This paper discusses some of the variations that occur in the Earth-ionosphere waveguide that can contribute to errors in the Omega lines of position that are used to obtain navigational fixes on a world-wide basis. Effects due to conductivity variations in the Earth's surface, night to day changes in the lower ionosphere, multi-mode propagation, and solar disturbances of the ionosphere are considered and attention is drawn to the use of the multiple frequencies transmitted in the Omega format to overcome some of these sources of error. The paper was presented at a Marine Navigation Symposium held in Sandefjord, Norway, on 24–26 September 1969 and is reproduced with the permission of the organizers. (Crown Copyright, reproduced with the permission of H.M. Stationery Office.)

Geophysical exploration involves the measurement, at the surface of the Earth, of physical quantities which will provide information about the structural configuration of the Earth's crust. Geophysical surveys are made for petroleum and mining companies to discover subsurface structures favourable to the accumulation of minerals of economic significance.

When geophysical exploration was extended to sea, pinpoint marine navigation became a requirement so that the prospector could return to the exact site of the geophysical anomaly. At first, operations were so near the shore that position determination was no problem. Visual observations were quite adequate. As operations pushed farther from land, high-accuracy electronic systems were pressed into service. Such names as Decca, Lorac, Raydist, and Shoran are familiar in the oil industry. But when operations extended beyond the range of precision radio systems and into areas where they were neither available nor could readily be made available because of hostile terrain, natives, or politicians, or where adequate surveys of shore transmitting stations were impractical, other means of navigation were needed. Navigation satellites, used in conjunction with other navigation equipment, fulfil this need.

This paper considers a practical solution to the stopping distance of ships, with particular reference to modern giant tankers. One solution to the problem has already been evolved by Captain H. Topley of the Honourable Company of Master Mariners. The present paper tackles the same subject from quite a different viewpoint.

The basic assumptions on which the mathematical treatment has been based is presented in Section 1, which also includes the calculation formulae of the speed and distance run at any time in a manœuvre, without proofs. Section 2 deals with clarifying the essential differences between Captain Topley's theory and the author's. The validity of the theories is examined in Section 3 by comparison with the results of actual ship tests. Section 4 presents calculation diagrams prepared by the author.

The only reliable data available by means of which captains can predict the stopping behaviour of their ships after ordering STOP ENGINES are the results of inertia tests conducted at the sea trials when the ships were built.

The inertia tests, however, are usually performed for only one case in which the approach speed is assigned to HALF AHEAD or the so-called manœuvring full ahead speed. Therefore most masters are glad of any knowledge of how to predict the movements of ships from any reduced speed.

The rapidly growing demand for more information on the manœuvrability of ships is distinctly recognizable nowadays, especially by an industrial service institute in the field of ships’ hydrodynamics like the Netherlands Ship Model Basin. At this moment, means like manœuvring basins, rotating arms and towing banks with planar motion systems are available at many places. The information obtained from ship-model tests in such facilities is still insufficient to satisfy all questions. There is a growing interest in training people under the circumstances which will confront them on ships in the near future. Governments, harbour authorities and shipowners like to know the criteria by which a decision to enter a harbour with a large ship can be taken. The human aspects of manœuvring very large ships have raised an interest in designing semi-automatic pilots. A clear explanation of the role of the human operator was presented by Segel at the ‘First Symposium on Ship Manoeuvrability’ in Washington in 1960. That paper discusses the many items that influence the path of the ship, which the pilot, captain or helmsman desires to follow. The block diagram presented in Fig. 1 illustrates the complexity of the phenomenon.

While the position fixing techniques employed in offshore drilling and exploration are in many ways similar to those used by the shipping industry—and, indeed, many systems are available to both—there are, nevertheless, several important differences. Accuracy and repeatability are two, in particular, which stand out. It is difficult to state in precise terms what accuracy is acceptable in an offshore survey because the customer is often obliged to accept the best of what he is offered but something of the order of 100 metres is likely to be the target. This is very much better than is required by the average ship out of sight of land or, for that matter, is obtainable in many cases with the instruments available. Repeatability means little to most navigators who rarely have any requirement to return exactly to any position denned in the past. The surveyor, on the other hand, has a continuing need to do this, running lines across his survey grid for check purposes, or at a later date when carrying out another survey or positioning a drilling rig.

When we look at the sea today we find a new world being unfolded. We find oceanology, the art of living on and using the sea-bed, no longer the sole domain of Jules Verne. Whole areas are devoted to the production of oil and gas from the seabed, with their rigs bringing literally new horizons as well as new hazards. Whole areas of the sea required for mankind's subsistence will be set aside in the eyes of civilization for purposes other than navigation. The sea will no longer be sacrosanct to ships and seamen alone.

Marketing a marine radar may not sound the most promising subject for a navigational paper. But in an age when almost anything is technically feasible, the direction of progress will be governed by many considerations which, if they are not themselves navigational, are nevertheless of great interest to those concerned with the subject. A new range of equipment for example must be related to the level of skill and training which actually prevails at sea; research and development costs must be seen in relation to the cost-effectiveness of the system; and finally purely operational factors such as traffic separation schemes may have to be taken into account. In this paper, originally presented in Paris to the French Institute of Navigation, some of these considerations are discussed in relation to the new Decca anti-collision radar.

Just over 25 years ago, in the summer of 1944, a United Kingdom conference on radio for marine transport concluded that radar would be of great value to merchant ships. They asked the Royal Navy to draw up a specification for the average ship. Discussion with various shipping interests confirmed that there was in fact a requirement for a radar set ‘for navigation and pilotage as distinct from a collision warning set, which would, of course, be a much simpler and cheaper device’. The later 1946 Ministry of Transport Specification referred to the requirement ‘to provide warning of the proximity of other surface craft and obstructions which will enable collision to be avoided’. Now of course, after 25 years of hard experience, we know that the matter of avoiding collision at sea is not apparently so simple.

This paper contains a brief survey of a series of instruments which have been developed for use in sailing yachts. It then outlines the principles of two computers; one navigational, the other for sailing performance indication. It does not cover radio navigational aids, echo sounding or radar. The data requirements are: 1. Navigational, comprising distance run through the water, heading, leeway angle. 2. Functional, comprising speed through the water, direction of the apparent wind and speed of the apparent wind.

For measuring distance run, the classical towed rotator type of log, fitted with a mechanical or electro-mechanical revolution counter has been largely superseded in racing yachts by logs employing through-hull sensors on account of drag considerations and the inconvenience of having to shorten the line when sailing slowly in shallow water. It still finds favour in cruising yachts on account of its generally lower price and its simplicity.

If the present Collision Regulations are defective, it is largely because the principles underlying them are not sufficiently developed for today's circumstances. In this paper Admiral García-Frías of the Spanish Navy attempts such a development and proposes a new set of rules, adapted to present circumstances, for vessels in sight of one another. These proposals, with the set of rules previously suggested in this Journal for restricted visibility using radar, form a complete system for avoiding collisions in both situations so that it would be easy to pass safely from one situation to the other when necessary, because of the unity of principles they present.

It is encouraging for certain schools of thought—which started some years ago advocating the revision of the Collision Regulations for occasions when radar was being used in restricted visibility—that there now seems to be a general dissatisfaction amongst seafarers with the lack of guidance provided in the rules. Consequently, they are at last interested in a fundamental review of the Regulations.

In this paper the history and development of inertial systems for the merchant marine is traced from the gyro-compass, familiar at sea since the beginning of the century, to complete inertia systems and integrated systems such as doppler/inertia.

The paper was presented at the Marine Navigation Symposium held in Sandefjord, Norway, on 24–6 September 1969 and is reproduced with the permission of the organizers.

The gyro-compass was first fitted on board a ship as long ago as 1908. Its function has been as the main reference by which the ship is steered and to which navigation by dead reckoning and direction finding is referred. The compass has been developed continuously to provide a more reliable, more accurate, and smaller instrument costing typically £1000 to £2000.

Following an invitation by N.A.S.A., the Bundesrepublik Deutschland carried out an experiment with the U.S. satellite ATS-3 (Applications Technology Satellite). The satellite is synchronous, or stationary with respect to the Earth's surface, at an altitude of about 35,800 km. above the equator.

The object of the experiment was to determine the system parameters for a navigation satellite system. This included investigation of the bandwidth of the ultra short-wave band used, and testing speech and data transmission between ships and the mainland, as well as carrying out determinations of baselines. The results are published in Research Report FB69—37 of the Bundesministerium für Bildung und Wissenschaft. The experiments were carried out during two expeditions of the German research ship Meteor, under the direction of the Deutsche Hydrographische Institut. The expeditions were to the west African coast in the spring of 1968, and in the summer to the Faroe Islands. In the fall of 1968 investigations were completed by measurements from a mainland station which was installed on the institute building of the Deutsche Forschungs- und Versuchsanstalt. This paper describes only the position experiment.

Captain F. J. Wylie is, of course, the complete master of the cumulative turn in all its aspects, not for a moment omitting the mathematical. And Commandant L. Oudet has greatly contributed to the study of this important and interesting subject in collision theory. He has provided detailed and lucid information on actual cases, brilliantly researched and reconstructed in a manner that would do credit even to the immortal analyst the Chevalier C. Auguste Dupin. There is indeed little that can be added to what these two and other distinguished authors have already recorded in the pages of this Journal, most notably in Wylie's 1963 article, Collision at Sea in Fog: The Commonsense Approach (16, 100), Oudet's 1965 article, Collision and the Courts (18, 188), and Wylie's article, Legal Aspects of Radar and Collision (18, 203). It also turns out that Wing Commander E. W. Anderson has made a most important contribution to this subject.

The problem of the autonomous determination of the position of a moving object (inertial navigation) on the Earth is solved by gyros, accelerometers, integrators and a computer. We will indicate three possible schemes of inertial navigation.

Continued discussions on techniques of rhumb-line sailing might well be considered irrelevant in today's climate of navigational technology. However, there is apparently one group of navigators who have a need for rhumb-line sailing by computation as opposed to direct measurement from a chart: this group comprises the navigators of merchant ships.

It may well be argued that traditional methods are adequate and that, although imprecise, the resulting errors are swamped by the errors of the data used. This argument is satisfactory for established navigators but, with the great improvements that have taken place in nautical education, does not hold for the teaching of newcomers.

In the July number of the Journal there appeared a series of contributions on the revision of the Collision Regulations, preceded by an introductory note which referred to a number of the more important papers on this subject published in the Journal during the last ten years. Partly as a result of this series of contributions, and of a questionnaire recently circulated by the International Chamber of Shipping, Captain Thompson, Master of the S.S. Magara, after discussion with those concerned with the Rules on board his vessel, has drawn up, for general discussion, draft revised Collision Regulations. Naturally they depend heavily on ideas published in the Journal and elsewhere; indeed their particular value is that they take account of many of these ideas and attempt to express them in a practical and seamanlike fashion. Clearly there are loopholes in the draft: it is the work of seamen, not lawyers. What matters at this stage is the intention, which is to provide rules and a code of conduct which are simple, unambiguous and clear. Commander P. C. H. Clissold made some useful comments on the original draft.

Of those who took part in the discussion on the Collision Regulations published in the Journal (22, 285), some favour amending the present rules. and others refraining them completely. There are grounds for thinking that a similar dissension exists among seamen.

Some publicity has recently been given to a new plan proposed by Trinity House and the Honourable Company of Master Mariners for the separation of traffic in the Dover Strait. This would reverse the direction of flow established by Imco in 1967 according to which the main streams of traffic between the Channel and the North Sea keep to the right.

The authors of the scheme suggest that the number of collisions in the Sandettié-West Hinder area has increased dangerously since 1967 because of an unforeseen increase in the size, draught and speed of ships. Their aim is to prevent, in this area, crossings between traffic coming out of the Scheldt and traffic bound for Rotterdam, Germany, Scandinavia and the Baltic.

In a book entitled The Black Tide, Richard Petrow presents a panoramic view of the events concerning the loss of the Torrey Canyon on the Seven Stones on 18 March 1967. The massive spillage of oil made it into a world disaster which called for a complete revision of many of the principles on which maritime transport is based. For seamen, however, the really important part comes before the spillage, when the ship stranded in apparently ideal navigational conditions. The Liberian Commission of Inquiry threw little light on the subject and criticism of the master does little to satisfy those with a professional knowledge of the sea. Here Commandant Oudet, relying heavily on the facts disclosed in Petrow's book, examines the circumstances of the disaster and comes out with strong criticisms of the Commission of Inquiry. If the subject is not exclusively navigational, it must be of great concern to all navigators.

Mr. Petrow's book contains what professionals need, even though the author recognizes that many questions must still remain unanswered. He has had access to the record of the Commission's investigations, but not to the report of the observer whose presence at the inquiry was secured by the British Government in spite of the owners' protests. While Mr. Petrow was able to spend four days interviewing Captain Rugiati, six months after the accident, he was unable to pursue his investigation by speaking with eye-witnesses, either those whose evidence was received by the Commission or those whom they failed to question.

The coverage of this paper, which was presented at an Ordinary Meeting of the Institute held in London on 18 March 1970, includes:

(1) A brief review of current aircraft flight control systems.

(2) A discussion of the benefits to be gained in terms of manual handling and full automatic pilot modes, in using feedback control techniques in the primary flight controls (Manœuvre Demand Control).

(3) A description of the work done on Manœuvre Demand Control at the Royal Aircraft Establishment, Farnborough, in the Avro 707C aircraft and in the Hunter Mk. 12 aircraft.

The introduction of marine radar into the general market immediately after the last world war, offered the promise of reducing the many economic losses sustained through failure to keep schedules during periods of reduced visibility. These promises have been only partially fulfilled. Initially it was accepted that radar needed little introduction—that it established the range and bearing of targets in the vicinity and no more was required. With radar available on only a small proportion of vessels, this limited information was sufficient to enable these few to avoid other, slower-moving craft which were not so fitted. Radar is now fitted on almost all vessels and speeds have increased, while manoeuvring characteristics have changed because of increased tonnage of vessels. The situation is now far more complex.

It is generally accepted nowadays that, to obtain full value for anti-collision purposes from the use of radar by a ship proceeding in poor visibility, it is necessary to plot, or to compute in some other way, the raw data which may be obtained from the radar. It is also usually conceded that, for this to be done effectively in frequented areas, without the aid of mechano/electronic devices, a great deal of time and expertise is demanded from the radar observer and a great deal of responsibility thereby rests upon his shoulders.

To reduce the load of work and the possibility of human error and to give the observer more time to use his intelligence in appraising the situation and keeping it under review, radar engineers are already pressing forward the development of automatic devices which, in one way or another, produce computed informatioa in the form ultimately needed.