatment might be in order. On my jon boat the transom wood can be removed in about ten minutes, so why would I bother to spend countless hours creating a lifelong repair....if you get my drift....

Valid points. Thank you!