I chose to go the wood replacement route because Seacast is significantly more expensive and seems very geared toward
outboards. The cost to go Seacast was around $1600, cost for wood -
$400. If done right, wood will last longer than I'll ever own the boat,
so I'm fine with it. I also chose to replace the whole thing versus a
partial repair because I'm like that. A partial repair or a "patch
job" would bother me to no end. Keep in mind I'm not saying Seacast is a bad product or that you can't do a patch job. I'm sure those solutions have their advantages.
To remove the transom, you'll need to remove the engine, drive and all the wiring from the engine bay and bilge area. Depending on your boat, you may even need to remove the deck, or cut off the back section to get to the wood. I'm lucky in that my transom can be removed and re-installed with the deck intact. If you do need to remove or cut it, I don't cover that here.
Engine and Drive First
In the following picture, the engine and drive are removed and I've started cutting things away. Removing the engine from one of these things is easier than removing a car engine, but there's a few things to consider. You will need an A-frame hoist, not a cherry picker (unless you can get the boat off the trailer, which I don't recommend doing if you don't have to) as a typical cherry picker can't get the engine high enough to clear the gunwales, and you have to understand how to disconnect your trim pump. Don't just unplug the lines (the process is described in your engine/drive maintenance and repair manual). Label everything, keep everything clean if you can. Bag any small parts, and get a service manual. You'll thank yourself for that last one!
You may need to remove more things, like seats or other structures. I didn't; my engine compartment is pretty big.
Getting to the Transom
To get to the entire transom, I had to cut the stringers and battery trays back a bit (about 8" on the stringers, about 12 at the battery trays). Stringers are the tall (approximately 6"x6" boxes) that run the length of the boat. The engine probably sits on the stringers. The battery trays are the flat surfaces to the sides of the engine. Don't worry about cutting your stringers, but only cut back what you need to in order to access the transom. Unless, as was with my boat, your stringers are rotten. Then cut away, Jack. You're not going to make anything worse. Again though, only cut out the rotten stuff. We'll fine-tune our cuts later. I found a bunch of floatation foam under my battery trays. It's not hard to remove, just stick a pry bar under it and shove, it'll come out in chunks. Be careful that you don't cut through the hull. It's fixable if you do, but is simply more work you don't want to have on your todo list. Tools I used were: sawzall with a short wood blade, rotozip with the general purpose bit, gasket scraper (mostly as a small pry bar), thin, strong pry bar (the kind used for removing trim and working with doors and such), a big tire iron (for leverage when I needed it), and a dead-blow hammer.
When cutting with a sawzall be very aware of where your blade tip is going. It can disappear behind stringer boxes and other structures, and it can slice through your hull before you know it. Cut the tops off everything first so you can see what's underneath, then decide whether you need to cut further, or if you can pry the wood loose from the fiberglass holding it down and remove it that way.
Remember to take photos of and measurements for anything you remove. Getting your engine mount height wrong during re-construction is a show stopper.
Tearing it out
My process for transom removal was simple, but not easy. I set the depth of the rotozip to just enough to go through the wood but not into the fiberglass, and cut grooves from top to bottom about 12" apart. (this went through rotozip bits like CRAZY). I then used the gasket scraper, pry bar and dead blow hammer to "chisel" enough away that I could fit the pry bar between the fiberglass skin and the wood and with enough pounding and moving the prybar around, I could eventually pop the transom out in chunks. Removing the transom is no magical process. You will fight, swear and bleed. It'll come out though, just keep working at it.
This was typical of the crap that came out when I couldn't get big chunks of the transom out. I had to settle too often for tiny pieces, but I stuck with it.
I used a rotozip around the perimeter of the transom, cutting away any fiberglass that was holding the transom to any part of the boat. DO NOT underestimate how well a 1" high lip of fiberglass or even just resin can hold the wood in the boat. Cut it away before trying to pry the transom parts out and you will save yourself a TON of work.
See the dark spot on the lower right? That's where it was rotted the worst. It was pretty bad around the bottom of the drive hole too, but was almost missing in that area to the right. Gross.
On to the next step: Prepping for the New Transom