An accurate knowledge of the service speed of a merchant vessel is becoming increasingly important. Service speed and average speed (the former traditionally implying a long-term average, the latter a short-term average) are both derived by dividing the sum of a number of observed distances by the relevant time elapsed. In this way fluctuations in observed distances arising from random fix errors and the effects of change of draught, weather and variable currents are smoothed. Service speed may be used as a basis for determining log errors, engine efficiencies, hull surface condition, liner schedules and charter party speeds. It is therefore relevant to consider possible systematic errors which may be introduced in the calculation of these speeds.

The paper describes and reviews some of the work done by NPL over a period of twelve months in a climate of growing concern about the present and future safety of marine traffic, especially in narrow and restricted waters. The increase in number, size and speed of ships in the last decade emphasizes the need for information on the characteristics of marine traffic affecting safety of navigation, while the use of very large tankers and new types of carrier has increased the potential consequences of pollution to the environment in the event of a serious casualty. The situation in the Dover Strait is further complicated by crossing traffic and by the existence of fishing grounds.

The note by V. L. Bosazza (on page 112) raises a number of interesting points. First it must be noted that there is no indication in Ryder's book that the horizon method, viz. ‘To observe from the cross-trees or other convenient place the angle subtended between the horizon and the enemy's waterline’, was used before it was introduced by Ryder in 1845. Ryder remarked that in not a single man-of-war which he visited before the time of the publication of his book did he find any method in use that would denote satisfactorily the range of a ship at sea; and it was to meet this deficiency that he suggested his horizon method.

It has become increasingly apparent that there is a pressing need to amend the Collision Regulations with special regard for the requirements of high-speed vessels. My experience as a Commander of a hydrofoil on a scheduled passenger service, in an area of high traffic density, has led me to write this paper and to add weight to the argument in favour of an early alteration of the existing Rules.

There are more and more types of vessel today capable of speeds in excess of 40 and indeed up to 60 or more knots. In the Solent area alone, there are two hovercraft services and a hydrofoil service. In addition there are the experimental craft of the National Physical Laboratory, the Inter-Service Hovercraft Unit and several manufacturers use the area as a testing ground for their vessels. There are all types of high-speed vehicles proceeding in all directions, at speeds which 10 years ago would have been considered impossible.

As vessels become more efficient and shipping demands continue to grow the population explosion of vessels at sea is outdistancing even its famous human counterpart. This increases the risk of accidents, particularly in confluence areas and straits, and to avert future disaster it is important to predict trends in global traffic flows so that appropriate measures may be taken in time. This poses a difficult problem. Due to the diversity of nationalities involved, the autonomy of ships and competitive secrecy, it is only possible to account for the present at-sea ship population within about 16 per cent. Geographical distribution is even more doubtful and predicting changes more speculative still.

The very interesting short note by Cotter in the July issue of the Journal is of importance in the history of survey methods used in charting the harbours of East Africa and the delta of the Zambezi. In my researches into the achievements of the Zambezi Expedition of 1858, I finally found in Francis Owen's book that the vertical angle method had been used in 1820 and also in the voyages of Leven and Barracouta from 1821 to 1823. In 1820 Captain W. F. M. Owen in collaboration with the staff at Woolwich calibrated rockets in order to measure distances at sea.

The number of collisions and groundings and the contact damage suffered by merchant ships every year is considerable, the averages for the years 1965–70 inclusive showing that some 15 per cent of the world's shipping over 500 g.r.t. has been involved annually in such accidents. United Kingdom shipping is no exception, and collisions and groundings alone as reported in Lloyd's Daily Lists during the first four months of 1971 show that ships from some 27 companies were involved, some with more than one incident reported although none had more than three. Collisions, groundings and contact damage are likely to occur if a ship's captain and his bridge watch keeping officers do not have immediately available in a simple form, complete information about their ship and her navigational equipment, and detailed information covering the essential tasks performed on the bridge. Unfortunately however, in a great number of ships, most of this information is not provided in an easily usable form and, as a result, even the most competent of navigators is all too often unnecessarily placed in a difficult and sometimes dangerous situation.

A Marine terminal influences the flow of traffic which sails at a lower speed and is congested. Navigation must be in accordance with the total amount of traffic and not, as in the open sea, in accordance with one or two other ships. Shore based authority must be accepted. The flow of traffic along the coast passing a terminal meets this congestion, certainly if the terminal is in shallow water frequented by large vessels. Crossing also adds to the congestion for the passing flow of traffic. The congestion will be less if the marine terminal and outer channel can accommodate the total traffic flow.

King's observation that a false impression could be gained from long-term savings that do not take account of the time value of money is no doubt true if all aspects and factors of comparative projects are taken into account. However, he must think readers a little naive if he offers his Fig. 3 as a full interpretation of the possible savings from installing the various levels of shipborne automation explored in my recent article. An examination of Section 8 (Cost Equations) will show that the DCF technique was deliberately discarded in order to simplify the argument. In fact, there was an additional note—deleted by the Editor through lack of space—which observed that the appraisal could be based on the assumption that the discount rate was equal to the escalation rate of the savings occasioned by taking into account the rise in wages, victualling, &c. over the equivalent project period.

Although the economic theory of congestion as applied to road traffic has been known since at least the time of Pigou its application to marine problems has been much slower. It is the purpose of this paper to remedy this somewhat by interpreting the theory in a marine context and to suggest some of the practical implications of taking proper account of congestion effects.

A. White's study of navigational accuracy near Strumble is artificial and draws some wrong conclusions. He seems to assume that it is a crime to be outside the airway. But this airway is isolated, with no mountains near cruising altitude, and no one infringed a neighbouring airway. In a terminal area I am sure accuracy is much higher, because it needs to be. Airway widths vary from one country to another and are unimportant and the boundaries are not evident to pilots, who try to stay not within the arbitrary boundaries but not too far from the centre line. The area just outside the official airway is just as safe and good as the airway, and indeed safer than the centre line where traffic density is highest and only an altitude mistake by controller or pilot is needed to promote a collision—natural dispersion is still safer than extreme accuracy. Crews generally fly only as accurately as necessary, reserving their energy for the most important tasks: the study of Strumble shows adequate accuracy. Incidentally routes and airways should follow the curved path of aircraft instead of the right-angled bends, for instance the standard inbound route to Gatwick: Lydd-Cliff-Mayfield.

After studying Captain J. S. McKenzie's very interesting paper on the above subject (Journal24, 174), and recognizing the need for an improvement in the safety of navigation, it would seem worthwhile considering whether safety could be improved while still reducing costs.

Using Captain McKenzie's assumed costs, and his Table III as a model, the accompanying table shows the costs and savings for two versions of an all officer bridge manning scheme.

The Man/machine interface. People who design motor cars also drive them, but whoever heard of a radar design engineer who also had a Master's ticket? Of course, the designers of marine instruments do go to sea occasionally, but not for longer than they can help; sea-time is apt to interfere with the weekend. So it happens that the people who make marine radars are rather remote from those who use them, and from the environment in which they work, the sea. The engineer might argue that no two seamen ever seem able to agree on what they want, so the easiest thing is to decide for them, and that, in any case, it is only a matter of ergonomics. On the other hand, it may be that the people who write books on ergonomics have not been to sea either. Radars are used in the dark, as are motor cars, but the darkness of the bridge is not the same as night driving.

A Survey of marine accidents has been carried out as part of a study aimed at predicting the probable future frequency of accidents likely to result in pollution of the United Kingdom coastline. The survey covers all marine accidents in the North-western European area, i.e. North Sea, English Channel, Irish Sea &c, and all tanker accidents world-wide; it covers the 10-year period 1959–68 inclusive.

When our Norwegian ancestors wished to navigate in the open sea they could find their bearings by the Sun or stars if the sky was not overcast. In foggy weather they used the sólaisteinn or sunstone, ‘a stone with which one could see where the sun was in the heavens’. A knife blade will do equally well as may be seen from Fig. 1. If you place the point of the knife on your thumb nail, as shown in the figure, on a sunny day you can easily see the shadow it casts; turning the blade a little one way or the other the shadow widens, but when the knife edge points towards the sun the shadow is reduced to a narrow line.