Abstract: An on-board marine electrical power generator (14) containing a conventional four-stroke, water-cooled outboard motor engine (50) coupled to an alternator (52) upon a transportable frame (44) suitable for mounting on-board a boat. In one embodiment, the crankshaft (60) of the engine extends vertically and is coupled to a vertically oriented rotor (72) of the alternator, either directly or laterally spaced from the engine shaft. In another embodiment, the engine is modified for operation with its crankshaft extending horizontally. The physical size of the overall package is advantageously within a range suitable for installation on pleasure boats, even below deck.