Sea Technology

JUL 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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(Top) The Ocean Observatories Initiative (OOI) Regional Scale Nodes (RSN) Primary Node 3B was launched from the aft deck of the cable installation ship TE SubCom Dependable on August 18, 2012, marking deployment of the seventh, and fnal, node installation on the OOI RSN cabled infrastructure. (Photo Credit: University of Washington) (Middle) RSN Primary Node 1C was deployed from TE SubCom Dependable. (Photo Credit: Cecile Durand) (Bottom) OOI RSN primary node on the deck of TE SubCom Dependable during dockside deployment testing on April 18, 2012 in Portland, Oregon. (Photo Credit: Brian Ittig) a product with increased strength and lighter weight. One key element in the strength of the latest synthetic cables on the market is Spectra fber. According to Honeywell (Morristown, New Jersey), who developed the fber, synthetics equipped with Spectra are 10 times stronger than steel of equal weight. Resistance to Abrasion. Beyond its light weight and strength, perhaps one of the most important properties of an HMPE synthetic rope is its ability to withstand prolonged exposure to rough or corrosive conditions. The U.S. Department of Labor's Occupational Safety and Health Administration states that wire rope with a fber core is usually fexible but less resistant to environmental damage. Steel-wire rope requires periodic lubrication to reduce friction between the ropes to prevent corrosion, but synthetic ropes equipped with HMPE are maintenance-free. 16 st / July 2013 Spool Performance on Single-Drum Winch Lines. Another advantage to using synthetics in a deepwater application is ease of use when vertically lowering or raising payloads off of a vessel. The shape of the rope is vital. The round-shaped HMPE synthetic cable L-3 MariPro chose is the higher-tech version of a product called Uniline, which has been used by TE SubCom's (Eatontown, New Jersey) cable-laying ships and the electrical utility industry for years. The rope's performance in those two applications gave L-3 MariPro the confdence that unloading payloads off of a vessel would happen without incident. The cable's round shape ensures the rope lays smoothly and maintains its form when wrapped onto a single-drum winch line. This is important because if a rope lays smoothly, it will likely unwind smoothly during the vertical lowering of payloads. Conversely, some HMPE synthetics move or meld on a spool and can overlap or cross over layers. The inward pressure created from overlapping or crossing over layers then forces the rope to dive or knife down like water going through a crack. Wire rope wrapped on a drum stores excess energy and has the tendency to expand beyond its wrapped position, sometimes causing it to jump uncontrollably if sudden stops occur during the pulling motion. Synthetics do not expand on a drum, resulting in productivity gains for operators who otherwise must reconfgure an improperly spooled drum or remove a stuck winch line. Steel wire rope is also subject to deformation called peening, which occurs on drums caused by rope-to-rope contact during spooling. Peening can cause metal fatigue, which in turn causes wire failure. Unitrex has a protective external layer wrapped with neoprene tape and is overbraided with a tough jacket of high-tenacity polyester. The result is a synthetic cable that is stiffer than your usual rope and much like wire in its stretch characteristics. The rope's core fber also prevents it from external damage. Additionally, the ability to twist synthetic flaments both clockwise and counterclockwise prior to the braiding process results in superior torque balance as well as low stretch and low elasticity, which in turn reduces risks upon breakage and recoil. And unlike its steel counterpart, users do not have to be concerned with broken wire strands that can result in puncture wounds or load-induced torque, which can cause both single- and multiple-part hoisting systems to rotate. Conclusion As the marine industry continues to pursue deeper waters, proven methods of deploying infrastructure at greater depths will be even more important. In the case of OOI, NSF and UW are going to advance ocean science by changing the way humans interact with ocean events. Just like the undersea technology industry has advanced to make this research possible, so too has the synthetic rope industry— making deepwater deployment of equipment possible with unprecedented safety and effciency. n Bill Putnam joined Yale Cordage in 1984. He has served the company as a rigging shop supervisor, purchasing manager, plant manager and executive vice president. He was named president in 2012. www.sea-technology.com

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