Just a late thought - have a look at
http://modelboats.hobby-site.com/The site owner has a liking for the simple kits that were around in the '50''s. The plans are available for download, and can be resized as required. The originals were printed balsa, so tracing and cutting should be no problem. Radio was non existent then, but batteries are smaller, motors are more powerful for a smaller sixe, and fitting a modern radio should be no problem.