AVS Hull is A Very Simple Hull editor for plywood boat design. The program allows you to define the shape of the hull and then it computes the shapes of the panels you will need to create the hull. You can export offset files that tell you how to mark the plywood for cutting.
The software is available here
A blog showing the building process as well as discussing features of the program is available here.
A (preliminary) users manual for the software is available here.