I have given a lot of thought about enclosing your transom. It depends on how the open transom is framed. can you get access to the corners to bolt or bond a transom in place. As far as the transom piece itself. You can build a splash mold of the white board found in home centers in the bathroom section or a formica faced plywood that is bent around the transom. With the stresses involved. I would build new transom piece using a heavy structural glass lay up. You could core it with foam to minimize twisting. A solid glass flange is necessary so you can thru bolt it in place. If you provide pictures of the stern and deck, there may be other ideas on how to enclose your transom
I helped my friend do this some years ago. A lot depends if the workdeck is in or if the hull is bare. In my friend's case, he had already removed the deck for other reasons. So we were able to apply our "mold" to the outside of what remained of the transom and do our layup from the inside. Our "mold" was 5/8 junk plywood covered with Malamine sp? bent into sawn 2x6's then screwed to the outside of the old transom edges w/ sheetrock screws after heavily scarfing the old transom edges. As I recall it came out looking good and not knowing the strength required we laid up many too many layers just in case. A sawn 2x6 along the top edge provided the "mold" for the transom deck lip.
If you have to layup from outboard, you are in for a lot more fairing and finishing.
Thank you both for your inputs. I am currently looking for a DE to fish tuna out of however a lot of the boats in my price range are open transomes. My dream boat is a 35 RP and there are a few open transome ones currently on the market. If I pull the trigger I will post the entire project on here and hopefully be able to pick your brains about any problems I run into thanks again
I am planning on glassing in my transom and adding a door and swim platform. The transom insert is the original transom that was cut out and is in two pieces with a teak wash board. It is heavy and awkward to remove as often as my little ones want to swim. I am also looking for any advice and guidance. My plan was to get the transom pushed out to the original curve of the transome and glass in vertical posts to hold the form. Glass the seams fill and fair and cut the door. If anyone has input it would be appreciated. I'm not trying to hijack this thread but thought we could trade some ideas since it seems we are doing similar projects.