There have been two distinct phases in the development of radio aids to navigation. The first, which must be regarded as the true pioneer period, followed rapidly upon the development of wireless telegraphy by Marconi and others; it was soon realized that the early aerials employed had directional properties and that this phenomenon could be used to obtain a bearing.

In 1947 Dr G. M. Clemence, then Director of the Nautical Almanac Office at the US Naval Observatory, and I visited a number of US institutions engaged in the development of digital computing machines, with a view to their application to the calculation of astronomical ephemerides. We were, at that time, planning the revision of the almanacs for surface navigation which led, in due course, to the unification of The American Nautical Almanac and The Nautical Almanac, Abridged for the Use of Seamen in essentially its present form as (from 1960 onwards) The Nautical Almanac. We were told (actually by an astronomer, Dr T. E. Sterne) that our efforts were pointless since, in the near future, a navigator would be able to calculate the astronomical data that he required to reduce his observations by digital computer; conventional almanacs would no longer be needed. Thirty years later that optimistic forecast, although not yet realized, requires consideration. However, no one could have foreseen that the microprocessor of today is far more powerful than the most elaborate computer that was then practically visualized. For that matter, few would have thought that there would still have been a demand for astronomical data for navigation; the basic principles of many other aids to navigation were rapidly being developed.

When planning the replacement of an existing shore-based radar advice chain, which may have admirably served the port area under consideration for the past fifteen or twenty years, a number of basic elements have to be reviewed. The review and the ensuing process of analysis should be steps towards the adoption of a basic philosophy for the eventual development of a replacement system; this is necessary to judge requirements in relation to the many possible solutions, ranging from a simple shore-based radar advice service to sophisticated vessel traffic management systems. Elements for consideration include:

(i) The area to be served, present and future.

(ii) The traffic pattern, present and future.

(iii) The technology available or under development.

(iv) The other operational and administrative services available to shipping.

(v) The quality of manning and manning scales.

(vi) The economics of the shipping industry.

(vii) The cost of the new system.

(viii) The distribution of this cost over shipping and the community in general.

(ix) Legal aspects.

Besides these factual considerations and their analysis we should develop a philosophy regarding the aims of the system, which could be an improvement in port operation efficiency, in traffic safety, or in vessel turn-around time. The realization of these aims will probably result in economic benefits both for the port and for shipping and these will have to be weighed when investigating the distribution of system cost over shipping and the community in general.

Depending on how the encounter rate is defined, different values can be found for the crossing angle or speed giving the smallest encounter rate. When dealing with ‘optimum crossing angles’ or ‘optimum speeds’ it is therefore proper to know which definition is taken as a basis, i.e. which expression is minimized.

D. H. Sadler writes: I am indebted to Mr Luis de Sobrino of 1976 West 14th Avenue, Vancouver BC, Canada, for pointing out the need for the following correction to my paper ‘Lunar methods for longitude without time’ (Journal, 31, 245, lines 16, 17). The altitude corrections CM and CS should include corrections only for parallax and refraction; the word ‘semi-diameter’ should be omitted.

The Amoco Cadiz and the Work of the Institute. Seaborne trade calls for international agreement but it is not a matter that attracts much public attention. That is why, as Beattie has pointed out very clearly in his paper ‘Traffic Routing at Sea 1957–1977’ presented to the Institute on 14 December 1977, all the major steps taken to bring some order into the regulation of maritime traffic have been due to the initiative of mariners or maritime organizations. International action was only taken later, to give a legal sanction to such proposals as were felt to be necessary. In any case there was no international authority until 1958 when IMCO (the Inter-governmental Maritime Consultative Organization) took over the direction of maritime affairs between the International Safety of Life at Sea Conferences, and these were not convened at regular intervals. One can easily see that under these conditions progress was slow, depending as it did on either the initiative of seafaring people or on some turn of events that demanded a new approach.

In Virginia's splendid State House at Richmond there stands a marble bust of Matthew Fontaine Maury, one of Virginia's more eminent natural scientists. It might be a matter for dismay for a mariner to read the inscription below the elegant bust, to the effect that this remarkable man owed his fame to having invented an electric torpedo; Maury's fame stands on a much firmer foundation than this! In 1916 the State Board of Education of Virginia set January 14th as ‘Maury Day’ in honour of its celebrated son, and each year on that day Virginian schoolchildren observe and commemorate his birthday. Because of his service to navigation Matthew Fontaine Maury merits the title ‘Pathfinder of the Seas’.

Automatic collision avoidance systems are being installed on board more and more ships and this necessitates verifying their characteristics, as compared with postulated requirements. The requirement for such anti-collision systems may be specified as follows:

(i) Radar echoes should be tracked automatically, regardless of weather conditions, the number of echoes, or the relative distance between tracked targets.

(ii) The system should be operable by a single observer, assuming that the information given is used efficiently.

(iii) The information should be displayed in the clearest and the most comprehensible form.

(iv) The system should facilitate alterations of course and speed.

(v) Information relating to collision risk should be provided in ample time if the system is to operate in dense traffic.

(vi) The system should include alarm devices which operate in pre-determined circumstances.

Inertial navigation systems have for many years been mechanised as a cluster of gyros and accelerometers mounted in a servo-controlled gimbal system which isolates the cluster from the motion of the carrying vehicle. Until the spectacular advance in computer technology over the last decade no other mechanization was really feasible, but serious consideration is now being given to strapped-down systems. This paper compares the two mechanizations, outlines some of the advantages of strapped-down systems, and considers some of the contenders for rate-sensing in such systems.

The current situation with aircraft inertial systems is that virtually all are based on gimballed platforms so that this technology is very well understood, including the cost of maintenance. Strapped-down IN promises the already well demonstrated advantages of gimballed equipment but at a much lower cost of ownership; but although the technical feasibility of strapped-down systems has been demonstrated, the realization of the economic advantages is still in process.

Recent advances in the speed and capability of miniature computers have made possible a strapped-down mechanization for airborne inertial navigation systems. The implementation of this mechanization is critically dependent on the availability of suitable accelerometers and gyroscopes able to measure, and yet withstand, the effects of vehicle motion. The laser gyroscope is now considered a major contender for angular measurement in that it offers the possibility of a cheap, reliable instrument with the wide dynamic range required for strapped-down implementation.

It is now more than thirty years since Commander W. E. May, R.N. (formerly of the Admiralty Compass Observatory), drafted this hitherto unpublished paper, recording his opinions based on a study of documents made available to him in 1947 by Messrs Kelvin, Bottomley and Baird. The documents referred to in the paper are:

The Thomson v. Moore case as presented to the House of Lords in the Thomson v. Moore case (Patent Design and Trade Mark Cases, Vol. VII, No. 36.)

The case of Thomson v. Hughes (Patent Design and Trade Mark Cases, Vol. VII, Nos. 9 and 22.)

Report of Proof of case of Kelvin v. Whyte Thomson &. Co.

Bound volume of patent specifications referred to in the last named.

It is a curious habit of editors and publishers to invite well-known persons to write articles on subjects outside their normal orbit. Thus in 1874 Sir William Thomson was invited to write for Good Words an article on the mariner's compass. He took up the task and soon realized that he did not know enough of the subject to complete the article. He then began to study the compass and the final part of the article was published in 1879. Such is one of Lord Kelvin's explanations of how he came to interest himself. In 1885, in an affidavit for the Moore case, he said that he took up the study of the compass in 1871, whilst elsewhere he said that it was the necessity of writing for the Royal Society an obituary notice on Archibald Smith, who died in 1872, which first turned his attention to compasses.

In a previous article about Escape Time the writer mentioned automatic acquisition; this is taken by the writer to mean acceptance by the computer/processor of a radar echo and the subsequent initiation of the tracking process if the echo satisfies the requirement of one or more paints every 6 scans, and is one of the 40 (in Digiplot) closest to own ship. But he took the advantages of it to be so obvious that no special stress was laid on the desirability of its inclusion as standard practice. However, it is clear from the replies to the IMCO questionnaire on Radar Plotting, notably that of the International Chamber of Shipping, that although a very high percentage of informed maritime opinion (97) is in favour of automatic (computerized) radar plotting, a somewhat smaller though still a preponderant (65) percentage favours automatic acquisition. A similar view is taken in the United States' reply. Although to the writer this seems to be illogical or without good reason, it may be of interest to examine some possible subjects of controversy.

As a watch-keeping officer on ships daily crossing the North Sea and English Channel 1 was interested to read Commander Paton's paper on ‘Navigation in the English Channel and the Southern North Sea’ in the January 1978 issue of this Journal. Since the introduction of the traffic separation schemes many of us have been concerned about the possibility of an accident whilst crossing the lanes. It is an almost nightly experience to have ‘near misses’ and occasionally more than one ‘near collision’ inside the hour, with people who appear to think that, because they are in a traffic lane and going the right way, everyone else must keep clear of them. No attempt is made to avoid crossing vessels in accordance with the Collision Regulations and, in spite of flashing the warning five shorts and blowing five shorts on the whistle, we often have ships call us to demand we keep out of their way, contrary to all regulations, and frequently forcing us to take drastic evasive action.

Many runways lack an ILS/GS but have DME on the centre line (e.g. Lagos R/W 19) and DME can provide information in conjunction with the pressure altimeter to define a glide slope. For Lagos R/W 19 I have developed a method of calculation and have tried out the resulting table on two occasions. The pilot not flying the plane consults Table 1 and calls out deviations above or below the glide path (which meets the sloping runway 1500 ft from the threshold for a DC-10).