In a previous paper the Author summarised facts on the inadequacies of present day hydrographic charts for shipping and oil resources exploitation and proposed equipment to tackle this urgent problem. The present paper describes the new sonar equipment and its fit to a hydrographic survey vessel and gives details of preliminary results obtained in trials. It is suggested that this sonar presents hydrographic surveyors with a capability not previously seen in civilian offshore operations. It is now possible for the surveyor to inspect rapidly 100% of the continental shelf seabed for hazards and profile or contour with the same equipment, providing a complete bathymetric capability.
In a previous paper (1) the Author discussed the problems inherent in hydrographic surveying in 1976 in the light of shipping statistics, draughts of modern very large ships, causes of accidents, the hazards involved, defects in survey techniques, and the extent of the hydrographic surveyor's task. Possible designs of new equipment were evaluated, and an Advanced Forward Looking Sonar for hydrographic surveying proposed. The present paper updates the situation and describes the new equipment and its performance.
The rate of discovery of unknown seabed hazards in shipping lanes (1) has not decreased since 1976. The UK Hydrographer reported (2) that in 1977 the survey vessel HMS Bulldog, with conventional sidescan sonar equipment, located over 500 contacts in 41/2 months in a 200 square mile area of the Dover Strait, which had previously been surveyed in 1960 using the then available hull-mounted sonars, and was thought to contain 169 seabed wrecks. Each contact was subsequently carefully investigated and, while over 100 were confirmed as known, 60 proved to be previously unknown wrecks, many with a least depth of water over of 23 m (76'), the draught of the largest sized ships to use this heavily trafficked area. He also reported the discovery of banks in Traffic Separation Scheme routes which decreased the general water depth previously reported on charts from 50 m to 21 m (last survey by sailing ship in 1843). In presenting other examples of fresh hazards revealed by his survey fleet, he instanced a conventional draught ship (12 m) on a shipping route normally followed by large vessels discovering that had it traversed the route at a time of low water spring datum its clearance would have been 0.3 m rather than the 4 m to be expected from the chart based on data of 1911 1914 vintage. He concluded that it was not possible to approach the Humber from Dutch ports without passing through waters inadequately surveyed, or completely unsurveyed.
By the end of 1977 approximately 28% of the UK continental shelf had been surveyed to modern standards, the remainder being unsurveyed or covered only by lead-line surveys up to 170 years old. Only some 30% of designated deep-water routes, Traffic Separation Schemes, and other designated shipping routes had been surveyed to full modern standards.
