A Signal from a marine light is the oldest and simplest of the means available to the navigator for determining his position: so old, indeed, that one may well wonder whether anything can still be added to our knowledge of it, and so simple that one may question, too, whether anything is to be gained by seeking to perfect it while such vast fields of inquiry still await imaginative scientific research. However, like all human activities, navigation is caught up in a rapid evolutionary process which calls for an adaptation of time-honoured methods to new conditions of operation. Moreover, whatever advantages modern methods of position-finding may offer, the marine light will always have one great advantage that cannot be replaced, that of being directly perceptible to the human eye. It is well worth our while, then, to have a look at any defects in the present system of marine lights and see how they may be put right.

1. Journal de bord de Juan de la Cosa, second de Christophe Colomb. Presenté et commenté par Ignacio Olagué. Paris, 1957, 870 frs.

2. The Journal of Christopher Columbus. Translated by Cecil Jane, revised and annotated by L. A. Vigneras with an appendix by R. A. Skelton. Anthony Blond and The Orion Press, London, 1960, 45s.

Writing an Introduction to the Four Voyages of Columbus over thirty years ago, the late Cecil Jane remarked: ‘It might with justice be added that no event of such moment can ever occur again, unless, perhaps the tracts of space be bridged and communication established between the Earth and her sister planets.’ The fact that we are on the very eve of placing a man in the Moon should enable us to appreciate more justly the various ways in which, during the late fifteenth century, different people reacted to the daring proposal of Columbus to sail west to Asia.

Before commencing an analysis of the subject matter at hand, it will be as well to present some definitions which we have adopted, in our own work, even if they represent in part arbitrary interpretations of our own.

(a) Pressure altitude is, of course, nothing but barometer pressure at any given elevation, converted into equivalent altitude (feet) units; hence a variable.

(b) Sea-level in connection with altimetry is only a theoretical reference value which does not necessarily conform with mean-high water; in terms of pressure altitude, needless to say, it is also a variable.

(c) True altitude (above sea-level) cannot be obtained with satisfactory accuracy by merely correcting for sea-level barometer pressure. On the other hand, we must dispel the notion—not uncommon—that one can obtain more accurate altitude values by correcting for temperature and humidity at a particular flight level. There are such things as inversions and convection currents; we do not need cold weather to have a high barometer, and sometimes it is warmer a few thousand feet up than at ground-level.

(d) Performance of pressure instruments is properly expressed in parts of the pressure range—not in per cent of altitude—and the reason is simple: at, say, 60,000 ft. you have about 16 times as may feet per unit of pressure as at sea-level.

(e) Sensitivity is—technically speaking—the smallest part of the pressure range that will produce a measurable response.

When motor-cars were first invented, they were sometimes called horseless carriages, so naturally some early automobiles were designed to look (as far as possible) like a horse and carriage without the horse. We may be in danger of making similar errors. Some Doppler Navigators appear designed to perpetuate methods of navigation which doppler itself should help to render obsolete.

Basically, the doppler phenomenon, measured in the aircraft, gives the aircraft's velocity relative to the reflecting terrain as a vector referenced to the aircraft's axes. In other words, angle of attack, drift and ground-speed are measured directly.

The possible application of this information to improved methods of aircraft operation is almost infinite in its variety. The ways of applying, for example, accurately measured angle of attack, to the take-off, approach and landing phases, or to performance analysis, are numerous. Perhaps the most wildly esoteric suggestion for the application of angle of attack information was that aircraft could be weighed in flight by doppler given equivalent air-speed and the lift/drag polar of the aircraft; unfortunately the question of how to obtain a usable accuracy was not precisely explained! Of course, if sufficient accuracy were possible in this application, we could have a rather novel fuel flow-meter since, on all well conducted flights, fuel flow = rate of change of aircraft weight.

The cocked hat problem is a difficult one and though Captain Cotter in a recent article, has gone a long way towards clarifying it, I believe that the fundamentals of the subject are more difficult than this article suggests. A brief treatment of these, together with an indication of how they may be applied in practice, may be worth while.

An attachment giving a number of accurate straight or curved climb or descent flight paths has been developed for use with the Australian-designed airborne distance measuring equipment (DME). The electrical output from a special altimeter is converted into a time delay which increases with altitude. In the DME distance is measured, fundamentally, in terms of a similar time delay. The h/d flight path is defined by keeping these two delays equal as the aircraft climbs or descends. The ILS glide slope meter is used as the pilot's path indicator. Nominal slopes from 1° to 6° may be selected. In terms of height, deviations from the path of ± 250 ft. produce full-scale deflections on the meter, while the maximum error is ± 1000 ft.

This paper develops a method for the prediction of wave height, period and direction on a 200-mile grid over the North Atlantic Ocean, using a wave spectrum technique. The method could be useful in conjunction with optimum ship routing across the ocean.

AS discussed recently by Hanssen and James, ship routing across the ocean, using the optimum route with respect to weather conditions, is now becoming a practical possibility. One essential requirement is to predict the wave heights and lengths over all parts of the area concerned. This would require first, of course, a forecast of the wind conditions. At present the Meteorological Office issues prognostic weather charts 24 hours ahead and wave predictions must be tied to them. Wave conditions are not determined instantaneously by the weather conditions at a given time, but tend to be an integration of the weather conditions over two, three, or even more days before and so wave predictions 24 hours ahead are likely to be more accurate than the wind forecasts.

In order to provide facilities ashore for obtaining experience in the use of radar in conditions approximating to those at sea, a marine radar simulator has been developed by the Ministry of Transport as an aid to training. In this way, ships’ officers can obtain experience, particularly in the avoidance of collision, which could rarely be obtained at sea without endangering the ship. The instrument shows synthetic target echoes on a standard marine radar display and the effects of their movements and manœuvres. Helm and engine controls are provided to allow the observer to manœuvre as he thinks fit to avoid collision.

In this paper the Professional Officer and Chief Nautical Surveyor of the Ministry of Transport describes the simulator, the courses for ships’ officers that the Ministry has instituted, and the results of these courses. The paper, with three appendices which are not reproduced here, was presented at the Annual Meeting of the Ausschuss fur Funkortung held at Kiel from 12–17 September 1960, and is published with the kind permission of that body.

In the July Journal (14, 362) Klerk and Steensma describe a new and ingenious method of radar plotting. The following comment, sent in at the invitation of the editor of the Journal, follows closely my remarks on a similar article in the Dutch review De Zee (December 1960).

The use of leading marks in pilotage is a procedure familiar to all seamen, and wherever leads are sufficiently easy to recognize on the screen the technique can be extended to use with radar, due note of the lowered degree of precision being taken. In this account of a passage through the exit to Singapore Strait, Captain Robb, a shipmaster of the Blue Funnel Line, and author of several works on radar use at sea, describes a less well known method in which off-set marks are used for conning the ship by radar. A similar technique was suggested in the Journal (9, 445) by Mackay.

A description is given of sea trials of two types of narrow-beam echo-sounder developed with a view to obtaining information as regards both the depth and the slope of the seabed. One system involves a two-channel interferometric arrangement, which provides a family of several spaced receiving beams; the other uses an eight-element hydrophone array with electronic sector-scanning of the resultant narrow beam. Photographs of typical displays show that comparable values may be derived for the slope of the seabed beneath the ship for both systems in simple situations. Difficulties in interpretation of the interferometer record with more complex slopes render the use of the electronically-scanned system advisable in such circumstances.

To the layman navigation may sometimes appear as an old lady whose fads have acquired the sanctity of tradition. In every tradition, however, there is something venerable; and we would be very wrong to laugh at the traditions of the sea, for they are a legacy we have inherited from all our seafaring ancestors since the days of Noah.

The core of this inheritance is the notion of freedom. For centuries the freedom of the seas was absolute and unconditional; all men were free to use the sea, for no man can plant his flag on its restless immensities; and all were free to choose their routes and navigate as they pleased, for encounters at sea were so infrequent that it would be only a most uncommon stroke of ill-luck that produced a collision between two vessels in the vast emptiness of the oceans.

A star globe is described which can be immediately set up for evening or morning twilight by adjusting the latitude and date only; no reference to the Almanac is involved. The azimuth of the below-horizon Sun is also directly evident. The paper discusses the theory involved, and the accuracy attainable both with and without certain simple corrections.

If we examine the traffic in the Strait of Dover, which in its most narrow part is 17 miles wide, we notice that nearly the whole of this traffic, about 98 per cent, is concentrated and strangled under the British coast, in a narrow pass about five miles wide. Very heavy traffic coming from all parts of the world gathers together in the bottleneck which is the Channel. Thus innumerable vessels, when still in the Strait of Dover, spread out fan-wise at the very place where traffic in an opposite direction concentrates in order to make the same narrow passage. It is the unorganized convergence of these many routes which concentrates this very dense traffic at the mouth of the Strait of Dover and is the cause of all too many collisions. One immediately concludes that by relieving congestion and by organizing or canalizing the traffic, the problem will have received an acceptable answer.

The Decca method of conducting speed trials and its considerable advantages over other methods have been described in this Journal and elsewhere. Decca is nowadays widely and successfully used for acceptance trials (speed, calibration of (Sal) log, turning circles and (crash) stopways) by Royal and Merchant Navy ships of Britain, the Netherlands, France, Denmark, Sweden and probably of other nations.

The results of speed trials of Netherlands Merchant Navy ships are given in the present paper. Those of the equally successful turning circles and stopways are not given here, since their numerical results would be of little interest to the reader; a pictorial representation—among other things allowing for a comparison between various interesting turning habits of different ships—would be more suitable, but would occupy too much space.

Short Description of the Method. Each speed determination consists of 4 to 6 runs, alternatively in opposite directions. In each run 20 photographs of the decometers are taken at 30-second (or, for very high speeds of 30 kt. or more, 15-second) intervals and one single run therefore takes 9½ minutes. Specially calibrated Decca receivers are used to ensure a much higher accuracy than is achieved (and needed) for normal navigational purposes.

With the aid of special, large-scale, Decca charts or special tables, all these decometer readings—80 in 4 runs or 120 in 6 runs—are converted into rectangular coordinates X, Y.

A joint symposium of the Institute and the British Interplanetary Society was held at the Royal Geographical Society's house on Friday, 18 November 1960.

At the morning session the Chair was taken by Wing Commander E. W. Anderson, o.b.e., d.f.c., a.f.c., President of the Institute, who introduced the speakers. In the afternoon, Dr. W. R. Maxwell, President of the British Interplanetary Society, took the Chair for the papers by Cashmore and Stewart, and Air Marshal Sir Edward Chilton, k.b.e., c.b., presided over the main discussion, which was opened by Dr. J. G. Porter.

While engaged in the observation and prediction of the position of Sputnik I, it was realized that, if a reliable orbit were available, and an observation of the satellite against the background of stars were made to a precision of about 0°·1 and timed to about 0·2 of a second, then the position of the observer could be determined to a precision sufficient for most navigational purposes. The following account demonstrates how this has actually been done from a single visual observation of the American Balloon Satellite Echo I (designated 1960ι1).

Principle of method. The direction in which an observer on the Earth's surface sees an artificial satellite at any instant differs from that in which it is seen by any other observer and from that in which it would be observed from the centre of the Earth. The amount and direction of the parallactic shift can be determined from the comparison of the direction of observation with that calculated from the geocentric ephemeris of the satellite; and the position of the observer on the Earth's surface can be uniquely calculated from this parallactic shift. Only a single observation is required, without reference to the vertical.

When reading articles on radar-navigation in various nautical magazines, one is constantly struck by the difficulty of comparing the different targets on the screen and of interpreting the changes that take place in the right way. So plotting becomes still more necessary in order to get: (a) the nearest approach, and (b) the present course and speed of other vessels, before we can manœuvre to avoid collision, especially in thick weather. When plotting, comparisons are hampered by the fact that the echoes must be recorded on a piece of paper or on the reflection-plotter, and that the different distances, courses and speeds must be measured very accurately. And nearly all these tasks depend upon the skill and accuracy of one man.