A ship drive system (10) according to the invention comprises at least one first and one second drive shaft (11, 12) for driving a respective propulsion unit (2), in particular of a water jet, wherein each of the electric drive shafts (11, 12) comprises at least one speed-variable generator (4) driven by an internal combustion engine (3, 6) for generating a motor voltage having a variable amplitude and variable frequency, and at least one speed-variable drive motor (5) that is supplied with said voltage and coupled to the propulsion unit (2). The first and second drive shafts (11, 12) can be switched from a first operating state, in which they are electrically disconnected from each other, to a second operating state, in which they are electrically coupled to each other such energy can be transmitted from the at least one generator (4) of the one drive shaft (11, 12) to the at least one drive motor (5) of the other drive shaft (11, 12). To this end, the at least one generator (4) preferably comprises a superconductor winding. A preferred use of the ship drive system (1) is found in trimarans.