A vessel includes electric connectors for receiving one or more direct voltages from a shore-side electric power system. The vessel includes a transmitter for transmitting, to the shore-side electric power system, a control signal enabling the shore-side electric power system to control the one or more direct voltages to be suitable for the vessel. Alternatively, the vessel includes one or more controllable direct voltage converters and a control system for controlling the one or more controllable direct voltage converters to convert the one or more direct voltages into one or more direct voltages suitable for the vessel. The vessel can be for example a ship, a boat, or a ferry.