SolidNav has a line of electric motors for boats. Svend's in Alameda, CA has the "Traveler" model on display . . . an outboard. Stats in the owner's manual indicate an equivalent 4-hp from 3.0 kw. Here's the pitch:

"SolidNav proudly announces a real electric option for sailboats without an existing inboard, pontoon boats and for small craft that require reliable outboard performance. Our long shaft and remote engine controls make docking enjoyable without the dread of lethal oil sheens and clouds of foul smelling fumes. Actual outboard construction and solid frame construction position the traveler as the only choice for real world applications.

$2,499*"

http://www.solidnav.com/traveler.html

From my limited observation, the shaft and head should fit in the A-C well. Not sure, however, about the clearance distance from the aft bulkhead in the lazarette, as I did not have access to a measuring device.