Giants of AC 33
Giants of AC 33
Gilles Marin-Raget/BMW Oracle Racing and Carlo Borlenghi/Alinghi
|Wider equals faster, usually. The more beam a multihull has, the more sail it can carry. BMW Oracle Racing's trimaran (bottom) has an advantage over Alinghi's catamaran (top) in this respect. However, the cat, with two hulls as opposed to three, is likely lighter.|
They may disagree, the few thousand people forced to seek alternative employment as a result of the two-year (and counting) America's Cup legal feud between Ernesto Bertarelli and Larry Ellison. But the battle of the sailing billionaires has one big upside: the creation of two ground-breaking craft. Not since the era of the J-Class yachts has the America's Cup seen such revolutionary designs. While the multihull dust-up next February in Ras Al-Khaimah is unlikely to feature any of the close racing of Valencia 2007, as a technological showcase and on-the-water speed fest, the 33rd match will be unparalleled.
That's hardly idle praise considering the recent performances turned in on the North Atlantic by mega multihulls. While setting a new transatlantic record, the Banque Populaire V maxi-trimaran lifted the 24-hour record to a remarkable 908.2 miles. At 131 feet, BPV is longer than both Alinghi's catamaran and BMW Oracle Racing's trimaran, but is more conservative in many respects. BPV's beam-often the best indicator of the power of a multihull-is a modest 75 feet. The BMW Oracle Racing trimaran is 90 feet wide, the Alinghi cat only slightly narrower. BPV's mast height is a towering 154 feet, but come next February, the rigs on the America's Cup contenders are expected to approach 200 feet, while each boat's all-up displacement should still be less than Banque BPV's 26 tons.
So it's within reason to expect these America's Cup multihulls to be capable of 25 knots upwind and 50 knots on a reach. Sadly, however, in the light sea breeze conditions off the United Arab Emirates, teams will not be looking for ultimate speed, but for ultimate efficiency in 10 to 15 knots. The big question is, in these conditions, which will do that more effectively?
|To overcome the inherent stiffness concerns in such a wide catamaran, Alinghi's designers use an innovative system of composite rigging running under the trampoline both side-to-side and fore-and-aft.|
Cloaked in secrecy during its build, there was rampant rumor about what the new giant Alinghi multihull would look like. Only in early July was the public allowed its first glimpse of the America's Cup defender's futuristic-looking catamaran.
The most astonishing aspect is its extreme beam, which is 80 to 90 percent of the 90-foot waterline length. This gives the boat one of the highest beam-to-length ratios of any catamaran ever built.
The choice of a catamaran, however, shouldn't be a surprise. For two decades, syndicate head Ernesto Bertarelli has successfully helmed state-of-the-art catamarans on Lake Geneva, including the 41-foot Le Black, which was retired after winning the Bol d'Or race three times from 1997 to 2001, and more recently the Alinghi D35 one-design. The D35's beam-to-length ratio is 63 percent; however, these boats could almost be considered trimarans due to a central hull that never touches the water, but helps with fore-and-aft rig tension. Catamarans typically struggle upwind due to forestay sag. In this sense, Alinghi 5, which has no center hull, is a more conventional catamaran.
Its two crossbeams are immense. Equally as substantial are the 50- to 60-foot bowsprit, which extends from the mast step to forward of the bows, and the two additional aft support beams, which run diagonally from the mast step to the aft beam. To sustain the forestay tension necessary for upwind performance, Alinghi 5 has a complex network of composite rigging running beneath its fore-and-aft beams.
"The biggest problem with cats, and any multihull, is that stiffening it out with the hulls and the beams is nearly impossible," says Rolf Vrolijk, Alinghi's lead designer. "Sometimes you have angled beams and all kinds of other solutions, but here all the rig loads are going straight into the spines and the rigging [beneath the crossbeams]. There is no mast force going into the hulls other than the forward thrust of the sails. That is the biggest difference with this kind of structure."
This solution allows the team to crank up rig tension through the use of powered hydraulics. "You can really pull it up to max tension," says Vrolijk. "You have to. It is like an iceboat: the more you pull on the sheets, the flatter you make the sails, the faster it goes. And downwind it is the same, your apparent wind comes around the front and it is only a 10-degree difference [from upwind]. It is always apparent wind from the front and it's always flat sails, and max tension makes you go fast."
Offshore maxi-cats typically have three crossbeams-aft, main, and forward-with the middle beam supporting the mast step. Alinghi 5 did without the forward crossbeam, which reduces weight and the possibility of the beam burying into waves. However, the challenge of this arrangement is that the two bows lack lateral support-at least against inward bending-forward of the mast step. A decade ago, Pete Goss's radical Team Phillips catamaran tried this and failed, with one bow snapping off forward of the main crossbeam during a shakedown sail. To prevent this from happening on Alinghi 5, the hulls have their largest cross-sectional area at the main beam, tapering considerably forward and less so aft.
An unusual feature of the boat is that the two crossbeams are shaped differently. The main beam is a shallow inverted 'V,' while the aft beam is arched where it connects with the hulls. According to Dirk Kramers, Alinghi's Chief Structural Engineer, this is due to the differing bending moment between the hull and cross beams. "Quite a large part of the load that goes into the forward beam is bending moment from the daggerboards," says Kramers, "while the aft beam has the curve on it for water clearance."