In retrospect, cutting/grinding/destroying/ all the rotten stuff was the easy part. Unfortunately, because the boat had no internal super-structure, it was sagging over the sides of the trailer, which is not the 'designed' shape of the hull. Before I could start replacing the stringers and bulkheads, I first had to return the hull to its true shape. My boat has what are called 'hard chines'--which means the sides go more or less straight down to the waterline, then the hull curves gently to the centerline, and curves gently at the same arc to the other side. In order to recreate this, I had to figure out some way of hoisting the entire boat off the trailer to return it to the true shape, then build a cradle to match that true shape. This would ensure that the hull would follow the proper arc, then I could cut out the stringers and bulkheads and epoxy them into place.
Of course, boats do not have any right angles, so in order to do this, I had to learn the subtle art of 'spiling' which is the term for tracing an arc from one object onto another using an offset. I had to build a separate rig for the cradle and each individual stringer and bulkhead, to keep the piece of plywood onto which I was tracing the arc from moving. There are three different directions in which the plywood can move (pitch, roll, and yaw, like an airplane) so the rig had to account for all three of these. Then to keep the marker itself at a constant offset height I cut an old broom handle to size, and to keep it from moving side to side, I drilled a Sharpie-sized hole at the top. This all seemed to work fairly well, but took a lot of trial and error.
Once I had all of the wood bits cut to the proper shape, it was time to epoxy them into place. Epoxy is an amazing adhesive. It comes in two parts, neither of which are super-sticky on their own, but when you mix them they combine in an exothermic reaction that results in a virtually bomb-proof material. When fillers are added, such as sawdust or colloidal silica, the epoxy becomes goopy and almost peanut-buttery, and when this version of the epoxy dries it is so strong it can actually be considered a structural part of the boat. Fortunately, I did not blow anything up as I made my way up the epoxy learning curve.
My standard outfit for grinding fiberglass and epoxy.
After many, many hours of work I had a bare hull to work with.
Unfortunately, to repair the boat properly, I had to determine the proper hull shape. To maintain the proper hull shape, I had to build a cradle. To build a cradle, I had to trace the hull shape, which means I had to hoist the entire aft end of the boat off the trailer, by using a 3:1 block-and-tackle system attached to the rafters. This was a very educational process.
Here is the cradle I built, after spiling the transverse curve of the hull. The padding is composed of old cloth diapers.
Once the boat was safely lowered down onto the cradle, I could start spiling the stringers and bulkehads. This picture shows the rig I contrived for the port-side stringer.
Another view of the spiling rig. I moved a variation of this setup around the boat until I had traced all of the stringers and bulkheads.
The super-duper high-tech device I contrived to hold the marker steady as I traced the shape of the hull onto the plywood.
One of the bulkheads, before I cut out the opening for the deck.
All of the stingers and bulkheads, cut out, sanded and epoxied in place.
After the undercoater was applied.