Even without being an aerodynamic engineer, to me this notion seems half-crocked at least. But, assuming you were able to build such a high velocity fan, light enough to have little affect on boat trim & balance, but powerful enough to produce a force great enough, it perhaps is possible.
With that said, the orientation of the "fan" would be most effective if at a beam or close reach, and at a far enough distance from the sails to produce enough low pressure on the leeward side for forward propulsion. This is where your idea becomes a ridiculous fantasy.
True Blue . . .
sold the Nauticat