Circumstances of collision. Over a fourteen-year period more than 80 per cent of all collisions in the Dover Strait occurred in reduced visibility. The majority of the ships concerned were carrying radar, so a possible inference is that the information available from this source is less effective than direct vision in successfully resolving close-quarters situations. The introduction of the Imco recommended routing scheme, the support measures mounted from the two sides of the Channel and sustained improvements in navigation have together led to a significant reduction in the number of collisions in poor visibility. However the risks, though reduced, remain higher than in good visibility.

The circumstances leading to collision are very rarely known reliably or in any detail, but such facts as are known can be helpful if treated with caution. Reference 1 gives details of manoeuvres preceding 47 collisions, nearly all in fog, where helm orders were noted in crew reports (Table 1). About three-quarters of these collisions (and of collisions as a whole) occurred when ships were on opposing courses, as defined by their ports of call.