In this paper, which was read at an Institute meeting in London on 11 February 1976 with Mrs. Mary Pera in the Chair, Captain Cockcroft examines the incidence of collisions in relation to the numbers and classes of ships at risk and their trends, pre-war and post-war. Total and partial losses are included and compared with other forms of loss, e.g. strandings.

In several previous papers statistics of marine collisions have been given for particular areas such as the Dover Strait, Western European rivers, the Baltic Sea and Japanese waters. This paper is concerned with worldwide statistics with particular reference to sea collisions. The information is mainly derived from the Statistical Tables published by Lloyd's Register of Shipping and from the casualty reports compiled by the Corporation of Lloyd's. Statistics of shipping casualties must obviously be related to the number or tonnage of vessels at risk; for insurance purposes loss ratios are usually expressed in terms of tonnage lost to tonnage afloat but navigators are more concerned with the number of casualties and number of vessels at risk in various categories.

Historically, radar has been villified as a source of the many accidents, either as collisions or strandings, which have occurred around the world since the end of the war. More truthfully the blame should have been laid not so much on the equipment as on the operator, and it would appear from the many court findings that it is the man who has been unable or perhaps unwilling to extract the level of data needed to navigate his ship successfully from the basic range and bearing information that the radar sensor provides. This shortcoming has been recognized for many years and attempts to correct it have been manifold. There has been heavy investment both by shipowners and education authorities to provide simulators, to offer short courses and to provide anti-collision training, and there has been a marked emphasis on the significance of plotting and radar interpretation in the certificates of competency and D.T.I, examinations. Nevertheless, the lessons which it was hoped would breed good radar practice and which were germinated in the classrooms rarely seemed to come to fruition in the more hostile environment of the ship's bridge. The reasons or the excuse for this lack are not hard to find. There is insufficient space, there is no table, the bridge is single handed, there is too much to do. There are numerous excuses or reasons offered. Many of the arguments are well founded, but these tend only to be a cloak for a more fundamental reason, a reason which is rarely expressed.

Recruitment and assessment of the sample. Recruiting and interviewing began in December 1974. Over 220 hours were spent interviewing the sample, which comprised 68 men. Senior officers were preferred because more informed criticism was expected from them. The watchkeeping record of well over two-thirds of the sample amounted to more than ten years' experience; these were masters, chief officers, second officers, uncertificated third officers, senior pilots and, in addition, two lecturers. Many nationalities were represented and the majority held masters' certificates or were attending the college studying for them. The recruitment of serving officers had a rather poor response, numbers being made up by officers on leave. These men came in for a day, a morning or an afternoon, and thus were not exposed to all the systems since such high exposure in a short time might have caused saturation. There was therefore a proportion of the sample which saw only part of the systems though the majority did see it all. There were men who saw just one system, possibly volunteers who did not particularly want to continue, or others who were snatched away from the college by commercial pressures. The approach to these men was important. The sample was exposed to a two-hour lecture period, usually on modern radio aids, and each group was shown the teaching exercises and an explanation of the research objectives as well as the systems.

Traditionally, when some new concept or equipment comes along, one first makes a rough judgment based on a philosophical analysis. If this looks sensible the next step is usually to put the new device to sea and evaluate it there. The early philosophy, the users' reports and a simple economic evaluation usually lead to a sufficiently sound decision. A collision-avoidanoe radar of the new generation presents a substantial philosophical hurdle both to the marine superintendent ashore and to the man at sea, and it represents a fairly substantial capital expenditure. Deciding what is the ‘best buy’ becomes a complex matter for which traditional selection methods may be inadequate. Like others, in our efforts to provide the most useful installation at economic cost, we have attempted sea-trials of some of the new systems. It has proved most difficult to reach objective conclusions, mainly because normal trading does not permit a free choice of encounter situations or manoeuvres, and there is no ‘control’ experiment. In addition, user reports were sometimes dominated by lost confidence due to technical teething troubles. We therefore felt a need to break the problem down into its elements and to attempt a controlled and objective analysis of these elements.

The least spherical distance between two points on the surface of a sphere is that along the minor arc of the great circle on which the two points lie. It is an easy matter to demonstrate this using a cord stretched between two points on a small globe; noting that the circle whose plane coincides with that of the cord contains the centre of the sphere and that it is, therefore, a great circle. It is a little more difficult to prove the fact analytically. The practice of sailing along the shortest route on an ocean passage—sometimes known as ‘orthodromic’ as opposed to rhumbline or ‘loxodromic’ sailing—would require the course to be continually changed (except, of course, in cases in which the rhumb-line and great circle arc coincide). This would clearly be impossible; the term ‘approximate great circle sailing’ is sometimes used to describe the techniques of following a great circle route as closely as practicable.

This paper, which was presented at a meeting of the Merseyside Branch of the Institute on 24 February 1976, is a sequel to Captain Emden's paper on the setting up of the Dover Strait Information Service which was published in the April 1975 issue of this Journal.

It will be recalled that in 1971 the Marine Division of the Department of Trade set in motion a number of activities designed to improve the safety of navigation in the Dover Strait. It is convenient to group these activities under three headings: scientific studies of marine traffic, surveillance and the Information Service, and future developments. It is the purpose of this paper to give an up-to-date report on each of these subjects.

The device described, which is in prototype form, accepts ship's speed from the Harrier electronic log and heading data from the Halcyon transmitting compass and continuously displays the north–south and east–west components of the water distance traversed from a starting position. It is a development of the Hadrian distance-offtrack computer which, with the Harrier log, has been described in a previous article published in this Journal.

The Sensors. Harrier is a through-hull impeller-type electronic log which records distance run in steps of 0·01 n.m. on an electromagnetic counter and indicates speed on a suitably calibrated milliammeter. Halcyon is a recent development, being a two-axis fluxgate transmitting compass which senses the Earth's magnetic field directly, thus avoiding the major problems associated with the use of pivoted magnetic systems in fast power vessels. The two rectilinear fluxgates are mutually perpendicular and are pendulously mounted with their axes in the horizontal plane. Viscous damping prevents their oscillating when subjected to vibration and shock. The outputs of the compass circuits are two d.c. analog signals which represent in magnitude and sign, the sine and cosine of the heading angle respectively.

The International Association of Institutes of Navigation (IAIN) was represented by the Secretary-General (M. W. Richey) at the eighteenth session of Imco's Sub-Committee on Safety of Navigation from 22–26 March, under the Chairmanship of Captain W. S. G. Morrison (Canada), and the thirty-fourth session of the Maritime Safety Committee (MSC) from 3–7 May, under the Chairmanship of Dr. L. Spinelli (Italy).

In accordance with the recommendations of the Sub-Committee on Safety of Navigation the MSC approved:

1. Amendments to the traffic separation scheme and deep-water route in the Sandettiearea.

2. An amended traffic separation scheme off the Casquets.

3. A traffic separation scheme in the Gulf of Suez.

4. Amendments to the separation schemes off Delaware Bay and the approaches to New York.

With the ever increasing information rates characteristic of modern electronic systems it is not surprising that display technology is one of the most vigorous fields of current research. A wide variety of phenomena is being exploited in order to produce displays suitable for a diversity of applications. This paper, which was presented at a meeting of the Institute in London on 17 December 1975, with Captain B. J. Calverb in the Chair, reviews recent developments in both emissive and passive displays, emphasizing the advantages of alternative types for particular applications.

Man's knowledge of the world in which he lives is steadily increasing and, compounded with a rapidly increasing capacity for communication, this leads to a need for new means of displaying the available information. The development of computers further increases this requirement since they make large quantities of information quickly accessible. It is to be expected that in many situations, where formerly the printed page or spoken word would at best have been the only practical possibilities, the advantages offered by modern electronic displays will increasingly be appreciated. In both civil and military applications it is clear for example that much information transmitted at present by letter could be better sent telegraphically, once suitably convenient displays are available; the need for ‘hard copy’ can be met where required. Considerable savings in time and convenience, not to mention paper, could clearly be made.

In my article (this Journal, 1, 290, 1948) on The Provision for Astronomical Navigation at Sea I called attention (p. 302) to the possible advantages of dividing the standard PZS triangle of astronomical navigation into two right-angled (or quadrantal) triangles by a perpendicular (or quadrantal arc) from the pole P to ZS, or ZS produced. In particular I wrote ‘the method is one which might be further explored,…’; it is only recently that I have had occasion to do so. As far as I have been able to discover from the material available to me (including, by courtesy of Captain Charles H. Cotter, a copy of the typescript of his A History of Nautical Astronomical Tables), the only published method or tables using this principle is ‘Tables for the Abbreviated Computation of Zenith Distance and Azimuth of Celestial Bodies’, by Frane Flego (Split, 1957). Unfortunately, as pointed out by W. A. Scott and myself in a review article (this Journal, 11, 207, 1958), Captain Flego failed to overcome some of the technical difficulties of the method.

Anyone who has read articles by the present writer about automatic radar plotters but has not handled at sea one of those systems in which the vector lengths are time-correlated and have a fine (minute-by-minute) adjustment, might think that they tend to exaggerate its importance as an aid to realistic and rapid appraisal. I hope that the pictorial presentation which follows may serve to reverse such opinions even though, with still pictures, it is difficult to create the sense of a continuous and rapid series of brief manual movements and mental assessments.

Far from needing elimination, as suggested by Riggs (Journal, 28, 143), the rapidly extensible vectors lend apparent acceleration to the radar picture, which always changes so slowly on the PPI, and thus convey with verisimilitude a sense of the predicted movement of the entire complement of echoes in their proper mutual relationship. Further, in situations demanding particular care or perhaps a change of course or speed, they can be used to give a rapid forecast of the probable duration of the emergency.

The author's personal experiences under operational conditions have been with the CBM (Commodore Business Machines) S.R. 4148R, which has proved quite adequate for position comparisons in a surface warship fitted with a Magnavox satellite navigation system primarily used as a DR recorder. It is fed with ship's course and speed, corrections to the positions found being up-dated from satellite passes. Occasionally the criteria for up-dating from a satellite pass are not met and the system may run on DR for several hours without up-dates. Since the system is unable to compensate automatically for tidal or current drift and set or for leeway, the accuracy of the DR will deteriorate with age. The possibility of component malfunction, albeit temporary, may also contribute to DR error. In such conditions a series of astronomical observations is made; the calculator is capable of finding the average of such a series if required.

In an earlier paper the present writer drew attention to the distinction between mixed and aggregated distributions. Incidentally, two minor mis-statements in that paper should be corrected. The first sentence in the last paragraph of section 2 (page 72) should read ‘As σ2/σ1 (=k say) tends to either zero or infinity, X/σ increases indefinitely; whilst for k nearer unity, X/σ is smaller’. Also the last line of the Appendix should not terminate with ‘X/σ = 3·724’ but with ‘X/σ→∞’.

Mixed distributions arise when for example an error occurs either from one distribution with probability p, or from another with probability 1–p, as in a set of position line errors due sometimes to one and sometimes to the other of a pair of observers of differing precision. An aggregate distribution occurs when the error consists of, say, two sub-errors, one from each of the two distributions; as when Captain Flint marks the chart and Long John subsequently reads it.

Jocobrad (devised by K. D. Jones, G. R. Cowap and M. R. Bradshaw) has been devised in the light of research into the reactions and responses of mariners to various computer-based radar plotting and forecasting systems. It is a new concept in computer-based radar plotting systems which allows the operator to ascertain very quickly a safe manoeuvre in any encounter, having regard to every other target in the vicinity and to the time period associated with a contemplated manoeuvre. The system assumes that some means of echo filtering, acquisition and tracking is available and that a simple program calculates the true course and speed of every target which approaches within radar range. Automatic acquisition and plotting of every such target is essential as manual acquisition would detract from the more important features of JOCOBRAD. JOCOBRAD can be operated in one of three separate modes; useful information being conveyed by interswitching between true and relative motion while operating in two of the three.