In my opinion, anything can be made R/C. I have seen the 1/350 Tamiya kits built as R/C ships, and I have seen a 1/700 scale Iowa built as R/C.
http://groups.msn.com/ModelersAndHobbyForum/portlandregatta1.msnw?action=ShowPhoto&PhotoID=84
1/72 and 1/700 come together on the pond
http://groups.msn.com/ModelersAndHobbyForum/portlandregatta1.msnw?action=ShowPhoto&PhotoID=88
With todays (and tomorrows) technology, All it takes is a solid goal to make model move. The biggest model kit available is the Lindberg Blue Devil. It was actually my first r/c boat.
This is not the most accurate or best sailing model, but there is running equipment and information in the kit to get it sailing on a small pond. The biggest drawback for any r/c conversion of a model kit is weight. But even this can be over come with the correct battery cofigurations and careful planning.
If you are up to the larger investments of fiberglass hulls and scratch building then the scope of your project is limited only by your imagination and pocket book.
See Modelwarships underway for more inspiration.
http://wmunderway.8m.com/home/home.htm
And you can get plenty of help at R/C Groups - boats if you get stuck on anything.
http://www.rcgroups.com/forums/forumdisplay.php?f=54
Here is a typical plastic model conversion done by Tony O in the UK
http://www.rcgroups.com/forums/showthread.php?t=173262&highlight=revell+trawler