INTRODUCTION

Dangerous cargoes lost in the North Sea must e salvaged before they can cause accidents. Lost cargoes must be found using sonar, and then identified with still and video cameras mounted on a remotely operated vehicle (ROV). Finally, the cargoes must be salvaged or neutralized. The practice of search, locations, selection, identification and salvage of cargoes and dangerous goods lost in the Dutch sector of the North Sea is presented in this chapter. Special attention is paid to technical and operational aspects of locating and identifying lost cargoes. The applicability of a diver, a swimming ROV or a seabed crawling ROV for these operations is examined. Two recent cases are elaborated.

INTRODUCTION

Shipping lanes in the North Sea have a very high traffic density, with vessels carrying a diversity of cargoes. During bad weather accidents can occur whereby cargo, stored on the upper deck, is lost overboard and sinks to the sea bed. Some cargo lost in this way, such as poisonous, explosive or radioactive material, can form a threat to users of the sea, and to the environment.

Adequate survey techniques are therefore needed to locate and identify these cargoes. This is made difficult because information on the position where a particular incident occurred is often poor. The problem is further complicated if a cargo is lost over a wide area, or when lost containers become embedded or buried in the sandy bottom.

Containers resting on the sea bed are usually located using side-scan sonar, although the first indications as to the whereabouts of a cargo are often reported by fishermen. Containers covered with sand can be detected with a magnetometer or a sub-bottom profiler once the location where the cargo was lost has been pinpointed.

Until recently, detailed surveys of potential areas and identification of lost cargoes were carried out by divers. Poor visibility and strong currents, together with unsystematic operation procedures, hampered these operations, so that survey seldom achieved the desirable results. A remote operation vehicle (ROV), whether swimming or crawling along the bottom, used in combination with a dynamically positioned vessel, now makes it possible to carry out systematic and accurate surveys. A ROV equipped with a variety of sensors; still and video cameras, an obstacle avoidance sonar, a profiler, a magnetometer, an acoustic positioning responder and an air lift systems is used as a bloodhound to search the sea bed. Using this method, engineers from the North Sea Directorate of Rijkswaterstaat have achieved good results. The ROV is directed along a fixed pattern of survey lines, inspecting every square metre of the sea bed.

Lost Cargo Reports

Accidents such as the shipwreck of the Mont Louis, with its cargo of radioactive material, are very much in the public eye. In this case, containers containing radioactive uranium hexafluoride store in the holds broke loose, and there was a very real danger that some of these containers would be lost. It is easy to imagine that, in such a case, the containers could eventually be unwillingly retrieved in uncertain conditions by fishermen.

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