18 ft transom replacing

[erebus]

I just finished replacing a portion of the transom on my 1975 18SF.
Found slightly mushy plywood around the original engine bolts during my winter repower.
Cut all the core out from the outside to about 6 inches past the splashwell sides vertically and about 6 inches above the transom horizontally. Found good dry plywood out there.
Laminated in two sheets of 3/4 coosa board as well as a few layers of 1708, and a new outside skin of 3/16 thick pre-fab fiberglass sheet from mcmaster-carr.
I could easily tell that the original core was two sheets of 3/4 ply from the cross section.

You could go 1 3/8 for your core and add a lot more layers of glass to make up the difference.
Would sure be nice and solid!

I also, just for fun added a nice big knee in where my baitwell was from the inside of the transom to the top of the fore and aft stringer. Also made from 3/4 coosa and a lot of glass.
I used epoxy for the whole project.