The two papers which follow, by the late Captain (and Dr) Charles Cotter, are the last of a number of papers he submitted for publication in the Journal, and which have appeared from time to time. Now that he is no longer with us it seems appropriate that they should be published simultaneously.

The paper describes an experimental analogue computer used with a civil marine radar set for determining the closest point of approach of selected ship's echoes and the time to closest approach. The equipment was installed on shore and measurements made of shipping passing to and from Portsmouth and Southampton harbours. The projected track of a ship echo was displayed on a 5-in. diameter cathode ray tube and the closest point of approach read as the distance of this track from the centre of the tube. The results show a high probability that under these conditions errors in C.P.A. will not exceed ±0·5 n.m. for targets between 10 and 6 n.m. range, and ±0·3 n.m. for targets nearer than 6 n.m.

Waves, tides and ocean currents might not be expected to produce electric currents, but by moving water, as a conductor, through the Earth's magnetic field they do in fact produce measurable voltages and flows of electricity. Young, Gerrard and Jevons, who made the first detailed study of this phenomenon, thought it conceivable that measurements of electric potential gradient might be used to estimate the drift of a ship at sea, and Von Arx showed how indications from electrodes towed behind the Research Vessel Atlantis were used to keep her on a direct course from Bermuda to Woods Hole, across the Gulf Stream. In recent years the method has been used extensively in studies of ocean currents and more ships might use it if the necessary equipment were readily available.

As every schoolboy learns, a point has position but no size, and a line has length but no breadth. Nevertheless, to a navigator concerned with fixing his ship, points and lines are represented on his chart as fine pencil marks.

The manner of representing the results of observations as pencil ‘points’ or ‘lines’, has undoubtedly led to the belief that a ship's position must be represented as lying at a point on a position line which is drawn on a chart. Nothing short of perfection in position lines is ever expected by most practical navigators, and two position lines crossing at a point are usually regarded by seamen as yielding a perfect position: and if three position lines meet at a point! … there is seldom even the slightest doubt in the mariner's mind about the reliability of such a fix. On the other hand, three position lines which do not meet at a point are usually regarded as being something not quite respectable.

In the sixteen years since the last paper on this subject was published in the Journal (1951, 4, 288), some notable changes have taken place in the design and capabilities of submarines. Nautilus, the world's first nuclear submarine, was laid down in 1952 and completed in 1955. Since then a further 120 nuclear submarines have been commissioned. Now, a large proportion of the world's submarines are ‘true’ submersibles, self-sustaining over periods of months in everything except food; capable of proceeding submerged faster than the average surface ship; and rarely requiring to surface or even to come to periscope depth.

Disasters result from the breakdown of navigational faculties. Those concerned with the ‘practical’ aspects of navigation naturally assume a standard and infinitely flexible nervous system by which the individual can adjust to the stresses created by great speeds in the absence of habitual sense information. This paper outlines the nervous basis of adjustment to environment (personal navigation), the forms of breakdown in disease, and the nature of hallucinations. Some forms of disturbing experiences likely to be felt in modern navigation are predicted and explained. Such problems are seen as integral matters of aviation planning, design and practice.

‘The main aim … is to enable interested persons with quite different backgrounds of knowledge and experience, to come together and consider collectively a subject of common interest from their various standpoints.’

(A. M. A. Majendie, ‘The Significance of Blunders’, this Journal, 12, 28.)

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.

In this paper, which was read at an Institute meeting in London on 11 February 1976 with Mrs. Mary Pera in the Chair, Captain Cockcroft examines the incidence of collisions in relation to the numbers and classes of ships at risk and their trends, pre-war and post-war. Total and partial losses are included and compared with other forms of loss, e.g. strandings.

In several previous papers statistics of marine collisions have been given for particular areas such as the Dover Strait, Western European rivers, the Baltic Sea and Japanese waters. This paper is concerned with worldwide statistics with particular reference to sea collisions. The information is mainly derived from the Statistical Tables published by Lloyd's Register of Shipping and from the casualty reports compiled by the Corporation of Lloyd's. Statistics of shipping casualties must obviously be related to the number or tonnage of vessels at risk; for insurance purposes loss ratios are usually expressed in terms of tonnage lost to tonnage afloat but navigators are more concerned with the number of casualties and number of vessels at risk in various categories.

This paper, with Dr Lyon's was presented in Paris in November 1983 at an international colloquium organized by the Centre d'Etudes Arctiques of the Centre National de la Recherche Scientifique, by whose kind permission they are here reproduced. The theme of the conference, at which some 35 papers were presented, was the Conquest of the North Pole; the subjects covered included both the history of Arctic exploration and contemporary problems and the future of polar transport, sea and air. Mr Kerr is Director of the Canadian Hydrographic Service's Atlantic Region; both he and his co-author are at the Bedford Institute of Oceanography in Dartmouth.

One of the major concerns in the operation of an air traffic system is the maintenance of adequate separation between aircraft. The assurance of an ‘acceptably low’ risk of collision is a crucial element in the system design. A number of factors need to be assessed in this process. What is the navigational performance of the aircraft in the system ? What are the possibilities for radar surveillance ? Are procedural arrangements together with position reporting a suitable mechanism? What difference would be made by collision avoidance or warning systems? Given that any combination of these or other factors has an implication on the minimum separation between aircraft, the level of safety ‘assured’ has to be balanced against the costs of the various alternatives which may present themselves.

In planning for change the implications of new operating practices or devices have to be assessed carefully. For most changes the process is one of evolution rather than revolution, although collision avoidance devices may have more of the latter's characteristics. Even for ‘revolutionary’ changes it may be possible to model the new system. Thus the existing situation is studied and its characteristics observed, then there are hypotheses of the ways in which the change alters the mechanisms in the system and finally the likely effects on system performance through mathematical and computer (often fast-time simulation) modelling.

This paper by the Principal Scientific Officer of Trinity House was presented at an Institute meeting in London on 28 April 1976 with Mrs. Mary Pera in the Chair.

Mr. Reynolds describes the use of lights to convey positional and other information by the assignment of characteristics of rhythm and colour and discusses the problems of visual discrimination, the choice of light intensities and the effect of atmospheric conditions on the ranges of lights. He also describes the new buoyage system and other moves towards international agreement. A paper on the IALA system by the Hydro-grapher of the Navy appears at p. 94.

Lighting is used in various ways in maritime applications. For operations at night in vessels, in harbours or on drilling platforms general lighting is necessary; such lights may also be of value in indicating a hazard or suggesting a route to be followed but are not expressly intended for that purpose. Fixed lights in vessels are arranged in a spatial pattern and employ colour to give indications of the presence and aspect of the vessel to other vessels. Indirect lighting is also sometimes used, as in the floodlighting of lighthouse towers to reduce bird deaths by collision.

Bridge design has undergone changes in the last few decades resulting in increased awareness of the need for safety while maintaining the minimum of personnel. The concept of the one-person bridge has been studied fairly extensively with respect to military and large merchant vessels, but much of this work has been ignored by those designing for smaller ships, particularly fishing vessels. This paper derives principles for positioning the electronic fishing aids of ‘single ticket’ fishing vessels while applying, where applicable practically, the ergonomic principles developed from the wider community. The paper then applies the principles to the wheelhouses of two fishing vessels and suggests modifications for greater compliance. A conceptual wheelhouse design is given that satisfies all the principles while including the usual suite of electronic aids typically carried by such fishing vessels.

The GNSS-R technique brings out the need for signal receiver systems to process both direct and reflected GNSS signals. This paper describes the architecture of a new GNSS-R receiver system (GRrSv.2) that features enhanced capabilities for remote sensing based on reflected Global Positioning System (GPS) signals. Signal processing issues including DDM calculation, Carrier and Code Generation and DDM Synchronization are presented. Aircraft- and land-based verification experiments for ocean winds, ocean Significant Wave Heights (SWH) and soil moisture have been performed and some primary results are presented in this paper.

Vector map databases offer the potential for customised cockpit moving-map displays, in which user-specified cartographic features can be layered to meet mission requirements. The disadvantage of vector moving-maps is the potential for increased user workload. In 1995, the Naval Research Laboratory and the Naval Air Weapons Center jointly performed a preference study, during which aircrew viewed demonstrations of prototype moving-map displays and responded to a detailed questionnaire concerning the usefulness of each display. This paper summarises aircrew interviews from that study pertaining to both vector moving-map displays and vector feature overlays, including Height-Above-Threshold (HAT), threat rings, and Clear Line-of-Sight (CLOS).

Reasonable stochastic model and function model are the premise of accurate velocity determination, especially in the time-differenced carrier-phase (TDCP) method. This paper presents, first, an elevation-dependent stochastic model (ESM), and then gives a simplified and unified Galileo/GPS combined TDCP function model, where the inter-system bias (ISB) variations are analysed based on correlation coefficients and the scaled sensitivity matrix. To evaluate the performance of the proposed models, datasets collected at 10 multi-GNSS experiment (MGEX) stations and a vehicle kinematic experiment are employed. The results indicate that the ESM model can improve the accuracy of the velocity solution, especially for the Galileo/GPS combined system, in comparison with the equivalent weight ratio method. In contrast to the Galileo-only velocity solution, the Galileo/GPS combined velocity solution can bring improvements of about 1–1⋅5 mm/s, 0⋅5 mm/s and 1⋅5–2⋅5 mm/s in East, North and Up components, respectively. Compared with the traditional Galileo/GPS TDCP model, the simplified and unified model shows no obvious differences in all components in the environment with more visible satellites, but it performs better in a challenging environment with few visible satellites.

This, and the following two papers, were presented during the European GNSS98 Symposium held at the Centre de Congrès Pierre Baudis, Toulouse, France, from 20–23 October 1998.

It is now clear that Global Positioning Systems (GPS) will be the primary navigational and positioning tool used as we move into the 21st century. As a result of the continued expansion and development of GPS, concerns have been voiced about the liability associated with development, construction, and use of the system. No short paper can explore all of the various liability issues associated with GPS. However, this paper will touch upon various liability issues in the hope that this analysis will continue with the development of GPS.

The objective of this paper is to explore a hybrid Global Navigation Satellite System (GNSS) architecture that efficiently meets the stringent needs of safety of life systems. An architecture is proposed that allocates error bounding and alerting functionality between the space, ground and user segments based on refining the assumptions of the leading-order fault free error sources expected in the near future from developing GNSS technologies. By revisiting the first principles used to derive standard RAIM fault detection, a modified detection algorithm is developed to more accurately accommodate these new fault-free error distributions while supporting timely user alerts. The results of the analysis and simulation indicate that this optimized receiver algorithm and associated architecture can provide significant development and operational benefit for navigation users requiring high levels of integrity.

A large interest in developing commercial Location-Based Services (LBS) and the necessity of implementing emergency call services, have led to the intensive development of techniques for mobile users' localisation. In this paper, a Public Land Mobile Networks (PLMN) -based technique for initial position determination is proposed as an alternative to satellite-based methods in environments with obstructed satellite signals. Two positioning models, based on handset available Received Signal Strength (RSS) measurements from Global System for Mobile Communications (GSM) base stations and the use of Support Vector Machine (SVM) algorithms, are proposed. Performances of proposed models are verified using field measurements, collected in a suburban environment. Models are analysed in terms of positioning accuracy, complexity and latency, and compared to some other promising PLMN-based techniques. Using proposed SVM-based positioning models a median error of 4·3 m–6·2 m and latency of less than a second can be achieved.