A diesel-electric propulsion system similar to SAVe Line, where generating capacity can be reduced by up to 30% by introducing energy storage. The vessel can operate on batteries alone when in harbour or for limited periods with zero emissions, dependent on the specified battery capacity. Energy storage provides load smoothing, reducing the number of generators required to be operating. Those that are running operate at constant load and optimum efficiency. The batteries also store energy from other onboard equipment that regenerate power, like cranes and winches. For added safety there will always be continuously power available for the thrusters, and they can be operated with a dead switchboard. Hence biggest single system failure will be losing one thruster.