I've been researching transom replacements, and in every blog or video they cut either the inner or outer skin, but not *both*. They then go to a lot of effort trying to get the core to separate from the remaining skin.
Why is this?
It seems to me that just cutting all the way through, replacing the core, then re-skinning both sides would be *much* easier.
I was able to cut the inner layer out on my 59 Whitehouse and leave the outer skin. I used one of those oscillating tools which was a lifesaver. Each layer of marine plywood was coated with resin and a layer of chop strand in between. Because the transom is curved I did it all in one day and clamped it to form the curve. I actually ended up thicker as I used 3 layers of 1/2 inch. Then glass mat and layers of mat to rebuild the inner layer bonding and attaching to the boat bottom. This way preserved the rather thick exterior
IMHO if you cut out the entire transom inside and out you will compromise the integrity and strength. A few things to consider if you think you can put on a new outer/inner skin. 1. the boat flexes quite a bit while in the water and a "joint" that you feel is pretty strong when on a trailer will fail. 2. If you're hanging an outboard on the back with any horsepower it's going to weigh200 t0 300 pounds. Tilted up on a trailer puts enormous leverage on the transom. While under way the motor is pushing the boat so you essentially have X amount of horsepower pushing on that transom, that's a lot of strain.
Replacing a transom is not a quick easy job and just about all of them are different in some manner. I've done them both ways either inside or outside but never cut an entire transom off.
Here is a way that I installed a new on on an older 18' starcraft. By cutting out a main section on the outside but leave the outer corners, bottom, top intact you can access the rotted portions and maneuver new pieces in and then glue and skin them. 3M 5200 glue will forever hold the sections in place. After about a week of dry time you can replace the skin that you removed and make the cosmetics.
On this boat instead of sandwich plywood I went a different route and used 2X12 treated glued to the inside and then layered glass on the inside and outside before replacing the outer skin. Took some maneuvering to get everything to fit but you could pull stumps from the shore and never even crack a cosmetic repair.
I wasn't actually planning on cutting the entire transom out. I figured there was a good reason for leaving a skin. I was just wanting to understand the reason. <g>
On the Express, I'll be keeping the outer skin, since it's thicker. Although, the port side of the motor mount *has* punched through the skin. Just like a cookie cutter. Punchout's still attached at the top, though.
Now all I have to do is convince my wife to let me use Coosa board for the fix....