A neat alternative to replacing rotten stringers is to rebuild your boat the way Chrysler built boats in the 60's that are still around today: Completely remove the floor, stringers, and any foam (wet or otherwise). Then cut and fit in the new floor using 5/8" plywood glassed on the bottom . Epoxy the floor in place. Cut 6 or 8 2" holes in the floor and pour foam in the holes and allow it to expand and come out the holes. Once cured, cut off the excess coming out the holes, fit in the 2" holes cut out with the hole saw, and glass over the top of the floor.
The foam sticks to anything and everything so the hull is attached to the floor. It is all one piece and more rigid than you will ever believe or get from stringers. And its fast because you save the time of making, fitting and glassing in the stringers. And it will not sink. Also, the new foams are much more resistant to absorbing water than the stuff from the 60's and 70's that you really don't have to worry about water absorption and soggy foam in your lifetime.
