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engineering insights composite submarine camels win with long-term durability The U.S. Navy wisely opts for more expensive submarine moorings that maximize lifecycle cost-effciency. T Design and engineering frm Whitman, Requardt & Assoc. (WR&A;, Baltimore, Md.) and composites manufacturer Composite Advantage (CA, Dayton, Ohio) were tasked with developing a universal composite camel that would meet that challenge and accommodate any U.S. Navy sub type, anywhere in the world. Te Navy's criteria for the new camel included not only the ability to absorb the energy generated by a berthing submarine, but also the freeboard (how much of the camel would sit above the waterline), the list and trim angles, and the overall fotation stability requirements. Te Navy's request for proposal (RFP) specifed that the level foating position of the camel must be maintained within a 1-inch/25.4-mm tolerance side to side and front to back. Further, the freeboard must be maintained within a 1-f/0.3m tolerance. Te RFP also stipulated that the camels must meet performance requirements in three load scenarios: berthing of a submarine, mooring of a submarine and lowering and lifing the camel into and out of the water. Berthing assumes a submarine velocity of 0.4 f/sec (0.12m/sec), which is approximately 200 f-kip of energy. Mooring loads — caused by waves, wind and other forces — are, by comparison, smaller than berthing forces. Te load path for berthing and mooring are horizontal, but the load path for lowering and lifing the camel into and out of the water is vertical; discrete lifing points on the camel, therefore, would be required and would have to withstand an anticipated mass in excess of 45 metric tonnes (100,000 lb). "We were dealing with a unique shape and the criteria were somewhat at odds with each other in that if we designed to meet one requirement, issues surfaced with the other criteria," says Matthew Lambros, structural engineer for WR&A.; "Tis was largely due to the fact that a number of properties afecting A fnished camel awaits the berthing of a submarine. the camel, such as volumes and compositesworld.com compositesworld.com Source | Composite Advantage his story begins with an unlikely premise: the U.S. Navy needed to solve a problem, and it was willing to spend more money up front on a solution if that solution promised net savings in the long run. Te problem? Poor durability of its deep-draf submarine camels. Tese large and mostly submerged metal or wood structures are attached to a mooring structure and ftted with rubber bumpers to provide a bufer between the Navy's submarines and the waterfront where they are berthed. Te camel defects or compresses with vessel movement and prevents damage to the hull, diving planes, screws, fairings, special skin treatments and other equipment by absorbing the sub's energy — which is considerable, given the 560-f/171m length and 17,000 tons of water displaced by berthed vessels, including the Ohio class submarine, the heaviest in the feet. Given the saltwater environment in which they work, metal and wood camels require removal every two years for inspection and repair, which can be substantial if corrosion has begun. Te other challenge the Navy faced was that it had 17 unique camel designs in ports around the world. Each camel was designed to accommodate a specifc submarine type, which, in addition to the Ohio, includes the Los Angeles, Virginia and Seawolf classes. 46 46