Wednesday, 6 April 2011

America's Cup: ORACLE Racing Stress Testing on the AC45

Crew from ORACLE Racing today narrowly escaped a big “moment” in their AC45 catamaran when they pulled out of what looked to be the start of a pitch-pole, which would have seen the boat flip tail-over-nose

ORACLE Racing on the edge on the AC45 with a 30+ knot gust off North Head. Image copyright Philippe Presti/ORACLE Racing.

by Peter Rusch

The crew was out training on the Hauraki Gulf in strong-to-high winds between 25 and 35 knots with a sea running. They were sailing off the wind under North Head when a strong puff hit. The leeward bow dug in the water and the trampoline was nearly engulfed before control was regained, before the distribution of buoyancy in the hull allowed the bow to pop out and avert calamity.

Coach Philippe Presti captured the puff – estimated by observers at 30 to 32 knots – from the accompanying RIB. The excitement is measured by the RIB crew, whose voices rise as the bows dig in and the rudders come out; as is relief when the submerged bows break the surface the crew regains control.

Watch the video here.

“We were actually happy afterward,” said Dirk de Ridder, the wing trimmer who was riding the tender during the mishap. “We’ve done similar things with other 40-footers and had bad results. We’re very happy we could get out of it. Nothing was damaged. The wing hit the sideshrouds very hard, but there was no damage. It was a very good day in the end.”

This video plus the one two weeks ago of the four 45s flying in formation are great illustrations of added bow volume at work. The ORACLE Racing Design Team created the AC45 to perform in a wide range of conditions and sea states and through aggressive maneuvers. To aid those performance characteristics, the bows of the AC45 were designed with extra length and volume.

To make the catamaran interesting in the light winds expected at some venues the wingsail rig was made tall. But the tall rig means this extra horsepower has to be managed in stronger winds and that is solved by making the bows longer and fuller.

Added bow volume also lessens the cat’s tendency to pitch-pole, where the bows dig in and the stern flips overhead. Today’s video shows how the added buoyancy kept the cat upright before the wing could be eased and order restored.

“It looks like they were trying to point the boat down,” said Dirk Kramers of the ORACLE Racing design team. “At some point the bows go underwater and the rudders come out. Once steerage is lost the guys have to dump the sails. Easing the wing puts the center of effort to leeward and helps the boat spin up into the wind.”

The added volume and a rig positioned optimally to balance forces gives the AC45 the ability to still be sailed at the upper reaches of the wind range.

America's Cup