strange transom and transom replacement brain storming

I fitted some transom furniture recently and was amazed at the lack of thickness of my transom. The boat was originally laid up for twin 150hp race outboards. Currently running single 250 outboard.

When I drilled a hole with a holesaw, it blunted my holesaw, yet the transom was probably not even 2" thick, although it has 2 foam ridges inside running horizontal too. Strangely when i cut it out it had wood, and foam, and a really tough horizontal which appeared to look like fibreglass laminate maybe 10mm thick, running through this strange core combination. All this got me thinking about if I dare replace it, maybe not now but someday....

In order to get a gel finish, why dont people lay a transom up off of the boat, on a flat surface, like glass for example, so a perfect finish can be obtained, SO gelcoat, then fibreglass, then the ply sandwich with more glass on other side of ply (roughly the size and shape of transom). Then once cured, or green. mount into boat and tab into hull. I cant find an reference to people doing it this way, so there must be a reason.

My other question, is how much tabbing should run off into the hull, and what thickness should a transom capable of 300hp be approx.

Thanks GT

 

I think I have found the answer to min and max transom sizes. Transom tabbing and layers of glass. But I still dont understand why people dont lay up a new gelcoat then transom on a flat sheet then trim, fit and tab. I must be missing something obvious.