Guidelines published by the Ministry of Land, Infrastructure, Transport and Tourism stipulate that in the event of an emergency involving an auto-operated vessel, the crew on board should quickly take over a navigational watch so that they are ready to respond at any time. In this paper, we report the results of an actual test using a ship-handling simulator to measure the time required to take over a navigational watch, with the aim of defining functional requirements concerning the timing of issuing an alarm and the information to be notified to the navigation officer for them to take over a navigational watch appropriately.