Proceedings magazine is a communication tool for the Coast Guard's Marine Safety & Security Council. Each quarterly magazine focuses on a specific theme of interest to the marine industry.
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www.uscg.mil/proceedings 20 Proceedings Winter 2013–2014 ment and thrusters. The deck was strengthened at the turret assembly, fare tower, and at each of the modular support frames. Also, a new engine room was added to house additional generators, the existing pipe rack was expanded to more than twice the original height to allow for additional piping and electrical wiring trays, and berthing increased to accommodate additional inci- dent response personnel. The engineering side was also radically changed to meet the increased power requirements of a dynami- cally positioned vessel. The 12.2 megawatt slow-speed diesel engine was modifed to operate in one direction at continuous revolutions per minute, with a new tail shaft and controllable pitch propeller. Four medium- speed diesels — housed in the new engine room over the stern — were added to augment the three original 640-kilowatt generators. Some 181 kilometers of new wiring ties this all together. A new controllable pitch propeller, four 2.15 mega- watt retractable Rolls-Royce thrusters with redundant hydraulic power units midship, and a two megawatt Rolls-Royce tunnel thruster in the bow put all the power to work. An 800-ton turret and buoy assembly ties the surface and subsea components together. It is important to note that the assembly is designed for liquid transfer only, not as a mooring device. The turret is ftted with a motor- ized slewing drive. As the vessel alters heading, the slew drive maintains a constant riser heading, which keeps torsional stresses off the riser. The subsea part of the system can be set on the site in advance with a foating mooring buoy, which the modular capture vessel will pick up. Subsea Components The subsea system connects the well to the modular cap- ture vessel, using a free-standing hybrid riser, which is an insulated pipeline suspended by large submerged buoys that connect the surface component to the sub- sea containment assembly on the seabed. The insulation keeps the well fuids warm, so gas hydrate crystals will not form and block the fow. The surface buoy nests into the turret assembly and car- ries the well fuids up to the MCV. An umbilical controls the subsea containment assembly and delivers chemi- cals into the well fuids for hydrate and oil dispersant management. In water depths less than 2,000 feet, the freestanding hybrid risers are replaced with a fexible pipe riser to absorb MCV vessel motion and the force from ocean currents. The subsea containment assembly collects or redirects well fuids, depending upon the wellhead pressure and well integrity. It can interface with the well in three ways: • over the blowout preventer, • over the lower marine riser package on top of the blowout preventer, Changes from shuttle tanker to modular capture vessel. Graphics courtesy of ExxonMobil. Winter �2013_45.indd 20 2/10/14 9:31 AM