|The VIP Treatment|
2: Intermarine Savannah’s Vacuum Infusion Process continued
By George L. Petrie — August 2001
In Intermarine Savannah’s Vacuum Infusion Process (VIP), the laminate and core materials are laid up dry inside a mold that has been sprayed with gelcoat and a thin layer of chopped mat skin coat. Stiffener cores and reinforcement materials can also be laid up at the same time. The laminate is then covered with a layer of peel-ply, atop of which is placed an airtight membrane (a material similar to plastic wrap) that is sealed at the edges. A vacuum manifold is fitted along one edge of the mold and a resin supply manifold is fitted along the other edge.
With VIP, there’s no need for a separate resin infusion medium. Instead, the foam or balsa core facilitates distribution of resin through the laminate, using a system of criss-crossed grooves cut into the inner and outer surfaces of the core material. Widely spaced supply grooves running perpendicular to the length of the mold let the resin proceed uniformly from the inlet manifold to the vacuum manifold. Closely spaced, orthogonal flow grooves let the resin spread laterally, infusing the laminate between the supply grooves.
There’s no inherent limitation on the length of any part to be molded. For long parts, the yard just adds intermediate resin feed points. There is a limit on height, however. The vertical distance from the resin manifold to the vacuum manifold can’t be greater than about 12 feet, which is equivalent to the height that one atmosphere of pressure can lift a column of resin.
That limitation might have caused a problem for Intermarine with its 123-foot hull, which is deeper than 12 feet from keel to deck edge. The solution was to cut the mold in half along the centerline, then open it like a clamshell, putting each side in a more horizontal orientation. After the two halves were infused, they were raised back to the upright position and joined with a thick layer of solid fiberglass (a separate VIP lamination) along the keel.
Longitudinal girders in the hull are separately infused using VIP to bond the hefty foam cores, multidirectional laminates, and unidirectional reinforcements to the bottom’s inner skin. Done just a few days after the hull is molded using vinylester resin, these secondary bonds can achieve an impressive 80 percent of the strength of the primary laminate. Decks, including internal stringers for the 123 series and 145-footer, are laminated in a single infusion process with no secondary bonds. Bulkheads, and even integral fuel tanks, are all VIP-infused for the 123 series.
Intermarine’s chief naval architect, Gordon Lacy, estimates that VIP presently reduces the man-hours required to laminate a hull by 40 percent, and as the process is refined, future labor savings could reach as high as 75 percent. Moreover, according to Intermarine’s process engineer, Belle Gall, usage and waste of expensive resins can be cut by 20 percent or more.
Structurally, the big advantage of VIP is the higher ratio of fiber to resin that can be achieved. Less resin and more fiber reinforcement per unit of volume means that the laminate will have greater strength in relation to weight. Tests show that typical VIP laminates are 29 to 35 percent resin (by weight), compared with 40 to 50 percent or higher for hand lay-up. Depending on the specific combination of fiber and resin, this can yield up to 60 percent higher tensile strength, with an increase in stiffness ranging from 30 to 70 percent. And laminate strengths are more consistent because the variability inherent in hand lay-up is eliminated.
More important, VIP virtually eliminates styrene emissions, making for a cleaner, healthier workplace. Resin and any fumes from it are contained within the airtight membrane than covers the laminate. Not only is air quality improved, but also creation of nonconstruction solid waste products (protective gear, etc.) is reduced significantly.
To megayacht builders, VIP offers substantial benefits, with seemingly no drawbacks. This Vacuum Infusion Process could be a Very Interesting Proposition.
Intermarine Savannah Phone: (912) 234-6579. Fax: (912) 236-8887. www.intermarinesavannah.com.
George L. Petrie is a professor of naval architecture at Webb Institute and provides maritime consulting services. His Web site is www.maritimeanalysis.com.
This article originally appeared in the June 2003 issue of Power & Motoryacht magazine.