Speeds, lengths and positions of ships were measured by "Pass Time Recording Method" on the Keihin Canal where ship lengths were observed to be mostly in between 10 and 50m and speeds ranging from 5 to 10 knots. The effective area, necessary for the deduction of the naval traffic capacity was obtained from the distribution of the relative positions of the following ships and it is about 200m in the course direction and about 120m in the direction perpendicular to the course. The effective area of ships which following ships mostly avoid to enter is also obtained from relative positions of ships observed on the Uraga Strait by "Ship Locating Recorder" and it is about 700m in the course direction and about 350m in the direction perpendicular to it for such ships whose lengths are in between 50 and 250m and speeds from 6 to 20 knots.
