Since the large-scale development of offshore oil installations started in the 1970s the requirements for navigating men and machines around structures and on the sea bed have increased dramatically.

The earliest forms of navigation were by tracking with fish-finding sonar, either directly or with the aid of an acoustic transponder. The sonar would usually be fitted to a surface craft, whose position was found by using one of the commercial navigation systems such as HIFIX. The range and bearing of the object being tracked was then applied to this position. Most of this work was done by hand and the position up-date rate was of the order of minutes. The error of position was the sum of the surface system and tracking system errors and was of the order of at least 10 m.

The stringent maintenance requirements that apply to North Sea structures make the cost of inspection a significant factor in North Sea operations. A failure on a large production platform necessitating its shut down would result in a loss of revenue of between half and three-quarters of a million pounds per day. Current practice is such that the whole inspection process is very weather-dependent, and only a portion of a large structure can be examined during the ‘weather window’ (roughly speaking, the period between April and October). The area to be inspected has to be planned in advance, acoustic nets have t o be laid down and calibrated, a range of sophisticated equipment has to be deployed; divers also require relatively long lead times prior to the operation and considerable time for decompressing after the operation. The use of divers will, it is hoped, diminish. It is now general practice to use Remotely Controlled Vehicles (RCV) and television for sub-sea inspection.

The Meteorological Office makes full operational use of pictorial weather satellite data in preparation of routine analyses of the atmospheric fields of wind, temperature, pressure and humidity. There are two types of satellite, polar orbiting and geostationary: the polar orbiter scans the globe from a height of about 830 km and as the globe rotates beneath the satellite each area is scanned twice in 24 hours; the geostationary satellite rotates with the globe and takes frequent pictures of the same area from a height of about 35000 km.

The pictorial data are in the form of visual and infra-red images and when used together can provide considerable information about the height, type and density of the clouds. Vertical temperature profiles within the atmosphere are also retrieved from polar orbiting satellites using linear regression techniques, but there are problems yet to be solved in areas of heavy cloud and precipitation. The paper was presented at Oceanology International 1982, held at Brighton.

Radar operating in the dekametric or high frequency band permits the measurement of sea-surface parameters at very much longer ranges than is possible with other techniques: 0–200 km is practical using a coast-located radar and oversea propagation, while 1000–3000 km is achievable using ionospheric reflection from a radar which may be located inland. The paper, which was presented at Oceanology International 1982 at Brighton, discusses the extraction and mapping of wave height, wave period, non-directional spectrum and surface wind parameters from Doppler radar echoes. The techniques are illustrated by the results of the UK ground-wave and sky-wave measurements and computer simulation.

A swath sounding system is under development which is capable of being towed from ships of opportunity. The principle on which it is based is an acoustic interferometer to which a vernier has been added to resolve the ambiguity of phase ramp identification. The ‘fish’ is equipped with both rotational and translational attitude sensors, though no attempt is made to stabilize it. This is in the interest of size and hence of both instrumental and deployment economy.

The paper, which was presented at Oceanology International 1982 at Brighton, proposes a novel method to permit replication of the swath depth measurements, and also to provide an independent means of ground scale correction, which may obviate the need to deploy a positioning network for deep-water high-resolution swath surveys.

Weather satellites such as NOAA 6 and 7, which produce the imagery that appears on our television screens, are largely unsuitable for measuring sea-surface conditions since their sensors operate in the visible/infra-red part of the electromagnetic spectrum and, whereas weather patterns can be inferred from images of cloud formations, for much of the time these clouds also deny the sensors a view of the sea surface.

Captain Maybourn's paper, and that which follows by Kerr and Anderson, were presented at a hydrographic symposium entitled ‘The Nautical Chart – The Future’, held during the 12th International Hydrographic Conference at Monaco, April 1982. It outlines the Merchant Mariner's requirements of the chart and speculates as to the effect of new navigation aids on both chart making and use. All the papers presented at the symposium, together with the ensuing discussion, will in due course be available in book form from the International Hydrographic Bureau in Monaco.

Various writers have discussed the origins of the nautical chart. In this paper we wish to show how the marine cartographer has responded to developments in navigation and the changing needs of shipping. The development of the chart has been greatly affected by changes in navigational techniques. For example, Portulan charts, with their criss-crossing loxodromes, developed from a need to illustrate the pilots books, called ‘Portulans’ by the Italians. On these were carefully recorded bearings and distances between points of departure and arrival. As the measurement of latitude became established, the graduation of latitude began to appear on charts early in the sixteenth century. Problems developed on longer voyages through the convergence of the meridians which were temporarily overcome by the use of an oblique meridian. In 1569 the solution to this was finally found when Gerardus Mercator published his famous world map, although the general use of this projection did not take place until much later. Charts of the sixteenth century showed considerable detail and even at that early date there were some who questioned the need to show information that was considered redundant. Bourne, writing in 1574, deplored the hydro-graphers' practice of filling vacant spaces of land ‘with so many flagges’ and colouring the compasses ‘with so many colours’ and that instead of wasting their time, they should include tidal information and the elevation of the shore from the sea.

In December 1981 the European Environmental Bureau (EEB) published a Memorandum on Shipping and the Environment, of which the following is a condensed version. Prior to publication, the Memorandum was favourably discussed at a one-day EEB Workshop on Shipping and the Environment, held in London, on 23 October 1981, and attended by representatives of the European Commission, the Marine Environment and Maritime Safety Divisions of the International Maritime Organization and shipping interests. The EEB is an independent, international liaison body which coordinates the activities of some sixty non-governmental environmental organizations operating in all the member States of the European Economic Community (EEC).

The EEB Memorandum intends to put into perspective various recent initiatives by the European Commission aimed at curbing pollution of the sea by ships, as well as improving maritime safety. These initiatives concern the development of a Community information system for marine oil pollution prevention and abatement, together with an advisory committee; the establishment of Port State control; and the adoption of a concerted action project on shore-based maritime navigation aid systems through European Cooperation in the field of Scientific and Technical research (the so-called COST-301 project).

After examining the complementary roles of worldwide and regional arrangements for maritime safety and the prevention of vessel-source pollution, and in particular the distinct but related functions of IMO and EEC in this regard, the EEB Memorandum indicates two major aspects of ship safety and pollution control: the inspection of vessels in port, to ensure compliance with generally agreed safety standards, and offshore vessel traffic management in areas of safety and pollution hazard.

It is recorded that Egypt was the first country to dig a canal to promote world trade; the first canal was dug in the reign of Pharaoh Senusret III (1887–1849 B.C.), to link the Mediterranean Sea with the Red Sea through the Nile delta. This canal, often abandoned due to silting, was reopened for navigation by later Pharaohs and finally by Amro Ibn El Ass in A.D. 640 after which it remained open for 150 years.

The present paper reports a small part of a research project aimed at finding the cost of marine casualties. It is hoped first to find acceptable ways of estimating the cost of casualties and, by applying cost/benefit theory, to help decision makers to choose the most cost-effective programmes of marine safety and environmental protection.

Many nations are debating the implementation of vessel traffic services (VTS) and it is envisaged that some regulation of the movement of marine traffic may soon be imposed. It is highly desirable that prior to any change a rigorous appraisal of the existing traffic be carried out to establish the level of risk in the area; this level can then be used to evaluate any proposed change. The following note describes a research project concerned with establishing a general method of determining the base risk level, developed from earlier research by M. Degré and M. Lefèvre who used a computer simulation of marine traffic in the Dover Strait to assess the impact of various suggested traffic separation schemes. A cost-effective tool has been developed at Liverpool which will enable traffic patterns to be studied in areas remote from the land. This is a computer simulation model which is being used to establish dynamic areas of risk in the Irish Sea, which could easily be transposed to study traffic patterns in any other area.

This paper, which reviews briefly the development of modern maritime electronic navigation aids, was presented at a meeting of the Scottish Branch of the Institute held in Edinburgh on 7 October 1981.

The electronic navigation systems dealt with in this paper are the principal position-fixing aids and the somewhat related computer radar data-processing equipment or Collision Avoidance Systems, inasmuch as these envelop a navigational task. The survey will thus embrace the principal hyperbolic aids – Decca Main Chain and Loran-C; the artificial satellite navigation systems – TRANSIT SATELLITE and NAVSTAR, the Global Positioning System; and the navigational role of collision avoidance systems.

In the eighth Duke of Edinburgh Lecture, presented to the Institute in 1976, Professor Thorn discussed the extent of Megalithic man's knowledge of astronomy and from surveys of ancient sites showed how a calendar was produced and sensitive methods of astronomical observation developed. Mr Watts suggests that the positions of ancient sites in the area he has examined show an early familiarity with the concept of parallels and meridians.

It is not normally assumed that latitude and longitude were in use in times as remote as the late Neolithic and early Bronze Ages. The New Forest with its relatively sparse set of major earthworks is, however, a good area to illustrate that ancient sites are set with careful regard for both latitude and longitude, arid particularly the latter.

The first point to note about the North Atlantic air traffic system is the diurnal pattern of flow. This is strongly tidal, with westbound flow predominant during daylight hours and eastbound flow overnight. There is some traffic which flows against the main stream, particularly during the day, but the strong tendency for one-way traffic results from the difference in local times on opposite sides of the ocean, together with the transit times of flight at current speeds. This means that the general pattern will probably persist, unless and until aircraft speeds change radically.

This paper outlines the phase of the flight planning operation in which airlines calculate minimum-time tracks for the purpose of advising oceanic control centres of their needs prior to the definition of the Organised Track System (OTS). The results are based on 12- and 24-hour forecasts for a level of 250 mb and aircraft assumed to fly at a constant Mach number of 0·82. The problem is defined in terms of a network in which the domestic route structure on each side of the North Atlantic is represented.

We are still in the process of collecting and developing ways of studying and analysing air traffic routes across the North Atlantic. The results presented in this paper must therefore be recognized as provisional. The data comprise some twelve examples of North Atlantic weather forecasts issued from Bracknell; they are sent to us regularly for the 2nd and 15th day of each month. We have also made arrangements to receive notification from the Heathrow Meteorological Office of any days in which there were significant changes in the weather forecast, so that we can request the additional information from Bracknell. Each set of weather data contains the ‘analysis weather’, that is the best estimate of the actual weather at 1200 GMT, and therefore applicable to the time when aircraft are making westerly departures across the North Atlantic from European cities, and also the weather forecasts issued for 12 and 24 hours before this time.

‘Conflicts Between Random Flights in a Given Area’

By S. Ratcliffe and R. L. Ford

The following misprints should be corrected in the paper published in Vol. 35, No. 1, pp. 47–74 (The authors' corrections to the original proofs were inadvertently ignored in the published version):

I am reminded that this was the title of a paper by Professor W. M. Smart, published elsewhere in 1946, dealing with the rhumb line on the spheroid, by references in recent issues of this Journal to a paper of mine entitled ‘Loxodro-mic distances on the Terrestrial Spheroid’ which appeared in this Journal 32 years ago: the subject crops up every few years.