Method for operating a drive system of a ship with two drive trains (3, 4), wherein each drive train (3, 4) comprises - a propeller shaft (31, 41), - a main drive (33, 43) embodied as an internal combustion engine for driving the propeller shaft (31, 41), - an auxiliary drive (35, 45) embodied as a rotary electrical machine, which can optionally be operated as a drive of the propeller shaft (31, 41) or driven by the propeller shaft (31, 41) as a generator, - and has a converter (36, 46) assigned to the auxiliary drive (35, 45), by means of which a frequency of an AC voltage supplied to the auxiliary drive (35, 45) and generated by the auxiliary drive (35, 45) can be changed, and - each auxiliary drive (35, 45) can be operated via the converter (36, 46) as a generator driving the other auxiliary drive (35, 45), - and the auxiliary drives (35, 45) are constructed and interconnected such that both propeller shafts (31, 41) can only be driven by means of work performed by precisely one main drive (33, 43), - by a first auxiliary drive (35, 45) being operated as a generator for generating electrical energy from rotations of a first propeller shaft (31, 41) directly driven by the main drive (33, 43) - and the second auxiliary drive (35, 45) being operated as a drive of the second propeller shaft (31, 41) driven by the first auxiliary drive (35, 45), wherein - a drive capacity for driving the two propeller shafts (31, 41) in a first capacity range is only yielded by precisely one main drive (33, 43), wherein - a first propeller shaft (31, 41) is directly driven by the main drive (33, 43) - and the second propeller shaft (31, 41) is driven by means of electrical energy, which is recovered from rotations of the first propeller shaft (31, 41) by means of a first auxiliary drive (35, 45) operated as a generator and is used for driving the second propeller shaft (31, 41) by means of the second auxiliary drive (35, 45), and wherein - a drive capacity for driving the two propeller shafts (31, 41) in a second capacity range is only yielded by precisely one main drive (33, 43) and capacity extracted from the on-board power supply, wherein - a first propeller shaft (31, 41) is directly driven by the main drive (33, 43) - and the second propeller shaft (31, 41) is driven by means of electrical energy, part of which is extracted from the on-board power supply and a second part of which is recovered from rotations of the first propeller shaft (31, 41) by means of a first auxiliary drive (35, 45) operated as a generator, and which is supplied to the second auxiliary drive (35, 45) via the converter (36, 46) assigned to it and is used to drive the second propeller shaft (31, 41) by means of the second auxiliary drive (35, 45) operated as a motor. - a propeller shaft (31, 41), - a main drive (33, 43) embodied as an internal combustion engine for driving the propeller shaft (31, 41), - an auxiliary drive (35, 45) embodied as a rotary electrical machine, which can optionally be operated as a drive of the propeller shaft (31, 41) or driven by the propeller shaft (31, 41) as a generator, - and has a converter (36, 46) assigned to the auxiliary drive (35, 45), by means of which a frequency of an AC voltage supplied to the auxiliary drive (35, 45) and generated by the auxiliary drive (35, 45) can be changed, and - each auxiliary drive (35, 45) can be operated via the converter (36, 46) as a generator driving the other auxiliary drive (35, 45), - and the auxiliary drives (35, 45) are constructed and interconnected such that both propeller shafts (31, 41) can only be driven by means of work performed by precisely one main drive (33, 43), - by a first auxiliary drive (35, 45) being operated as a generator for generating electrical energy from rotations of a first propeller shaft (31, 41) directly driven by the main drive (33, 43) - and the second auxiliary drive (35, 45) being operated as a drive of the second propeller shaft (31, 41) driven by the first auxiliary drive (35, 45), wherein - a drive capacity for driving the two propeller shafts (31, 41) in a first capacity range is only yielded by precisely one main drive (33, 43), wherein - a first propeller shaft (31, 41) is directly driven by the main drive (33, 43) - and the second propeller shaft (31, 41) is driven by means of electrical energy, which is recovered from rotations of the first propeller shaft (31, 41) by means of a first auxiliary drive (35, 45) operated as a generator and is used for driving the second propeller shaft (31, 41) by means of the second auxiliary drive (35, 45), and wherein - a drive capacity for driving the two propeller shafts (31, 41) in a second capacity range is only yielded by precisely one main drive (33, 43) and capacity extracted from the on-board power supply, wherein - a first propeller shaft (31, 41) is directly driven by the main drive (33, 43) - and the second propeller shaft (31, 41) is driven by means of electrical energy, part of which is extracted from the on-board power supply and a second part of which is recovered from rotations of the first propeller shaft (31, 41) by means of a first auxiliary drive (35, 45) operated as a generator, and which is supplied to the second auxiliary drive (35, 45) via the converter (36, 46) assigned to it and is used to drive the second propeller shaft (31, 41) by means of the second auxiliary drive (35, 45) operated as a motor.