The Amazing Race: Looking for Design Details
The Amazing Race: Looking for Design Details
|Dennis Conner's Cat runs away from Sir Michael Fay's Dog in the 1988 America's Cup, aka the Coma off Point Loma.|
Twenty-two years ago, the America's Cup was decided by a Deed of Gift mismatch between a 65-foot catamaran and a 90-foot monohull. They were each amazing yachts in their day, but the resulting races were boring parades of what were facetiously called The Cat and The Dog. But that was then. The speculation going into the 33rd America's Cup, in contrast, is favorable to both boats, each having its strengths that might produce a horses-for-courses match. Talk from the teams tilts toward Alinghi 5 in lighter conditions, and USA in increased wind. Even if this is so, though, no one knows where the crossover is, above which windspeed does USA have an advantage. Furthermore, the differences between the competitors may show up not only in the strength of the wind, but also in downwind versus upwind performance.
Often in the America's Cup the favored horse becomes apparent in the first five minutes of the first race. Don't count on that this time. While you keep watching, with the advantage of helicopter coverage, here are some of the design details that you might spot.
BMW Oracle Racing had to target a broad bandwidth of performance in its challenger, because Alinghi would make the choice of venue, and, hence, have some control over anticipated wind conditions. Alinghi initially chose a light air venue in the United Arab Emirates. That venue was ruled to be contrary to the Deed of Gift, leaving either a southern hemisphere venue for the February match, or Valencia if both teams agreed. So here we are in Valencia in the winter, with the wind varying significantly from day to day, and Alinghi no doubt hoping to be blessed with light air on the 8th and 10th.
In virtually any sailboat design, stability buys sail-carrying power, and sail power buys speed. Stability in multihulls comes primarily from the distance from the athwartships center of weight to the leeward hull-true of a proa, a catamaran or a trimaran. Subject to diminishing returns of construction weight, more beam is good. Both of the AC33 multihulls have chosen essentially square proportions of overall breadth to waterline length, and both sail on just one hull in all but the lightest winds-USA taking a bit more wind to fly its center hull. Sailing on one hull minimizes hydrodynamic drag by having less wetted surface on one hull carrying the boat's weight than when it's shared by two hulls.
Another subtle contributor to stability is the curved daggerboards. The leeward board produces not only horizontal force in the normal way to counteract the side force of the sails, but also a vertical component that, effectively, pushes up on the leeward hull. This has the same effect as prying down on the windward hull-like hiking or sitting on the weather rail.
Weight is more damaging to resistance than it is helpful to stability. Consequently, there isn't much on these boats that isn't carbon fiber. An exception is water ballast, which is twice as far away from the leeward hull as the overall fixed weight of the boat, so it's very effective in producing even greater righting moment, and can be jettisoned when not needed. Since both boats have been exploring just how much sail area they can pile on, they are both using water ballast.
|Alinghi 5 during training off Ras Al-Khaimah: From left to right, Peter Evans on the runner, Ernesto Bertarelli at the helm, Warwick Fleury on the mainsheet, and Pierre-Yves Jorand on the traveler.
Not insignificant, also, is aerodynamic drag. When these boats are doing around 25 knots upwind in a pleasant 12 knots of true wind, they're seeing around 35 knots of apparent wind across the deck and over the sails. In this much wind, aero drag becomes an equalizer in performance-their clean aerodynamic design is not there just for its looks. Both boats have experimented with lightweight fairings extending aft of the crossbeams; we'll see on race day what their tech juries have decided about them. USA has gone to the extreme of eliminating all but a few strategic vestiges of its trampoline to reduce drag. It's turned the sailors into acrobats as they traverse the boat for tacking and sail handling along the narrow crossbeams. Alinghi's increased need to move crew across the full breadth of the boat makes her trampoline more essential.
The helmsman has a long hike across the boat after tacking or jibing while an alternate helmsman takes the con for a short time. Look for Ernesto Berterelli himself as Alinghi 5's primary helmsman, with French multihull master Loick Peyron as his second. James Spithill rides the very exposed-looking helm platform on USA, with John Kostecki covering the transfer when tacking. Since James is frequently facing 30- to 40-knot apparent winds as he balances on his perch, it's a good thing he has a wheel to hold onto.