Cable handling operations
- Cable laying – When laying off, the primary need is to control the speed and tension at which the cable departs the ship. This control is done by means of cable machines: a Linear Cable Engine (LCE) or Cable Drum Engine (CDE). Where a LCE is used, cable is pulled up from the cable tank or carousel along the trackway and fed into the first wheel pair of the LCE. The LCE is driven from a control room where the operator is following a lay plan driven from survey data. With a CDE, cable is led from the static tank or carousel along a trackway to the wheel pair of a Draw Off – Hold Back Engine (DOHB) and then around the cable drum, usually for four turns. The cable is led off the drum by a traversing diverter over a roller sheave at the vessel stern or bow. During laying operations, the CDE is pulling the cable from the tank and the DOHB is in holdback mode, thus the cable is driving the wheel pairs allowing a preset tension to be set up between the DOHB and the CDE.
- Cable burial – Offshore activities, fishing, earthquakes and landslips can threaten submarine cable integrity. Cable burial is commonly regarded as the most effective protection. Burial depth can be up to 10m under the seabed in areas of soft silt (normally between 1m and 3m).
- Cable repair – The primary activity performed during a repair operation is raising and lowering cable from the ocean floor. This is accomplished by cable machinery hauling on grapnel rope over large-diameter sheaves. The cable hauling machinery is either a large round drum or a series of rubber tires mounted in pairs driven by a hydraulic motor. In order to reduce friction and protect the cable from sharp bending, large roller sheaves are installed at the deck edge.