In an outboard motor control system, equipped with two outboard motors and actuators for steering, changing shift position and regulating engine speed, two navigation units responsive to operations of the operator for producing outputs indicative of actuator operation commands, two ECUs that control the operation of the actuators based on the outputs from the navigation units, an output forwarding ECU which forwards the outputs of one of the navigation units to the ECUs, and two switchover buttons for changing the outputs to be forwarded. Therefore, only the set of outputs for the one navigation unit selected by the operator is sent to the ECUs. In other words, in the case where multiple navigation units are provided, use of the navigation units is limited to a desired one thereof, so that the outboard motors can be stably controlled even when the control inputs to the individual navigation units are different.