Every sailor, at the back of his or her mind, is aware that the nearest land is likely to be directly beneath the ship's keel and he or she is interested to know just how near. For over two thousand years, mariners measured depth of water by using a sounding rod in shallow areas and the lead and line in deeper water. This paper considers how, during the “Dark Ages”, sailors in the North Sea might have navigated, including the use of sounding rods and lead lines for way-finding during a time when no other navigational instruments were available. Because of the lack of contemporary records the authors firstly consider the use of depth finding in earlier and later times to shed light on how the early North Sea sailors might have operated. The latter part of this paper takes account of the earlier discussion, together with some records of North Sea voyaging, to suggest how “Dark Age” sailors might have used sounding rods, the lead and line, and other techniques to navigate around and across the North Sea.

Safety of life at sea and assistance to persons in distress are matters of great importance to seafarers, shipowners and maritime administrations and have been addressed by the International Maritime Organization (IMO) since its foundation.

The problem of the autonomous determination of the position of a moving object (inertial navigation) on the Earth is solved by gyros, accelerometers, integrators and a computer. We will indicate three possible schemes of inertial navigation.

Most navigators will, at some time or another, have noticed the effect of changes in humidity on the dimensions of paper maps or charts pinned up for display purposes. A display chart, or any other large sheet of paper, neatly pinned to a notice board in a warm dry room will tend to sag in an untidy manner if the atmosphere is allowed to become damp. Similarly a chart pinned up in a moist atmosphere is liable to contract and tear away from its anchoring pins if the weather becomes warm and dry. In the same way, the size of a paper chart in use in the air will vary appreciably with changes in atmospheric conditions; and it follows that if the size changes, so does the true scale. Such changes in the scale are of little consequence so long as dividers are used for measuring distances, since it can be assumed that the distance graduations on the chart all expand and contract in proportion to the change in size of the sheet as a whole. But if a graduated rule or straight-edge is used (and this is practicable only in the case of maps or charts based on some projection giving near-constancy of scale) then, quite apart from the scale errors of the projection, changes in the size of the chart will give rise to errors.

Like any other vehicle a ship needs to be started, stopped and steered safely; the art of doing this is sometimes called ship handling. Successful ship handling depends upon three distinct operations: acquiring the right information, making the right decisions and performing the right manoeuvres. In this paper we assume that the Captain has all the facts and knows the right thing to do, and examine the physical ability of the ship as a mechanism to respond to his will.

Recently, integration of different radionavigation systems has become very popular, since it improves system integrity, availability, accuracy and reliability. This paper discusses a new, flexible and cost-effective approach to system integration, centred on a single-chip application specific processor (ASP). An overview of this integrated system is presented and the application of the ASP for the implementation of a six-channel GPS, OMEGA, Loran-C and MLS receiver is given. The ASP is currently being implemented on a 180000 transistor 1·6μ, m CMOS Sea of Gates chip, and is expected to run at 100 MHz clock speed.

The 600-ton Norwegian sealer Norsel, commanded by Captain Guttorm Jakobsen, made the last of her annual relief trips to Queen Maud Land when she went south last December to bring home the Norwegian-British-Swedish Antarctic Expedition from Maudheim. During this trip the writer was attached to the expedition as naval observer. The ship remained at Maudheim for three weeks while an aerial survey was being carried out by the Swedish air unit which she had brought with her; during this time advantage was taken of fine weather and favourable ice conditions to make two survey trips along the barrier, one to the eastward and the other to westward from Norsel Bay where the ship was harboured.

A device has been developed to enhance the radar conspicuity of navigation buoys. It is also very effective on small craft. This paper describes the specification and testing of the device and discusses the regulatory position regarding its use.

In the course of a summary of established views about the still unknown origins of portolan charts (this Journal, 36, 124, 1983) the hypothesis was advanced that they originated as a result of the maritime interests of Frederick II of Hohenstaufen. It should perhaps be made clear straight away that this is no mere attempt by a German author to further German pretensions in this matter. In fact, of course, Frederick II (1194–1250) was the last emperor of the Holy Roman Empire and, according to the excellent biography by Kantorowicz, felt himself more and more the spokesman for cosmopolitan thought as his years advanced. He spent his youth in Sicily and was known as ‘The Sicilian’, and learned to speak German only during the third decade of his life during his first visit to Germany; by then he was fluent in half a dozen other languages. Sicily of course, where he spent most of his life, meant not simply the island but the kingdom of the two Sicilies which, since the Norse conquests, comprised extensive parts of southern Italy and notably Apulia, where Frederick had his court at Foggia. His dominions bordered papal territory, which accounts for the hostility to him of several popes.

The fisherman's task in navigating his craft are threefold:

(i) to guide his craft safely and by the most direct route between his terminal ports and the fishing grounds;

(ii) to shoot, tow and haul his fishing gear in such a manner as to prevent it being damaged or becoming fast to any obstruction on the seabed;

(iii) to search for aggregations of commercial fish species and by lures, snares and the use of towed nets to capture viable quantities of the fish located.

The navigation to and from the fishing ground poses the same problems as for other marine craft, but once on the grounds, using towed or encircling nets, the position of the nets, not only horizontally but also in the vertical plane, are as much his concern as is the position of the parent vessel. Most fishing grounds are situated where there are irregularities in the seabed topography or where oceanographical factors provide a rich feeding area for a range of fish species. Alternatively many fish species carry out an annual migratory journey to their spawning areas or towards more favourable environmental conditions, their shoaling behaviour at this time making them particularly susceptible to mass capture.

For centuries, celestial navigation was the main method of determining a ship's position at sea, especially when sailing into more exotic areas. Later on, vast areas of the oceans were only covered by the Omega system and there was still every opportunity of finding a position by using the sextant. Nowadays, with GPS coverage worldwide, we consider celestial navigation as an interesting back-up.

For farming in the future, positional information is of particular importance. Out of a multitude of positioning systems, GPS/DGPS is the most suitable one. This system does not require any additional infrastructure and at the same time guarantees complete coverage of all tilled surfaces. The major application of positioning with GPS/DGPS is to be seen in the area of local information and documentation. By generating both planning and process data, it facilitates the operation and control of work processes (organic and mineral fertilization, plant protection). In the end, positioning leads to navigation, which, in the case of single vehicles and vehicle pools, will in turn provide completely new possibilities for development and application. For the first time, vehicles without drivers are conceivable. Thus, the completion of any kind of work on schedule, without time limitations, would become possible with the least possible stress for soil and environment.

At the present time with the increase of air traffic across the Atlantic (and still more so in the future when jet aircraft will be numerous) it becomes very necessary to know what is the safe separation between aircraft, and whether some form of controlled paths may not economically be imposed between America and Europe.

This paper and the following five papers were presented at the NAV91 Conference on Satellite Navigation held at Church House, London, 6–8 November 1991. Copies of the conference proceedings are available from the Director, price £85 (non-members) and £65 (members).

In the last two years, the idea of a civil geostationary overlay (augmentation) to GPS and GLONASS has moved from the discussion/concept stage to something approaching reality. Many details of implementation have been or are in the process of being determined. Major developments that have taken place in this period of time include: (i) INMARSAT'S adoption of a four ocean region satellite deployment (three had been employed previously), now including one region (AOR-West) that covers the conterminous United States, (ii) Inclusion in the specifications, and contracting for, navigation repeater payloads in the four INMARSAT-3 spacecraft, now under construction, (iii) Major improvements in the Test Bed, bringing the test signals closer in function and structure to those to be provided through the INMARSAT-3 navigation payloads. (iv) Plans in the US and Europe to employ the Test Bed, or a facsimile thereof, for field trials of the GPS/GLONASS integrity channel (GIC) concept, (v) Endorsement of the ‘Wideband GIC’ concept (transmission at GPS L, frequency of a spread spectrum signal) by many members of the aviation community, (vi) Introduction and study of the possibility that the Gic might be able to carry some form of differential corrections in addition to the basic integrity and constellation augmentation functions. In other words, whereas two years ago we were still considering the possibility of a civil element of global satellite radionavigation, this year we are deeply in the process of putting the necessary elements into place.

Use of multi antenna GPS equipment for determination of a vessel's attitude holds some promise for the development of accurate and inexpensive attitude systems. An application for such systems might be to provide very accurate roll information for multibeam echo sounders.

The present state-of-the-art GPS attitude systems cannot meet the required accuracy and update rate for such applications. GEOTEAM A/S has therefore developed a PC-based system which combines GPS-based attitude with roll and pitch information from a Vertical Reference Unit (VRU) and heading from a gyro compass.

In such a combined system, the long-term high accuracy of a GPS-based attitude system is combined with the short-term accuracy and fast update rate of conventional VRUS and gyro compasses in order to achieve a resulting performance that is better than any of the systems. In effect, the GPS attitude is used to calibrate the VRU and the gyro compass in real time.

During the past year extensive tests have been performed with a system using a Trimble VECTOR II GPS attitude system with a 1 metre baseline between the antennas, both on a van (with an inertial navigation system as reference) and on a vessel. During November and December 1993 further tests were made with an Ashtech 3DF attitude system with longer baselines (7·5 m). These tests were made on a vessel where the combined GPS/VRU attitude was fed into a multibeam echo sounder. These tests were performed in cooperation with Simrad Subsea A/S, the multibeam echo sounder EM 1000 manufacturer.

The Panama Canal Company's Marine Traffic Control is being designed primarily to minimize ships' average transit-time and obtain optimum use of Canal facilities, but it also includes features contributing to collision prevention. It prepares an operation schedule consistent with the number and characteristics of ships that are in transit and with operating conditions. Actual operation is continuously monitored and signals currently displayed to pilots to facilitate close adherence to the schedule. If the contemplated schedule is cancelled, as by trouble in locks or sudden periods of poor visibility, re-scheduling is rapidly formed and signals transmitted to pilots in conformity with the new schedule.

The system's contribution to collision prevention includes elimination of several hazardous situations: (a) Undue crowding of traffic; (b) Lock-entrance stand-off delays due to untimely ship arrival, during which ship handling is difficult; (c) Meets or overtakes at potentially hazardous locations.

Further, when approaching a bend on which other ships would not be visible and at which the meet would be hazardous, a pilot is advised of the number of ships which will be round the bend before he reaches it. Also indicated is the number of meets due to occur immediately beyond the bend, a distance through which the manœuvrability of his ship would be affected by the manner in which he rounds the bend. The automatically operating system is based on transmission of data comprising ships' identities and locations to a central control point where the data is analysed by an electronic computer and from which advisory signals are automatically transmitted back to the ships.

The Earth's magnetic field can evidently be divided into its horizontal and vertical components, the horizontal component being of more immediate interest to the navigator since it directs the compass needle in the horizontal plane. Whereas on the magnetic equator the full field is horizontal (about 0·400 c.g.s. units), in high latitudes, with the angle of dip between 60° and 70°, H, the horizontal force, maybe about 0·180 c.g.s. units. At the magnetic pole H is negligible and, given the opportunity, the compass needle would point vertically downwards, the instrument then having no directional properties in the horizontal plane.

Most lists of the seven wonders of the world include the Colossus of Rhodes. This bronze figure of Apollo, which the sculptor Chares took several years to construct, stood near a harbour on the island of Rhodes in the Eastern Mediterranean. It is reported that ships in full sail could pass between its legs whilst navigation lights were kept burning in its eyes. Whilst such descriptions are coloured by romance and myth, there is little doubt that early lighthouses were substantially tall towers supporting an open wood or coal fire. Such lights existed in Britain until as late as 1819, when Flathom light in the Bristol Channel was replaced by more modern equipment.

In time the open-flame coal brazier gave way to tallow candles. In 1696 Winstanley introduced a chandelier with tallow candles into the lantern of his famous Eddystone Tower. In 1759 Smeeton's Tower, which now stands on the Hoe at Plymouth, incorporated two superimposed iron rings that contained twenty-four candles.

By and large it was the improvements in optical systems that governed the development and introduction of oil and then, at a later date, electric illuminants.

The first attempt to intensify a lighthouse beam was in 1727 by the French at Cordouan. Mariners had complained that they could not see the light at more than 2 miles. In an attempt to improve on this, a cone of wood was covered with tin plate and suspended above the open fire.

For a considerable time fishing vessels, merchant ships, long-range forecasters and oceanographers have needed up-to-date sea ice information. This paper describes how the heterogeneous mass of ice information combined with the very thorough climatic analysis now available has been used to produce for the first time an up-to-date picture of the entire distribution of ice in the Polar Basin and areas adjacent to the Atlantic Ocean.

For over a century a function of the Marine Division of the Meteorological Office has been the recording of Arctic and Antarctic sea ice, particularly since the Titanic disaster. However, the comprehensive hemispherical ice maps produced internationally have been several years in arrears. Ice information supplied to ships was therefore usually based on average conditions which suffice for planning well ahead or on long-range weather forecasts where it is necessary to follow ice development closely. It was decided in 1959 to organize a synoptic ice map with up-to-date ice and sea temperature information. Ice being more conservative than the weather, a map produced every ten days has proved to be sufficient.

The continuous data (groundspeed and drift angle) given to high accuracy by airborne doppler equipments, could be adapted for handling by automatic computers which, accepting certain other inputs, can be designed to extract a great variety of information. This paper attempts to outline the contribution that such computers could make to long-range civil air navigation.