Rhinoceros and Maxsurf for all your boat design needs. Both based on similar mathematical/modelling methods and both fairly intuitive with good help.

Rhino, from McNeel & Assoc, can be downloaded free for 25 saves or prints. Maxsurf, from Formation Design Systems, has a no save demo. Both are unlimited use otherwise.

http://www.rhino3d.com/index.htm
http://www.formsys.com/