The following paper was presented at a meeting of the Institute held in London on 21 February 1979 with the President, Captain R. Maybourn, in the Chair. It considers some of the factors which apply in the context of overall safety and the weightings which they should be assigned in estimating the optimal speed for ships in given circumstances and conditions.

In air traffic control the speed of individual aircraft cannot be significantly varied without unacceptable economic penalties, or the aircraft falling out of the sky. In the case of ships the speed is a useful variable for traffic management and individual ships can choose, or be assigned, any value between zero and their normal service speed. The following discussion concerns the choice of a suitable speed for marine traffic in terms of safety criteria.

The purpose of this paper, which was presented at the seminar on Coastal Navigation described on p. 448, is to consider the role of ‘dead reckoning’ at the present time, in the context of coastal navigation, and to indicate one or two devices which might alleviate the navigator's task in trying conditions and perhaps improve the accuracy of the result.

In this paper, which was presented at the seminar on Coastal Navigation referred to on p. 448, the author describes a new system of radio navigation particularly suited to small craft and coastal vessels.

This paper reviews the objectives of a new radio aid termed the Radio Lighthouse and describes its scope and use. The results achieved to date are given, as well as plans for the immediate future. A consideration of the options available in implementing the system and methods of obtaining navigational data from the system conclude the paper.

The paper by Captain Burger and Captain Corbet was presented by Captain Corbet at a meeting of the Arab Institute of Navigation held in Alexandria on 9 April 1979. Before the meeting M. W. Richey, as Director of the Royal Institute of Navigation, gave a short talk to the Arab Institute.

On the 9 August 1974 the steam tanker Metula grounded in the First Narrows of the Magellan Strait. The grounding of this deeply laden VLCC provoked very little publicity either on television or in the press, probably because of the remoteness of the area. The Metula was a first-class, well-found vessel manned by properly qualified and experienced personnel, and had two Chilean pilots on board to assist with the navigation through the Strait. How could such an accident happen?

There has recently been some discussion on the suspected ‘sailing effect’ experienced by ships lying immobilized in a seaway. It was suspected that drift direction may not be truly down-wind, and that on VLCCs in the ballasted condition the sailing effect could be magnified. Few practical data were however available and could easily be spoiled by the effects of current, or become unreliable if established under the influence of light to moderate winds.

An unusual set of circumstances combined on the 3 August 1977 when I was Chief Officer of the Shell tanker SS Lima on her maiden voyage to the Persian Gulf. As can happen early in a ship's life, trouble developed in the engine room requiring the boiler to be shut down for about two days. The first signs of the problem were discovered a few days earlier but the stoppage was planned so that the ship would have plenty of sea room when undergoing repairs. A position off Maputo was chosen, and when within the selected area the ship was stopped and the repairs carried out. During this period the ship was allowed to drift freely and as usual daily positions were obtained at morning and evening twilight and at noon. Figure 1 is an outline chart of the area showing the observed positions. For these times the ship's head is also given, in addition to the associated wind direction and speed.

The Global Positioning System, Navstar, is an advanced satellite-based navigation system which is currently under development and evaluation in the United States of America. Progress has been very fully reported in the open literature and a definitive paper on the concept has in fact been published in this Journal. The concept has now been experimentally validated and much of the evidence which supports this validation has in turn been published.

The impact of Navstar on navigation in the period beyond 1985 is potentially very great indeed in that it offers, worldwide, a navigation capability to surface and aerospace users of a standard of accuracy combined with continuous availability which is currently associated only with short-range aids.

This paper has the objective of presenting (a) a general introduction to the physical principles on which Navstar is based, followed by (b) a survey of its potential relevance to the operational needs of various classes of user. Finally there is some more speculative matter in the form of (c) a discussion of the potential impact of successful implementation of Navstar on current and projected future navigation systems.

Separation standards are used for assuring the safe and effective operation of aircraft in a traffic control environment and as aircraft operations increase in number the need to reconsider separation standards is strongly voiced both by operators and controllers. A panel, the Review of the General Concept of Separation Panel (RGCSP), has been organized by ICAO and the possibility of reducing conventional separation standards has been discussed. Mathematical models for estimating collision risk due to loss of separation between aircraft require data on navigation accuracy. In general, three-dimensional radars are used for height finding but these are complicated and expensive.

The altitude of the cruising aircraft is required within about 100 ft. In the simplified radar here described a rotating antenna produces a fan beam for scanning aircraft flying overhead. The data obtained from several scans are processed by a mini-computer and the height of the aircraft estimated by a least-square method and sequential approximation. Between the items of information obtained for each scan (the distance, the elevation angle and the data acquisition time) a theoretical relationship is established as an observation equation, one of the coefficients of which includes the height information. The coefficient is determined by a curve-fitting method. The paper first describes the method of analysis for height estimation and then an evaluation of the accuracy of the method by a computer simulation.

Every day several hundred subsonic aircraft travel between the European and North American continents. Because of noise limitations at major airports, aircraft turn-around times and the time difference between the continents, the direction of the main traffic flow changes through the day. In the afternoon (GMT) the flow is predominantly westbound, while in the early hours of the morning the flow is predominantly eastbound. Oceanic air traffic control for the North Atlantic region has evolved into what is now known as the Organized Track System; traffic is divided into streams, each stream flying at a specified set of flight levels on one of several adjacent tracks. Figure 1 shows an example of the subsonic track system during the westbound peak. To secure operating economy the layout of the track system on any day is matched to the pattern of the upper winds.

The adoption by the International Civil Aviation Organization of the MNPS requirement in the North Atlantic Region was based on two premises:

(i) The need to maintain an acceptable level of safety in an ATC environment in which a major systems change was taking place—the withdrawal of the Loran A Navigational System on 31 December 1977.

(ii) The evidence of an option to take economic advantage of the provision of advanced navigation systems now being used by the majority of traffic operating in the Region. This advantage would be a reduction in the lateral separation minima.

The following paper was presented at an Ordinary Meeting of the Institute held in London on 21 March 1979 with Mr S. S. D. Jones in the Chair.

This paper is not so much a forecast of future navigation systems as a personal view of the philosophy of the increased use of micro-processors. Digital computers were first introduced into airborne systems in the late 1950s to meet the demands of new sensors such as inertial navigators and star trackers for which analog computation methods proved inadequate and inaccurate, but their cost restricted their application to specialized high accuracy systems.

The practice of safety can be treated as the operation of a system with which it is intended to control the level of some parameter ‘risk’. The following is an attempt at a description of the behaviour of a population of individuals engaged in a risky occupation in terms of such a system. In the first section the casualty figures for commercial airline operations are analysed to show that there is a prima facie case for a belief that in this case risk level is regulated by those immediately engaged in the industry. The second section contains a description of a proposed ‘input/output’ model of an individual regulating his own risk, and preliminary results are given for a simulated population of aircraft operators having these characteristics. Lastly, the credibility of the model in terms of known human behaviour is examined, some tentative conclusions are drawn and an indication is given of its proposed use and development.

During the months of October and November 1835 a series of magnetic observations was made, under orders of the Lords Commissioners of the Admiralty, on board the iron steamship Garryowen by Commander Edward J. Johnson R.N. The results of Johnson's observations paved the way to Airy's solution to the crucial problem of compass management on board an iron ship.

Johnson related in a paper in which he described his experiments, that he proceeded to Ireland taking with him the necessary instruments for ascertaining the deviation of the magnetic needle produced by the local attraction of an iron steam-vessel, together with instruments for measuring dip and magnetic intensity. Every facility was afforded him by the owners of the Garryowen, the City of Dublin Steam Packet Company, and by the builders of the vessel, Messrs. Laird of Liverpool.

The Garryowen, built in 1833, was a paddle steamer of length 130 ft, breadth 21 ft 6 in and depth 11 ft. She was equipped with two engines each rated at 85 h.p. and her tonnage was 281 tons burden. She was fitted with four water-tight transverse bulkheads of wrought-iron ¼ in thick. Her hull and boilers were of malleable iron and the total weight of iron in her structure amounted to 180 tons.

Dr Corlett's paper on hydrodynamic interaction (Journal, 32, No. 2, May 1979) is of great interest, coming as it does from a practising naval architect with considerable experience of dealing with complex issues arising from casualty investigations. His paper gives an insight into the causes of interaction and the practical illustrations given in the paper add weight to his arguments.

Model experiments to study interaction between ships in shallow water have been undertaken at the National Maritime Institute for some years now and many of the results obtained agree with conclusions reached by Dr Corlett. For example experiments carried out with models close to sloping surface-piercing and flooded banks have shown that at moderate to high speeds the side forces and turning moments induced by the banks vary not as the square of the speed, but as the speed raised to a power greater than two. It is of interest to note that the rudder force used to counteract these bank effects varies roughly as the square of the speed, so that when close to a bank at too high a speed, use of the rudder is less likely to maintain control than would be the case at a more moderate speed.

The author correctly emphasizes the advantages of a ‘kick ahead’ with a single screw ship, but it is well to bear in mind that this device is not applicable to some ships, notably those with twin-screws and a single centreline rudder.

This paper first presents some of the results of my recent work on error distributions in navigation which may be worth summarizing for navigation practitioners. Some further explanations and insights in the second part may be useful for future studies on the subject.

Discussion on this subject was initiated by E. W. Anderson who questioned the adequacy of the gaussian distribution as the probability model for navigational position errors. He observed that empirical position error distributions are usually long-tailed (i.e. with raised skirts) compared to the gaussian and have a strong tendency to form an exponential function of error magnitude, especially in the far tail-region. Attempts to explain this phenomenon have been made by Abbott, Crossley, Lloyd, Parker, Lord, O. D. Anderson, etc., based on various aspects of navigation performance. To provide a general structure for characterizing the error distributions, Anderson and Ellis made a significant step forward in suggesting ‘Student's t’ distributions as error models. As pointed out by Parker, however, this suggestion has to be taken with reservation and requires further verification based upon empirical data. My own recent work has indeed taken the direction advocated by Parker and has attempted to fill a theoretical deficiency in Anderson and Ellis's work, to provide examples of empirical model fitting and to discuss the merits of Student's t distributions relative to the double exponential model. The main findings are summarized below.

The provision of Rule 10 of the 1972 Collision Regulations, that if vessels are obliged to cross traffic lanes they shall do so as nearly as practicable at right angles to the general direction of traffic flow, would appear to be simple enough. Could it be however that in areas of high traffic density, such as the Dover Strait, the theoretical simplicity of the right-angle crossing introduces problems of its own?

Crossing the Dover Strait several times a week, I am constantly alarmed by the apparent lack of regard for Rules 15 and 16 by vessels using the traffic scheme (The rules governing crossing situations and action required by the give-way vessel). I accept that some vessels using the lane believe, albeit incorrectly, that they have the right of way, but feel that a large proportion of these ‘port-side charlies’ are the result of the right-angle crossing.

Because of the pattern of traffic the speed of crossing vessels in the Strait is generally considerably greater than that of vessels using the lanes. Under the present Regulations a situation frequently arises in which a vessel using the lane finds herself as the give-way vessel to another six points or more on her bow. An initial reluctance to alter course by this amount is followed by the thought that there is not sufficient sea-room in which to alter, and the give-way vessel stands on.