High-Tech Hull Page 3
|Tripping the Light Fantastic|
Part 3: The hull was laminated with Kevlar and E-glass woven into a quadaxial fabric.
By George L. Petrie
So, what weight-saving measures did NEB use to build the Hunt 90? For starters, it used only epoxy resins throughout the entire yacht, rather than the polyurethane and vinylester resins commonly used in the trade. Epoxy has much greater strength compared to conventional resin and pound-for-pound produces a lighter, stiffer, stronger laminate. It also offers more strength in “secondary” bonds, such as to join a frame or bulkhead to the hull after the hull laminate has cured. The main drawback with epoxy (aside from its higher cost) is that it must be heated to about 175°F to properly cure and thus develop its full strength. So to cure the hull, NEB fabricated an “oven” (actually an insulated tent) more than 90 feet long that would completely contain the hull, then raised it to the required temperature with an array of electric heaters. Temperature was monitored by thermocouples at more than 50 locations in the mold and the oven, to make sure that temperature changes were uniform and not too sudden.
The hull was laminated with Kevlar and E-glass woven into a quadaxial fabric. Kevlar adds strength and impact resistance to the E-glass (conventional glass fiber), while the quadaxial fabric assures uniform strength in all directions. The hull fabrics are all pre-preg, meaning they have been impregnated with epoxy resin at the factory to ensure uniform application of exactly the proper amount of resin. The challenge in using pre-preg fabric (in addition to its higher material cost) is that it must be kept refrigerated until ready for use so that the epoxy resin doesn’t begin to cure prematurely.
The hull is also cored, with two-inch-thick CoreCell foam in the bottom, as many builders now use, to gain stiffness, sheer strength, and impact tolerance, but in the hull sides, NEB uses a 1 1/2-inch Nomex honeycomb core, which it claims is lighter, stronger, and more thermally stable than a foam core. At each stage of lamination (between each layer of cloth and after application of coring), the hull is vacuum-bagged, to ensure uniform distribution of resin, and thermally cycled in the oven.
NEB also employed a full measure of conventional weight-saving strategies, including foam-cored decks and Nomex-cored bulkheads, interior panels, and joinery. Even the deck liners are foam, covered with a thin wood veneer. The yard has gone the extra mile to cut weight, so the yacht can deliver many extra miles of cruising range for her owner. And that’s a noteworthy accomplishment in any boat, sail or power.
New England Boatworks Phone: (401) 683-4000. www.neboatworks.com.
This article originally appeared in the August 2003 issue of Power & Motoryacht magazine.