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classical towed rotator type of log, fitted with a mechanical or electro-mechanical revolution counter has been largely superseded in racing yachts by logs employing through-hull sensors on account of drag considerations and the inconvenience of having to shorten the line when sailing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.

Mr. Blake has given us an outline of what is needed in the context of Navigation of Long-Range Subsonic Transports in the 1970's. I now intend to pursue the theme by saying what I think v.l.f. navigation techniques can contribute to the solution of the navigation problem. In particular, I want to talk very briefly about the contributions that we feel v.l.f. might make towards the particular problem of limiting the numbers of aircraft which creep beyond Mr. Blake's navigation tolerance ‘fringe’ in addition to, possibly, by adding navigational information, increasing the effective M.T.B.F. of the total navigation system.

Clearly, addition of equipment cannot reduce M.T.B.F. in the narrow sense of the term—more equipment must have more faults—but if one interprets ‘fault’ as the incidence of a navigation error beyond the specified limit rather than narrowly as an electronic malfunction, I do think that v.l.f. navigation has its contribution to make to effective M.T.B.F.

Since the last Institute meeting on the Admiralty chart in 1967 the compilation office, formerly at Cricklewood, has been moved to a new building at Taunton, alongside our printing works established there in 1940. Thus, except for a small office in Whitehall, which keeps in touch with the ever changing defence scene, the whole of our organization is now concentrated at Taunton, from where every week between 30,000 and 40,000 Admiralty charts are despatched, through our agents, to navigators in every part of the world.

As readers of the Institute's Journal will know, to mark the 21st anniversary of the Institute a special edition, entitled The Navigation Explosion was published. Papers published in this edition highlight the very rapid advances which have been made during those 21 years as a result of a happy marriage between the ancient art of navigation and modern science and technology.

The basic concept of case and cluster rotation in inertial navigation (IN) systems is introduced, and the reduction in the errors caused by changes in gyro and accelero-meter biases is illustrated. The general properties of cluster rotated systems are summarized and it is concluded that, although errors inside the Schuler loops may be drastically reduced by rotation, care must be taken to avoid error sources outside the loops.

Marine and air navigation can still learn from each other. Mariners are following aviation in adopting some routing and control but aviation could follow mariners in their refusal to accept routing and control unless it is cost effective. However it may be easier in the marine case to measure the cost and probability of a collision than it is in the aerial case. But many states have established mandatory airways and routes; originally their navigational aids were very useful and in the event of forced landing the search and rescue people knew where to look. But many airliners now have self-contained navaids like the inertial navigation system (INS) or doppler so that they can navigate off airways, and also forced landings are rare. In the history of air traffic control at first it applied only around airports; when it spread to routes many aircraft were quite happy to fly off airways. But now airways have proliferated and have become customary and respectable to airline pilots so that few complain when some states force aircraft to follow lengthy and costly routes. The only virtue of airways is their freedom, theoretically, from uncontrolled traffic and from military dangers. If A.T.C. were confined to those situations where the risk of collision without A.T.C. would be worse than, say 1 in 10,000,000, flying would be a little more expeditious, but everyone feels secure within the system and insecure, guilty and uncomfortable outside it, so A.T.C. is used universally by airliners.

GNSS relative positioning technique is an important field of study, in which the standard ‘GNSS Baseline Model’ is often used. Differencing between observation equations is used to construct the mathematical model, since this method can eliminate some common errors in the GNSS signal measurements. The ‘Orthogonal Transformation’ method can also construct the GNSS Baseline Model. However, as is described by some scholars, this model may avoid some drawbacks of Double Differencing (DD) while maintaining all the advantages. For comparison purposes, this model is evaluated and the theoretical equivalence of both approaches is proved for the short baseline from two aspects: the Integer Ambiguity Resolution and the conditional least-squares baseline vector.

COMPASS or BeiDou is the new satellite navigation system under construction in China. In this paper, the standalone performance of COMPASS is compared to the Global Positioning System (GPS), including: Single Point Positioning (SPP), differential positioning (DGPS and Differential COMPASS) and single epoch ambiguity resolution and positioning. Based on the results, it was found that COMPASS SPP performance is clearly worse than that of GPS, due to larger broadcast orbit and satellite clock errors, especially the latter. Differential positioning performance of COMPASS and GPS are essentially similar, with GPS marginally better. COMPASS single epoch ambiguity resolution performance is obviously better than that of GPS due to more observed satellites and the single epoch positioning performance of COMPASS and GPS are similar.

Current crises in the air traffic industry demonstrate that changes are required to present systems. The levels of delay and poor safety standards being experienced around the world dictate the need for improved Air Navigation Services (ANS). A multitude of reasons explain these problems. For instance, fragmentation of national systems prevents optimum use of the world's airspace. In addition, inherent limitations of present ANS technologies and procedures mean that it is usually not possible to separate numerous aircraft on random routings. Thus, aircraft must often plan their flights along routes and be channelled so that the necessary separation can be maintained. This results in fuel and time penalties, in addition to airspace capacity being consequently constrained. Accordingly, this paper provides an analysis of changes that should occur to ANS during this decade by evaluating current and planned technologies and procedures.

The United Nations Convention on Law of the Sea (UNCLOS) came into force on November 18, 1994 to provide the legal framework for maritime boundary delimitation. Understanding the geomatics aspects of UNCLOS is vital for coastal nations to claim the ownership of the natural resources within the limits of their Continental Shelf. This paper discusses some of the geomatics aspects of UNCLOS, namely the geodetic and uncertainty issues. A case study for Egypt's outer limits is also presented.

There is increasing pressure from commercial interests to obtain radio bandwidth for both terrestrial and satellite radio-communication applications. Existing civil radio-navigation and military radio-location bands are now being scrutinised by these interests. This background paper is about those pressures and the factors that marine navigators need to be aware of now and will need to deal with in the future.

This paper studies the application of several nonlinear filters for the problem of Mars entry navigation by using radiometric measurements from Mars orbiters and Mars Surface Beacons (MSBs). A suitable dynamic model of Mars entry is developed. The movement of MSBs due to Mars rotation is also considered in the measurement model. The performance of an Extended Kalman Filter (EKF), First-order Divided Difference Filter (DDF1), Unscented Kalman Filter (UKF), and Particle Filter (PF) is compared in terms of estimation capability and computation costs. The theoretical Cramer-Rao Lower Bound (CRLB) of estimation errors are derived for Mars entry to evaluate the performance of the filters. A consistency test is also carried out to verify the filters. In simulations, by the comparison of estimation errors, position and velocity Root Mean Square Error (RMSE), error standard deviation versus Square Root of CRLB (SR CRLB), credibility and computation time, it is concluded that DDF1 is preferred for Mars entry navigation.

In the existing Steering and Sailing Rules there are seven classifications of vessels for assignment of responsibility in the open sea. Three of these classifications (Rules 18, 19 and 24) are based on the bearing criterion, two (Rule 17) on the wind bearing criterion and two (Rules 20 and 26) on the hampered vessel criterion. The only classification of vessels implied in the present writer's collision system is based on the bearing criterion. The object of this paper is to show that it is also possible to establish a single classification based on a turning criterion which offers some advantages over that based on the bearing criterion.

In 1963, in addition to examining the characteristics of the Omega system, we were also very concerned with a comprehensive navigation system study which was designed to examine all aspects of a world-wide navigation system operating in a B.O.A.C. type environment. This concerned a study of dead reckoning as well as externally referenced sources of information. You have the choice of an all dead reckoning system probably employing multiple sensors of the same type, triple IN is typical, or you could have a mixture of externally referenced and self-contained, in other words dead reckoning sensors. Occasional reference could be made to short-range aids or even a satellite system if available to increase the integrity of the position-fixing information. The inertial and computer aspects have been examined by the Avionics Department at R.A.E. whereas the radio sensors, which are externally referenced, and the relevant software have been the responsibility of the Radio Department.

This country, and the marine industry in particular, is in the throes of a change that it has been decided shall be called metrication. It is evident from what is both written and spoken that not everyone is aware of what metrication means, that many people assume that it is simply a change from imperial units to metric units. However, what is really intended is the adoption of the S.I. system of units and this implies much more than just the use of metric dimensions. The two main points of the S.I. system are (i) that every dimension is measured in decimal multiples of a basic unit and (ii) that the system of units is a coherent one. The educational advantages of such a system are too well known to require restating here. Antagonists of change usually point out that time does not conform to condition (i) and while this is true, nevertheless the S.I. system will be a great improvement on our present one and the non-conformity of time should not be used as an excuse for other non-conformities.

In an earlier paper the present writer drew attention to the distinction between mixed and aggregated distributions. Incidentally, two minor mis-statements in that paper should be corrected. The first sentence in the last paragraph of section 2 (page 72) should read ‘As σ2/σ1 (=k say) tends to either zero or infinity, X/σ increases indefinitely; whilst for k nearer unity, X/σ is smaller’. Also the last line of the Appendix should not terminate with ‘X/σ = 3·724’ but with ‘X/σ→∞’.

Mixed distributions arise when for example an error occurs either from one distribution with probability p, or from another with probability 1–p, as in a set of position line errors due sometimes to one and sometimes to the other of a pair of observers of differing precision. An aggregate distribution occurs when the error consists of, say, two sub-errors, one from each of the two distributions; as when Captain Flint marks the chart and Long John subsequently reads it.

There is no doubt that the increasing size and speed of aircraft, and in particular the continuing growth in air traffic movements, pose unique problems for the development and use of efficient and safe methods of air navigation and control. The scientific, technological and operational difficulties involved are, of course, quite fundamental. This paper, however, is based on the propositions that such technological opportunities and regulatory systems as may be developed necessarily affect directly or indirectly the use of real resources; and insofar as these resources have a value in alternative uses, they incur costs on the community (as well as prospectively providing benefits). Situations involving economic choice, therefore, necessarily are involved. Air navigation and control systems are not immune from the general objective of achieving an efficient overall distribution of national resources.

For a number of years ship's equipment has included automatic steering, off-course alarms, speed and distance logs, &c., all of which make use of separate electronic or electro-mechanical devices. The digital computer has meanwhile come into use for a large number of control systems, mainly ashore, and has improved in reliability and cost. The question therefore arises whether ships could be operated more efficiently and safely by making use of the rapid and accurate calculations which the digital computer can perform. Data loggers may produce such a profusion of information that it becomes an embarrassment and we may not see the wood for the trees. The ability of the digital computer (or processor) to edit and analyse information, as well as to store it, makes it a logical step in developing optimum performance.

Whether Henry Ford or someone else gave us this famous quote, ‘If I had asked people what they wanted, they would have said faster horses’, we may agree that it implies there is a limit to what we can expect from the performance of an existing solution. Science and technology always try to push the boundaries and ‘improve’; improving the quality of our lives or improving the quality of technologies. We, as researchers in the area of navigation, are no exception; we want to improve the quality of navigation services. And there are many ways to do so, and challenges and limitations to those attempts. Some researchers look to improve the accuracy, the reliability, the integrity through different approaches. Some try to reduce or model noise, some try to minimise human error, and some use novel techniques and algorithms for better prediction. Of course, when ‘our horses cannot go any faster’ and there is not much space for improvement for a certain technology or service, researchers may come up with a completely new solution, such as an automobile. Almost all new technologies go through the same exploration period; at the beginning, we want to see how and if it works so we try simple tasks, but then we become more ambitious (or greedier!) and so we introduce it to more difficult challenges until it hits the breaking point. At this point, curious researchers and inventors try to push the boundaries and make the technology better, and if improvement is not possible, they build (invent) a new solution. But what is the ‘quality’ that many of us want to improve? How the quality of a technology or service can be measured in the first place?