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www.sname.org/sname/mt April 2013 TOP: The Wave Star Energy marine hydrokinetic en- ergy concept was invented by sailing enthusiasts Niels and Keld Hansen in 2000. The half-submerged buoys rise and fall, allowing en- ergy to be continually pro- duced despite waves being periodic. The buoyancy of the ?oat is 20-40 times its dry weight, made possible by composite construction. Photo by Eric Greene. BOTTOM: The Skjold is a lit- toral combat craft built by Umoe Mandal in Norway between 1999 and 2006. She has an air-cushioned catamaran hull (surface eect) that relies on lightweight construc- tion for high speed and maneuverability. Photo by Eric Greene. repair stronger than the original to avoid future failures, but this can sometimes create a stress concentration if the cause of the failure is not rst determined. Major damage to areas of complex geometry can be repaired by molding a replacement section and bond- ing it in place using scarf joints. In boat hulls where the core of sandwich laminates has been compromised by water intrusion, the outer skin and damaged core can be removed and replaced. Organic resin systems used in composites will sup- port combustion if exposed to a high enough heat ux. Unprotected marine composite structure cannot meet the non-combustibility standard established for steel ships. However, sandwich composite structures are excel- lent insulators, which has proved to isolate large res to a single ship compartment. In the wake of a re on a com- posite Norwegian minesweeper in 2002 that resulted in a total loss, re protection guidelines in the International Marine Organization (IMO) High Speed Craft code have been adopted to ensure that res are contained and dont spread on composite high-speed craft. e United States Navy spent more than a decade testing the performance of composite structures in res and devel- oping re protection guidelines before building the DDG 1000 deckhouse. Indeed, these re protected marine com- posite structures retain their structural integrity better than unprotected steel in long-duration hydrocarbon pool res. Blisters occur to the underwater portion of berglass boats when water that has penetrated the outer layer of the laminate mixes with water-soluble materials to create an acidic uid, which can attack the resin matrix or resin/ ber bond. e acidic solution attracts additional water via osmosis, which can create a blister or what is know as osmotic blistering. e primary causes of blistering are improper resin handling or contaminants that leave water- soluble material in the laminate and an insucient barrier layer to keep moisture out. Since the problem rst became apparent in the 1980s, builders have improved QA methods to eliminate water-soluble material and have adopted more water-resistant resin systems, such as vinyl ester or epoxy, for at least the outer laminate layers. Although osmotic blis- ters rarely compromise a hulls overall structural integrity, detection and repair of blisters in older boats remains a challenge for the industry. Meeting todays needs Weve shown how far marine composites have come in the last fty years, as well as some of the engineering challenges that have been overcome. e industry has been driven by the recreational boating market and high-performance innovation tends to germinate with competitive race boats. Design tools, manufacturing processes, and at-sea experi- ence has matured to the point where marine composites are poised to enjoy an increased maritime market share and the United States has the expertise to benet from it. High performance boats Recreational boaters and law enforcement ocials will always strive to go faster in their boats and lightweight, composite construction makes this possible, while at the same time mitigating shock loads felt by the boats occu- pants. Another trend we are seeing is the desire to minimize fuel consumption, both to reduce operating costs and to minimize environmental impact. Trimarans such as the John Shuttleworth-designed Adastra illustrate how light- weight construction is used to create innovative, very low resistance hull forms. e military and scientic communities are very inter- ested in exploiting the capabilities of unmanned surface and