The question of the reverse stopping ability of a ship is well known but is yet a fresh problem. Until about twenty years ago the distance required to stop a.ship from a service sea speed ahead by using her engines full astern with helm midships was comparable to her advance while stopping with helm hard-over. However, at present this head reach of a 100,000- d.w. supertanker may range from 10 L to 15 L while her advance with maximum helm angle might only be from 5 L to 7 L. At first sight this appears to be a surprising phenomenon, but it is little wonder since the mass of the ship and hence the inertia increases with the cube of her length, while the total resistance of her underwater hull only with the square of her length.

The question of stopping very large supertankers is one of some significance both from the viewpoint of preparing to pick up a pilot, anchoring, berthing, or similar everyday operations and of avoiding collision or grounding in an emergency.

Professor Tani's paper (p. 119) describes recent work on the problem of calculating head reach for mammoth ships of one kind and another. Handling these vessels in confined waters and bringing them alongside the berth also poses particular problems to pilots. This paper illustrates some of these problems, which of course differ to some extent for each port, by describing the pilotage procedures used in one of the new Japanese ports built to accommodate very large vessels.

1. The inland sea and large vessels. The Inland Sea has a coast line of about 4272 kilometres and covers an area of 18,000 square kilometres, equal to that of Lake Ontario. The distance from east to west is about 260 miles and the broadest part from north to south is about 30 miles wide. Navigable channels or waterways for large vessels run in all directions.

The problem of collision-avoidance at sea by means of radar is constantly under discussion in maritime circles within the U.S.S.R. This paper, and that of Captain Bukhanovski (Journal, 20, 247,), describe one direction of research that has been actively pursued in the Soviet Union.

The device described was developed by the Central Scientific Research Institute for Water Transport for the Ministry of Merchant Marine and sea trials were carried out in the Black Sea during the summer of 1962. The present paper describes the principles of the device and the performance during trials. It has been prepared for publication in the Journal in collaboration with Captain G. Shoomayko.

Articles on the prototype have appeared in Morskoi Flot (no. 122, 1959, no. 2, 1964), Die Seewarte (Hamburg, October 1961) and Navigation (Paris, July 1962).

The advantages of a standardized avoidance manoeuvre as distinct from a late collision avoidance manoeuvre are discussed with reference to passenger comfort. The general use of plan type displays suggests the possibility of having a standard manoeuvre based upon turning one aircraft on to a new heading.

An analysis of this manœuvre was undertaken in order to obtain data as to the closest permissible approach between pairs of aircraft on various collision courses. Results show that the permissible closure is smallest if the faster of the two aircraft is manœuvred, and that little is gained by changing the heading by more than 30°. The results of this type of analysis can assist also in the programming of the computer in a future automated A.T.C. system.

By having a better understanding of the criteria needed for Category I operations we not only aim for an improvement in safety in Category I operations but we can move off from a more rational basis into Category II. In any case the dividing line between Category I and Category II, that is 200-ft. decision height and 800 m. RVR is not very well chosen as far as the RVR quantity is concerned and in the U.K. we generally refer to Category II as meaning a lowering of the decision height as airlines have been using lower RVR minima than 800 m. for a number of years. With the final part of the approach still having to be made visually, the main instrument approach criteria with which we are concerned are the weather minima—the critical height or decision height and the RVR or Met. visibility.

Before an aircraft is given its Certificate of Airworthiness the aircraft constructor has to satisfy the Air Registration Board that the standards laid down in the British Civil Airworthiness Requirements (B.C.A.R.s) have been met. However, if you go to B.C.A.R. and try and find something under Instrument Approach Criteria, you will be unlucky. This is because the requirements for low weather minima and blind landing operations are still in the form of A.R.B. Technical Notes and working drafts. This state of affairs has come about because of A.R.B.'s reluctance to become bureaucratic and devise arbitrary rules and regulations concerning an operation as new as automatic landing.

It is abundantly clear that improvement in regularity and safety of operations in poor visibility can only come about through increased precision during the non-visual phase of the approach and missed approach and through continuing use of the instrument guidance to the lowest possible height within the prescribed limitations during the visual phase. In common with most other airlines, B.E.A. is planning to introduce Category II operations in the near future and this paper deals with some of the problems which we have met and the way in which we plan to tackle them.

By virtue of being an exclusively short-haul airline, B.E.A. flight times are! short compared with time spent on the ground. As a result, flight schedules need to be closely integrated to provide a high rate of utilization of both aircraft and crews, and so any serious disruption of services by the weather affects B.E.A. to a greater extent than other airlines.

A method of measuring wind variations along an aircraft glide path is described. The technique uses a ground-based pulsed doppler radar to measure the line of sight velocity of precipitation particles. At low angles of elevation this velocity is that of die horizontal wind component toward the radar.

Wind variations likely to be encountered by an aircraft as it lands or takes off from an airfield are estimated almost invariably from a nearby anemometer placed 10 m. above the ground. It is obvious that this wind is not fully representative of conditions at higher levels; however, winds other than near the ground are difficult to measure. This note describes a method of measuring the line of sight wind using a pulsed doppler radar and presents some observations of the wind variation along a path at an elevation of 3°, which is typical of the glide path of many aircraft. These winds are compared with those recorded by a nearby anemometer.

In this paper, presented by the International Air Navigators Council, and written by its Executive Vice Chairman, the navigation of the S.S.T. is considered from the practising navigator's point of view. Extrapolating from present procedures the conclusion is drawn that navigation system verification should continue to be the responsibility of flight-deck management, that self-contained D.R. systems should be monitored by an externally referenced aid, that raw navigational data should continue to be available to the flight crew and finally that simplicity and reliability in navigation systems should be preferred to finite accuracy.

Consideration of an environment in which operational data and experience are limited to the military is a difficult assignment at the best of times. In order to discuss, with some degree of intelligence, the long-range navigation system considered desirable in the supersonic environment, we have relied mainly on the process of extrapolation using existing data and operational ‘know how’ to formulate practical guidelines.

The Executive Secretary has referred to me two notes on this subject, one by M. S. Dixon and the other by Bruno Ortlepp. Although submitted independently, and at different times, they clearly relate not only to the. same technique, but also to the same set of observations.

Now much has been recently written on the determination of time, and thus of longitude, from observations of the Moon's altitude (for example, in this Journal, reference can be made to the notes by Francis Chichester, 19, 106, 1966; D. H. Sadler, 19, 107, 1966; J. J. Evans, 19, 392, 1966; and to the comments in the article by H.M. Nautical Almanac Office in 19, 133 and 1 $2, 1966) and it should be unnecessary toNrestate either the principle or the practical disadvantages of this method.

The publication of Admiral Ritchie's E. G. R. Taylor Lecture (Journal, 20, 1) brings into perspective so many names familiar to the practising navigator; indeed the achievements of these great men are surveyed and charted with great clarity. Captain Flinders receives mention only in passing and his initial surveys of the greater part of Australia do not appear on the summary diagram. Yet, in other contexts, his ship, his mentor and his kinsmen all obtain special mention.

In his note (Journal 21, 81) on this subject, Ronald Turner says ‘No longer will orbital periods of the rotation of the Earth on its axis be measures of time’. This is not so, either in general or in the particular, case of navigation.

Universal Time (U.T.), which is the generally accepted name for Greenwich Mean Time (G.M.T.), continues to be essential for all purposes (in astronomy, geodesy, surveying and navigation) for which are required astronomical observations related to the precise position of the observer on the Earth's surface. The Nautical Almanac must continue to tabulate the positions of the Sun, Moon, planets and stars with G.M.T. as the time-argument; and observations should be timed in a time-system related to U.T., such as the broadcast time-signals of Coordinated Universal Time (U.T.C:).