Why Not Wet-Preg?

In his article about Boston BoatWorks (“The Builder Under the Bridge,” Professional BoatBuilder No. 157), Paul Lazarus writes that he is surprised that more production boatbuilders haven’t also adopted pre-impregnated fabric construction.

Back in 1990, when our senior editor first wrote about the technology, in “Fabric Impregnators” (PBB No. 5), he predicted that they were “destined to become increasingly important tools of the trade,” and for good reason. The mechanization of the lamination process reduces labor, and provides a better-quality and more consistent fabric laminate. It also cuts down on toxic emissions, helping boatbuilders meet air-quality regulations in the workplace. (Legislation empowered agency-created regulations that require compliance.)

That reduction of labor is especially important to Boston BoatWorks. As the exclusive builder of Bob Johnstone’s MJM yachts, it needs to efficiently produce these high-quality lightweight motoryachts (ranging from 29’ to 50’/8.8m to 15.2m) to satisfy increasing demand.

The company was also an early adopter of wet-preg. Builder Mark Lindsay, Boston BoatWorks’ cofounder with Scott Smith, bought his first fabric impregnator in 1991 (that machine is described in “Smooth Operators,” PBB No. 99). This year, when Boston BoatWorks opened its new facility in Charlestown, Massachusetts, it also invested in a new impregnator to help keep up with increasing production.

“What an impregnator gives us is the ability to wet-out various fiberglass fabrics quickly, consistently at desired glass-to-resin ratios,” says John Lexion, who’s in charge of composites at Boston BoatWorks, in the video above.

In the video you can watch the new machine in action as a technician rolls out the impregnated fabric. The impregnator was designed by Rich O’Meara of Core Composites (a division of ROM Development in Newport, Rhode Island), and built by A & E Machine Shop in Cocoa, Florida. (For a more in-depth description of the new machine and how it works, see the “The Builder Under the Bridge,” in PBB No. 157.)

The concept is pretty simple, Lexion explains. “What we do is we introduce resin, which is mixed epoxy in our case, into a bath area that is between these two dams and the two nip rollers.”

Then: “The glass fabric is introduced between the two nip rollers. It’s drawn through the resin bath and impregnated with epoxy resin by being squeezed through the two nip rollers, and in our case we’re looking for a glass-to-resin ratio of 60/40, which is 60% glass to 40% resin, by weight.”

Still a believer in fabric impregnators, Lazarus also provides us with some solid reasons why wet-pregs are a good idea for production boatbuilding. For those who are considering adopting the technology, he includes a list of considerations—with more pros than cons—from the machine’s designer in the sidebar “O’Meara’s List,” in PBB No. 157, page 56.

Of course, Lindsay also has reasons for Boston BoatWorks’ choice of wet-preg epoxy lamination. In “The Builder Under the Bridge,” Lazarus shares notes he took during Lindsay’s presentation in a seminar on wet-pregs in production boatbuilding at the International Boatbuilders’ Exposition & Conference (IBEX) in 2007. He writes:

“Epoxy gives us the highest-strength resin matrix; the wet-preg process keeps the weight low; the relatively low cost and simplicity of a wet-preg resin system in materials and process are an advantage over manufactured prepregs; and a mechanized wet-preg system provides consistent, predictable results.”

And so the question remains: Why not wet-preg?

—Melissa Wood, Associate Editor