A propulsion system controller configured to control a propulsion system of a watercraft, said propulsion system comprising: - a switchboard (1,2); - a further switchboard (1,2); - an inter switchboard converter coupled to said switchboard (1,2) and said further switchboard (1,2), said inter switchboard converter comprising a first power converter (4,5) coupled to said switchboard (1,2), a second power converter (4,5) coupled to said further switchboard (1,2) and said first power converter (4,5), and a battery coupled to said first power converter (1,2) and said second power converter (1,2), - one or more electric propulsion motors (16,17) coupled to said switchboard (1,2); and - one or more electric generators (11,12,13,14) coupled to said further switchboard (1,2), characterized in that said switchboard is a variable voltage switchboard, said further switchboard is a fixed voltage switchboard, and said controller is configured to be set to one of a plurality of modes, and is further configured to: - in a first of said plurality of modes, control said one or more electric generators (11,12,13,14) to generate electricity at a constant voltage and a constant frequency, to control said second power converter (4,5) to convert AC power from said one or more electric generators (11,12,13,14) to DC power with a voltage suitable for said battery, and to control said first converter (4,5) to convert DC power from said second power converter (4,5) and said battery to AC power with a voltage and a frequency corresponding to a speed or power selected for said one or more electric propulsion motors (16,17), and - in a second of said plurality of modes, control said one or more electric generators (11,12,13,14) not to generate electricity and to control said first converter (4,5) to convert DC power from said battery to AC power, said AC power being provided to at least said one or more electric propulsion motors (16,17). - a switchboard (1,2); - a further switchboard (1,2); - an inter switchboard converter coupled to said switchboard (1,2) and said further switchboard (1,2), said inter switchboard converter comprising a first power converter (4,5) coupled to said switchboard (1,2), a second power converter (4,5) coupled to said further switchboard (1,2) and said first power converter (4,5), and a battery coupled to said first power converter (1,2) and said second power converter (1,2), - one or more electric propulsion motors (16,17) coupled to said switchboard (1,2); and - one or more electric generators (11,12,13,14) coupled to said further switchboard (1,2), - in a first of said plurality of modes, control said one or more electric generators (11,12,13,14) to generate electricity at a constant voltage and a constant frequency, to control said second power converter (4,5) to convert AC power from said one or more electric generators (11,12,13,14) to DC power with a voltage suitable for said battery, and to control said first converter (4,5) to convert DC power from said second power converter (4,5) and said battery to AC power with a voltage and a frequency corresponding to a speed or power selected for said one or more electric propulsion motors (16,17), and - in a second of said plurality of modes, control said one or more electric generators (11,12,13,14) not to generate electricity and to control said first converter (4,5) to convert DC power from said battery to AC power, said AC power being provided to at least said one or more electric propulsion motors (16,17).