A marine steering system operable in either power steering or manual hydraulic modes. The system employs a modified helm pump having a single rotatable input shaft connectable to a steering wheel and dual hydraulic and electronic output. An encoder, such as an optical incremental encoder or hall effect device, is mechanically coupled to the input shaft for generating an electronic steering control signal representative of the change in position of the steering wheel. In the power steering mode, the electronic steering signal is processed by an amplifier controlling the operation of an auxiliary pumpset connected to the rudder steering cylinder. A bypass manifold disposed between the helm pump and the steering cylinder disables the hydraulic steering system in the power steering mode. In the event of power failure, the bypass manifold valves are opened and the system automatically switches to manual hydraulic steering.