The presence of any structure in the sea is a potential hazard to shipping navigating in its vicinity. It is therefore of considerable interest both to mariners and to engineers placing structures such as oil platforms in the sea to try to assess the attendant risk of collision, with such a structure.

We have over a period of time attempted several methods of assessing these risks and it was felt important to link this with our work on marine traffic flows, as experience of the traffic patterns in the southern North Sea was a useful input to the study. Hence we considered an area in the southern North Sea, to the eastwards of the outer Thames Estuary as far as the Middlebank and between the parallels of 51° 08´N and 52° 15´N, since we wished to look at the offshore situation; the area is nowhere less than 3 miles from the coast.