I would not dream of replacing only part of a wooden transom, especially given the extent of your damage. I'd replace the whole thing with high quality marine grade ply coated on all sides with epoxy at a minimum. IMO wood and polyester resin are not a long term recipe for success, use epoxy. Keep in mind epoxy will stick to polyester but not the other way around. Many people don't want any wood in their boats and will go with foam core. On a small boat like that I'd be comfy with the ply and epoxy. On a larger boat where the materials alone are going to cost $$$$ I'd go with foam core. But that's just me. Some of the guys on here do this sort of thing for a living, they can give you the bottom line on what the professionals would do. I'll admit I'm a hack with a little experience compared to some.
Good luck, I hope it will be a rewarding and successful project.
good advice - very good advice
polyester based resins are pourous,and provide a "surface bond",when used with wood
epoxy is allways the best choice,when working with wood...
nothing "wrong" with using wood,provided that wood is sealed completley with an epoxy
word to the wise:
the garboard plug is often the most overlooked area,it's best to drill that area out much larger than what's needed - fill that hole with epoxy/mixed with a thickening additive - i like west system 403 - it's an adhesive,after that mix kicks,drill the hole to the correct size
another tip:
allways coat wood to be laminated,with a coat of epoxy first - no additives,then spread the laminating mix
do not throw the epoxy mixing containers in the trash - as it kicks,it makes heat - enough to start a fire
a drawback to using epoxy is amine blush - some epoxy resins do not blush,others do - west system,what i use,it blushes - this needs to be removed with soap and water,before sanding...
a guy i know,mad mike,a nice gentleman,but,he has a problem - he believes his skill level is way beyond what it is - he borrowed some supplies from me before.he was attempting to make gutters on his boat - he laminated some parts with epoxy and attempted to use a polyester chop strand putty on top of that west system,without removing blush - he complained to me,"that stuff would not set","it's trash" - after i asked him a few questions,the problem was explained to him... :
