Rotten ply - how much to remove?

[Victorianna]

I removed what I thought was a very small area of peeling paint on my ply transom, which as always turned out to be more extensive. Water was getting in through the joint where the transom meets the sole and also as it turns out through the backstay through bolt - when I removed this both the ply and backing plate were wet .
As you can see from the pic, I have scraped back all the rotten/wet ply and my plan was to:
1. Treat wood with penetrating epoxy sealer
2. Build transom back up with ply and epoxy fillers
3. Paint
4. Relocate backstay attachment to somewhere else!

My question is, have I removed enough ply to stop the rot? I want to keep the repair as limited as possible but don't want to have to rip it all out again in 12 months to deal with more rot.

Boat is a Van de Stadt Dolphin 26, cedar strip built btw, hence the ply transom.

 

[Victorianna]

 

[Yngmar]

Looks dry to me. If it's not wet or rotten (soft and easily pierced with a screwdriver), I'd just build it up with layers of glass and epoxy, which will make it much stronger than before and then attach whatever was there before. Skip the ply where the bolt is, avoid future rot!

 

[Poignard]

https://www.westsystem.com/app/uploads/2022/10/0617-Wooden-Boat-Manual.pdf

Page 31 et seq.

 

[Tranona]

Your plan is sound. I have done similar many times over the 40 odd years of owning plywood boats. Before building back up again coat it in unthickened epoxy of the same type as you will use for laminating. difficult to tell from the photo how thick your new material will be, but I have found that using veneers is sometimes easier than ply. A combination of veneers or thin ply plus glass cloth works well with a final layer of cloth blended into the surrounding surface. Not sure it is necessary to relocate the backstay fitting. Line the hole with epoxy and bed the fitting in a good sealant will make it watertight and your repair will be at least as strong if not stronger than the original.

 

[Victorianna]

Thanks, very reassuring to know I'm on the right track. I like the idea of adding some glass/glass cloth to the repair so will try that.