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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.
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