The need for measures to guide shipping in congested waters to reduce collision risk has received a very considerable amount of attention over the past few years. The Safety of Life at Sea Conference in 1960 recognized the danger of collision in congested areas and required ship owners to formulate ways whereby some measure of control of traffic could be introduced with a view to reducing collision risks. Shell Tankers accept this responsibility and are, therefore, anxious to make some contribution towards the solution of the problem.

Many valuable papers on the subject have been published in professional journals recently. Most of the authors have emphasized the difficulties in which Masters are placed when called to navigate their ships through heavy traffic in reduced visibility, and Calvert in his study of the collision-avoidance problem reached a first conclusion that whatever might be done to improve anti-collision manœuvring, there was an urgent need for regulation of traffic in areas of congestion.

The problem of introducing any system of routing at sea is how to achieve effective control at an international level without drawing up hard and fast rules or imposing restrictions that might well, in view of the impossibility of policing vast ocean areas, prove nugatory. We hold that it is better to replace the rigidity of the prescribed route (the only relevant example, and that inconclusive, is the North Atlantic Track Agreement) by the much more fluid notion of the ‘recommended and protected route’, for which we have adopted the name ‘naviroutes’.

In the discussion which followed the Institute's proposal on routing, Captain Oudet proposed that the collision problem should be investigated in other areas where the risk was known to be high. This paper discusses the origin of NEMEDRI routes and the collision problem on specific NEMEDRI routes in the North Sea.

The origin of NEMEDRI (Northern European and Mediterranean Routing Instructions) routes is a matter of history and necessity, some understanding of which is necessary in any analysis of present problems, NEMEDRI routes are those swept routes through declared danger areas due to mining in World War II in North European waters, the Mediterranean and Black Sea. These routes take their name from the NEMEDRI publication issued to mariners giving the relevant hydrographic information for these particular areas. The swept routes and declared danger areas in many other areas, such as the remote Kerguelen Islands, Tonga or off Korea, have no such special publication and are notified in Notices to Mariners. The present navigational significance of the NEMEDRI routes is that they carry a very substantial amount of the world seaborne trade.

It is not the purpose of this paper to enter too deeply into the controversy between heading reference systems (combined with a velocity sensor) and full inertial systems. Rather it is intended to indicate what may be achieved at the present time, and in the next few years, using a heading reference system combined with a velocity sensor such as doppler radar. In conclusion the performance, weight, size, cost and reliability of such systems will be compared with similar figures for a full inertial system in the hope of stimulating thought and discussion as to what is the correct choice of system as well as to what the user may be able to afford.

In the early part of the last decade the most widely used heading reference was the gyro-magnetic compass—a flux-valve being used to give good long-term heading accuracy whilst short-term variations are smoothed out by the integrating action of a' directional gyroscope. The directional gyroscope was in fact slaved to the magnetic reference. Accuracies of 1°·0 (r.m.s.) are typically achieved by such a system, although higher accuracies are sometimes claimed under certain specified conditions.

During 1960 the French civil and military authorities decided to coordinate their efforts and to step up the programme of research and practical tests on landing in poor visibility. They felt that they could best contribute to the development of air transport in this vital field by adding their own vigorous and intensive efforts to the considerable body of work already undertaken by other countries. Numerous automatic landings had already been made in the U.S.A., and the British Blind Landing Experimental Unit had made several thousand. Yet, in spite of the results obtained, many problems still remained unsolved and many questions unanswered. There was evidently still room for much more practical work and theoretical research.

Only ten years ago it would have been premature to imagine that ILS was likely to provide the basic means for completed landing in zero visibility. The system, designed in 1939, had then received only technological improvements, and no feature seemed to lend itself to any notable development. A frequency of 110 Mc/s is much too low to obtain a narrow beam; all the rival systems now being developed experimentally use frequencies 10 to 100 times higher. Nor is the measurement of difference in rate of modulation the most accurate operation possible with electrical magnitudes; pulse-systems or phase-comparison systems are better adapted.

In view of the number of installations in use on the ground and in the air it was, however, practically impossible to envisage any other guidance system to replace ILS; for modifications would have to be ‘compatible’, i.e. not involve a change in airborne receivers.

The inter-relationships between the application of such airborne devices as automatic landing, head-up instrument displays, flare-out computers, and the like, their effect on operating weather minima, and the consequential benefits that may be derived in scheduled regularity, are very involved. The purpose of this note is to set out in simple terms the more important factors so as to provide a framework for further discussion. A cardinal theme of this discussion is the close association between the techniques needed to improve regularity, and those needed to improve safety.

The landing of a transport type aircraft is a task of a routine and repetitive type. It takes place within a fixed envelope of conditions that can be fairly strictly defined, and a high order of precision is needed compared with other phases of normal flight. The repetitive consistency that can be achieved by automatic means makes it natural to consider such a solution. Once such a system has been developed to a satisfactory level, the accuracy and consistency of the landing manœuvre will undoubtedly be much better than can be achieved by a human pilot.

Dr. David Lewis, better known for his own remarkable feats of navigation, which include single-handed transatlantic passages, illuminates the background to various theories on early Polynesian navigation. Reviewing the evidence, which includes the wide dispersion of the Polynesians and their culture as well as methods of navigation and seamanship that were still practised at the period of European contact, Dr. Lewis concludes that they could determine both course and, in effect, latitude with sufficient accuracy to make a landfall within the area of a known island group, and so proceed to any intended destination.

The navigator at the present time relies greatly on both optical devices and on radio systems utilizing electromagnetic waves ranging in wavelength from millimetres up to hundreds of metres. The laser extends the coherent properties of radio waves into the visible part of the spectrum. It is natural therefore to expect that this increased facility should lead to the possibility of devising systems based on the laser which might help to overcome problems that still exist in navigation.

It is the purpose of this paper to describe the principles and performance of present-day lasers, to survey some of the techniques used in navigation in order to discover those in which the laser might conceivably play a useful part, and to comment on the laser's advantages and disadvantages in comparison with existing methods. Finally, a particular form of laser called the ‘ring laser’ is described and discussed in some detail. The ring laser is of great interest in that it provides a completely novel way of measuring direction relative to inertial space, and is therefore a possible competitor to the gyroscope for inertial navigation. The ring laser can also measure the velocity of a transparent medium moving relative to it, which could be of use in determining vehicle velocity.

In several studies of the Spanish and Dutch voyages in the Pacific in the sixteenth and seventeenth centuries it has been suggested that an apparent consistency in errors of latitude determined by the navigator in question can be used as evidence in the identification of island discoveries, and can be regarded as confirming the identification of one or the rejection of another possibility. I am extremely doubtful about the validity of using such apparent consistency of error, even as secondary evidence combined with other indications, and have no doubts about its invalidity as primary evidence.

Andrew Sharp, for instance, when considering the identification of the Los Bajos de la Candelaria of Mendaña's voyage of 1568 in his The Discovery of the Pacific Islands, remarks that whilst both Ontong Java and Roncador Reef in the Northern Solomons are possible identifications: ‘The steady southerly error in Gallego's latitudes … points to Ontong Java’.

For a quarter of a century now we have struggled in a curiously impotent way with the problem of long-range navigation of civil aircraft and the associated problem of control of traffic in oceanic control areas. The deliberations of technical conferences of the International Air Transport Association alone during the past 15 years on the subject of Long-range Navigation of Civil Aircraft would fill a library.

The development of navigation has always been retarded by difficulties with the analysis of the operational requirement. It is, for example, inconceivable that if the operational requirement for astronomical navigation had been properly explained to eighteenth-century astronomers, they would have waited for practising seamen to invent the position line almost by accident. As neither the authors of Long-range Navigation of Civil Aircraft (D. E. Hampton and J. R. Mills. This Journal 17, 183) nor any of the speakers recorded in the subsequent discussion are directly involved with the operation of aircraft some remarks on the assumed requirements may be helpful.

‘Surprise has sometimes been expressed by mathematicians who have been led by circumstances to look into the subject of nautical astronomy that no method is practised by sailors for reducing a longitude observation to the prime vertical in the same way that an observation for latitude is reduced to the meridian.’

This quotation forms the opening paragraph of the first of three papers by Mr. H. B. Goodwin, R.N., written in 1904–6 relating to the problem of reduction to the prime vertical. The following description of Goodwin's work in this connection may not be without interest in view of the recent interesting paper by D. H. Sadler in which the author describes the investigations into the same problem made by G. F. Cunningham.

The vast difference, to which Mr. Sadler refers, between proposing and translating into practice, a new navigational table, is exemplified in the case of Goodwin's P.V. Tables. All the intermediate steps between proposing and producing are described with utmost clarity in Goodwin's three papers.

(1) Through the above contribution by Captain Charles H. Cotter, my attention has been drawn to the fact that the essential principle of the ‘Rectofix Tables’ is not only quite old but has been incorporated in a set of published tables —the Position Line Star Tables (for fixing ship's position by reduction to meridian and prime vertical without logarithmic calculation) by H. B. Goodwin, R.N., J. D. Potter, London, 1906.

Understandably, there are considerable differences in methodology and presentation, but all the essential concepts underlying the method are incorporated in Goodwin's tables; the main improvement introduced by Dr. Cunningham (who was, of course, quite unaware of these tables) is the inclusion of tabulations for the azimuth (Journal 17, 17).

Although none of the colleagues to whom I showed my short article called my attention to the existence of Goodwin's tables, I must accept sole responsibility for not having made a more thorough search of the published literature on the subject. This omission does, however, serve to underline the general note in that article on the difficulty of assigning priority for particular methods.

I have read with great interest the article entitled ‘Manned Space Flight Navigation Techniques’ by Major R. C. Henry in the October issue of the Journal.

It would appear that much of the imagined difficulty in interplanetary navigation is due to the fact that until now man has really been concerned with fixing his position and controlling his path on a spherical surface, the third-dimensional problem in air navigation has been one of altitude—i.e. definition of the surface concerned. Now, for the first time, we are involved in what at first sight appears to be a truly three-dimensional problem, and its solution appears difficult, partly because we are to be removed from our familiar graticule of earthly meridians and parallels.

If the problem be divided into two parts, an obvious solution presents itself. At sea, a ship must be on the surface of the water, and is mainly concerned with its position and course on that surface. An aircraft determines its surface of reference by barometric pressure (which by tradition is termed Pressure Altitude and expressed as a linear measure), and again is then concerned with a twodimensional problem on that surface.