Installation and protection of electrical cables in the surf zone on rock seafloors

Alternative techniques for cable installation across rock nearshore zones are introduced. (The nearshore zone is variously defined as extending from the beach to water depths between 30 and 200 m.) The alternative techniques are made possible by new equipment developments in directional drilling of oil wells and in rock trenching. First, it is feasible and sometimes economical to directionally drill a borehole from the beach to emerge from the seafloor some 4 000 m offshore. This report describes the techniques available to drill, case, and install cable in such a drill hole. Second, it is feasible and economical to cut a trench in soft rock (coral) to medium hard rock (shale, sandstone) using a bottom crawling, modified terrestrial trencher. The equipment modifications necessary are described.