At a meeting of the Technical Committee of the Institute held on 9 January 1963 it was suggested that recent theoretical treatments of the collision problem could usefully be extended to include a discussion of the near-miss situation and the effect of observational errors. The basic mathematical relations for near-miss encounters have been set out in this Journal on several occasions, notably by Sadler and Morrell, and in graphical form by Wylie. The recent paper by Parker deals with the effects of both systematic and random errors of radar observations of relative range and bearing.

My previous discussion of the collision problem was presented in terms of the idealized situation where two ships are on an actual collision course, in which case the sight line is in the same direction as the relative velocity vector (the relative track). To extend the results to a near-miss situation, one has only to redefine the angle α (see p. 24s of ref. 3) as the angle through which the relative velocity vector rotates when one or both ships manœuvre. I have pointed this out on a previous occasion: ‘The two craft need not be on a collision course; this definition of α applies equally well to a “miss” situation provided that no reference is made to the sight line.

The consideration of the effect of observational errors on the problem of manoeuvring ships at sea has, surprisingly enough, only recently become the object of attention by contributors to this Journal, though the basic background was provided many years ago by Sadler. The discussion at the Technical Committee of the Institute emphasized the importance of a statistical treatment of the problem and this led first to a brief note by myself in which systematic and random errors in range and bearing were discussed, and later to a full survey by Hollingdale in which it was shown that the total time to the instant of closest approach should be divided between observing time and manoeuvring time. An article by Proctor, though rather out of the main stream of the ideas pursued by the above mentioned contributors, breaks new ground in the sense that comparisons are made between different types of manœuvre on a probabilistic basis.

The shortest route from the Great Lakes and St. Lawrence River to Europe passes through the Strait of Belle Isle. The alternative routes pass through the Cabot Strait and are between 100 and 400 miles longer according to the European port of destination. The Strait of Belle Isle is, however, normally closed to navigation from the end of December until the middle of July due to the presence of pack ice and icebergs.

Air reconnaissance patrols flown over the Labrador, Belle Isle and East Newfoundland areas seem to indicate that, for the past few years at least, ice conditions have not been so severe as to hamper navigation throughout the normal period of closure. Consolidated ice is only present from the third week of January to mid-February and clears in mid-April to mid-May; only icebergs present a problem in May and June. It is hoped t o show that with proper air reconnaisance at the beginning and end of the ice season, navigation through the Strait could be extended to eight or nine months of the year, or even longer, instead of the present short season of only 5½ months.

The Great Lakes of North America, four of which form the border-line between the United States and the Dominion of Canada, increase in size from east to west, Lake Ontario being the smallest but still 180 statute miles in length. Lake Erie is the shallowest, with an east to west extent of 236 statute miles. Lake Huron has a maximum length of 247 statute miles from south to north. Lake Michigan is the only one of the lakes entirely within the confines of the United States, extending 321 statute miles from north to south. The largest and deepest of the group is Lake Superior, where the principal sailing course from Sault Ste. Marie to Duluth is 383 statute miles.

The structural changes in shipping since the war and the trend towards super-tankers, large bulk carriers and fast freighters is unmistakable. Fast ships are expensive and it is natural that the large investment in these ships should be balanced by increasing the number of voyages and reducing the time spent in port. In this connection radar provides a welcome aid towards faster voyages, for even in foggy weather ships equipped with radar can reach their destinations earlier.

Whereas almost everyone seems to be agreed that a system of routing ships in the Strait of Dover offers the best solution to reducing the tragic wastage of life and ships that occurs each year in these congested waters, opinions differ on the system of routing that should be adopted.

A Working Group sponsored by the British, French and German Institutes of Navigation has considered the problem and their report has been published in the Journal. They recommended that the navigational aids in the area should be revised and that ships should be advised, by means of Sailing Directions and Notices to Mariners &c., to follow the tracks shown in Fig. 1.

At the end of 1963, to assist ships making use of the extensive facilities in the Gironde estuary, the port of Bordeaux installed surveillance radar covering the mouth of the Gironde. As it is still too early to assess its potentialities, this paper describes the technical arrangements and makes some general comments on the use of radar, suggested by the new installation.

Ships approaching the Gironde estuary from the open sea follow the buoyed channel from the landfall buoy BXA, 18 kilometres west of Pointe de la Coubre. After picking up the pilot they enter the western or outer entrance passage, whose seaward termination lies 8 kilometres from the coast. This provides a dredged channel, 800 metres wide and 3500 metres long, running east–west. The depth of 12 metres at low water springs enables ships to cross the annular river bar separating the deep water on the seaward side from the mud banks at the mouth of the inner channel.

When designing a bridge for a naval vessel the designer faces a number of requirements which are quite different from those of a merchant vessel. Besnard states that besides a good view, the officer of the watch requires by him the instruments for determining direction and distance or speed, position finding instruments and other electronic aids, and the means of communicating with the helmsman and engine room as well as some check on these communications. He concludes that a cockpit arrangement of the instruments would suit the requirements. Rees, on the other hand, doubts whether the officer of the watch would remain alert for long periods when sitting in an enclosed compartment, and suggests that a cockpit arrangement is only appropriate where there is little space. Further he argues that the duties of the officer of the watch extend beyond those of simply directing the ship.

The Dutch professor Polak has suggested that an increasing number of higher order specific human thinking functions such as memory, supervision, guidance, schooling, &c. will soon be eliminated and replaced by machines. This sounds alarming, but it should be viewed against the general background of the relationship between man and electronics. The entire structure of the working community in general, and on board ship in particular, is already and will be further influenced and changed by the ever increasing introduction of electronics in general and remote control and automation in whatever form in particular.

The observation of a radar display by a human operator leads to the establishment of aircraft tracks. These tracks are subsequently used by the controller. More and more often, it is proposed to replace both PPI display and human observer by an automatic computer, either special or general purpose, to perform tracking.

In the present paper the basic performances of these two modes of operation are examined, taking into account the psychological and physiological features of human vision and hence the mental association of the viewer. The computer is more precise, but more costly and, when saturated, the drop in performance is abrupt. The number of tracks handled by a human operator is small, but the brain is very versatile and works very well in confused situations, with a slower drop in efficiency than the computer.

At present there is no means of measuring the external temperature directly from a fast aircraft. This temperature is calculated by using the formula To = Ts/(1 + 0·2M2), using the mach number M given by the static and dynamic measurements of pressures, and the ram temperature Ts, measured by a resistance or thermocouple element. At high altitudes and when M is high, precision ranges from 1° to 4°, and the time constant from 3 to 4 seconds.

The navigational problems presented by supersonic aircraft do not differ essentially from those with modern four-jet aircraft. Navigation will still entail three main tasks:

i. To ensure that the crew knows the position of the aircraft at any given moment, within a reasonable time, and with the necessary accuracy.

ii. To ensure that the aircraft is operated under the best conditions of route, speed and height for profitable operation.

iii. To ensure compliance with air traffic control.

One of the principal functions of air traffic control is to ensure that aircraft do not conflict, that is, do not approach each other sufficiently close to give rise to the possibility of collision. (Another function of air traffic control is to ensure that aircraft do not conflict with terrestrial objects, but this is outside the scope of this paper except in so far as such objects can be treated as aircraft with zero velocity.) The ‘possibility of collision’ is, of course, a matter for definition. It is often treated as an approach within 5 miles in plan and 500 or 1000 ft. in height (Fig. 1). The definition must depend upon the form of the aircraft track information available to the air traffic service—essentially flight plans updated by pilot reports—or the radar observations with which this paper is primarily concerned.

Information on the shape of the ground can be required in the air for two quite different reasons. First, for visual fixing of position, that is to say, for ‘map-reading’; and second, for ensuring terrain clearance when flying on instruments. Obviously the second is of far greater importance than the first, yet unfortunately it is the first that, for historical reasons, has received the greater attention from cartographers; this paper will try to redress the balance, and indicate where action is needed at the present time to satisfy the second requirement.

T‘HAT there is a general problem in avoiding high ground has been demonstrated somewhat catastrophically in recent years, but this paper deals with the descent phase of flight in a jet operation, where most of the incidents and accidents to scheduled international services have occurred. My own examination of these incidents and accidents (in some cases somewhat cursory) has led to the conclusion that in stating the problem in terms of ‘the avoidance of high ground’ there is the danger that we will miss the primary problem and indeed mislead the experts who might have little difficulty in providing us all with airborne radar designed for this particular purpose.

An important nautical manuscript in the Bibliothéque Nationale, Paris, containing a number of separate sections on Portuguese navigation methods, and written in the early sixteenth century, has been translated into modern Portuguese and edited by Professor Albuquerque of Coimbra. It is the Livro de Marinharia of André Pires, a Portuguese pilot only known by this collection, of a small part of which he was the actual author. The 13th section, which is quite short, deals with the ‘Balestilha of the Moors’, i.e. the kamal. The use of this title confirms the point, for which there is some other evidence, that although the quadrant and the (sea) astrolabe were the official navigating instruments on Portuguese ships, the cross-staff or balestilha was known and used. The principle of the kamal was, of course, that of the cross-staff. A wooden rectangular tablet was held up with one edge on the horizon, the other on the heavenly body. A knotted cord running from the centre of the tablet was held taut between the observer's teeth, and all he had to know was the meaning of the knot in his mouth in terms of ports and landmarks. The first knot—nearest the tablet—measured the ‘altura’ of Mascat, which was east-west with Diulcende, on the coast of Diul in India. The fifth knot marked the altura of the Curia Muria Is., east—west with Dabul, and so on.

There are occasions when, because of the density of shipping and/or lack of sea room, ships navigating by radar in thick weather cannot avoid passing within a distance of two miles, the least distance usually considered desirable. In such a situation a simple plan of procedure and of avoiding action, if possible to devise, should greatly reduce strain on the navigator and so increase the safety of navigation generally. Also, if such a plan came to be generally followed, safety would be further enhanced, because each navigator would know what the others were likely to do.