The geometry of collision at sea has been dealt with in a series of papers published in the Journal, notably by Sadler (10, 306), Calvert (13, 127), Garcia-Frias (13, 316) and Morell (14, 163); and a further contribution from Calvert (to which reference is made in this paper) will be published in the next number.

The object of the present paper is to examine whether anti-collision manœuvres, here considered for the case of two craft moving in a plane, can be formulated on a rigorous logical basis. If they can, then clearly a proper appreciation of the geometry of collision is a prerequisite to the formulation of any rules and regulations. In this important paper the author gives a precise and complete answer to the basic problem, and he proves mathematically that it is the only answer. As Dr. Hollingdale freely acknowledges, however, this can only be a contribution to the study of the collision problem, which involves innumerable operational factors in addition to the geometry of the situation.

The convention adopted in the present paper is that each craft shall manœuvre so that if the other craft stands on, the sight line always rotates in the anti-clockwise direction. The analysis shows that a simple set of manœuvres can in fact be developed on this basis and that such manœuvres are the only ones that, geometrically, meet all the specified requirements. In all cases the combined manœuvre converts a collision situation into a ‘miss’ of at least a specified magnitude.

In the last number of the Journal (14, 243) Hollingdale showed mathematically that anticollision manoeuvres for the case of two craft moving in a plane can be formulated on a rigorous logical basis; and that a simple set of manoeuvres could be devised to meet all the geometrical requirements for anti-collision. The convention adopted was that each craft should manoeuvre so that if the other craft stood-on, the sight-line (the line joining the two craft) would always rotate in an anti-clockwise direction. The analysis showed that, mathematically, this was the complete and only answer to the basic problem.

The author of the present paper compares systems, such as that represented by the Collision Regulations and the Rules of the Air, based on onus to avoid, with a system based on a convention as to the direction of rotation of the sight-line. The first type of system, he holds, is defective for visual sightings and almost useless for radar sightings. The system put forward in the paper can be applied to both visual and radar sightings whether unilateral or bilateral by orientating a simple diagram with own course. A means of inter-communication is desirable but even without it such a system can, the author believes, safely be employed in the greater proportion of encounters.

The collision problem as a whole is beset by operational factors which are entirely distinct from the geometry of the situation, and for that reason no purely mathematical approach can, in isolation, be entirely valid. Nevertheless, there can be no doubt that studies such as the present one, based on a proper understanding of the geometry, can contribute greatly to the solution of this most pressing problem of navigation.

The wind pattern in the North Atlantic (Fig. 1) is more or less clockwise, and therefore the easiest way to cross the Atlantic from east to west is by the southern route, and from west to east along the northern route. In between, in the middle of this rotary system, are the horse latitudes where winds tend to be light and variable. Superimposed on this wind system, of course, is a series of depressions which commonly move from west to east across the North Atlantic, each depression having its own system of winds rotating anti-clockwise: on the south side of the depression winds tend to be westerly whilst on the north side they tend to be easterly.

Six years ago, Mr. D. H. Sadler, in a memorable Presidential Address, answered the question ‘What is the Institute?’ This leads to the complementary and perhaps even more controversial question ‘What is navigation? What is its scope and its general pattern?’

If we look at the word Navigation in a dictionary, we may very well find that it is associated only with the sea. Today, of course, a much wider view is taken and the word is accepted as having to do with the land and the air and even with space. The definition: ‘the art of conducting a vessel on its ways’, may therefore be amended in words such as:

Navigation is the business of conducting a craft as it moves about its ways.

This paper is concerned with a limited part of the marine radar field, namely the equipments intended primarily for the larger ships. In these sets the greatest refinement and versatility is aimed at, to cover the wide variety of circumstances met with by the ocean fliers, the great tankers and the deep-sea tramps seeking port in any corner of the world. The paper is a factual record of radar characteristics as we enter the sixties and the fifteenth year of commercial radar; it seeks to make no invidious comparisons, but it is intended mainly to provide food for thought.

Marine radar has reached a very interesting stage in its progress. From 1947 to 1952 there was a gradual development in the United Kingdom towards a common, rather strict, specification. In the United States there was a similar trend towards a somewhat different standard. Between 1953 and 1959 the American tendency was to move towards the high definition favoured by Britain while British manufacturers began to offer the large diameter displays, 15 or 16 in., which were always popular in the States. Other trends on the whole have been similar, that is towards high definition, operational refinement, general reliability and better control of rain and sea clutter.

Tactics were clearly going to be vitally important in this race, and the first tactical decision was obviously which route to take across the Atlantic. Using a dry-sail method, I worked out the speed at which the boat should sail over about twelve routes or combinations of routes. The method used was to compute from the appropriate monthly Pilot Chart of the North Atlantic (issued by the U.S. Hydrographic Office) the time it would take to cross each area measuring 5° of longitude by 5° of latitude, using the average winds determined over a long period of years. For example, in the first area (Fig. 1), from Plymouth to 5° west, the average wind blows from the west for 18 per cent of the time in June, which should give a rate of advance towards the objective of something like 2½ knots for that period. For the north-westerly and south-westerly winds which, according to the chart have blown for thirty two per cent of the time, at an average of force four, I estimated that I should travel at 4 knots towards the objective: so, similarly with different speeds for beam and following winds, I calculated that I should be able to cross this area in 62 hours. In practice it took 103 hours—more than 4 days instead of 2½—due to head-winds of from force 6 to gale force. However, this wrong estimate did not spoil the value of comparing the routes.

The year 1932 was one which had no great apparent significance for navigators, and yet it saw the commencement of two new lines of research which today, after an interval of more than a quarter-of-a-century, promise important contributions to the safety of navigators both at sea and in the air.

The two lines of research were superficially quite unrelated, but fundamentally they relied upon the same principle—the detection of radiant energy emitted by objects solely as a result of their temperature. The first of these small beginnings was the discovery by K. G. Jansky that radio waves could be detected from extra-terrestrial sources: the second was the commencement by the U.S. Signal Corps Engineering Laboratories of an intensive study of infra-red devices with the object of obtaining night vision without illumination of the field of view.

From Jansky's discovery has sprung the whole science of radio astronomy, which has revolutionized our ideas about the universe, and brought in its wake, as one practical benefit, the radio sextant. From the work of the U.S. Signal Corps there resulted a number of very useful infra-red components, including the pneumatic detector, better known as the Golay cell.

This number of the Journal goes to press just before the third international Convention sponsored by the Institute with the Ausschuss für Funkortung and the French Institute of Navigation. As members will know, the theme of the present series of meetings is the prevention of collisions, at sea and in the air, by systems or methods based ashore or on the ground. An account of the meeting and summaries of the papers presented will be published in the next number of the Journal, and a selection of the papers themselves will be published in future numbers. Wing Commander Anderson's paper, in which he introduces the concept of a collision index by means of which travel risks may be related to the risks of other human activities, forms a suitable introduction to the series.

As part of an investigation into the difference of absolute sea-level across the English Channel, a detailed series of measurements of currents at all depths was recently made in the Strait of Dover. The main object of the measurements was to relate the residual non-tidal flow of water to the voltage on a cross-channel cable generated by electromagnetic effects. Over 6000 readings of current strength and direction were made during ideally calm conditions. This paper describes the results of analysis of these measurements, which covers vertical current profiles and tidal components, besides the non-tidal flow. Distinction is made between mean current measured at a fixed depth or at the surface, and the mean volume flux of water which involves tidal variation of depth. A method of tidal analysis based on Fourier sums, which is convenient for use with an electronic computer, is outlined in the Appendix.

This article reports the discovery of two documents of considerable interest in the early history of navigation in England. When Henry VIII was planning to send ships of the royal fleet to Harderwijk in Guelderland in 1539, no pilot's book or chart of this part of the coast of northern Europe could be found in England. Therefore two experienced shipmasters, John Aborough of Devon and Richard Couche of Dover, were sent in haste to the Low Countries to make a survey of the coast and chart the route the king's ships would have to follow. Working with speed and secrecy, they compiled and brought back to the king a rutter giving sailing directions for Zeegat van Texel and the Zuider Zee and also a rough chart showing in detail the channels through the Haaks Banks, the entry to Marsdiep and the channel from thence to Enkhuizen. These two documents are the earliest original examples of such navigational directions drawn up by Englishmen which have so far been discovered. Both are reproduced in full and discussed in detail in this study.

Among the Marquess of Salisbury's family archives at Hatfield House is a document of great interest in the early history of navigation in England. It is a seaman's rutter giving directions for the navigation of Zeegat van Texel and the Zuider Zee which was compiled by two English shipmasters in 1539 on direct orders from King Henry VIII. A narrow roll of manuscript fashioned by roughly sewing four strips of parchment end to end, being not quite 6 in. wide and nearly 3½. long when fully opened out, this appears to be the earliest original English rutter which can be found today. It is true that the well-known set of fifteenth-century ‘Sailing Directions’ published by the Hakluyt Society in 1889 were compiled at an earlier date. But these have only survived in a copy transcribed by a professional scribe, William Ebesham, among a number of treatises on heraldry, chivalry and similar matters contained in a volume called the Great Book, part of the library of a country gentleman of East Anglia, Sir John Paston. The parchment roll at Hatfield would appear, therefore, to be the earliest example of an original English rutter which has yet been discovered.

This paper by the Director of Control and Navigation at the Ministry of Aviation, reviews the present state of planning for air traffic control in the United Kingdom. It indicates that whilst progress is evolutionary and continuous, big steps take place approximately every ten years. The author concentrates on four principal facets of air traffic control which cause the most acute problems, namely the medium-haul operations in densely populated areas; the terminal problem; long-distance operations over the Atlantic; and low-level, short routes in the south-east of England.

The paper outlines the basic air traffic control system of the future and indicates the ways that data processing and radar may be used. It makes a short reference to the specific problems of the supersonic aircraft and concludes by referring to two principal experimental projects now in hand to enhance our knowledge of data processing with respect to air traffic control.

In this paper presented on 17 June 1960, with Captain F. J. Wylie, R.N. in the Chair, the Harbour Master of Southampton considers the problem of coordinating shipping movements in a major port. The experience of Southampton is largely drawn upon and a description is given of the communications systems and the use of the harbour radar in that port.

A method is presented for quick calculation of the frequency of cross-wind components which limit the landing of aircraft on runway layouts at aerodromes ánd for deriving the best runway layouts for a site with a known or deducible wind distribution. The method depends on some initial study of the relevant wind rose but an exact solution is obtained by the application of the empirically derived formula nv = Ce–bv2 where nv denotes the percentage of time that a wind exceeds a velocity v and C and b are constants for a given site. This formula was originally verified only for the British Isles but later it has been found to be valid elsewhere where there is a wide range of wind speeds. Allowance can be made in the calculations for bad weather, e.g. dense smoke or low cloud approaching the aerodrome from certain directions, for use of one end only of a runway and for a permissible tail wind component.

The paper was originally issued in 1944. The method described has not been changed and the description is only slightly modified. The chief changes are the substitution of numerical integration using Meteor computer instead of the original planimeter measurement of curves and the introduction of the ‘bisector’ correction. Certain details of the calculation notably four-figure tables of L(i) (eqn (5)) and of the bisector correction, a complete example of the method, the way to remove ‘bias’ in wind summaries and the derivation of the bisector correction are given in a duplicated Addendum to this paper which is available on request from the Institute.

This paper describes a number of occasions on which German ships have successfully avoided tropical revolving storms by using information which is at the disposal of the mariner today. Similar accounts could obviously be given of storm-avoidance by the vessels of other countries, but it is thought that this compilation, by a member of the German Weather Service, will interest many seamen. The paper was presented at a meeting of the Ausschuss für Funkortung held at Kiel on 10, 11, 12 September 1960, and is published with the kind permission of that body.

In order to find out what type of doppler navigation equipment would be most suitable for the S.A.S. fleet of DC-8s it was decided to start a programme of doppler evaluation in Spring 1958. The doppler evaluation programme included evaluation of doppler equipment from Canadian Marconi, General Precision Laboratory (G.P.L.) and Collins Radio Company.

The programme started in April 1958 with evaluation of Canadian Marconi doppler equipment. The evaluation period lasted six months. In April 1959 evaluation of Collins and G.P.L. doppler equipment started and lasted for eight months. In March 1960 evaluation of Collins and Canadian Marconi doppler equipment started and is still in progress. And finally by the middle of May 1960 evaluation of G.P.L. Radan 500 was in progress.

From an inspection of upper-air contour charts for 300 and 200 mb., the location of the axis of jet streams of 80 kt. or more has been assessed once daily over the two years 1957–8. Results are presented for each of the four seasons by means of isopleths of frequency (Fig. 1) and also by means of frequency-roses in areas of 5 degrees of latitude by 10 degrees of longitude (Figs. 2–5); each rose shows the number of occasions of direction of the axis from the eight compass points. The area covered extends from latitude 30° N. to 70° N., and from longitude 60° W. to 30° E. An Appendix contains some discussion of the technique of locating the axis of jet streams on contour charts.

The characteristics of jet streams were described in a paper by Chambers in this Journal for July/October 1959. The present paper goes a stage further by giving the number of occurrences of jet streams per season over a two-year period in an area from the North Atlantic to the Mediterranean. The number of occurrences depends very much on the chosen definition, about which there is no general agreement. Whilst a jet stream may be fairly described as a fast-moving stream of air in the upper troposphere with great extension in the direction of the wind and persistence of the order of days, for statistical purposes it is necessary to be more precise. In this paper a critical speed of 80 kt. is required at the 300- or 200-mb. level in order that the stream shall qualify as a jet stream. Further discussion of this point is given in the Appendix, but any definition is largely subjective and it does not matter a great deal what definition is used provided the reader is aware of the limits to which the statistics refer.

In December 1958 the Institute held a meeting at the Royal Geographical Society at the suggestion of the Hydrographer of the Navy, to sound sea-going opinion on the Admiralty Chart. An account of the meeting was given in Volume 12 of the Journal. The discussion printed below took place at a meeting of the Institute held on 17 February, again at the suggestion of the Hydrographer of the Navy, to take account of what steps had been taken as a result of the last meeting and to examine the situation further. The discussion was introduced by Rear-Admiral E. G. Irving, O.B.E., the Hydrographer of the Navy who had with him the heads of the various branches within the Hydrographic Department.

The Hydrographer referred to the many points which had been made by Masters at the last meeting and in correspondence resulting from it and an account of what has been done as a result of these suggestions is given as an appendix to this discussion.

The Hydrographer: Of the general topics raised at the last meeting I would like to mention a few because I wish to stimulate discussion on these points in order to obtain guidance for future policy.

When two ships encounter one another at sea, there is a possibility that they will collide. Whether there is actual danger or not depends on the physical facts of their respective positions and motions. If danger does exist, the motions must be changed. The purposes of Dr. Morrel's paper are (1) to inquire what facts must be known, both to distinguish the cases of actual danger and to choose effective remedial action; (2) to determine when and how well these facts must be known; and (3) to consider how these facts may be obtained and how they may be best utilized.

The paper attempts to construct an integrated treatment of the whole problem, in terms of the fundamentals that define its nature and shape its solution. The problem is large and complex. Consequently, a compact treatment of it must perforce omit most of the details; both of the evidence and analysis by which the principles are established and of the technology by which they may be exploited.

Much of the treatment uses mathematics; but emphasis is placed on the implications rather than on procedures.

The paper was presented at the meeting of the Ausschuss für Funkortung held at Kiel on 10, 11, 12 September 1960 and is printed with that body's kind permission.

When, in 1958, B.O.A.C. undertook to evaluate the Marconi AD 2300 doppler navigator, the exercise was planned with great care. The aim was to determine the performance of the system in quantitative terms, and to express the results so that their operational significance was clear.

In preparing this evaluation, three objectives were stated, as follows:

(a) To obtain quantitative data on the performance of the AD 2300, considered as a measuring device, in terms of accuracy, consistency and reliability.

(b) To obtain qualitative information on the optimum methods of system application, by reference to observer reaction.

(c) To introduce the doppler system in operation to a wider selection of B.O.A.C. flying staff, in order to develop a body of informed opinion.

It is the first of these objectives with which this paper will deal.

The problem of presenting barometric height in aircraft altimeters is discussed. The alternative methods of presenting a numerical value are outlined and their characteristics analysed with reference to available comparative evidence providing a quantitative assessment. The properties of various methods of presentation are examined with reference to the varied uses of the altimeter. The conclusions are discussed with relation to the recommendations of the U.K. Altimeter Committee.

It is concluded that no single means of presenting height information will meet all of the roles in which the altimeter is used and that the recommended solution is a combination of a digital counter presentation giving an unambiguous height value combined with a circular scale and pointer rotating once per 1000 ft. providing rate and angular cue information for control purposes. Freedom of choice in presentation can only be achieved by the use of a servo-operated display.