Boat manufacturers in the U.S. have enjoyed several growth years driven by increased demand for new, larger boats. To serve this rebounding marketplace, manufacturers are taking a new look at fabricating techniques and materials for the cost-effective, environmentally sound production of advanced composite boat designs.
One of the leading developments in the marine business is the increasing use of next-generation closed molding processes with advanced epoxy resins to produce hull structures. Infused epoxy represents a significant improvement in boat quality and performance while, at the same time, eliminates volatile organic compound (VOC) emissions to meet U.S. and European Union governmental standards.
Historically, manufacturers built boats using wet/hand lay-up to build up a resin/fabric laminate. Alternatively, a higher-cost fabricating method utilized pre-impregnated fabrics to produce composite hulls with higher, more uniform quality and reduce waste, mess and labor required.
Both boat manufacturing methods typically relied on polyester (PE) and vinyl ester (VE) resins to produce the laminated boat structures. The materials are relatively strong with good resistance to water and are easy to use with short cure time. However PE and VE exhibit high shrinkage of 7–10%, producing undesirable fabric “print-through” that causes cosmetic blemishes. Both PE and VE resin systems have high styrene contents requiring special ventilation systems to minimize worker exposure.
Infused epoxy
Based on advances made to both the infusion process and epoxy resin handling properties, production manufacturers are today fabricating lightweight boats with improved hydrodynamic performance and speed as well as a Class A, blemish-free surface finish even on dark hulls. This new ability is creating opportunities for building higher-quality boats in higher volume than ever before while, at the same time, improving workplace cleanliness and reducing VOC emissions. (See Scout Boat Case Study.)
Experience with infusing wind blades and aerospace parts have helped drive this new trend in the marine industry. The ability of design engineers to increase fabric content and realize better control of resin flow and infusion speed is a tremendous benefit for boat manufacturing. Moreover, epoxy manufacturers like Huntsman have formulated new resins for infusion that represent significant improvements over conventional PE and VE resins. These epoxy systems exhibit lower viscosities and longer work lives for easier infusion via multiple injection lines along the length of a large part. In addition, the epoxy resins cure with lower exotherm than previously possible and at lower temperatures, eliminating the need for in-autoclave curing. The resins have good adhesive properties to bond well to the gel coat, core and fabric used in reinforcing structures as well.
Epoxies, as a class of materials, are 20 to 30 percent stronger than PE and VE with higher elongation, tensile strength and modulus/stiffness properties. As a result, boat fabricators can decrease the number of laminate layers used for a hull without affecting strength or performance. The reduced layers cut overall structure weight providing for greater hull speed and reduced fuel consumption. In addition, because epoxy resins have a cured shrinkage of <2 percent, they produce an outstanding smooth surface directly from the mold. This significantly reduces the labor-intensive secondary finishing typically required on boat hulls.
This article appeared in the July/August issue of Reinforced Plastics.
