Estimation methods and filtering techniques are nowadays an integral part of any computer-based navigation system. The purpose of these techniques is to provide an estimate of required variables which is sufficiently accurate for real-time command and control purposes. Repeatability, which is important for so many applications, is deemed to be a by-product of the estimation process. For this requirement it is not strictly necessary for the process to be accurate, it is sufficient if it is only consistent; these are closely linked but one does not imply the other. The modern approach is to minimize the variance of the noisy observations or the sum of the squares of the residuals, and the methods available for doing this are increasingly refined. The impression given in the literature (and it is extensive) is that data processing can somehow compensate for the shortcomings of the basic sensors with respect to the operation being considered. Within certain limits this is true, but the real reason for the sudden surge of Kalman filtering for real-time on-line applications was the relative simplicity of the computational process. In a way, Kalman filtering has done for estimation theory what the Fast Fourier Transform has done for spectral analysis.

The concept is simple enough to state. It consists of combining two independent estimates of a variable to form a weighted mean. One of these estimates is a forecast and the other is the current measurement.

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.

The history of manav goes back fourteen years to 1967 when Esso placed a contract with the Ministry of Technology (mintech) to carry out work to develop a system to assist in ensuring the safe operation of its Very Large Crude Carriers, which were then coming into service. The 1967 era saw much public, governmental and company concern about the stopping and manoeuvring ability of large tankers, particularly when close to shore in estuaries or when berthing.

manav was therefore one of a number of developments or studies initiated by the introduction of VLCCs. Some years were to pass before coordination of the various study results proved possible.

The Racal-Decca (or Decca as it then was) involvement began in 1969 when Esso and mintech decided that an industrial partner should be sought. From the firms approached, the Decca Navigator Company was contracted to undertake a design study. The cost of this study, which started in January 1971, was equally shared between Decca and mintech. This said, it is remarkable how even with a wealth of supporting data having been collected in the intervening fourteen years, the objectives for manav, as set by Decca and mintech, have not radically changed.

The present Department of Industry involvement in funding the sea trial evaluation of manav has its roots in yet a different study; namely the Bridge and Wheelhouse Ergonomics Study, which resulted in the DOI Code of Practice for Ship's Bridge Design.

Sailing Directions nowadays implies ‘Pilots’, with which all mariners are familiar. However, the term in a broader sense embraces a wide range of printed and descriptive material of help to the seaman. In his paper, which was presented at a meeting of the Solent Branch of the Institute in December 1979, Dr Cotter traces the origins of the publications – pilot books, light lists, tide tables, and indeed charts – which are now available to the navigator. The paper has been abridged.

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.

With the rapid changes taking place in so many countries – new ports, new terminals and anchorages and new buildings of significance to mariners – it is essential that users report back to us whenever they feel that our charting service could be improved. Whilst it is flattering that we seldom do have criticism, this is not always very helpful. At the recent International Hydrographic Conference in Monaco preliminary results of a recent questionnaire issued by the International Chamber of Shipping on the use and availability of navigational charts and Notices to Mariners were made known; it was flattering to hear that over 2000 of the replies stated that they used British Admiralty products as their primary series, but disconcerting that about a quarter of the replies said that arrangements for the supply of both charts and Notices to Mariners were less than adequate. Even for the various national or world-wide series of charts, it has given me food for thought to hear that our own arrangements were considered to be ‘adequate’ in Western Europe (including the Mediterranean) by only 504 out of 1150 ships, by 753 out of 2547 ships in North American waters, and by 457 out of 1507 ships in the Middle and Near East. Many other areas seem to reveal reports just as conflicting as those which we have heard at earlier Chart Users' Panel meetings, when we have repeatedly asked for reports of areas where our service could be improved, but seldom if ever have had any reports of difficult areas.

In this paper we investigate the applicability of a second-order differential equation in the physics of mechanical vibration as a model for aircraft lateral position errors obtained from the VOR environment. Navigational interpretations of the parameters in the model are constructed analagous to a vibrating mechanical system. One interesting observation is noted and used to narrow down the potential range of a key parameter. Solutions to the second-order differential equation are described, and the properties and phenomena implied by the model are explained. In extending the theoretical reasoning, we discover phenomena that are embedded in the aggregated data. We also find ways to explain the most salient features of VOR position errors based on the suggested model. Steps required for future empirical confirmation, clarification, and calibration of parameter values are sketched. This paper is only intended as a starting point of a further systematic construction of theory and models useful for the design, evaluation, and regulation of VOR navigation systems.

Figure 1 shows the present state of surveys over the UK continental shelf. Out of an area of some 173 000 square miles contained within the British Fishery limits, 36 per cent has been surveyed by echo sounder, but not necessarily to a scale suitable for modern standards, and only surveys to full modern standards are sufficient to ensure safe navigation within r m of the seabed; a modern standard survey must be carried out using a modern echo-sounder and include a thorough sonar sweep. All hips of the Survey Flotilla are now fitted with a Kelvin Hughes MS48 echo sounder and an OAL side-scan sonar.

New technology, such as the towed side-scan system, has enabled the surveyor to examine the whole of the sea bed between a regular pattern of sounding lines, spaced to ensure that the sonar beam from one line searches at least 50 m beyond the adjacent lines either side. This ensures that all wrecks, rocks and other obstructions on the sea bed which could be a danger to navigation are located, and subsequently closely examined for the least depth over them. Side-scan sonar is best operated at a speed of 5 or 6 knots, which means that the time taken to carry out a survey to full modern standards is far longer than twenty years ago, but during the last five years almost 8 per cent of the UK continental shelf has been fully surveyed to modern standards.

Our Survey Flotilla comprises eleven vessels, four Ocean Survey Ships – Heda, Hecate, Herald and Hydra; four Coastal Survey Vessels – Bulldog, Beagle, Fox and Fawn; and three Inshore Survey Craft – Egeria, Enterprise and Echo.

The standard height rules applied in off-route airspace are examined to assess the degree of intrinsic safety they provide, i.e. the reduction of conflicts without action being taken by pilots or ATC. The yardstick used is the conflict rate which would obtain if the aircraft were uniformly randomly distributed in the height dimension and flying straight and level on uniformly randomly distributed tracks. It is shown that the application of the standard rules can lead to a reduction in intrinsic safety unless significant height-keeping errors are present. An alternative height rule apparently having more desirable characteristics is examined on the same basis.

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.

Among the major problems encountered in the control of air traffic are those concerned with conflict prediction and resolution. An interesting method by which many of the associated difficulties could probably be overcome would be by employment of a suitable type of computer-controlled Airborne Traffic Situation Display (ATSD). This would operate in a manner similar to that described for the Fully Automated Pilot-Monitored ATC, utilizing information derived from an ATC Centre via ground/air data link.

In addition to the ATSD and the associated digital computer the airborne equipment required for this system includes an electronic data display (EDD) and a bulk storage unit for enabling flight plan and map data to be set up on the relevant display. The ground-based ATC subsystem could automatically provide the pilot with information concerning other air traffic in the vicinity, warning him of any potential conflict situations and advising him of an appropriate evasion manoeuvre. The air traffic data could automatically up-date the back-up information for both the ATSD and the EDD, whilst details of any proposed collision-avoidance manoeuvre could appear on the EDD. The pilot would be able to employ his airborne computing and ATSD system for monitoring the situation. He should therefore be able to confirm the likelihood of a collision, to check the time available before a potential impact and to determine the most suitable manoeuvre for collision avoidance. This manoeuvre will generally agree with that selected by the ground system.

Users of Admiralty charts will be familiar with the fact that the specifications which are followed in respect of content and design evolve continually; some of the changes are in response to suggestions put forward by users. It is intended, for example, to add the morse identification of racon signals on charts, following a suggestion by Trinity House. The Hydrographer is always anxious to encourage comments from sea and the Chart Users' Advisory Panel is dedicated to that end. Some changes result from new developments in the navigational field: the representation of vhf radio lighthouses, for example, is now being considered so that they may be charted by symbol when they emerge from their present on-test status to become fully operational. Other changes stem from office considerations, such as new cartographic techniques or the requirements of effective maintenance of the published charts. The more important of these changes are announced through Admiralty Notices to Mariners as corrections to the Symbols and Abbreviations booklet, 5011, a document indispensable to chart users since charts do not themselves carry a key to the symbols used; over 40000 copies of 5011 have gone into circulation in the past two years alone. Other innovations, less significant or self-evident, are not normally announced by Notices to Mariners in this way but implemented through office instructions to the cartographic staff of the Department. Recent examples have been the decisions to include notes giving the relationship of charted latitudes and longitudes to WGS-based positions, so that SatNav observations can be reliably plotted on charts; and, on a minor level, to add the label ‘o’ (zero) to the drying line at intervals in the same way that other depth contours on metric charts are labelled with their values, a step deemed to be useful in case copies of charts have to be printed without the superimposed colour tints.

The squadrons of the Army Air Corps are intended for deployment with ground troops in the forward battle zone in roles which include reconnaisance, observation, fire direction and, to a limited extent, the movement of men and material. These roles indicate the nature of the navigational requirement.

We recognize that in the general line of trade (or, as we have had underlined again recently, of war) there will be places where ships have to go but where, with the best will in the world, we have not been able to provide adequate charting or even to recommend anyone else's chart as fit for use. The master and his owners, or the naval commanding officer and his operational authorities, have got to weigh the advantages of calling at that port, or using that route, against the danger to the ship and decide whether the gain justifies the risk.

In 1973 we were astonished to hear that a foreign coaster on passage from a Bristol Channel port to Penzance had attempted to go between Godrevy Point, the north-eastern head of St Ives Bay, and Godrevy Island, some 2½ cables offshore, at low water. Fortunately for her, she was spotted by the local coastguard before she was irrevocably committed to the passage – and dissuaded. The largest scale chart of the area, Chart 1168, is on a scale of 1: 25000, and shows the passage as some ¾ inch across from high waterline, or less than half an inch between drying rock shelves. Admittedly it did show a narrow gap where the contour lines suggested that more than 5 m of water could be carried through the centre of the passage. The sailing directions state that the channel outside the island, between it and the outer shoals, should not be used without local knowledge. The inner passage is briefly mentioned but no instructions for passing through it are given.

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.

The first edition of the English Channel Passage Planning Guide was published in February 1981, over a year ahead of the July 1982 routing changes, to familiarize navigators with this new type of publication and to gain experience from users. Edition 2 was published on 2 April 1982 to give advance warning of the full details of the new routing measures; it includes many suggestions from those who answered the questionnaire printed at intervals in Admiralty Notices to Mariners. Even before publication of Edition 1 we had had much useful advice from various professional bodies and, throughout, we have tried to meet the known wishes of those who would be using the Guide.

Format is not the most important feature but it is one on which strong views were expressed. Edition 1 was plainly over-large and unwieldy. We have now reduced the width to standard chart size and completely redesigned the panels to permit folding to a size of about 10 × 14 inches. This compromise between chart and booklet should combine the virtues of a chart (quick correction and filing with other charts where its existence will not be overlooked) and some of the virtues of a booklet (folded, it will not cover the whole of a standard chart which may be in use at the same time).

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.

Conventional survey methods for position and azimuth as practised in the Royal Artillery, although sufficiently accurate, were slow and expensive in manpower, while vehicle-navigation systems based on distance measurement by odometer and directional gyros were not sufficiently accurate. In the early 1970s therefore a General Staff Requirement was issued for an equipment designated PADS (Position and Azimuth Determining System) which would provide the necessary combination of speed and accuracy for gun batteries and observation posts, which may have to move frequently, by day or by night, in poor visibility. Precise knowledge of battery and target location, together with an azimuth reference, can help to achieve the first-salvo hit capability that is essential, not only from the point of view of surprise, but also to reduce risk of detection by shell-locating radar.

In 1970 a review of the Sailing Directions was undertaken to find out if they met the needs of the twentieth-century mariner. This review was based mainly on the response to a questionnaire promulgated by Notices to Mariners, to which some 900 replies were received. The general assessment was that considerable improvement was required in the port and pilotage information; a loose-leaf type of book, for ease in correction, was also suggested.

The outcome of the review was the adoption of a new style, involving a stricter geographic sequence in dealing with the coastal features, more headings to divide up the text and proper names highlighted by the use of bold type at the principal mention. At the same time the international A4 size was adopted to provide a shorter line of print in two columns, and a better page size for graphics. Much pure description of the chart has been removed, but there is still rather too much repetition of detail which can already be seen from the chart.