As the term occlusive area is not defined so clearly in the marine traffic engineering, then the author defined the occlusive area from a point of ship maneuviring taking account of the characteristics of marine traffic flow in Japan. According to his definition, the occlusive area is a void area enclosed by the envelope of tracks of ship's relative motions around a certain ship. In this paper, some occlusive areas are shown using data obtained by radar. Qualitatively speaking, the shapes of the areas are similar to the shapes composed of stream-lines which can be seen in the fluid with ship-shape body, for different meeting conditions ; e.g. encounter, crossing and taking over.
