Both the argument and the geometry in this paper require careful study before they can be appreciated; it is hoped that the following notes, which are restricted to purely geometrical considerations, will assist readers to understand them.

The author's fundamental argument is that it is geometrically impossible for ships A and B, at distance r apart and moving with constant speeds v and u, to approach each other more closely than distance d (less than r) if the courses of ships A and B are each restricted to a semi-circular anti-collision sector, depending only on the angle δ sin δ = d/r, and on an agreed universal convention. This is illustrated in Fig. 1 in which the two sectors are indicated by vv' for ship A and uu' for ship B. Adopting the convention that the ships pass ‘port to port’, the permissive anti-collision sector for each ship is, relative to the bearing of the other ship, from δ to starboard, increasing to 180° and to port from 180° to 180° −δ . This is equivalent to restricting the course so that the other ship bears more than δ to port or more than 180°−δ to starboard.

It is pointed out that the demand by navigators for more information in a given time or for the same information in a shorter time can only be met at the price of increased complexity (and, therefore, cost) and unreliability. To provide examples supporting this statement, a number of well-known systems are described briefly; for example, in the family of hyperbolic systems there is a clear indication that those providing immediate access to an unambiguous fix are more complex, in the wide sense, than those achieving similar accuracy but at the expense of ambiguities. This is even more true when various degrees of automatic operation and display are considered, and the paper includes a description of some of the techniques involved in the provision of these facilities. Finally, brief reference is made to the suitability for automatic computing of the geometry of the various systems and it is pointed out that those working in polar coordinates or Earth axes (such as VOR/DME and doppler/compass respectively) have advantages over the hyperbolic systems.

In this paper, by the Director of the Radio Advisory Service, a comprehensive survey i s made of all the main trends of development in commercial marine radar since it first went to sea in 1946. The opinions of a representative group of seamen on the value they get from radar is analysed, and finally some views of manufacturers and seamen on what the future may hold are examined. The paper was presented at the annual meeting of the Ausschuss fur Funkortung held in Kiel on 10, 11, 12 September 1960, and is reproduced with the kind permission of that body.

The last fifteen years represent almost exactly the whole life of commercial radar in merchant ships; in the United Kingdom the first commercial types were beginning to go to sea towards the end of 1946. The period has been an intensely interesting one from almost every aspect of the subject and the writer is fortunate in having been associated with merchant ships, and their owners, for thirteen of these fifteen years and with the subject of radar at sea since 1936.

A computer known as the Radio Track Guide, of which both air and ground trials have been held, is described. As a system it can provide accurate automatic guidance for all anticipated operational conditions in a manner which is of value for both navigational and movement-control purposes. Mr. Britnell's paper was presented at the Paris convention on automatic navigation.

The criterion for assessing the efficiency of a navigational aid must include a reference to the ease and precision with which it enables a vehicle to maintain a specified track. In aircraft navigation the most accurate tracks are, of necessity, those made in the vicinity of the runway during the landing and take-off phases. At such times the errors must be limited to a few feet and such small values are a result of the pilot using an ideal reference frame for lateral guidance purposes. This is centred upon the runway and within it he is able to detect, with a high degree of accuracy, the two quantities necessary for precise track keeping. These two quantities are the displacement and rate of displacement from the required track.

Dr. Ramsayer's paper, presented at the tripartite meeting on automatic navigation held in Paris last April, describes a dead-reckoning computer on which position is presented instantaneously on a map.

The so called Automatische Koppelkarte has been developed by the Institute of Air Navigation of the Technical University of Stuttgart, and is a new type of dead reckoning computer differing from the usual navigation computers in that position is immediately indicated on a map; there are many possibilities for combining the device with other navigational aids.

Fig. 1 shows a schematic diagram of the computer. It consists of the computer, the map display and the course and track indicator. The station selector and the coordinate transformer shown in Fig. 1 are additional units, only used when monitoring by tacan is desired, as will be described. The computer is fed by a gyro-magnetic compass and a true airspeed transmitter. The wind is set at the map display, and ‘grivation’ at the course and track indicator. From these data both the flight path and the track are computed. The flight path is resolved in two rectangular components and is displayed by a light pointer on a map of conformal conical projection. The standard parallels of the map are selected in such a way that the distortion in length is practically negligible for the area of interest.

The doppler track computer is a navigation device which accepts inputs of ground-speed and track from a doppler radar, and computes and displays miles to go and miles transverse to a selected track. Several types are available on the market.

The heading input to the doppler may be from a magnetically slaved gyro or from a free gyro corrected for Earth rate. Thus, either magnetic tracks or gyro tracks are fed to the computer. Also, navigation may be carried out with reference to airways, mercator, conformal conic, oblique mercator, or polar stereographic charts.

Much has been written from time to time about the disaster which befell the fleet under Sir Clowdisley Shovel (or Shovell) among the rocks of the Scilly Islands on 22/23 October 1707. Although many writers have discussed the cause of the catastrophe I have come across no one who has examined the D.R. positions of the various vessels involved, and it is these which I propose to consider here.

It may be as well to recapitulate the story of the disaster. (At this time, it should be noted, the day at sea was measured from noon to noon and began twelve hours earlier than the civil day. Consequently, the afternoon at sea had a later date to that ashore. Noon positions logged were those at the end of the sea date.)

The requirements of navigation entering or leaving harbour or in narrow waters are exacting, and a very accurate position is usually essential. For this reason it is believed that inertial techniques should be applied in the first instance only to ocean navigation as, although the system will give the ship's position continually, the accuracy will be of the order of one mile.

The latitude and vertical references are absolute, but the longitude reference is relative to a known starting point. Besides position, an inertial system can also provide course, sidereal time and roll and pitch and, by comparison of successive positions, course and speed made good, and leeway. Furthermore the system could be used to feed position into an automatic plotting table, with a chart of suitable scale superimposed, so that the vessel's geographical location would be visible at a glance.

The route direction-finder is a device giving an accurate directional reference. It uses two distant transmitters, A and B, radiating two continuous waves, the frequencies of which are different but very proximate. The paper was presented at the Paris convention on automatic navigation.

Classical methods of navigation by dead reckoning have been considerably improved in recent years by the use of autonomous systems such as doppler and inertia which enable true speed to be measured. When using these systems, the principal cause of errors is the unreliability of the directional reference, which may be the meridian or any arc of a great circle, since it is with respect to this that the speed vector is obtained. The directional reference is given by the magnetic compass which often has an error of up to several degrees or is given by gyroscopic devices which can have considerable drift after several hours' operation. Errors in directional reference are especially marked in polar regions where magnetic or gyro compasses cannot be used.

The following discussion took place at an Ordinary Meeting of the Institute held at the Royal Geographical Society in London on 19 February 1960, with the President, Wing Commander E. W. Anderson, O.B.E., D.F.C, A.F.C, in the Chair. Dr. J. G. Porter is at the Royal Greenwich Observatory, Herstmonceux, Mr. D. J. Cashmore and Mr. T. McClymont are both with English Electric Aviation Limited.

Some general features of inertial and hybrid inertial systems are examined in relation to the navigational problem in its two essential aspects:

(i) The present situation.

(ii) The action required.

As the fundamental D.R. system, inertial navigation has the virtue of independence but suffers from time-dependent errors. The engineering complexity and delicacy of adjustment of purely inertial navigation systems of long-period accuracy detract from its general application where other aids are available. On the other hand, increasingly stringent demands on flight-path computation and control justify an examination of the benefits to be derived from exploitation of the particular short-period merits of an inertial element used in conjunction with other aids.

Principles of mixing are discussed in relation to quantity and quality of information inputs. Examples are then given of fallacies which may arise from the omission of essential information or from ignoring cross-coupling, and of the impracticability of mixed systems which assume too much of the quality of the input information.

After summarizing the main features of inertial, radio/radar and astro aids, examples are given of practical and useful mixed systems which do not require the highest precision of inertial components. For example, auto-astro and inertia/doppler/ground fix contain the necessary and sufficient ingredients for combining long-period accuracy with short-term memory, speed of response in manoeuvre and instantaneous outputs such as are required for precise control and for flight path monitoring.

Summarizing, it may be said that the value of true and hybrid inertial systems in the military context is evident. For more general application we may hope to see a gradual evolution of small, accurate and reliable central reference systems which will permit the employment of inertial methods suitable for mixing, especially with doppler in an accurate D.R. system. The outputs will be suitable not only for flight-path monitoring, but as providing information of a quality very well suited for integration into the control system and so into any overall system of flight automation.

In this paper, methods of defining heading are enumerated and the limitations of magnetic and gyroscopic devices are analysed in detail. Particular attention is paid to the development of the rotated race principle which is likely to be responsible for a large improvement in the basic azimuth gyro. The gyro-magnetic combination is scrutinized and the errors inherent in this compass system are classified. The possibility and consequent effect of diminishing certain categories of error are presented. The current position is summarized and an attempt is made to suggest possible future trends. The authors are, respectively, with Smiths Aircraft Instruments and the Sperry Gyroscope Company.

Doppler-operated computers which perform plane D.R. navigation are currently offered to the airlines. A datum track and distance to go are set; from the time of selecting ON, the computer resolves small elements of distance run (input doppler and heading reference) as follows:

Change in across-track dist. = element of dist. run × sin (actual tr. − set tr.)

Change in along-track dist. = element of dist. run × cos (actual tr. − set tr.)

These relations are true for a plane Earth.

The basic principles of radio sextants are reviewed and their application is compared and contrasted with that of infra-red and visual wavelength sextants. For maximum versatility an automatic sextant should be able to operate both on radio wavelength and at one of the others. A complete automatic system requires not only a means of making automatic celestial observations but also a means of carrying the data forward—that is to say, as inertial reference. In the paper presented in Paris the development of inertial systems was briefly reviewed with particular reference to linear vibration gyrostats which lend themselves readily to light and compact systems where the highest accuracy is not required.

It is suggested that future developments in automatic navigation may well see novel forms of inertial reference coupled to radio sextants of millimetre wavelengths.

In the development of instrument systems for the purpose of flight control, traditional designs have consistently failed to solve three particular operational problems:

• (a) The difficulty of transition from instrument to visual flight conditions at the final stages of an instrument approach to land in bad weather.

• (b) The preservation of instrument control when the pilot±s attention is, for any reason, directed away from the appropriate instruments. Preoccupation with other duties, lack of concentration due to fatigue, keeping a look-out for other aircraft, &c, are examples of situations when the maintenance of accurate flight control may be lost.

• (c) The effective monitoring of the accuracy and precision with which an automatic pilot is achieving its selected function. Admittedly this can be achieved by the pilot continuously watching his appropriate primary instruments, but this tends to be extremely monotonous, and to a considerable extent reduces the advantages to be derived from effective automatic control. This particular problem reaches its peak under high altitude, high-speed, conditions of cruise of a jet transport, and in the final stages of an automatic approach, automatic flare, or automatic landing, on any type of aircraft.

Three types of self-contained navigation systems may perhaps be found, operating independently on airliners flying polar routes; doppler, astro and inertial. We may also find hybrid systems with doppler, astro and inertial components. The combination of doppler and astro systems should be the first step towards self-contained automatic navigation and this combination could be used with great advantage by the airlines for global operations. The more sophisticated doppler and inertial combination may be found too expensive for airline operators and may therefore be restricted to military uses.

IN the Meteorological Office, great accuracy is not usually attainable in determining or forecasting the position of significant weather features. Special projections of charts are therefore not often required; the normal conic projection with two standard parallels or (near the equator) the mercator projection is quite adequate. However, in the radiolocation of thunderstorms a chart drawn on a gnomonic projection is required. The bearings of each lightning flash within one or two thousand miles are recorded from a small number of special stations (SFERICS stations). When these bearings are plotted on a gnomonic chart by straight lines drawn from the appropriate observing station the coordinates of the source of the lightning can be quickly determined and reported through normal meteorological channels. Speed is essential and therefore the charts on which the bearings are drawn are specially designed with the SFERICS stations grouped more or less evenly about the tangential point of the projection plane of the gnomonic chart.

A description is given of a floated rate-integrating gyroscope and of the way in which it may be used to provide a high-accuracy aircraft heading reference. The sources of error of the system are examined and the overall heading accuracy is estimated as being comparable with the distance accuracy of a doppler system. This paper was presented, on 15 January, at the same Ordinary Meeting of the Institute as the preceding paper by Green and Glenny.

The advent of the high-accuracy single-axis floated gyroscopes which have been developed so rapidly over recent years, primarily for inertial navigation use, has raised the question of whether the accuracy of these instruments can be made use of in other applications. Can systems which have been employing the older established types of gyroscope benefit from the greater stability of the new type? If a direct change of instrument with no modification of the method of use is considered, the answer will in many cases be no. For example, an improvement in the accuracy of the north-seeking marine gyro compass may not be found rewarding with existing marine navigation techniques, as other factors such as the accuracy with which a ship can be steered would become limiting, defeating the advantage of improved compass accuracy. The introduction of the doppler system has created a different situation in the field of aircraft navigation. Doppler navigation equipment enables an aircraft's drift angle to be measured accurately. That is, the aircraft's track can be defined with an accuracy dependent on the accuracy with which its heading can be measured. In this new situation the overall navigation accuracy is limited by the accuracy of aircraft compasses. These have in general been magnetic compasses, given improved dynamic performance in later years by the incorporation of a gyroscope or use of an associated directional gyro but still dependent on the magnetic element for long-term accuracy. Such a direction reference, though simple and reliable, is at no time precise by modern standards, and as the region of the magnetic pole is approached it becomes practically of very little value. For this reason in recent years the technique of using a free gyro alone as a long-term memory, to store direction information, has been developed, particularly by the airlines operating transpolar services. It is a system such as this that can reap most benefit from use of the new gyroscopes.

These methods were briefly described in the Journal (Vol. 13, No. 2). They were prefaced by some comments designed to draw a comparison between the air and sea problems and collision rates. Statistics are liable to be misleading if not perfectly understood and definitive, and marine collision statistics as much as any. It should be realized that Lloyd's List figures include almost every collision incident to ships of joo tons and over and that a comparable air figure would probably need to include damage to aircraft by aircraft on airfields and in hangars and whether under their own power or in tow.