The Navstar Global Positioning System (GPS) is a satellite-based passive radio-navigation system under development by the US Department of Defense (DOD) and due for operational deployment in the late 1980s. Each satellite carries an atomic frequency standard and transmits L-band spread-spectrum signals whose carrier frequencies and code epochs are synchronized with the satellite clocks. A suitably equipped user may measure the arrival time and frequency of the signals from at least four satellites to obtain accurate three-dimensional position and velocity information and, as a by-product, an accurate ‘system’ time.

It must be stated at the outset that the present author has a technical knowledge of Navstar GPS based only on fragments of the literature open to the public, and no knowledge whatever about the plans for its military use. An attempt will be made to discuss, from first principles, the consequences to both civil and friendly military users of the availability of a global, satellite-based navaid that makes possible the determination of position in three dimensions to a high accuracy. For civil users, confined to the ‘coarse acquisition’ mode, there is a 95 per cent probability that the horizontal position error will not exceed about 20 metres. For military users holding the key to a more sophisticated mode of operation, a significantly greater accuracy is available. The GPS also determines velocity, and data can be updated every second or so. It will be assumed that the navaid covers all the Earth's surface of interest, down to ground level. The cost of the satellite system is assumed to be high.

Seafaring has always been an occupation which exposes the seafarer to more than an ordinary degree of risk, and a significant part of that risk arises from his inability always to know his position with sufficient accuracy as and when needed. This lack of precision has always had a fundamental impact on the practice of navigation, the development of navigational aids, the production of charts and so forth, and to a much greater degree than is, perhaps, generally realized. As we are now approaching the time when a global capacity to fix position on demand and to a high degree of accuracy is becoming available it seems sensible that we should go back to first principles before forming a view as to its likely impact on future navigational practice.

Work on integrated navigation for aircraft started at RAF Farnborough at least as early as the mid 1950s. At that time the Inertial Navigator (IN) for a guided bomb was being developed and the navigation of the aircraft to the target used a combination of the weapon IN, Doppler radar and position fixing. An output of the navigation process was a calibration of the weapon IN. The operational concept was interesting in that after weapon release the aircraft had to return home using Doppler and compass.

Development of this system included flight trials in raf and a & aee aircraft using the Decca Navigator chains in Southern England for position reference. The same method was used in the development of the FSP 100 IN intended for the TSR 2 which took place in 1960/63. On these trials an early airborne digital computer on board the trials aircraft enabled Decca, Doppler and the IN information to be recorded and processed in-flight in a form suitable for post-flight analysis using a ground digital computer. This technique formed the basis for producing the reference navigation system which has been used for all our subsequent trials. The production of a position, velocity and attitude reference system for trials of inertial and other navigation systems has formed a major objective for RAE work on integrated navigation since that time.

The history of aeronautics has been marked by a number of revolutionary breakthroughs influencing both designers and users. A major example is the advent of jet aircraft. In flight deck instrumentation the technical revolution has followed a steadier course, enabling a gradual evolution from the rudimentary instruments used on yesterday's aircraft to the sophisticated instruments used today.

In this respect, the information displayed has evolved both in quantity and quality. This has gradually led to new flight deck designs such as that used in the Airbus A 300. The impression of a gradual evolution in instrument technology is due to the fact that information is often displayed in the same manner as before, i.e. using dial indicators. Today, a new revolution is taking place in commercial aircraft flight decks: the use of digital systems displaying processed data on cathode ray tube (CRT) displays.

Preliminary Studies. The use of CRT in flight deck instrumentation has been under study for a number of years. Many aircraft are already fitted with CRT for specific applications such as weather radar information and computer-processed data (on display units linked with computers).

The present CRT breakthrough is tending to compete with or replace conventional instruments. This tendency started in 1968–70, giving rise to a number of preliminary studies, with military aviation quickly taking the lead. Studies were also carried out in commercial aviation, for example those of the Boeing SST programme which, as is commonly known, was later cancelled.

An examination of accounts of sixteenth-century voyages shows that the estimations of latitude then arrived at by astronomical means were subject to widely varying error. The purpose of the present study has been to discover by practical experiments at sea, with replicas of instruments in use at the time, to what extent the size and irregularity of the errors can be attributed to the characteristics of the instruments and to what extent they arise from other causes. Observations were made from a 9-ton yacht under conditions not wholly dissimilar to those obtaining in some of the very small ships whose voyages are recorded.

The evidence for latitude errors is derived from published studies and from the writer's own analyses of three voyages made in northern waters by ships of the Muscovy Company: those of Stephen Borough of 1556 and 1557 and that of Arthur Pet and Charles Jackman of 1580. These were chosen because the masters in that Company's service received the best nagivational advice of the time3 and from the early 1550s onwards regularly recorded both latitude and compass variation. Furthermore, the relatively low altitude of the Sun in the higher latitudes was conducive to greater accuracy with a cross-staff.

The paper, an edited and shortened version of the original, discusses a new approach to the display of collision threat parameter areas, obtained as a result of theoretical considerations. It can be applied to radar-computer anti-collision systems as well as manual radar plots.

With the development of digital techniques, and electronic digital computers in particular, radar-computer anti-collision systems are now aboard ships. Digital processing of signals and data in such systems can be divided into three stages as follows:

(a) Primary processing, which includes an analysis of radar signals within one rotation of the radar antenna. A result of this processing would be the position coordinates of detected objects. For relatively simple algorithms and high speed of analysis, special devices are usually employed.

(b) A secondary processing, which includes a correlation of the information obtained in the primary processing stage; the objects' position coordinates in consecutive antenna rotations; and an estimate of position, motion and approach parameters. For secondary processing devices general-purpose mini- and microcomputers are usually applied.

(c) A graphical display of the calculation.

French maritime surveillance centres have been operating for several years. Experience gained over this period, and the French government's desire to take all steps to limit the possibility of catastrophic pollution, has led the French lighthouse and navigation service, in cooperation with the transport research institute, to implement an updated programme for maritime surveillance centres to allow them to carry out their existing tasks more efficiently and increase the scale of their activities. For this reason, a new system is being tried out at Gris-Nez Centre. It comprises a computer, which receives radar data from the radar tracking computer and effects partial automatization of the operator's tasks. In the future, it is hoped to use this new computer to help the operation centre detect the most dangerous encounter situations between vessels.

Obviously the centre is not intended to replace the officer of the watch, who will retain full responsibility, but it can assist by putting him in touch with vessels which he could encounter. A typical case where the centre might help is that of a vessel whose radar is out of service, or a vessel hindered by her deep draught and limited manoeuvrability.

The participation of such centres in preventing collisions is a new factor in maritime operations and can only be introduced when all preliminary investigations have been carried out.

In recent years it is probably true to say that the main pressures for inprovements in navigational safety have come from public and hence political sources. The pressure has usually taken the form of proposals for increased regulation of marine traffic. Often there is a defensive reaction from the professional mariner on the grounds that there is no real evidence that the proposals will produce a significant improvement in safety. Shipowners are also worried because of potential increased costs and curtailment of operating freedom.

It is therefore important that more information is made available so that both the safety aspects and economic aspects of additional regulation may be assessed. This paper is an account of a study into the development of danger criteria for marine traffic flows. This study was the key part of a larger one which was funded by the Department of Industry through its Ship and Marine Technology Requirements Board, now superseded by the Marine Technology Committee.

Collision rates on their own are usually not suitable for measuring safety risk, as collisions in a specific area are normally a very rare event. It is also not advisable to use data collected over several years as the traffic is likely to change, e.g. size of ship. Another approach might be the reporting of near misses, but there are considerable problems if navigators are asked to do this especially as there might be subjective judgments on whether to report an incident or not.

This paper, which was presented at an Ordinary Meeting of the Institute held in London on 26 January 1983, outlines the development and analysis of the ship domain in restricted waters and illustrates some of its uses in a buoyed channel.

The analysis of marine casualties raises the question of how casualties occur, and may indicate the circumstances most likely to lead to a casualty. In addition, information may be gained as a basis for estimating the risk of a casualty and for assessing the effectiveness of proposals for improving the safety and efficiency of navigation in the area.

The use of casualty statistics as a measure of marine risk has distinct limitations. In most areas a casualty is a reasonably rare occurrence, so that any systematic analysis of casualties will normally have to take place over a period of a few years; and, if improvements are made, a further period of time is necessary to measure their effectiveness.

The paper deals with the formulation and analysis of the problem of ship's traffic control in separation schemes. The branch and bound procedure has been used for optimal solution of the problem. The proof for a possible computational process is given together with the results of a numerical example.

In view of the rapid development of the world merchant fleet the problem of safety at sea appears now as neither fully defined nor sufficiently analysed. Some measures and partial solutions to improve the safety of sea traffic have been suggested and implemented, e.g. in papers by Ciletti and Glas. As examples of such implementation one can mention traffic lanes, the calculation of separation-scheme optimal crossing angles, etc. In areas with heavy traffic where either natural constraints such as islands, submerged obstacles or traditional routes exist, all the separation lanes create sophisticated systems called traffic separation schemes. Many steps now being taken to improve safety of navigation are based essentially on traffic separation. Some innovations and improvements in designing the structures of the separation schemes must be taken into account. It seems that all such passive measures will be efficient up to natural limits connected with the magnitude of the traffic flow. In heavy traffic the author believes active control should be established.

The International Regulations for Preventing Collisions at Sea contain several important terms which are open to different interpretations such as ‘safe speed’, ‘close-quarters situation’ and ‘risk of collision’. It is not possible to give exact definitions of these terms as some of the factors involved are difficult to quantify but there is little doubt that mariners would welcome some official guidance on their application.

The following paper by Dr Hilgert proposes a method of defining ‘close-quarters situation’ in terms of the principal factors which apply. The method is of particular interest because it is actually used by the maritime administration of one government and has been submitted to the International Maritime Organization for consideration. The IMO Sub-Committee on Safety of Navigation has taken note of the suggested approach and has invited comments.

It is suggested in the paper that a simplified version of close-quarters situation could be determined in terms of the quantifiable parameters of speed, manoeuvrability and angle of approach. The method could be used to establish minimum values of a close-quarters situation but other factors would have to be taken into account such as the close presence of navigational hazards or other vessels, radar performance including the effect of errors and the desirability of keeping out of audible range of the fog signals of an approaching vessel.

Despite some obvious limitations the method serves to indicate the least values which should be used and the paper contributes to a better understanding of this aspect of the avoidance of collision at sea.

Traffic separation was first introduced on a voluntary basis in the Dover Strait in September 1967, just over fifteen years ago. Compliance with the IMO provisions relating to traffic separation schemes has been mandatory for all ships during the last five years and for some ships for as much as ten years. It may therefore be appropriate to assess the effectiveness of routing off North West Europe by comparing collision statistics for five-year periods since 1957.

The results given in the following tables apply only to collisions involving trading vessels of over 100 g.r.t. under way and not engaged in any special activities. Collisions in harbours, rivers and congested port approaches where special circumstances apply are not included. The figures quoted for the Dover Strait have been checked against the results obtained by the National Maritime Institute but are based on different criteria, and there may be some discrepancies.

The area covered is the coastal region from the south-western approaches to the Ushant TSS to the approaches to the Elbe including all parts of the English Channel and the Dover Strait, but not including waters off the East Coast of England which are well clear of the traffic separation schemes and deep-water routes.

The numbers of collisions are based almost entirely on Lloyd's Weekly Casualty Reports. Information relating to encounter situations is based on voyage data supplemented wherever possible by information received from additional sources relating to the actual courses steered by each vessel. It is not claimed that the figures constitute a precise record but they should provide a good indication of changes in the incidence of collision off North West Europe.

This paper deals with the work of the International Hydrographic Organisation (IHO) during the last ten years towards the standardization of nautical charts. The work began with the devising of a regional scheme of medium- and large-scale sheets of the north-east Atlantic area, to be co-produced by member nations as contributions to an International (INT) set of charts. It subsequently became clear that, as well as the scheme, a detailed set of specifications would be necessary to secure uniformity of choice of symbols and abbreviations throughout the International series, and also in the various national chart series of which it would form a part.

The history of nautical chart standardization has recently been traced by Ritchie – gradual at first after the beginning of the International Hydrographic Bureau in 1921, and later speeding up when the International Hydrographic Conference of 1967 established a study which led to two series of INT charts on very small scales. After this the process gathered further speed with the successful establishment of the two bodies with whose work this paper is primarily concerned: the North Sea International Chart Commission (NSICC) in 1972 and the Chart Specifications (later Standardization) Committee (CSC) in 1977. The ten-nation NSICC, in drawing up the network of INT sheet-lines for its area, established the principles on which such schemes would be extended worldwide and also did extensive groundwork for the Chart Specifications of the IHO. These were completed for worldwide application by the seventeen-nation CSC.

Many vessels trading on North Atlantic routes are equipped with weather facsimile receiving devices of various types. Ship-masters engaged on regular voyages in this area are thus able to conduct their own passage planning using the information readily available from these intruments. The capital cost in relation to other ship operation costs is negligible; in US dollars (1983) it is likely to be of the order:

There would be no problem in planning a vessel's route across an ocean if it were possible to forecast with total accuracy the actual sea state existing for the duration of a voyage. Such an ideal circumstance does not yet exist and a method must thus be used which incorporates flexibility to modify a voyage plan as actual weather varies from the prognosis. This means that a subjective approach to storm avoidance may, on occasions, be preferable to the stringent demands of a least-time track. The obsession of routing agencies with the latter method may be one reason why weather routing has not achieved the success it perhaps deserves.

A ship may be damaged or delayed by the action of sea waves on her hull or structure. Hull form and ship dimensions are usually selected on the basis of calm-water performance, rather than for sustained sea-speed.

An announcement of Wing Commander Anderson's recent death appears on another page. Mr William's spirited criticism of Anderson's ‘Rotations in Navigation’, and by implication his more recent note on Coriolis (May 1983 issue), was of course written before the sad news was known. It is published here without modification (and in spite of the author's offer to withdraw it) as would undoubtedly have been Wing Commander Anderson's wish.

At the end of the last war Wing Commander E. W. Anderson was one of the most distinguished practising navigators in the Royal Air Force. ‘Andy’, as he is known to so many, has since become navigation's leading exegete through his work in this Institute, his articles, lectures and books. ‘Rotations in Navigation’, however, has got him in a flat spin. The reason why has wider implications worth examining.

Andy starts by suggesting that the difficulty of explaining Coriolis ‘may be due to the intellectual danger of trusting mathematics without making sure that the right circumstances surround the formulae which emerge’. This observation illustrates how well one can write English without saying what one means. Circumstances, right or wrong, cannot surround a formula although the statement a formula makes may be irrelevant to our circumstances. It is precisely because pure mathematics is the language, as Russell put it, ‘in which we do not know what we are talking about or care whether what we say about it is true’, that applied mathematics is the language in which we are obliged to say what we mean or be seen to use the language wrongly.

Van de Ree has provided a solution to what must be a fairly common problem in navigation. The problem may be stated as follows.

A ship on a rhumb-line course encounters head-winds and heavy seas requiring her to reduce speed. If she alters course, but does not change the rate of fuel consumption, her speed will be given by (a + b sin A), where A is the course change, a is the speed into the head sea and a + b is the speed in a beam sea. How far should the navigator alter course so that, after a given time, the ship will be nearer the destination than on any other course and, in addition, the labouring of the vessel will be reduced?

Van de Ree's trial-and-error solution assumed the destination to be initially 63 miles away, a = 12, b = 5, and the optimization period 1 hour. His solution was to alter course by 20(± 2·5)°. It is possible to obtain a general algebraic solution to this problem, but it requires differentiating complicated trigonometric functions and solving a complicated trigonometric equation, and so the algebraic solution is not practically useful. It is also possible to solve the problem graphically. This solution is by far the simplest one and would be recommended in place of either Van de Ree's laborious numerical solution, or the equally difficult algebraic solution.

However, one could question whether the chosen tactic is the appropriate one.