With the known methods for the operation of a vessel (1) having a propulsion system with waste heat recovery, wherein at least one main engine (2) drives a shaft unit (3) coupled with a vessel propeller (4), waste heat of the main engine (2) is transmitted to a working substance, thereby evaporating the working substance. The evaporated working substance is then relaxed and the energy thereof is converted into mechanical energy. The mechanical energy in turn is converted into electrical energy, supplying electric consumer (13, 15) of the vessel with power.