In 1961 the Institutes of Navigation in Great Britain and France, with the Deutsche Gesellschaft für Ortung und Navigation, formed a representative Working Group to go into the question of regulating traffic in converging areas at sea with particular reference to the Dover Strait. The Group's Report, which was published in October 1962, made certain proposals for routing traffic in the area which were accepted, in April 1964, by the Maritime Safety Committee of the Inter-Governmental Maritime Consultative Organization.

Capitaine de Frégate Oudet's paper was presented at an Ordinary Meeting of the Institute held at the Walker Art Gallery in Liverpool on 20 May 1966, with the President in the Chair. The paper was, in the absence of its author, read by the Executive Secretary who also summarized for the meeting the report of the Working Group on Traffic Separation at Sea (see p. 411).

In December 1962, at a meeting of this Institute, I gave an account of the work that had led to the adoption of one-way routes for the Dover Strait. I now have the honour of describing the balance of work effected since that time, or more exactly, since the Eastbourne conference where the decision was made to carry on the organization of converging areas.

The Rules for Navigation were established originally by custom and prudence some 400 years ago, but they were not presented in a codified form until 1863. Since then they have been modified several times, with the most recent modification becoming effective in September 1965.

The Rules apply to all British ships, together with those belonging to signatory countries of the International Conference on Safety of Life at Sea, 1960. They apply also to all ships navigating within British territorial waters, but, in areas governed by local rules, they serve to supplement not to override those local rules.

This paper gives a general picture of the use of electronic aids in the British fishing industry and describes experimental and development projects now in hand. Some of the problems involved have so far defied solution because of technical or economic difficulties. Although much of this work is not directly concerned with navigation some navigational problems are involved, and these aspects of the fishing industry may be of general interest.

The Fishing Industry in Britain. The British fishing industry is divided into two main sections, the white fish industry and the herring industry. Between them they account for a total annual catch of approximately 800,000 metric tons which realizes at first sale, that is on the quayside, approximately £50 million. Of this total the herring industry accounts for about 15 to 20 per cent by weight. It is in the other section, the white fish industry, that I have been engaged for the last three years or so and this paper therefore deals mainly with electronic problems and developments in the white fish industry.

The Loran C radio position-fixing system has been described in technical detail at international conferences and elsewhere. This paper tries to convey the general ‘feel’ of the system and its characteristics and to indicate, with as few irrelevancies as possible, what sort of process makes the two readout counters go round and give the navigator his position fix. The equipment to which the paper refers is the AN/SPN-31 marine Loran C receiver, which was designed and produced by Decca to a U.S. Bureau of Ships specification. Individual makes of Loran C set differ in various ways, but SPN-31 will serve for illustrative purposes.

Before considering in detail the instrumentation involved, it is necessary to establish first of all what is meant by microwave radiometry and mention briefly its possible applications. A radiometer is a device for measuring heat radiation and the title ‘Microwave Radiometry’ is a little surprising in that it implies heat radiation at microwave frequencies. In fact a consideration of the underlying physics shows that heat radiation and electrical thermal noise are indeed the same phenomenon, although their properties were investigated independently by physicists and electrical engineers. This concept is particularly valuable in microwave radiometry, where the electronic techniques are appropriate to ultrasensitive noise measurements, but the system applications are most easily visualized in terms of heat, or, more particularly, temperature.

There does not appear to be a standard British notation for the parts of the spherical triangle formed by the pole (P), the zenith (Z) and the observed body (S or X) that is such a familiar feature of astronomical navigation. The main value of such a standard (or generally accepted) notation would be academic and theoretical rather than practical, since most navigators are concerned only with the one system that they use. However, it can be most confusing when comparing different methods to find that (for example) both h and H are used for both hour angle and altitude.

Summary

Examples have been given of certain words which seem to be used correctly by navigators where there is any chance of ambiguity. It is suggested that, if these and other terms can be formally denned and agreed by the Institutes of Navigation, bad language will gradually die out and confusion in navigation terminology will be reduced to a minimum. A similar exercise might also be undertaken with regard to abbreviations.

It may be that the British Institute of Navigation working with other English-speaking Institutes of Navigation could make a start by defining certain words in the hope that they will gradually come to be used with a specific meaning. The alternative is a continuation of the present chaos whereby an official body such as the Airlines Electronics Engineering Committee can decide that ‘course’ and ‘track’ have the same meaning and therefore that a direction is a line.

This note is published with the kind permission of Mr. K. Fearnside, Technical Director of Smiths Aviation Division, but is not intended to represent Company views. Mr. M. W. Richey's advice and help is gratefully acknowledged.

In a recent note, D. A. Lloyd has obtained a formula for the frequency distribution of time dependent errors in terms of the exponential integral

This note clarifies Lloyd's derivations by referring to a theoretically identical, though conceptually different, time-independent, physical model, relates this distribution to one described by Anderson and concludes with a short appreciation of the role of the negative exponential distribution in navigational studies.

It is, I believe, generally agreed that if the aspect of a ship could be seen on the radar screen from a range of 4 or 5 miles down, the information provided by the radar picture would be sufficient to prevent collisions from occurring. The aspect cannot be directly observed on an ordinary 3-cm. marine radar, but I think such a set could be modified in the following way to enable the aspect to be shown.