The vacuum molded Tornado hull.
The vacuum molded Tornado hull.
The Tornado racing caramaran in action.
The Tornado racing caramaran in action.

Australian multihull specialist, Windrush Yachts, makes hulls for the Tornado catamaran using a GRP sandwich laminate design, following regulations from the International Tornado Association (ITA) that do not allow the use of any carbon fiber materials in hull building.

The hull is molded out of autoclave at low temperature (~100°C/ 212°F) using GMS EP-270 epoxy prepreg produced by GMS Composites Pty Ltd and an S-glass cloth multilayer combination, with a Nomex aramid paper honeycomb core, which helps to provide buoyancy.

The Tornado class multihull was selected by the International Yacht Racing Union for the first ever Catamaran open event in the 1976 Olympics in Canada before multihull sailing was taken out of the Olympic program and is competitively raced all around the world annually at both regional and world championships. It remains one of the fastest double handed small (20ft / 6.1m long) catamarans.

Maximising strength

According to Windrush, the ‘carbon free’ epoxy based composite hull and deck structure needs to be stiff enough to take the immense forces (mainly inwards at the bow) that the large rig exerts, yet still provide the high speed ‘slam’ impact resistance and flexural bending demands placed on a hull when racing. The team was been able to maximize the strength and stiffness modulus required, while at the same time reducing overall hull weight despite not being able to turn to carbon fibers.

‘We have found that the best combination is to use GMS Composites EP-270 epoxy prepreg, which we reinforce using a 200 gram +- 45 deg S glass in combination with a heavily unbalanced 300 gm glass cloth that together effectively produces an unbalanced Quad for the outer skin laminates, with a 12mm thick Nomex sandwich core for maximum stiffness, shear modulus and deformation resistance,’ said Brett Burvill, a director of Windrush Yachts. ‘Along with a careful laminate layout, this combination of materials for the sandwich structure gives us the very high stiffness needed in the hull, especially longitudinally, yet still provides excellent damage tolerance with a hard, but tough, outer surface.’

The complete finished weight of each 6.10m long (20ft) hull, which is only 405 mm at its widest beam point, is around 38kg (84 lbs).

This story is reprinted from material from Windrush Yachts, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.