A power source device includes a switching circuit configured to switch the power supply mode between a first power supply mode, in which power is supplied to a drive circuit for an electric motor byonly a main power source, and a second power supply mode, in which power is supplied to the drive circuit utilizing both the main power source and an auxiliary power source. A control device includes:a first control unit that controls the switching circuit on the basis of a value that matches power consumption by the drive circuit; and a second control unit that switches the power supply mode toa second power supply mode by controlling the switching circuit during sailing stop.