Transportable, compact power supply unit (100; 200; 300) for supplying a watercraft, in particular an on-board supply system of the watercraft, with electrical energy, and in particular for arrangement on the watercraft, containing in a plurality of transport containers connectable with each other, wherein the plurality of transport containers are transportable as a single connected unit: - at least one internal combustion engine operable with gas, in particular natural gas, - at least one generator for power generation drivable by the at least one internal combustion engine, - at least one control device for the at least one internal combustion engine and/or at least one control device for the at least one generator, - at least one fuel processing device for the at least one internal combustion engine and/or at least one exhaust gas purification device (109; 209) for the at least one internal combustion engine, and - at least one fuel storage device, wherein the fuel of the fuel storage device is gas, in particular natural gas, which is preferably present as liquid gas, particularly preferably as LNG, characterized in that the power supply unit (100; 200; 300) comprises a first structural unit (101; 201; 301) forming a fixed unit and at least a second structural unit forming a further fixed unit, wherein the first structural unit (101; 201, 301) contains - the at least one internal combustion engine, - the at least one generator for power generation drivable by the at least one internal combustion engine, - the at least one control device for the at least one internal combustion engine and/or the at least one control device for the at least one generator, and - the at least one fuel processing device for the at least one internal combustion engine and/or the at least one exhaust gas purification device (109; 209) for the at least one internal combustion engine, wherein the second structural unit contains - the at least one fuel storage device, wherein the first structural unit (101; 201; 301) and the second structural unit can be docked together and detached from one another, and/or in that the structural units (101; 201; 301; 111), both individually and docked to each other, are configured in predetermined grid storage dimensions of standardized transport containers, wherein in particular the grid storage dimensions of ISO transport containers are selected as predetermined grid storage dimensions. - at least one internal combustion engine operable with gas, in particular natural gas, - at least one generator for power generation drivable by the at least one internal combustion engine, - at least one control device for the at least one internal combustion engine and/or at least one control device for the at least one generator, - at least one fuel processing device for the at least one internal combustion engine and/or at least one exhaust gas purification device (109; 209) for the at least one internal combustion engine, and - at least one fuel storage device, wherein the fuel of the fuel storage device is gas, in particular natural gas, which is preferably present as liquid gas, particularly preferably as LNG, - the at least one internal combustion engine, - the at least one generator for power generation drivable by the at least one internal combustion engine, - the at least one control device for the at least one internal combustion engine and/or the at least one control device for the at least one generator, and - the at least one fuel processing device for the at least one internal combustion engine and/or the at least one exhaust gas purification device (109; 209) for the at least one internal combustion engine, - the at least one fuel storage device,