Actually, a fan blowing air at a sailboat sail would cause the boat to move. They say a sailboat on a close reach "makes its own wind" -- with a fan toward the bow, it would literally be true.
And if you put the fan at the stern blowing forward, the system would act like a jet engine with a thrust reverser (only facing the other way, of course). At least I think the curvature of the sail would deflect enough flow aft to generate net forward thrust.