Strange question and I'm not looking to replace a transom but I came across a photo elsewhere and thought I'd ask the brains trust on OSO.
Looks so simple but could it be done from outside rather than inside and still be done properly? I'll guess it would have limitations depending on how bad the boat is, stringers or cored hull etc.

RR

Rak, anything can be done. I built a completely new transom when I shortened my 35' Cigarette to 28'. In the one pictured it looks like there are stringers inlet into the plywood and some openings along the bottom. I would question the stringers integrity if so and the other tabbing in the bilge. Looks like a liner is involved and that certainly complicates things. Bob.

I doubt the stringer/transom interface can be done correctly from the outside.

I have a fiberglass repair book somewhere where that same process is used on a 20 ft O/B.

Looks like a lot of extra work.

I can see where it would be a better option on outboard boats with a well. That way you don't have to cut the deck up.

I can not tell how many outboard boats / BASS BOATS 21 ft and down are foamed and the top cap can not be separated. Its stuck completely to the hull because of the whole hull cavities and space voids has been flotation foamed.

I’ve done several and would put their strength against OEM and bet heavy on mine.

I do them if I can’t get to it on the inside.

I saw the pic while reading somewhere else and the poster (a professional glass guy) was asked how much it cost to do a transom. Answer, starting from about $1,000. Sounds awfully cheap but reading a few responses confirms it could be fine in some cases. ($1,000 is probably a simple outboard transom on a 16 footer.)
Thanks for the replies, hope it helps someone one day.

RR

the problem with doing a transom from the outside is actually two fold. First off its just plain wrong i dont care who says its ok . . . its just is. I'm not saying it "cant" be done, there are some with the talent to pull it off, i just dont think its worth the effort. You might get away with it on some low hp Alpha boat or low HP boat but I'd just not want to risk it any further. There are just so many reasons . . . second is in my experience some people pull this move to avoid disturbing any of the inside structure, turning a blind eye to what is also most likely bad as well. By only accessing a transom from the outside you literally tie your hands into not being able to asses the other critical areas of the boat . . . . . just my .02 cents . . . .