a ship maneuvering device rotates a propeller at a lower rotational frequency than the rotational frequency of the minimum idling speed of an engine . a control device has a crawling speed navigation mode . a crawling speed navigation mode button that selects whether or not to execute the crawling speed navigation mode is connected to the control device . when the crawling speed navigation mode is selected , and the amount of operation of a joystick lever is at or beneath a baseline amount of operation ms , the control device causes the rotational frequency n of the engine to be the rotational frequency nlow of the minimum idling speed , and in accordance with the amount of operation of the joystick lever , varies the duty ratio d , which is the fraction of time t 1 that a main clutch is engaged in a predetermined cycle t , within a range of no greater than 100 %.