Transom rot: repair or replace

Hello! I recently acquired a Poncelet 420, build in Brussels - Belgium in 1956. It is generally in good condition, stored inside a barn since 1980 (at least that's the tax plate that was on it).
The transom is rotten but not entirely: where an extra layer of wood was added to support the outboard water got between the layers, It's not all the way through: there is still a piece of hard wood between outside and inside. There is also a crack from side to side, above the waterline. Looking for pro's and con's for repairing the transom: penetrating epoxy + thickened epoxy + glass on the outside vs. removing entire transom and replacing with fresh multiplex.
Other options also considered.

 

Remove and replace. Penetrating epoxy does nothing, thickened epoxy and glass need a sound base to adhere to. If you replace with plywood seal the edges with epoxy, glass the whole panel and fill all holes with thickened epoxy before reboring them.

 

As Rumars says, there are no 'pros' and only 'cons' if you want to 'bodge' a repair - it is not a very large transom, hence it should be a fairly easy job to take the whole lot out and replace it.

 

Thanks Rumars and bajansailor, replace it is!

 

Well keep us posted. Do you plan to replace the entire transom or only the doubler under the motor?

 

Entire transom, as the rot exceeds the area under the doubler.

 

Transom entirely removed. Lots of nails! The siding is very thin, in some places completely gone. Suggestions? Hull will be painted.

 

Is that solid wood in the planks or plywood? The ends need to be replaced by scarphing in new material. Anything rotten needs to be cut out and replaced.

 

Most of the time; you need placeholders or a hull wothout transom will misshapen.

 

Removal of all loose materal and rot is next.

Remove exterior paint on edges.

Prewet all the wood with epoxy and allow gelation.

make a thick bog and fill all the holes and voids; I would use 1 epoxy-1 plus aerosil-1 plus milled fiber; you may need to make some type of form and coat it with ship tape for release

nip off the metal from the inside I'd say

nice looking boat

 

Those are thin solid planks

yes, I made some temporary reinforcements

 

Then the only way is to cut each plank back (at different lenghts in order to not create a weak spot) and glue in new wood using a nice long scarph and epoxy. I presume the wood is mahogany?

 

Interesting, but contradicting suggestions... The wood is two layers of African Mahogany ("Acajou").
I'm going to build a new test-transom out of MDF, fix that with a few screws. The old transom also had some screws.
Then turn her around and sand the bottom. Depending on additional damage I will decide on the repair method. I'm leaning towards the epoxy because it's only a small surface that needs to be beefed up. Also, since there are two thin layers of wood, this will complicate scarphing.
Thanks for your answers, I'll keep you posted.

 

Update: created MDF template, then 12mm Okoumé which I fiberglassed on the inside (on the inside the wood will remain visible).
Fixed the transom in place with screws, as original, and 3M 5200. Will add small nails once she's been turned upside-down and bottom completely sanded.
Now adding the engine support, inside and outside diagonal reinforcement planks.
Contemplating adding fiberglass around the edges for added strength.

 

You will need a clamping board.

You ought to consider some 6 oz glass on the transom. You could wrap it perhaps around the edges, but no idea what hull sides are like. 6 oz is essentially invisible. To wrap it; you need some radius.