No need for a plate. That isn't the way to repair a transom. I've seen that fail more than once, especially if it is mechanically attached. If you do go that way, I recommend you grind/cut the top down and thickly re-glass it. If you have a rotted/damaged transom, replace it. You will see why after you cut it out. It's not that big a deal. Once the transom is removed and the area is ground and ready, use that as your pattern to mark the wood for cutting. Keep in mind that the boat gets wider as you go forward. Cut three layers of 3/4" plywood (preferably marine grade or pressure treated). Grind the surfaces and using the matte, sandwich them together and screw them tight with drywall screws as you go. If you use pressure treated plywood as a core, simply pre-grind it with 36 grit, then with a 25% resin to 75% acetone mix, wet it all over to soak in to the wood. Start glassing it in after that kicks and while the surface it still tacky. Set the new transom in place about a 1/4" forward to compensate for the thickness of the glass on the outside of the stern. Tie it in to fore and aft stringers and the sides, varying the lengths of glass so as to spread the load. Use matte and woven roven to both tie it in and over the whole thing. I use a minimum of three layers of structural glass over the transom and additional to tie it in to the sides. Don't put too much glass on at once. The heat build-up can weaken the strength and even cause the resin to crack. Let the layers kick and cool as you go. Your glass guy will know how much to put on at a time. No hurry Mon, you're on island time! On the exterior, just use finish glass to pretty it up. All your strength will come from your work on the interior.
