A hybrid marine power train system is provided that facilitates selective use of one of multiple prime movers for powering and driving a boat. The multiple prime movers can include an internal combustion engine and an electric motor which can itself be part of a motor/generator assembly. The system further includes a power-take-in assembly that can have either an active or passive clutching device for selectively importing power from the prime movers into the transmission. The system is configured so that the second prime mover occupies relatively little space within an engine compartment of the boat, for example when compared to an amount of space occupied by the first prime mover and transmission. Since the second prime mover occupies relatively little space within the engine compartment, the system can be readily retrofitted to existing marine power train systems.