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Hybrid Speedboat Launched as Portable Research Lab

12 December 2010

A 29-foot speedboat ,designed and built by Joachim Grenestedt, professor of mechanical engineering and mechanics at Lehigh to serve as a portable research lab, has been unveiled and named The Numerette by Lehigh President Alice Gast.

This vessel is the result of 10 years of hard work, said Gast. It is a testament to the skill, passion and dedication of many Lehigh students, as well as our great research staff. The potential applications of the Numerette are limitless: The technology born in a Lehigh laboratory could one day enhance commerce on a global scale.

A hybrid material

But the boat could alter the future of shipbuilding. The Numerette is believed to be the largest craft yet constructed with a hull consisting of panels that are made of a composite sandwich material and bonded to a stainless steel frame. The goal is to use the hybrid material one day in large naval vessels.

The hybrid-material hull, says Grenestedt, offers several advantages. Composites are lightweight and strong, and they resist fatigue (repeated stresses) and other environmental impacts. They are also a good insulating material, they can be made flat for stealth purposes and they can be molded easily into complex shapes.

The stainless steel frame provides stiffness and ductility and is easy to mount equipment to. A steel-composite hybrid hull is easy to outfit. Heavy equipment can be mounted to the open and accessible steel frame before the large composite panels are attached. Both the stainless steel and the composites are nonmagnetic, which enables a ship to pass over explosive mines without triggering them.

One goal of the project is to evaluate how steel-composite hybrid hulls hold up in real-world conditions. Extensive laboratory tests, ranging from small coupon specimens to a 16-ton fatigue-loaded ship hull section, have been performed at Lehigh over the last 10 years. The hybrid structure is part of an effort to develop the technology needed to use lightweight composites in larger Navy ships.

We believe a steel-composite hybrid may be the optimal way to construct a larger vessel, such as a frigate or a destroyer, says Grenestedt.

The age-old problem of slamming

The main purpose of the Numerette, however, is to study slamming, the complex phenomenon that occurs when a craft bellyflops as it courses over the water. The Numerettes bottom panels are fitted with 123 strain gages (and soon with pressure sensors) to study slamming, which imposes the most severe loads on high-speed boats.

We hope to gain a better understanding of slamming and eventually work this into design codes that will lead to lighter and stronger boats and ships, both military and civil, Grenestedt says.

Grenestedt and his research group successfully tested the Numerette last month on Pennsylvanias Beltzville Lake (see video at right). In another test they approached speeds of 60 mph.

The Numerette was funded by the Office of Naval Research, which has supported Grenestedts work since he began studying steel-composite hybrid hulls a decade ago. The research team includes Bill Maroun, a technician in the mechanical engineering and mechanics department, and six graduate studentsRobert Thodal, Jian Lv, Scott Shirey, Drew Truxel, Brett Snowden and Jack Reany.

Before coming to Lehigh, Grenestedt played a role in the structural design and materials testing of the Visby, a 239-foot-long Swedish stealth ship that was the largest carbon-fiber ship ever built when it was launched in 2000.

The director of Lehighs Composites Lab, Grenestedt incorporates composite materials into much of his life. He owns and flies a two-seat airplane made of composites, and a beam supporting the deck of his house is made of carbon fibers. Last year, he set the U.S. land speed record for 125-cc gasoline engines when he skimmed across Utahs Bonneville Speedway at 133.165mph in an enclosed streamliner motorcycle that he designed and fabricated from composite materials.






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