Schooner features carbon fiber masts, booms, spreaders

#autoclave #adhesives #layup


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When Lion's Whelp, built by Portland Yacht Services (Portland, Maine, U.S.A.) embarked on its inaugural cruise, even seasoned marine observers saw a 65 ft white schooner, reminiscent of the early 20th century's Alden Schooners, complete with spars authentically detailed from wood with traditional brass fittings. But the masts, spreaders, three booms and spinnaker pole were carbon fiber, not wood, fabricated in a unique out-of-autoclave process developed by GMT Composites (Bristol, R.I., U.S.A.). GMT president and engineer David Schwartz worked with Portland to construct carbon spars that could survive any supporting shroud failure, yet blend with the yacht's traditional styling. Custom aluminum tooling for the masts and main boom was made in-house, to duplicate the complex shapes and tapers of the 1920s-era originals. Using a low-viscosity 250°F-cure unidirectional carbon fiber/epoxy prepreg supplied by Newport Adhesives and Composites (Irvine, Calif., U.S.A., ), GMT hand layed the spars, with vacuum debulking under 1 atmosphere of pressure carried at out numerous points during layup. During oven cure, temperature was ramped to 60°C/140°F, an intermediate dwell level at which the resin softens, facilitating laminate compaction. After several hours, the heat was raised to cure temperature (120°C/250°F), reducing viscosity further to ensure thorough wetout, with cure completed in 70 minutes. The relatively low pressure eliminated the risk of laminate thinning at outside edges, where compaction pressure is concentrated during autoclave cure, says GMT's Ben Sprague, adding that autoclave curing, in previous tests conducted by GMT, produced parts only 1 to 3 percent greater in compressive modulus than less-expensive oven cure. To avoid stress concentrations when mast sections were joined, GMT used a prepreg scarf splice (layed up from multiple layers of decreasing width to create a tapered transition in the wall thickness at both ends) cured by the same method. The resulting joint matches the stiffness and strength of the rest of the mast, eliminating the risk of local failure under the compressive load applied by the rigging. Bagging films were perforated to allow excess resin/escaping gasses to flow away from the parts during compaction. According to independent testing labs, void content is 0.5 percent or less, typical of that achieved in autoclaved parts. Finished spars received a "Faux Bois" finish for a painted wood look. Custom cast bronze fittings, boom ends and other rigging hardware completed the transformation.