plywood correctly coated with epoxy will last well. millions of boats nowadays depend on epoxy to seal a core of wood. not just the transom. there are threads here about exactly what you are doing. any na would recommend epoxy/plywood for your repair.
the gentlemen at the local hardware store said that the board was marine type, but clearly it wasn’t. the gentleman may not have been wrong. a year ago i did a boat renovation and looked in to different plywood options. marine grade is more about structural integrity. meaning no knots or issues.
yeah change the transom !! shape can give strength !! by making a completely new transom using shape to make it strong !! i did this a couple of years back , have a older hull with a tired omc 75 on the back so changed the transom completely and stepped the motor back 500 mm ,went from 20" to 25" inch motor and from 75 hp to 115 hp has no water drains and works a treat .
question about using pvc instead of plywood for transom post by jigngrub 07 aug 2011, 19:15 honestly your best bet is to use a marine grade or exterior grade plywood and seal the heck out of it with spar. if you can fit in something with a width of 1-3/4" an lvl beam (laminated veneer lumber) can be had in 14, 16 or 18" widths and
dangers of pressure-treated wood. which is copper based -- instead of arsenic based. warren says with the new technology, there is a cost increase of 10 to 20 percent. such as redwood or
re: marine plywood for transom i just picked up a 4x8 sheet of 3/4" pressure treated for my transom.. $32.00 each at lowes. it's odd how the pressure treating has a tendency to twist the wood. i found the strhtest sheet, and hopefully it will even out after its laminated and installed.