THE PILOT WAS EN ROUTE WHEN HE NOTED A PARTIAL LOSS OF ELECTRICAL POWER AND THAT THE FUEL GAGE WAS DE-ENERGIZED. HE CONTINUED THE FLIGHT, BUT DURING AN ILS RUNWAY 29 APPROACH AT THE DESTINATION, A TOTAL LOSS OF ELECTRICAL POWER OCCURRED. THE PILOT DECIDED TO DESCEND BELOW THE CLOUDS INTO VMC, WHICH HE ENCOUNTERED AT ABOUT 400 FEET MSL OVER CASCO BAY. HE STATED THAT HE WAS READING A CHART TO LOCATE THE DESTINATION AIRPORT, WHEN THE ENGINE LOST POWER. THE PILOT DITCHED THE AIRPLANE IN THE BAY, ESCAPED FROM THE AIRPLANE, AND WAS RESCUED BY COAST GUARD, BUT THE PASSENGER DID NOT ESCAPE FROM THE AIRPLANE. DURING AN EXAMINATION OF THE AIRPLANE, ABOUT 15 GALLONS OF FUEL WAS DRAINED FROM THE LEFT TANK AND ABOUT ONE HALF GALLON WAS DRAINED FROM THE RIGHT TANK. THE FUEL SELECTOR WAS FOUND POSITIONED TO THE RIGHT TANK. THE REASON FOR THE LOSS OF ELECTRICAL POWER WAS NOT VERIFIED.