In the not too distant past, custom builders used sticks and strings to layer plywood over jigs when constructing one-off boats. The end result was a beautifully crafted work of art, but each one was slightly different, and often heavy. Now, with computer-assisted design, computer-assisted routers and advanced design software, construction is infinitely more precise. Materials are more advanced as well. Dozens of fiberglass weaves are available for different applications. Custom-made epoxies, such as low-viscosity/high-strength blends for resin infusion, can be ordered. Most significantly, coring materials have gotten lighter and stronger. According to Spencer, cored materials weigh 5 to 6 pounds per cubic foot, versus 12 to 15 pounds for most hardwoods. The weight savings on a 60-foot composite Kevlar/carbon hull over a comparable wood-cored boat is about 10,000 pounds, and that adds up to better performance.