The Amazing Race: Looking for Design Details
The Amazing Race: Looking for Design Details
A pair of massively strong crossbeams connects each boat's hulls. The forward beam carries the mast compression loading from the windward shroud (side stay), pushing down, while the leeward hull is pushing up from the beam's other end. The aft beam carries the very highly loaded mainsheet, as well as the upward load of the leeward hull against the boat's weight. Both beams have to resist large torsional loads, as well, from such things as the running backstays and burying the leeward bow in a wave. USA's shrouds are set well aft on the outboard hulls, imparting very high upward load far aft; additional running backstays are inboard on the main beam. Alinghi 5's shrouds attach to the hulls about midway between crossbeams, with its runners near centerline on her aft
beam. Notice a pair of diagonal compression struts on Alinghi 5 that connect
from the reacher sheeting points to the mast step, part of the boat's clever truss system.
The aft beam carries some primary systems, too. Both boats have steering linkages connecting the port and starboard rudders and wheels. There are traveler controls for the mainsheet and reacher, and a few other devices. They also carry the engine for the powered hydraulic system used to trim the sails, cant the rig, and take on or transfer ballast water pumps. Given the huge loads on the sheets and halyards, as well as water pumping requirements, this was a controversial but eminently practical alternative to a large team of grinders for the sole purpose of muscle power. It leaves no shortage of demands on highly skilled and intelligent professional sailors to control all aspects of operating these speed machines.
Gilles Martin-Raget/BMW Oracle Racing
|Dirk de Ridder controls the angle of attack of the wing with the line in his hand, similar to the traveler on a soft sail. The wings shape is adjusted via a series of hydraulic controls.
The event's video coverage will give views of the deck and down the sails/wing that few have seen before. There is significant wind gradient from near the deck to 200 feet off the water, so sails will have to be set with twist. Port and starboard wind instruments mounted outboard on the aft crossbeam give clear readings on the windward side near the normal 10-meter reference height, to compare with the masthead readings at 60 meters-plus.
Alinghi 5's mainsail has a broad girth at the head for greatest power and efficiency, but its twist has to be controlled by leech tension. USA's wing has two fore-and-aft elements, with nine separate segments vertically in the aft element. This gives quite a lot of control over camber and twist. As the wind builds, the main elements can be de-cambered and the upper segments twisted off as needed, doing so with positive control. When tacking, there is no mainsail flogging, and the wing can quickly be put into optimum settings for accelerating. This is all done with relatively light loads on the control system.
These boats are extremely close-winded. Their blade jibs barely overlap the mast or wing at deck level, and leave an open slot over most of the leech. Where to sheet them is a limiting design issue on Alinghi 5, especially, since there's no deck aft of its forward crossbeam. There is an arrangement to lead the jib sheet somewhat aft of the beam, but it hasn't been clear to me what it is. USA is able to trim its jib to its deck.
When sailing their jibe angles downwind, these very efficient craft bring the apparent wind way forward. Huge, relatively flat reachers (Code 0's) extend from the tip of the bowsprit to near the aft beam, to which they sheet. The jib and reacher are on large furling drums and have integral luff stays.
At the right camera angles, you might see the rigs canted to windward. This is primarily to maintain the maximum vertical span of the airfoil for best windward effectiveness. It also reduces or eliminates a heeled rig's downward aero component, whose force acts like added weight. At the same time, it shifts the rig's weight to windward, as another form of moveable ballast.
Among some unconventional sailing gear you'll see are intercom headsets to deal with the distances and wind noise on these boats. Also, you might see knit hats. It's wintertime here, with temperatures that can be in the 40s before wind chill.
Whether you're watching the video or just reading about the races, try to appreciate the power and speed of Alinghi 5 and USA, the talent and focus of each member of their select crews, the genius of their design teams, the skill of their shore teams, and the spectacular pair of racing machines that their huge efforts have brought to America's Cup 33. Both teams deserve our respect and applause.