In the first six months of 1979 there were six collisions in the area of the Dover Strait (extending from the Greenwich meridian to 2° 30′ E and from 50° 30′ N to 51° 30′ N) that involved at least one vessel of 500 grt or more. (Two further collisions took place during the next four months.) Collisions have not occurred in these waters at a rate of one a month since 1969. Yet since then there have been several notable changes that should have led to greater safety. The IMCO traffic separation scheme has been made compulsory for ships of all nations through the coming into force of the new Collision Regulations on 15 July 1977. Secondly, the Channel Navigation Information Service was established in England in 1972, and it and its counterpart in France have been monitoring the traffic by radar and making regular broadcasts for more than five years. Finally, traffic discipline has steadily improved, as measured by the number of ‘rogue’ vessels that are held to contravene the routing scheme (Fig. 1).

To decide whether this spate of collisions represents a marked deterioration in navigational standards it is necessary to do rather more than merely count occurrences (Fig. 2). In the first place, any evaluation must take account of the amount of damage to the ships involved and to the environment, and of deaths and injuries to personnel.