Cool Cat

The little sister of the still-to-come AC72 turned all heads during its 14-day dress rehearsal on Auckland’s Waitemata Harbour. "Tech Review" from our March 2011 issue.

Sailing World

AC 45

In initial trials, the two-element wing provided for quick maneuvers, as camber is matched from tack-to-tack.

On time and as promised, the first AC 45 catamaran was handed over to America’s Cup Race Management in Auckland, New Zealand, on January 31 following two weeks of builder’s trials. Assembled, rigged, and commissioned just four days afer leaving in pieces from Larry Ellison’s Core Builders in Warkworth, north of Auckland, the sleek wing-sailed 45-footer turned in a scintillating performance on its first outing in 10 knots and shone in gusty 25-knot conditions the next day.

America’s Cup winning helmsman James Spithill delivered his upbeat verdict at the end of the first day’s trials, declaring: “Everyone who sails this boat will step off with a smile on their face, I guarantee it!”

Highlighting the wing’s versatility and ease-of-use, Spithill and his test crew from Oracle Racing sailed the cat off the dock on its maiden voyage, negotiating the confined channels of the Viaduct Basin with ease, and returned in the same relaxed manner.

Ten days afer their first sail, Spithill’s crew parked the boat overnight for the first time, leaving it on a prototype mooring inside the Viaduct Harbour. The buoy was an inflatable tetrahedron race mark, mostly filled with fresh water to dampen its movements.

Attached by a bridle, with boards up and the rudders toed inwards almost 90 degrees, the boat lay docilely, gently swinging in the breeze like a weathervane.

During February, Oracle and the confirmed challengers will each spend a week trialing the first boat before taking delivery of their own boats starting in March. Initially four boats will be available. Additional boats will roll out every two weeks. The first production run is 10 boats.

Power, grace, elegance, and relentless attention to detail all come to mind as one looks at the cat, ashore and afloat. The Oracle Design Team wanted a boat that was light, robust, easy to sail, and capable of delivering excellent performance across a range of conditions from 5 to 30 knots. The boat carries a crew of five, plus one guest.

Mike Drummond, a veteran Cup designer from the Oracle Racing Design Team, summed up the result. “You’re always hoping when you use CAD and CNC machines that everything will fit together like it is supposed to in the brochure, and yet sometimes it doesn’t. In this case everything fit, everything slotted together physically. Everything came together project-wise and time-wise and obviously the structural estimations and designs were on the money and the boat went sailing right away at full potential.”

The cat is reminiscent of a smaller, winged Alinghi catamaran. The boat features the same style of central, braced spine of the unsuccessful Swiss defender of the 33rd America’s Cup in 2010. The wing sits on a ball smaller than a standard trailer hitch, and is held in tension by the forestay and shrouds. The braced spine permits headstay loads of up to 2.5 tons. A load cell warns when the permissible maximum is reached.

Dirk de Ridder, who was the wing trimmer on BMW Oracle Racing’s victorious USA 17, is part of the team working on the new boat. “We’ve made an effort to keep it simple but still have it as a proper raceboat,” he says. “Things like the infinitely variable jib traveler sheet systems mean that the teams can use it as a tool as they develop their AC72s.”

The AC45 invites an invariable comparison to Extreme 40 catamarans and the design team gave serious consideration to modifying existing Extreme 40s to carry a wing. Ultimately they chose to go for a new design.

Five feet longer than an Extreme 40 and with a lot more volume in its hulls in front of the mast, the AC45 delivers more performance over a wider range of wind conditions. De Ridder estimates that the new boat has a margin of 5 knots more speed “before scary things start to happen.” He’s referring to the chance of pitchpoling, something the team doesn’t want to subject the wing to, despite its robust construction.

In a move to save weight and keep it simple, there are no cockpits or openings in the hulls, other than an inspection hatch on each hull just forward of the afi crossbeam. The trampoline is set 12 to 18 inches below deck level to facilitate crew work on winches and provide more clearance under the wing.

There are just three winches each side. There are Harken 3-to-1 ratio winches for the headsail sheets, another set for the backstays and smaller 2-to-1 ratio winches for the traveler that controls the wing’s angle of attack. The wing’s camber and twist controls are mounted under its base.

There is no mainsheet, as there is no need for one. The traveler control line leads from the wing straight out to the small winches port and starboard. “We use them in high gear most of the time,” says de Ridder. “It’s very responsive and easy to do. When sailing fully loaded upwind, to easing off to nothing, it’s less than a meter of sheeting. You can go from flying a hull to splashing down in the water in an instant.”

Mike Drummond credits Dave Hubbard and his_ Patient Lady _C-Class catamaran program in the late ’70s for the two-element wing. “It’s deceptively simple,” he says. “The biggest advantage of the wing control system is that it replicates itself on the new tack so when you tack the wing it just flops through with wind pressure and adopts the same camber on the new tack. We made no changes to the concept. For the AC45 we kept it pretty simple.”

Designed to be transported in a 40-foot container, each hull features 5-foot long bolt-on stern sections. The through-hull rudder assemblies that fit through these sections include a lower bearing in an oblong cassette that clips into a slot in the bottom of the hull and a separate upper bearing that plugs into the deck. Installing or removing the rudders takes only two or three minutes.

For launching, a substantial tower crane hoists the wing until it’s vertical, taking care to face its leading edge into the prevailing breeze. The gumboot, a wooden box fllled with water and attached to the leading edge at the foot of the mast, stabilizes the wing and ensures that it weathervanes. The boat is rolled under the wing and afier shrouds and headstay are attached, the boat is lified into the water. Straps around the hull at the forward beam pick up the load and are led though a temporary fairlead at the masthead to stabilize the wing. With a shore crew of ten, the boat goes from shed to the water in little more than half an hour.

AC45
LOA 44'1"
Beam 22'7"
Mast height 70'6"
Draft 8'10"
DSPL 3,080 lbs.
Wing area 914 sq. ft.
Jib area 516 sq. ft.
Draft 1,345 sq. ft.
Crew 5*
Crew weight limit 935 lbs.*
*does not include spectator position