Most collisions on inland waterways occur in daylight and in good visibility and it is here there is most scope for improvement. Elaborate traffic control schemes such as that planned for the Panama Canal may not be suitable on European rivers where the density of shipping is very high and the nature of the traffic mixed. Local control may be feasible, but between control areas vessels will have to rely on self-contained aids, ship-to-ship communications and local navigational rules to avoid collision. The congestion of traffic, particularly at Customs clearance points, must be relieved.

The paper discusses various aids to river-radar navigation, which are making fundamental changes in the methods on European inland waters.

The preceding papers have shown that the present generation of hovercraft being used mainly on overwater routes should be considered as ships. The problems of operating these very fast craft in the same media as conventional vessels is receiving a lot of thought at the present time and perhaps a few more words on this subject would not be amiss.

In framing operational rules for hovercraft it has been proposed that they obey the Regulations for Preventing Collision at Sea in so far as their size and construction will permit. This is in fact the point of view which has been put forward by the Hovercraft Operational Requirements Panel, representing Hovercraft Developments Ltd. and the industry, in their provisional British Air-Cushion Vehicle Operational Rules.

If this approach is accepted, three questions immediately spring to the mind of the mariner;

(1) How manœuvrable are these machines that skid around on a cushion of air? The present papers have shown very clearly how well the turning circles and stopping distances of hovercraft compare with conventional ships. Control systems have improved tremendously since the first generation of machines and they are now far more manœuvrable than ships proceeding at a fraction of their speed. Experience in driving these craft has shown that this problem causes, little trouble, and as a result of various hovercraft demonstrations their manœuvrability at speed now seems to be generally accepted as satisfactory.

Even as recently as 1954, although informed opinion ashore was otherwise, at sea, and here one can only broadly generalize, the principles of plotting were neither universally accepted nor practised, and it may be that this was due largely to the fact that there still remained disagreement as to the practicability of plotting. Indeed, even now, there must be a limit on the number of targets that can conveniently be manually plotted.

The Safety of Life at Sea Convention, 1960 amended the Collision Regulations to take cognizance of radar, and to give guidance on the use of radar in fog. The Admiralty Court has indicated that if a vessel is fitted with radar she is obliged to use it and, even more important, that there is an obligation upon the observer to use the radar properly. The phrase ‘using the radar properly’ has in Case Law been judged to necessitate some form of plotting, and it is of passing interest to note that the vast majority of collisions involving vessels fitted with radar can be attributed to immoderate speed, or a failure to appreciate the information provided by the PPI.

Captain Lumsden's paper was written for the convention held in Düsseldorf on 16, 17 and 18 May 1961 (Journal, 14, 480). It describes the siting of harbour radar equipment from the point of view of giving warning of approaching ships to the shore authorities, giving navigational assistance to shipping, and port surveillance. In most cases the choice of site for the aerials and displays will have to be a compromise with these three uses of shore radar in mind.

The three main elements of a harbour radar are the scanner, which must be sited to survey the area of interest, with the transceiver close by to avoid waveguide losses, and the displays which may be required in a room close to the scanner or in a room distant from it.

The Panama Canal Company's Marine Traffic Control is being designed primarily to minimize ships' average transit-time and obtain optimum use of Canal facilities, but it also includes features contributing to collision prevention. It prepares an operation schedule consistent with the number and characteristics of ships that are in transit and with operating conditions. Actual operation is continuously monitored and signals currently displayed to pilots to facilitate close adherence to the schedule. If the contemplated schedule is cancelled, as by trouble in locks or sudden periods of poor visibility, re-scheduling is rapidly formed and signals transmitted to pilots in conformity with the new schedule.

The system's contribution to collision prevention includes elimination of several hazardous situations: (a) Undue crowding of traffic; (b) Lock-entrance stand-off delays due to untimely ship arrival, during which ship handling is difficult; (c) Meets or overtakes at potentially hazardous locations.

Further, when approaching a bend on which other ships would not be visible and at which the meet would be hazardous, a pilot is advised of the number of ships which will be round the bend before he reaches it. Also indicated is the number of meets due to occur immediately beyond the bend, a distance through which the manœuvrability of his ship would be affected by the manner in which he rounds the bend. The automatically operating system is based on transmission of data comprising ships' identities and locations to a central control point where the data is analysed by an electronic computer and from which advisory signals are automatically transmitted back to the ships.

A system is proposed which would be capable of adding information concerning the true motion of objects, to the normal relative display. The method requires the use of two Tenicon storage tubes (ME 1260).

The use of marine radar has not eliminated collisions at sea. The reasons for this failure are generally associated with limitations in interpreting the available information, rather than in the equipment itself. One particular problem is the assessment of the time, course and speed of a ship from the information presented on a radar display, which is relative to the observer. It is possible to calculate this information, but the direct presentation of a true course on the display would be advantageous. A solution is to modify the final PPI display so that the centre of the scan, normally fixed at the centre of the cathoderay tube, is displaced continuously at a velocity corresponding to the observer. The true speed and course of a ship can therefore be assessed from the track built up from echoes received during successive scans.

A number of air traffic control authorities are now introducing electronic digital computers into air traffic control systems in order to speed operations and reduce the burden on controllers. These machines will initially be used for the routine clerical and data storage operations, but their full capabilities can only be used if they are given a much greater share of the control task and allowed to make logical decisions and intervene in the handling of the traffic. In such cases the computer will be performing a task that cannot be handed over to a human operator at a moment's notice in the event of a machine failure, and extreme reliability becomes probably the most important single attribute of a computer used in such a system.

Although computers of adequate speed and capacity are being produced for commercial and scientific uses, with reliabilities sufficient for these purposes, the frequency of faults and the time required for routine maintenance are both far too large to permit their full-time use in an air traffic control system. The reliabilities of typical components and systems are discussed in the following section.

1. The reliability of typical components and systems. The reports of a number of computer users suggest that ‘availabilities’ of 97–99 percent are readily attained, so that only 1–3 percent of the available working time is lost due to unscheduled maintenance.

This paper, which was presented at an Ordinary Meeting of the Institute held in London on 17 November 1961, discusses aspects of high-speed, high-altitude navigation which will have a bearing on the selection of a navigation system and control philosophy for supersonic transports. The effects of certain separation criteria on systems accuracy are described, as are meteorological factors bearing on operation of the aircraft. Estimated performance capabilities which relate to traffic control and navigation are described. An analysis is offered of the effects of particular system accuracies on the selection of components of a navigation system and, finally, an integrated system is described, with arguments presented for certain levels of redundancy, reliability and automation.

Collision-avoidance devices are all based on the use of either electromagnetic or acoustic waves, although the former (i.e. radar) is of particular interest for this purpose.

After reviewing briefly the fundamental theory which underlies all methods of detecting, locating and recognizing a distant target, reference is made to the successful development, in the Electrical Engineering Department of the University of Birmingham, of a narrow-band sector-scanning sonar system employing a multiplicative array to give improved target resolution. It has been demonstrated experimentally that the same principle can be applied to obtain a sector-scanning radar system capable of scanning rates as high as one million scans per second, which has applications for airfield surveillance radar. Attention is now being directed to the possibility of using wide-band signals, either to improve target detection and location for an array of a given size or to obtain additional information about the nature and behaviour of the radar target itself. Two possible methods of using wide-band signals are described.

The work of the air traffic controller is necessarily closely interwoven with the instrumentation of the control system and it is difficult without actual operational studies to establish which tasks ought to be automatized and which left to the man. This paper describes tests carried out with existing instrumentation to convert a conventional radar display into a television-type display. The indication from the tests is that a 1000-line system would be needed. The paper was presented at the annual meeting of the German Navigation Society in Dusseldorf, 5–7 June 1962, and is printed with the kind permission of that body.

The use of VLF radio transmissions as the basis of a navigation system has been under consideration for many years, and has been the subject of extensive theoretical work and field trials. Although a system of this kind has yet to reach operational status, the subject is of considerable interest in relation to marine and to air navigation. This paper indicates the main features that might be expected to characterize a practical VLF navigational aid, and outlines some of the work that has been carried out in this field. Brief reference is made to the question, so far largely unresolved, of the operational scope for VLF systems.

This paper, having first reviewed briefly the operational characteristics of present radar displays, deals with a new technique for presenting the radar data whereby a large, bright, high-contrast radar picture can be produced on a flat plotting surface by projecting in sequence rapidly processed photographs of a PPI cathode-ray tube presentation. It is followed by an account, by the radar officer in S.S. Canberra, Mr. D. W. Sims, of the use of the system at sea.

A great deal has been written, especially in the last few years, on the subject of collision at sea. The increase, however, in the speed of ships and in the density of traffic so magnifies the complexity of the problem that even closer and more earnest study is still called for. Three fields of inquiry demand our attention: technical advances, procedure, and the human factor. Of these, the widest and most promising might seem to be the first. Its importance is undeniable, and I am by no means the only one to have pointed out that with the new difficulties it raises it supplies also the appropriate solution. Even wider, however, and more complex is the field of human study; this covers both the others, for in this the final objective is to enable men to master what they have won for themselves, and this they cannot do—here we meet the familiar problems of philosophy, ethics and religion—unless they first learn to master themselves.

Compared with these two fields, the technical and the human, that of procedure must at first seem quite insignificant. Can one seriously imagine that there is in fact some new method of avoiding collisions, so abstruse that no one has yet been able to discover it? In my small book on the use of radar I wrote: ‘The Regulations envisage two ways of avoiding collision:

1. A movement carried out in concert with the other vessel.

2. A reduction of speed, if necessary to zero.

Separation of aircraft in terminal areas is made difficult by the convergence of tracks, continual changes of height, and traffic density. The application of longitudinal separation is too restrictive at busy aerodromes. Vertical separation is suited to the approach phase, but has limitations in the departure phase. The most useful form of separation is lateral, although it is often difficult to apply. The difficulties arise from organizational rather than operational causes and efforts to overcome them can be most rewarding.

Other difficulties of a terminal area arise from the conflicting patterns of adjacent aerodromes, the mixing of terminal and overflying traffic, and the mixing of departing and arriving traffic. Lateral separation can assist in all these problems.

A doppler navigation system measures velocity relative to the surface of the Earth. If the surface is moving, as for example when flying over an ocean, the doppler will indicate a false ground-speed and/or drift, according to the direction of surface movement.

Trials carried out by the Experimental Navigation Division of the Aeroplane and Armament Experimental Establishment at Boscombe Down show that there is a positive correlation between doppler system error and the surface wind direction when flying over the sea in an aircraft which has an accurate heading reference system. The analysis of all data is by no means complete, but as the spread of errors is so small it is thought that users of doppler navigation systems may wish to see the trend of results and to accept a few simple rules to compensate for the surface movement.

The value of the surface movement for a doppler equipment having a 1 percent correction for spectrum distortion is about 3 kt. for a surface wind velocity of 10 kt., 4 kt. for a wind velocity of 18 kt., 5 kt. for a wind velocity of 30 kt. and 6 kt. for a wind velocity of 50 kt. or more. The cardinal rule is that the doppler navigation system will indicate a position upwind of the correct position.

Clearly there is little point in applying an across-track correction of say 6 kt.

In areas of sufficiently high traffic density, air traffic control in some form will always be the primary mode of ensuring aircraft separation. Any traffic control system is concerned with separating aircraft in the future; therefore, the nominal separation criteria are determined by the accuracy of prediction of future movement of the aircraft and by the ability of the control system to correlate flight path predictions. The utilization of an airspace of a given capacity is determined by the distribution or flow of traffic.

The accuracy of prediction depends on track-keeping and maintenance of planned ground speed. Since improvements in track-keeping will be limited for some time by past I.C.A.O. decisions on short-range navigation aids, attention is directed in this paper to maintenance of flight-planned ground speed. The effect of this on the operating cost of a modern jet airliner is examined and compared with the cost of flying at minimum cost mach number at a less than optimum altitude. It is concluded that in a crowded airspace, speed maintenance is preferable in short-range operations.

The increase in space utilization by flow control is illustrated for a simple model, showing that speed control by A.T.C. increases utilization of a space capacity, which has already been increased by speed maintenance.

The following notes, from one of the contestants in the single-handed transatlantic race 1960, will be of great interest to a number of people concerned with wind and weather observations and the performance of small boats in heavy weather. Dr. Lewis's track in 1960 was by the great circle from Plymouth to New York, from New York up to St. John's, Newfoundland, and then back across the Atlantic to Lerwick in the Shetlands.

Airborne weather radar equipment, carried for detection of meteorological phenomena, is now well established as a standard equipment for most transport aircraft, and is even being specified for the larger executive types. It may be useful, therefore, to review the basic factors which influence the value of the information obtained and the progress made with equipment designs during the last decade.

Turbulence on its own cannot be detected by radar. The radar defines areas in which some form of precipitation is occurring, i.e. heavy rain, hail, ice crystals or snow. Of these, the areas in which large water droplets fall as heavy rain on the ground or exist in suspension in the cloud are of most interest, since they are inevitably associated with convective cloud formations. All other information relating to the possibility of turbulence, ice formations, hail, &c., must be deduced by the observer from his knowledge of the mechanism of such meteorological phenomena. However, it is clear that the radar must display information on large droplet type clouds only. The presentation of small water droplet clouds not associated with convective processes would serve only to confuse the picture.

The theory of reflections from meteorological phenomena is dealt with very thoroughly in the literature and here only the main conclusions will be summarized to show how the characteristics of a radar set affect the information produced.

The first shipboard installation of the Kelvin & Hughes rapid processing photographic radar system has now completed 500 hours service aboard the P. & O. liner Canberra and the navigational and technical staff in the ship have had a reasonable opportunity to evaluate the equipment from all practical aspects. The advantages of this type of display are, in summary:

(1) A full size plotting screen (in this case 24-in. diameter) is available for direct plotting.

(2) All operations may be carried out in broad daylight without the necessity of having to accustom the eyes to a dimmed PPI.

(3) There is no radar hypnosis. Information is presented as a solid, steady picture at the end of each cycle.

(4) A permanent record of the radar information is immediately available for playback at any later date.

(5) Several officers may view the screen at the one time and discuss the plot while it continues uninterrupted. This is a very favourable point in a large vessel of high speed where three or more senior officers may wish to know at all times exactly what is happening on the radar plot.

(6) By using a processing/exposure cycle of seven seconds or more, a build-up of picture strength, true track of vessels, &c. is possible.