As already stated, rot is largely a function of how well the boat was cared for. I bought a 1997 Crownie last fall, and was very concerned about rot. I started with the checklist that is stickied at the top of the forum... It was a great help for me - not just about rot by the way.
I "tap tested" around the motor mounts, walked every inch of floor that I could get my feet on, and then took a rubber mallet and tapped the entire floor looking for soft spots.
Mine seems to be solid. Im not exactly a seasoned veteran, but I did grow up around boats. This is the first one I have owned however. I think I had a couple of things going for me:
- Previous owner was a meticulous 70+ year old man who had obviously cared for the boat well. It was garaged 15 of 17 years, and he took me through all the maintenance he had done in excruciating detail. He showed me every inspection point, and fluid reservoir - not that I necessarily needed that, but it was indicative that he had done the work, and actually did monitor things.
- The boat was a Colorado boat... it is very dry here, technically we are a high desert. So even things that get wet dry out quickly. I took the boat out 4 times last fall after I bought it, would leave the cover off driving home, and the interior would be bone dry at the end of the day.
Core samples/Marine Survey is the way to go, but most owners are not going to let you core sample the boat before you buy it. Perhaps a putting contingency on the bill of sale? I had one on mine contingent on a satisfactory water test.
I helped my brother replace a floor in his '74 Silverline. Its possible, but not fun. Even putting the carpet back in was a joy - the glue fumes when getting it down under the bow gave me a 4 alarm headache for a day.
Good luck!
