Novice question on material and finish for pontoon transom

[Jon Grider]

My brother has a vintage pontoon that he is partially refurbishing. The transom that the motor was attached to has rotted out in several places. He called and I agreed to fashion a new transom to the dimensions he gave me. The old transom was [2] pieces of 3/4" plywood sandwiching a piece of 1/4" plywood with the outside grain of the thicker plywood pieces at a right angle to each other. The transom is above water line but of course does get wet. My solution seeing I already had some nice AD close grained QS white oak was to edge glue two pieces of the QS white oak and plane it to the 1.75" final thickness. I used dominoes and JB weld 2 part epoxy that says it can be used for marine purposes along with other applications. Now that it is ready for a finish, I have mulled over a few options. Epifanes spar was one I've seen folks here use but now I'm wondering if it would be crazy to use the Flex Seal [in clear] that we see in the ubiquitous TV ads? It's a fairly small piece, 24" X 10.25" X1.75" Anyone tried this? Anyone have suggestions? Thanks in advance for any input.

[Josko Catipovic]

I found this very useful for wooden boat repair: https://www.westsystem.com/wp-content/uploads/Wooden-Boat-Restoration-and-Repair.pdf
There's a chapter on transoms.

[Jon Grider]

I found this very useful for wooden boat repair: https://www.westsystem.com/wp-content/uploads/Wooden-Boat-Restoration-and-Repair.pdf
There's a chapter on transoms.
Thank you Josko for the link. Lots of info there. Now I'm wondering if I should have gone with Marine plywood instead of white oak because of wood movement [even though it's QS] allowing moisture into mounting holes. I figured WO in the first place because some of the old vessels used WO and also that it is used in whiskey barrels. Well, at least replacing won't be a very difficult thing when the time comes down the road.

[Josko Catipovic]

FWIW, in 1990 or so, I replaced a rotted marine plywood transom (on an Amesbury skiff) with white oak, and it's been solid ever since, despite the skiff's heavy use and general lack of care. One noteworthy trick is to dilute WEST epoxy with acetone, and use it as a wood penetrant for added rot-resistance.

[Adam Herman]

to really make it last, roll a coat of epoxy on it, and embed fiberglass mat on both sides. then paint with a good marine paint. i think the white oak is a fine choice. get it all fitted with the mounting holes in it before epoxy. sikkens marine paints are great as well.

[Jon Grider]

to really make it last, roll a coat of epoxy on it, and embed fiberglass mat on both sides. then paint with a good marine paint. i think the white oak is a fine choice. get it all fitted with the mounting holes in it before epoxy. sikkens marine paints are great as well.
Thank you Josko and Adam, I'll take your suggestions to my brother who now volunteered to put the finish on it.