Re: cutting aluminum transom down
I saw a couple boats that it had been done to... turned out fine.. These were tiller steer type fishing/utility boats. I talked to the guy about how he did it. IIRC, he lifted off the top trim piece, marked the new line, zipped of that piece with a sabre saw, and then put the trim piece/cap back on. Looked factory when he was done. Mind you, there were simple boats without splashwells, so that would complicate things.
By the way, I think the difference should be closer to 5"... shouldn't it?? My short shaft transoms measure ~16" from the top of the transom down to the bottom. That fits a "15" shaft" motor. I'm guessing your transom measure's ~21" now (?) to fit a 20" shaft motor.
Depending if it's a bigger, remote steer boat, you might want to re-think cutting the transom down. All that material you're cutting away is your freeboard, so you might make it relatively easy to swamp the back end.
Also if you ever decide to repower with a new/newer engine, you may find it difficult to find anything over about 30 hp in short shaft. Even fishing type boats, most new motors over 9.9's seem to be long shaft out there, so more people are finding themselves having to build up their transom rather than cut it down....
If you do cut it down, make sure you get the splashwell right and functional and that you seal up the spot where your steering comes through the splashwell (if it does). Even if the splashwell never got wet before, it would be much more likely to see water with the back cut down.
good luck.
