Looking Forward

    Current composite tether designs are leveraged to take advantage of existing oil-field manufacturing facilities. The wirerope stranding facilities, umbilical closing machines, steel anchors and installation methods used today for steel and synthetic cables can immediately accommodate rope-style composite tethers. However, future designs could be more flexible. Rods could be pultruded in any shape. Salama of Conoco adds, “We are looking at materials with a specific gravity lower than water to reduce the pretension.” For example, PVC profiles with a specific gravity of 1.4 could be replaced with polyethylene profiles that have a 0.9 specific gravity (10 percent lighter than water). Other lightweight options include polypropylene, polystyrene and acrylonitrile butadiene styrene (ABS). Alternatively, a tether could be manufactured from a single strand, which would greatly simplify the entire system. The Doris Engineering/Freyssinet partnership envisions an extension of composite cable technology to moorings for other floating deepwater structures, such as catenary cables for spars, semi-submersibles and production ships.