In case of a collision between a large vessel and a small craft, a compass bearing of the small craft observed from the bridge of the large vessel can appreciably change when the collision place on the hull of the large vessel is at a distance from her bridge. It means that risk of collision may sometimes exist even when an appreciable bearing change is evident. In order to investigate how the seafarers understand this phenomenon, the author has referred a report of the collision between the Japan Maritime Self-Defense Force vessel Ōsumi and pleasure boat Tobiuo published by the Japan Transport Safety Board and has made a simulator scenario. The scenario gives a moving image of a small craft approaching to the bow of a large vessel with a collision course like Ōsumi and Tobiuo. Thirty three seafarers have watched the small craft from the bridge of the large vessel reproduced by a ship-handling simulator. About half of them have misjudged that the small craft will pass the bow of the large vessel because the compass bearing of the small craft appreciably change to ahead. It is verified that seafarers can sometimes misjudge risk of collision due to appreciable bearing change.
