This paper describes a precision position and time service which could support the increased air traffic of the future, with an example of its application to air traffic control. Horizontal position and epoch time distribution are provided by Loran-C and vertical position by digital barometric altimetry. The proposed use of these systems for horizontal navigation, vertical positioning and landing approach is based on their successful use by current high-speed aircraft. The paper was presented at the 19th Technical Conference of I.A.T.A., Dublin, October 1972.

A discussion on current progress in the development of Omega as a world-wide navigation aid, on technical problems that still await satisfactory solutions, and on the probable magnitude of the resulting errors in position, took place at an open session of the Technical Committee held in London on 24 January 1973 with Mr. H. E. Smith, o.b.e., in the Chair. The discussion was opened by the President.

Dr. J. P. Hooft who is a Vice-President of the Netherlands Ship Model Basin at Wageningen, discusses the hydrodynamic forces which act upon a large ship sailing in shallow water. Their effects on the manœuvrability and control of the ship include a smaller response to a given rudder angle, a shift of the pivoting point aft towards the centre of gravity, a larger turning circle and less reduction in speed when turning. In general a ship becomes more sluggish in shallow water.

Since manœuvres with large ships are usually only performed in the proximity of harbours while in deep water the ship is kept on course by means of an autopilot, it will be difficult to compare the manœuvrability of large ships in shallow water with their manœuvrability in deep water. The influence of water depth on the hydrodynamic characteristics of the ship will therefore be the main subject of the present paper; the consequences of these ship characteristics on manœuvrability will then be considered. This term ‘manœuvrability’ is often replaced by ‘controllability’. In this respect a ship is said to be controllable when the navigator is able to manœuvre the ship with ease in such a way that departures from the anticipated manœuvre remain within acceptable limits.

There have recently been various investigations of avoiding action when a ship is navigating by radar. The present paper attempts a numerical analysis of the changes in the apparent motion of the echo of the other vessel on the radarscope when both vessels alter course and speed simultaneously.

First we consider the case where the echo of the other vessel is approaching the centre of the radarscope—that is the vessels are on a collision course.

In Fig. I AOB represents a velocity triangle:

OA = own vessel's course and speed

OB = other vessel's course and speed

AB = other vessel's relative course and speed

When both vessels alter course, by Δα1 and Δα2 respectively, the velocity triangle becomes A′OB′ and A′B′ represents the new relative motion of the other vessel. If the triangle A′OB′ is rotated through Δα2 about O, and OB′ coincides with OB, the triangle is represented by BOC and < CDA′ = Δα2. The change θ in the other vessel's relative course caused by both vessels altering course by Δα1 and Δα2 respectively is therefore:

Now φ can be shown to satisfy the equation:

In conditions of poor visibility it is common practice to plot radar measurements of the range and relative bearing of other ships with respect to own ship and to deduce the relative tracks and passing distances. Radar equipment is available which can to a greater or lesser degree relieve the navigator of the tedium of plotting, and which could be developed into aids of considerable sophistication within the limits set by their cost. However, errors in measurement limit the precision with which relative tracks and passing distances can be computed. An alternative to radar plotting would be a data link between ships to broadcast measurements of course and speed on demand; a radar transponder would transmit the required information in coded form.

This suggestion is highly controversial, but it seems worthwhile to derive the mathematical relationship between errors in the data and the ensuing error in the calculated passing distance and to compare the errors using radar data and transponder data. The value of the comparison is however limited because likely errors in the data are not accurately known. The analysis of the radar plotting method is probably of interest in itself because the deficiencies of the method are derived with some rigour.

In studying the behaviour of marine traffic in the Strait of Dover observations have been made of vessels contravening the recommendations of the Imco Traffic Separation Scheme. This report, originally published by the National Physical Laboratory (Crown Copyright), considers the risks attached to the courses of these vessels in terms of the number of encounters to be expected and in the light of the recommended routing principles.

The problems of integrating aircraft using area navigation into the terminal A.T.C. environment are discussed. It is concluded that area navigation systems currently available are incompatible with current terminal A.T.C. approach sequencing and that integration is only possible in the context of both computer assistance to the approach controller and data link between the A.T.C. computer and the aircraft navigation system. The benefits of Terminal Area Navigation are briefly considered and it is suggested that the deployment of vertical navigation in a procedural role might be the better first step. The paper was presented at the 19th Technical Conference of I.A.T.A., Dublin, 1972. Crown copyright.

Currently available area navigation (R NAV) systems range from simple station-oriented single waypoint systems, allowing flight on paths which do not coincide with VOR radials, to complex systems in principle enabling flight from origin to destination along a pre-programmed route, including flight on a standard terminal arrival route (from holding point or feeder-fix to the approach gate). As far as Terminal Area Navigation is concerned it appears that the main objective to the R Nav system designers has been to provide a system which enables automatic navigation along the standard terminal arrival routes, as depicted in the Jeppeson Charts, and to display to the pilot his progress along the route. It appears that designers of the more sophisticated systems have tacitly assumed that when an R Nav aircraft enters the terminal area A.T.C. will be able and willing to allocate it such a route.

In clear-weather conditions well trained mariners experience little difficulty in dealing with multi-ship encounters in all circumstances. In restricted visibility they do not display the same confidence in manœuvring even in the open sea, and the problem is amplified as the waters narrow and the traffic density increases. The plea of the mariner would be to find an anti-collision system that would make manœuvring in fog at least as straightforward as in clear weather. To satisfy such a request it might seem that there would need to be two systems, one for fog and another for clear, but it seems probable that a system evolved to work safely in fog would also be acceptable in the less demanding conditions of clear weather; this would in time be the only system adopted.

This paper was presented at a meeting of the Institute held in London on 12 January 1973 with the President, G. E. Beck, in the Chair. Mr. Prior, Director and General Manager of Kelvin Hughes, discusses factors influencing the commercial development of an innovation in navigational equipment and the inevitable time lag in production for the market. A technical description of Situation Display, the new marine radar system from Kelvin Hughes, was published in the April issue of this Journal. The discussion printed here relates both to Mr. Prior's paper and the technical description.

A joint study is being made by C.A.A. and R.A.E. of the operation of S.T.O.L. aircraft in terminal areas, with particular reference to airport capacity. In this paper we present some results of this study concerning a single S.T.O.L./R.T.O.L. runway, to show in particular the marked effect that the need to separate aircraft for turbulent wake considerations could have on this capacity. There is considerable advantage to be gained with the heavier aircraft if this turbulent wake effect is reduced by aircraft design. The paper was presented at the 19th Technical Conference of I.A.T.A., Dublin, 1972.

The development of short take-off and landing aircraft (S .T. O. L.) is being considered as one means of containing the expected growth in passenger and cargo traffic without necessarily incurring the cost and disturbance to the environment involved in building large airports for conventional aircraft (C.T.O.L.). Also for a comparable cost to that of building a C.T.O.L. airport, a number of S.T.O.L. ports can be built, thus making air travel more convenient for a larger number of people. In the system study of S.T.O.L. operations, the capacity (movements per hour) of a S.T.O.L. port is a significant parameter. A research study of future S.T.O.L. operations, using an existing airport complex as an illustration, has been carried out in the U.K. This study involved considerations both as to reducing the noise effects on the community and to increasing capacity, in order to match the future anticipated demand. This paper is limited to the capacity of a hypothetical single S.T.O.L. runway.

The discussion printed below took place at an open session of the Institute's Technical Committee held at the Royal Aeronautical Society in London on 2 May 1973 with Claud Powell in the Chair.

Captain Jones has indicated that the navigator needs improved technical assistance in avoiding collisions during conditions of inadequate visibility. When the aided eye fails to distinguish the aspect of a vessel until it is much closer than the optimum distance at which a risk of collision ought to be recognized, then visibility is inadequate. For large ships a warning can be required before the distance closes to three miles, for example, whereas a visibility limited to three miles is commonly experienced. However, more guidance on this point is still needed from navigators.

During my days of ‘tramping’ across the Pacific Ocean as an apprentice, I had heard vague references to the effect that the Polynesians used coconut shells as an aid to navigation. Intrigued as I was, the opportunity never presented itself for me to pursue the matter further until years later, by which time I knew that I was in search of the ‘Sacred Calabash’.

The Dover Strait is not the most congested stretch of narrow water in the world but it is the gateway used by ships of almost every kind on passage to and from nearly all the important ports in northwest Europe, Scandinavia and the United Kingdom. While the recent increase in shipping may not continue at its present rate, the modern trend towards larger vessels and higher speeds has enhanced the hazards to navigation in narrow waters and port approaches, while the volume and nature of modern cargoes have dramatically increased the risk of widespread pollution in the event of any major snipping casualty.

In recent years there has been a growing concern about the continuing occurrence of casualties in the Dover Strait. The unfortunate incidents in the Varne area early in 1971 raised questions about how casualties occur and what circumstances or combinations of circumstances are most likely to lead to a collision or stranding. Information was also required as a basis for estimating the risk of a casualty occurring in the Dover Strait and for assessing the effectiveness of proposals for improving the safety of navigation.

In this paper, based on an article printed on the back of the March 1973 issue of the Pilot Chart of the North Atlantic Ocean, Mr Fricker analyses three collisions that emphasize the necessity for adhering to the concepts of prudence and safety underlying the Rules of the Road; they are no less essential when navigating by radar in reduced visibility. Terms such as ‘right rudder’, readily understood, have not been altered to conform to English Martime parlance.

This paper describes a new radar system which aims to give the Master of a vessel, on a television screen, the kind of information which could be obtained visually from a wheelhouse window in daylight in clear weather. The system was described by Mr. P.O. Prior at a meeting of the Institute held on 17 January and an account of the discussion will be given in the next number of the Journal. S. R. Parsons is Chief Engineer of Kelvin Hughes and Captain J. P. Stewart a Marine Consultant.

The early history of marine radar when the phrase ‘radar assisted collision’ was coined, the setting up of radar simulator schools to assist in teaching the interpretation of the radar picture, and more recently the increased number of collisions at sea, particularly in congested areas like the English Channel and the approaches to major harbours, all call into question the adequacy of the presentation of radar data on conventional relative and true-motion radar sets.

This paper describes a method of constructing accuracy contours for a position line obtained by observing the horizontal angle between two stations. An example is given using an estimate made, from experimental evidence, of the observational errors that are likely to occur when such angles are measured by sextant. A recent paper by Cotter described the historical development of this method of obtaining a position line.