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October 08, 2007

Laying It Up

Boatbuilding basics from gelcoat to deck

Starting at the Bottom
Every boat on the market is built according to a "lay-up schedule" - a plan detailing the exact construction of each hull layer - from the specific materials used to their thickness, number of layers, types and design of stringers and transom and  finishing reinforcements. That plan comes together as the engineers decide how customers will use the boat and want it to perform.

Maverick Boats, which builds Maverick, Pathfinder, Hewes and Cobia boats, certainly keeps the weight of materials in mind when constructing a flats skiff. But lighter weight may not translate to strength, so the company must find the best combination and then balance that with price. In the marine industry, as in any other part of life, the challenge becomes trade-offs.

"You can overbuild a boat," says Charlie Johnson, Maverick's director of marketing and promotion. "It's the same as if you're nailing three pieces of wood together. You can use three nails or you can use 10, but usually three nails work every bit as well as 10. We're always looking for ways to use three nails."

Starting at the bottom, literally, the gelcoat creates the first hull layer. But that layer must flex and move with the subsequent layers of fiberglass in the hull. Everything works together. The composition and thickness of the gelcoat layer can vary. However, a thickness of 18 "mils" (.018 inches or .457 millimeters), plus or minus 2 mils, is considered ideal for all-around performance, Johnson says. Why? Because that's the optimal thickness needed for the gelcoat to properly cure.

Gelcoat is a synthetic, petroleum-based resin made from organic  compounds, similar to resins that bind fiberglass layers into the hull. Builders primarily use two types of resin in boat construction: polyester and vinylester. Epoxy resins may be used in custom applications and in conjunction with Kevlar or carbon fiber but are more expensive.

Most gelcoats are polyester resins, which weather better than vinylester resins, says Charlie Reeves, director of technology integration for Sea Ray boats, owned by Brunswick Corpor-ation, which makes more than 45 boat brands from Hatteras to Trophy. Gelcoat makers blend the polyester resins with color pigment and UV stabilizers to offer protection against fading, chalking and cracking.

Higher-end gelcoats offer the best surface properties; boatbuilders use pricier gelcoats to support today's  darker-colored hulls. That's why color options generally cost more.