I think you need to figure out just how bad the rot is. If the motor mounts have rotted out, you're going to need to replace the stringers. I don't believe that it is possible to repair them (and I tried almost every method possible to do so.)
Originally Posted by gogger
Turn some of the motor mount bolts and see if they can bite into good wood. If they can't, the first "repair" step to try and is to get some bolts that are 1-size larger. These might be able to find some good wood to sink into. If they don't.... either get insurance and head for deep water with the plug out, or be prepared for a big project.
The wood inside of the strings will be so saturated with water that the penetrating epoxy will never work. It can't bind or setup to anything with a high moisture content. When I cut my stringers open, water and mud poured out. And this was after I spent 12 months trying to dry it out with several dehumidifiers.
As far as other stop-gaps, be careful. I tried to "repair" my stringers with various methods. The engine in my boat ended up twisting when the mounts gave out. This caused the prop shaft to wear a hole through the shaft log. The hole in the shaft log caused the shaft seal to fail and my boat sank. Luckily I was able to get it to a place where the water was only about 2 feet deep, but.... knowing what I know now, I would have headed for deep water instead. I pulled the cap and replaced the stringers. That was before there was anyone on this board so I just figured it out myself.... I received quotes very similar to what you saw and didn't have any choice but to tackle it myself. In the end, I paid someone to reglass the stringers but I did everything else myself. It's not a project that I ever want to consider doing again but with the number of people that have documented the process on this board -- it's no longer as hard as it once was. Read through some of the pride and joy threads and you'll see some pretty good step-by-step projects.
Former owner of a 1987 Supra Saltare. Current owner of a Malibu 23LSV.