A professor builds a high-speed prototype that could change the way the us navy builds ships.
By Larry Webster

Ship manufacturers may one day abandon metal in favour of composite materials, shedding weight to gain fuel efficiency and corrosion resistance. But there are material science lessons that need to be learned before the vessels can take to the water. For answers, researchers at Pennsylvania’s Lehigh University, headed by mechanical engineering professor Joachim Grenestedt, designed and built the 8,8 m boat Numerette with funding from the Office of Naval Research in the US. It melds a steel frame with foam, glass fibre and carbon-fibre composite panels. “It’s difficult to bond different materials,” Grenestedt says. “There’s a big elastic mismatch that leads to severe stress concentrations at the joints.” The 10 panels of the Numerette’s lower hull are of slightly different construction to determine which best distribute hydrodynamic loads.

The Numerette is also wired to study “slamming”, the impact a boat experiences after cresting a wave. Grenestedt fitted each bottom panel with pressure sensors, while other sensors record factors such as temperature and wave height. “Slamming is difficult to study because it’s such a dynamic event,” he says. “No two impacts are the same.” The boat has been tested on a lake at 100 km/h, and Grenestedt plans to test its limits on the large swells of the Atlantic.

Numerette

Type: Hybrid-composite-steel speedboat
Materials: The boat’s rigid stainless-steel skeleton can support heavy equipment. The composite panels, bonded to the frame with an epoxy adhesive, are lightweight and corrosion-resistant.
Purpose: To study the interaction between the composites and metal in real-world tests, including repeated “slam” impacts against the water’s surface.

View a video showing the construction of Numerette.