It is helpful at an exhibition to have a catalogue of the items on view. As this symposium is in effect a display of the operational aspects of marine radar, it may be of value in this paper to attempt to catalogue these aspects. They can be divided into two groups as follows:

A. The aspects that determine the effectiveness of marine radar (the siting of the scanner and the operating policy followed, for example). These we propose to call the OPERATIONAL FACTORS.

B. The benefits obtainable from marine radar (i.e. those aspects that may be said to measure its effectiveness—the time and worry saved, for example). For these we suggest the term OPERATIONAL YIELDS.

The basic principles of the detection and location of objects by radar are now widely known, and the performance requirements of a marine radar equipment have already been covered by the British Ministry of Transport specification. This paper describes and analyses operational experience gained in fitting and in operating a number of equipments manufactured to this specification.

Experience gained in equipping some 24 vessels, varying in size from 700 to 4000 tons, with radar may be of interest, and perhaps of help in avoiding some of the pitfalls that can occur.

The problem of finding sufficient space in a small ship so that one instrument does not interfere with another is never an easy one. For example, to fit radar to a vessel whose wheelhouse superstructure is not more than 10 ft. long may entail building a radar tower of considerable height if the proper distance between the scanner and the magnetic compass is to be maintained. The magnetic effect of the tower on the compass will then have to be considered, and it may be necessary to build it of a non-magnetic material. Also the effect of the radar, when working, on the D.F. loop arises; a distance of 12 ft. between them is here necessary.

Once the performance requirements of the Ministry of Transport Specification have been met, there remains to be considered the arrangement of the equipment to enable the ship's officers to take full advantage of the high performance for which the specification provides. These considerations can be classed in three main categories: the method of presenting information to the navigating officer, the convenience of the various controls, and the facilities provided to enable superficial maintenance to be undertaken.

The flagship of the General Steam Navigation Company, s.s. Seamew (Captain T. C. Stone), 1209 tons, has recently completed various trips on which data relating to the use of her navigational radar have been noted. The data collected bear on many problems of presentation and practice and are described in this paper.

During a cruise by H.M.S. Fleetwood in Scandinavian waters last autumn the opportunity was taken of measuring the intensity of echoes received from the sea, for various wave heights. These echoes are commonly known as sea clutter and the object of the measurements was primarily to provide data on which to design suitable anti-clutter circuits for use in civil marine radars. The results obtained, however, show the need for increasing the radar echoing characteristics of small navigational marks and small boats.

No satisfactory means of securing positive identification of individual radar echoes in congested waters has yet been devised, although many ingenious suggestions have at different times been put forward. These ideas include systems for providing a special identification signal from selected buoys, or alternatively for a considerable increase in the number of buoys and their arrangement in groups in definite patterns at strategic points so that they may be easily picked out on the ship's P.P.I.

Some questions affecting the operational value of shipborne radar and on which there is, at the moment, no clear unanimity of view are discussed in this paper.

The best position for the console is discussed in the light of requirements which vary with the different uses to which a shipborne radar can be put. The advantages of a chart comparison unit are also considered and the conclusion is drawn that these can be more economically gained by other methods. In particular the use of P.P.I. photographs is advocated as a method of land echo identification which leaves the chart free for other uses.

This paper is confined to a non-technical survey of the particular application of radar to the maintenance of a fast schedule of ferry vessels operating across a busy tidal river. After some seventeen months' practical experience of this application it is possible to give some opinions of the value of radar as a commercial aid to navigation.

Wallasey Ferries operates a twenty-four hour service between Wallasey and Liverpool, and carries some twenty million passengers per annum.

This paper described how 53 ships of the United States Lines had been fitted with 10 cm. radar and how instructions for maintenance and operation were given by the Company and the manufacturers of the equipment. Instruction in its use is given by a representative of the manufacturer, and subsequently minor adjustments and fuse replacements are made on board, all other maintenance being done under service contract in port.

General instructions sent by the Marine Superintendent to the Master of each vessel fitted stressed the following points:

1. i. For the present the equipment is to be regarded solely as a collisionwarning device.

2. ii. The installation in no way relieves the Master from conforming to the Rule of the Road or any Pilot Rules.

3. iii. A complete radar log in which maintenance and operational work are recorded should be kept.

4. iv. Deck officers should acquaint themselves with the use of the equipment and should be encouraged to read the manufacturer's descriptive and operational booklet.

More than 1200 American radar equipments have been fitted to ships and this paper gave same American views on its operation; the views put forward were not necessarily different from those held in this country but certain experiences of inland navigation and blind pilotage which would be new to British operators were described. It was stated that when commercial production of marine radar started in the U.S., opinion was divided on the relative merits of 3 cm. and 10 cm. radar, some manufacturers concentrating on one and some on the other. Although 10 cm. equipment is still manufactured, all manufacturers now have a 3 cm. radar in production.

Certain advantages of radar assisted navigation were mentioned and these included the ability to determine another vessel's course and speed by plotting and the considerable saving in fuel and time that could be achieved by the accurate knowledge of the ship's position in coastal waters no matter what the weather.

Anomalous propagation in the Great Lakes region was described as being so common that shipmasters often regard the increased range of radar in the area as being the normal range of the set.

The use of radar by tugs on the Mississippi and its tributary the Ohio was described. Here up to fifteen barges of 100 ft. are ‘shoved’ by the tugs into narrow locks in weather which sometimes conceals half the tow. The small bump in the trace, representing the lock, is recognized by the pilots. One of the outstanding problems of this form of radar navigation was stated to be that the bridges (of which there are 1700 over the Mississippi) were such good reflectors that discrimination between them was not possible at a mile, at which distance the tow gets into position to pass between the piers.

It may be useful at the end of this symposium to ask broadly what has been achieved so far in the field of navigational radar and what are the outstanding problems.

In this country alone, in the four years since the end of the war, rather more than 300 commercial radars have been manufactured to an exacting specification and fitted to merchant vessels, and a much larger number has been produced in the United States; during 1949 the British radar industry states that it hopes to fit more than a ship a day.

A method of obtaining aircraft altitude to within 50 feet at altitudes of 10,000 to 20,000 feet is described. This accuracy is necessary in a few special cases. The method consists of determining the height of a pressure level at some convenient point by radar or other means, and then calculating from a knowledge of the wind vector the change of height of this pressure level between the check point and the point at which an accurate altitude is required. The limitations of alternative methods of height finding, such as the use of an aneroid altimeter corrected for temperature at the upper level, are discussed.

For most purposes the aircraft type aneroid altimeter gives a sufficiently accurate indication of height, provided corrections are made for the temperature at flight level. In the application of radar to topographical surveying, however, it is necessary to know the altitude of the aircraft used in the measurement to within 50 feet when flying at heights of 10,000 to 20,000 feet. This can be achieved only by special techniques. The method here outlined has been used extensively during investigations into the use of radar for surveying. It is simple and appears to give satisfactory results.

This paper describes how it was found possible to estimate the accuracy, under operational conditions, of navigators' wind-determinations by the 3-course drift method. This was done by studying the self-consistency of the set of three drifts logged by the navigator; the technique which was developed, using the size of the circle inscribed in the ‘triangle of error,’ can be used expeditiously by persons with no special training. This technique is applicable to other position line problems. Of the total inaccuracy of the winds found by the navigators, three quarters was contributed by the errors of observation of the drifts, and one quarter by the process of deriving the wind from the set of drifts, using the Dalton Computor.

The validity of the method was checked by comparing wind measurements by the 3-course drift method with the value obtained from Air Position Indicator readings taken in the course of practice bombing exercises; the accuracy of the latter value was also estimated from internal consistency. The check was satisfactory; and in particular, contrary to widely held belief, showed that the navigators did not systematically underestimate drift angles.

In planning a flight over polar regions, celestial navigation is of paramount importance: Loran and Consol coverage is doubtful and Gee chains non-existent; interpretation of the P.P.I. screen is hampered by lack of accurate survey and the camouflaging of coastlines by ice packs. Thus navigational accuracy and the amount of activity needed to maintain it depend largely on the foresight with which the flight is planned to render celestial information available.