One of the guys in our group has successfully made an old pond boat into rc by putting a small cabin on deck housing a receiver and battery with a rudder servo. Sails are still manual but with a mid setting she sails well in most conditions.
Cloth sails can be improved without changing them by putting on a clear proofing.
I use thompsons water seal
which is totally clear and blocks the holes in the cloth so wind can't go through.
Tent waterproofer has the same effect and you can get a spray can of it from most tent outlets. This gives a much improved catchment to the sail area.