The distribution of ship collisions in Japan is investigated and a method for estimating the number of collisions in harbours and straits is proposed, making use of maps of collision locations and the results of traffic surveys.

There are two major sources of information on marine casualties in Japan: the Report on Marine Casualty Statistics, made by the Ministry of Transport, and Report on Casualties Requiring Rescue, made by the Maritime Safety Agency. The former is based on the compulsory reports from either ship operators or owners, and casualties to foreign vessels are not included. A bibliography of collisions in the vicinity of Japan was made by taking the original report cards, overlapping data being carefully analysed.

This paper is primarily concerned with principles, not with practical implementation. It is therefore reasonable to start by constructing a simplified model of the physical situation in the hope that its analysis will provide guide lines for practical action.

Consider two vessels on a collision course in the open sea. An acceptable system of manoeuvres to ensure a safe passing should satisfy the following requirements;

(i) Each vessel must make a positive contribution to the safety of the encounter.

(ii) A mariner must be able to decide on his course of action on the basis of information readily available to him, i.e. on the compass bearing of the threat, not on its true motion or aspect.

(iii) All vessels must be able to operate in accordance with the same set of rules, i.e. use a standard diagram showing the prescribed manoeuvres as a function of compass bearing only.

(iv) The same set of rules must apply whether the two vessels are in visual or in radar contact.

Successful ship handling depends upon acquiring the right information, making the right decisions and performing the right manœuvres; this paper concentrates upon the last of these. Manœuvring here is taken to include starting, stopping and steering. The ship is a vehicle with remarkably low resistance to motion; merchant ship drags commonly lie in the range one-hundredth to one-thousandth of the all-up weight force. This is comparable with that of a railway wagon (say 1/500 of its weight) and the low drag accounts in part for the ship's extreme economy as a carrying machine.

It is suggested that there is a need for research into the problem of collision avoidance between ships with particular emphasis on human factors. Work already done is of interest, but is largely theoretical and it seems likely that the usefulness of this approach is nearly exhausted. Collision avoidance at sea is achieved mainly by the rules for preventing collisions, by routing schemes for separating traffic in certain areas and, within certain port limits, by local rules, advisory services or occasionally by direct control of traffic movements. Similar methods are adopted to prevent collisions in the air and on the roads, but with differences which reflect the respective environments. It is suggested that these are differences of emphasis rather than differences of kind. A great deal of research has gone into methods by which collisions between road vehicles and collisions between aircraft can be avoided. Analysis of this work to establish its application to marine collision avoidance should form a prelude to a study of particular problems in the marine field.

The principles and practice of routing are well established and well known today, 12 years after the conception and 5 years after the introduction of the idea in Western European waters. It is the accelerated rate of change that makes it necessary to review the present situation and consider some permanent form of review, and plan development and improvement when necessary. The changes are technological, social, political and economic. The technological changes seem predictable, are measurable and can be caught in mathematical models, and consequently are ideally suitable for modern research techniques. The econometrist endeavours to do the same with economic changes. The much later application of mathematics to often empirical data is however bound to render results with greater variance in the answers.

The situation in the Europoort region has changed markedly in the past ten years. Vast extensions of the harbour areas have been completed, partly by reclaiming land from the North Sea. The new entrance to the river is more than 3 km. further to seaward, and inside this entrance there are now separate entrances to the Rotterdam Waterway and to Europoort (Caland Canal). The number and size of ships visiting the port of Rotterdam has also increased and very large crude carriers and fast container ships are now regular visitors. For these VLCC's, with a draught of up to 65 ft., special fairways have been dredged and are in full use.

The shipowner is the customer and his views are coloured by whether what he buys, and ultimately is going to pay for, is what he wants. It is difficult to reconcile even the conflicting interests of various divisions of a single company for, say, a Dover Strait scheme. The division may operate passenger ships, cross-Channel ferries, deep-draught tankers or conventional cargo ships. The main product that shipowners are buying is increased safety, with a marginal bonus in some types of traffic regulation of possibly saving time in conditions of poor visibility, provided the scheme is cost effective. Most shipowners recognize a moral responsibility for ensuring the best possible conditions for safe operation of their ships and for avoidance of environmental pollution.

Queen Elizabeth I when enunciating the doctrine of freedom of the high seas said ‘…the use of the sea is common to all…’. Until very recently a more appropriate phrase might almost have been ‘a free for all’ for, except for the internationally agreed Rules for the Prevention of Collisions at Sea and the demands of safe navigation to avoid stranding, the seas were free for all to sail as and how they pleased. However, rapid advances in technological development in the last decade or so, combined with changes in transport economics and national ideologies, have brought about dramatic changes in the sea transport industry—both in the size and speed of vessels and in the nature of the cargoes they carry. Inevitably the risk and seriousness of accidents has increased proportionately and in some cases become so intolerable, both socially and economically, that the public attitude towards the traditional freedom of the sea began to change and that freedom was curtailed.

When considering what equipment is to be fitted either in the ship or ashore in order to ensure safe navigation in conditions of high traffic density, we can to some extent be guided by looking at what has happened in the aircraft world where these problems have been present for a long time. Here considerable use is made of radar and of radio navigational aids. Before assuming too readily that the same will apply in the marine world, we should perhaps recall that radar and the hyperbolic radio aids were born during World War II, and that since then fundamentally new techniques in navigation have been developed which should be examined to see if they have any bearing on our present problem.

In assessing the human problems which may occur in the development of a traffic system in an offshore area, some lessons may be learnt from the work which has been done on the similar problems arising in port approaches. There are several fundamental differences between the port and offshore problems such as the direction and density of traffic flow, the parochial as opposed to the international legislation and the difficulties that attend the positive identification of passing traffic. These considerations mean that it must not be supposed that the solutions which have been discovered in the port approaches may be simply transferred to the offshore case, but the similarity of aims in the two systems make a comparative study worthwhile. Basically, each authority must first legislate to allow control and guidance of the traffic. From this right to control must stem the obligation to organize the traffic into a scheduled stream, but this regulated stream will only reduce the risk of conflict if the schedule can be maintained by surveillance, communication and the cooperation of the mariner.

This conference is looking at a range of issues having a bearing on the flow of traffic and the safe conduct of vessels at sea. It seems clear from many of the papers that more needs to be known of the manner in which ships react one with another and, by implication, regulation of traffic at sea can no longer be a matter within the sole competence of the experienced and dedicated mariner, as it has been in the past. If optimum safety is to be achieved, both the mathematician and the operational research expert will also have their parts to play in assessing the merits of possible solutions.

The publication by the Hydrographic Department on 4 February 1972 of 23 new metric charts of the south-west coast of England was announced in Notice to Mariners 264 of 1972. This is a significant first step towards the metrication of all charts of the British Isles of which there are about 400, a programme that should be complete before 1980. The block areas with tentative dates for completion are shown in Fig. 1.