Resin infused boat sails into first
When a team of nine engineering students from Cedarville University (Cedarville, Ohio) returned to Buffalo, N.Y. this year for Solar Splash 2005, an international collegiate solar-powered boat competition, it was eager to defend its title as world champion. In 2004, the team's winning entry featured a hull hand layed in an open mold at Formula Boats in Thunderbird (Decatur, Ind.). Teams were judged on endurance, maneuverability, speed and visual appearance.
Although the winning entry's hull weighed only 120 lb/54 kg (gel coat and finishing touches included), the students elected to resin infuse a new 17.5-ft/5m long, 20-inch/51-cm high hull for the 2005 competition and again consulted with Formula Boats, which infuses several production components for its commercial boats. The key motivation was potential weight savings, says team leader Dr. Tim Dewhurst, professor of mechanical engineering. Rather than have Formula Boats fabricate the hull this year, however, the students elected to infuse the hull themselves. Using SolidWorks CAD software from SolidWorks Corp. (Concord, Mass.), they redesigned the hull as a sandwich construction, using TYCOR core material supplied by WebCore Technologies (Dayton, Ohio). Using the hull mold from the previous year, students created a cardboard pattern for the TYCOR, and then cut out and test-fitted the pieces in the mold. Trial runs showed it was critical that there be no gaps between pieces since the gaps would fill with resin, adding weight and causing shrinkage during cure.
The layup consisted of 6 oz. fiberglass cloth for the outside skin, the core, and a 6 oz. cloth for the inner skin. Formula Boats donated Coosa Board, a high-density fiberglass-reinforced polyurethane panel from Coosa Composites LLC (Pelham, Ala.), for the transom. For infusion, a peel ply layer was placed on the inner skin to peel away excess resin; a flow medium was placed over the peel ply to ensure good resin distribution. The transom and hull were infused together, in about 30 minutes, using AME 2000 resin, a nonthixotropic system formulated for infusion molding by Ashland Specialty Chemical (Dublin, Ohio). The hull was allowed to cure overnight before it was pulled from the mold. Ashland has provided supplies and technical assistance to the students for the past 10 years, says Ashland's global marine market manager Andy Beer. The finished hull, with a 3-ft/0.91m beam, has an average thickness of 0.75 inch. With 10 lb/5 kg of paint and 15-lb/7-kg walnut gunwales, it still weighed only 95 lb, 25 lb less than the 2004 hull. Because the thin outer skin raised concerns about print-through, the hull was molded without gel coat. Although the team also encountered pinholing in places, Dewhurst says, "We were able to touch up these areas and then cover up the blemishes with paint."
The redesign paid off. Cedarville placed first in the solar endurance, maneuverability, and visual display events, third in the sprint event, and first overall, earning 910 points out of a possible 1,000 to retain its title.
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