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Bruce Kirby 03-15-2000 07:00 PM

America's Cup Design Retrospective
 
<HTML><!-- eWebEditPro 1.8.0.2 --><P>The task was to win the America's Cup on New Zealand's Hauraki Gulf, where the breeze was always shifty, where it would vary in strength from 10 to 25 knots in minutes, and where races were won by beating the other boat to the next area of increased wind, or to the next major change of wind direction. </P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=244><IMG src="http://www.sailnet.com/images/content/authors/kirby/031600bk_2boats.jpg"><BR><FONT color=#ed4242 size=-1><B>Team New Zealand's <I>Black Magic</I>—"a highly specialized weapon"—maintaining it's usual, controlling position</B></FONT> </TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE><P>The black New Zealand sloop that won the event five races to none was a highly specialized weapon, conceived from the earliest design stages to do this specific job, and the fact that she did it so well is a tribute to the team that so thoroughly understood this multi-faceted puzzle. </P><P>The boat would not have been the same had it been developed for fleet racing, or for a different venue. This was a boat that could point as high as the opposition when it had to, could accelerate faster when it wanted to, and could achieve a higher top speed when that was important. It was a boat that could turn faster during starting maneuvers and come out of a tack faster during a tacking duel. It was a match-racing masterpiece and it succeeded even beyond the dreams of its creators and the sailors who made it perform its magic. </P><P>The design effort that produced NZL 60 began very soon after New Zealand won the Cup from Team Dennis Conner five races to none in 1995, and was a logical progression of the design work that produced the 1995 winner. There was a pause of only a few months before work began on America's Cup 2000, and this gave the Kiwis more than twice as much development time over any other syndicate. It is with more than passing interest that the second longest program was Italy's Prada challenge, which dominated the elimination trials only to be humbled by the Kiwi juggernaut in the Cup match. </P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=217><IMG src="http://www.sailnet.com/images/content/authors/kirby/031600bk_Schnackenberg.jpg"><BR><FONT color=#ed4242 size=-1><B>The grand wizard behind the magic, TNZ design coordinator Tom Schnackenberg.</B></FONT> </TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE><P>New Zealand Design Coordinator Tom Schnackenberg said that he had attempted to create the right environment for the design team. "We always tried for an open forum. When you said something, you were heard. We tried to make everyone feel they were contributing, and ideas were decided on their merits, not on who came up with them. We would have meetings on any subject—hulls, rigs, keels—and everybody could come. We might have 18 people at a meeting on a new rig idea."</P><P>New Zealand's Laurie Davidson and American Clay Oliver were the co-designers of the New Zealand boats. Each contributed-hull shape proposals, which were discussed and analyzed by the team. The most intriguing ideas were made into test models and towed in the tank. A promising model might come before the design team a second or third time to see if anyone had an idea that could improve it. </P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=135><IMG src="http://www.sailnet.com/images/content/authors/kirby/031600bk_davidson.jpg"><BR><FONT color=#ed4242 size=-1><B>Designer Laurie Davidson, another of TNZ's magicians.</B></FONT> </TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE><P>Davidson said, "We did not use computational fluid dynamics (CFD) to determine hull design, but went from the lines to the test tank in the U.K. Using one-quarter-scale models we refined our early ideas as much as possible, and then this testing was dovetailed in with the massive VPP program." This program has been developed over a number of years by Clay Oliver, who is from Annapolis, MD and has been working with the New Zealand design team for three years. Oliver also conducted the CFD testing of the keel, rudder, and bulb designs. </P><P>However, some of the scientific approach lost its glitter under the intense pressure of on-the-water testing. Davidson was quick to admit that many of the final decisions were made through exhaustive sailing trials between the two virtually identical boats. He said, "Sometimes the CFD program would tell us that, for example, Bulb A was better than Bulb B, but the crew would decide out on the water that Bulb B gave the better performance."</P><P>"This phenomenon was particularly evident in the position of the wings on the keel bulb. The CFD testing could not give a definitive answer for placement of the wings. We tried them right aft like they were in NZL 32, and on most other America's Cup boats, and we tried them in the middle of the bulb, and halfway between these two positions. There was no conclusive answer. Then we did the same testing full size on the boats, and after hours of sailing the crew decided the wings worked better in the middle of the bulb. So that's where we put them."</P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=114><IMG src="http://www.sailnet.com/images/content/authors/kirby/031600bk_peterson.jpg"><BR><FONT color=#ed4242 size=-1><B>Doug Peterson, a Team Prada design principal and erstwhile critic of TNZ's two <I>Black Magics</I>.</B></FONT> </TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE><P>Californian Doug Peterson, a principal on the Italian design team that produced the two boats of the Prada syndicate, had high praise for the Kiwis' effort. "Their boat was in a different mode altogether. It was stretched out and had more wetted surface. It had to go fast to do the job—but in match racing this can usually be accomplished."</P><P><EM>Luna Rossa </EM>and NZL 60 had very similar VMG (velocity made good.) numbers in moderate to light conditions. In upwind sailing VMG is the combination of pointing and footing that results in the best speed made good towards the next mark. In 12 knots of true wind, both boats sailed at 9.5 knots when making their best VMG. But when the wind got up to 14 knots, the Italian boat would sail at about 9.6 and the New Zealanders would jump to 9.8. The speed difference continued to widen as the wind rose. </P><P>In the stronger winds NZL 60 could jump quickly to 10.2 knots if it laid off only a few degrees. The Italian boat did not have this high-end speed and would get to only about 9.9 when cracked off the same amount. It was this high-end capability that made the big difference. Peterson lamented, "You don't necessarily sail your best VMG in match racing. You head for the lifts wherever they are. With their high-end speed, they were better at doing that, and the better wind was usually on the right, which Team New Zealand controlled most of the time." </P><P>The potentially higher speed enjoyed by the Kiwis was partially due to the very sophisticated manipulation of the hull measurement rule. Her bow overhang was considerably steeper than the overhang on <EM>Luna Rossa </EM>and most of the other challengers. Simply stated, in measuring the hull, an imaginary line is drawn 200 mm (eight inches) above the actual waterline. The distance between where this line meets the hull slope at the bow and stern is called LBG (length between girths). In measurement trim (no crew or extra gear aboard), the boats were virtually identical in length at this 200 mm waterline. But by having the more tipped-up bow profile, the New Zealand boat was a few inches longer at the actual waterline. </P><TABLE cellSpacing=0 cellPadding=10 width=160 align=right border=0><TBODY><TR><TD><IMG height=2 src="http://www.sailnet.com/images/content/authors/ddcksn/1pix_amcup.gif" width=160></TD></TR><TR><TD vAlign=top align=middle width=160><FONT face="Arial, Helvetica, sans serif" color=#ed4242 size=+1><B>The higher speed enjoyed by the Kiwis was partially due to the very sophisticated manipulation of the hull measurement rule.</B></FONT></TD></TR><TR><TD><IMG height=2 src="http://www.sailnet.com/images/content/authors/ddcksn/1pix_amcup.gif" width=160></TD></TR></TBODY></TABLE><P>With the crew and all its gear aboard, the boat could be trimmed a bit down by the stern, which would result in the long, flat stern overhang adding as much as two feet to the sailing length, while the steep, forward overhang would prevent the boat from getting shorter at that end. So in measurement trim, the boats sat on similar waterline lengths, while in sailing trim NZL 60 was considerably longer. If trimmed down by the stern, the Italian boat, with more balanced fore and aft slopes, would lose length as fast at the bow as it gained it at the stern.</P><P>Carrying this theory to the extreme it can be seen that if the bow were vertical, as it was in John Kolius's first <EM>Abracadabra</EM>, several more inches could be gained at the waterline with the boat upright in measurement trim. But the problem with the vertical bow is that it provides very little buoyancy as the boat heels over, and therefore the bow tends to drop and the stern rise as the wind increases. This defeats the purpose of manipulating bow shape to achieve greater sailing length when heeled over.</P><P>In the case of the New Zealand sisterships, NZL 60 and 57, the bow angle was not taken to the extreme, and through clever drafting of the lines, the above-water shape in this area was given enough buoyancy so that as she heeled the bow did not drop. The hull was therefore able to take full advantage of the long, flat aft overhang and the increased sailing length, compared to the Italian boat, was good for two tenths of a knot in medium to heavy winds.</P><TABLE cellSpacing=0 cellPadding=0 align=center border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=452><IMG src="http://www.sailnet.com/images/content/authors/kirby/031600bk_bows.jpg"><BR><FONT color=#ed4242 size=-1><B><I>Luna Rossa's</I> bow profile, at left, represents the more conventional IACC configuration, whereas <I>Black Magic's</I> more "tipped-up" profile, at right, allowed the boat to be a few inches longer at its actual water line.</B></FONT> </TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE><P>(America's Cup gurus will know that there are other measurements taken in determining the measured length of the Cup boats, but these were very close on the Italian and New Zealand boats, so they had little if any effect on measurement or performance.) </P><P>The sails on NZL 60, particularly the main, were noticeably fuller than <EM>Luna Rossa</EM>'s sails. This too was part of the package. The boat was big and powerful so it needed powerful sails to produce the speed that was designed into the hull. When Russell Coutts and his crew wanted to foot off to get to the next piece of favorable wind, the sails could be powered up to make that happen. </P><P>Before the match, Doug Peterson had questioned the wisdom of full sails on a high-pointing America's Cup boat; but after he had seen how well the sails suited the overall concept he was quick to admit that the system worked very well. "They could get the boat going very fast," he said, "and then they could go higher and higher. They could pinch us off when they had to, and make us head off in the wrong direction." </P><P>Davidson and Peterson agreed that the revolutionary New Zealand rig had a great deal to do with NZL 60's success. The 105-foot, carbon-fiber spar was 600 mm (23.5 inches) longer than minimum in the fore and aft dimension of its lower portions. "We felt we were getting some useful area out of this configuration," Davidson said, "and by using the diamond stays we were able to go with only three spreaders instead of four, and that saved windage and weight."</P><TABLE cellSpacing=0 cellPadding=10 width=160 align=right border=0><TBODY><TR><TD><IMG height=2 src="http://www.sailnet.com/images/content/authors/ddcksn/1pix_amcup.gif" width=160></TD></TR><TR><TD vAlign=top align=middle width=160><FONT face="Arial, Helvetica, sans serif" color=#ed4242 size=+1><B>The interplay of all these design features was almost endless.</B></FONT></TD></TR><TR><TD><IMG height=2 src="http://www.sailnet.com/images/content/authors/ddcksn/1pix_amcup.gif" width=160></TD></TR></TBODY></TABLE><P>Peterson said, "I would think the rig may have been the most significant feature of their boat." He recalled that the Kiwis removed their two upper backstays when sailing to windward, and said that they also had a cleaner mast, with smaller, lower-drag fittings. "We calculated that by removing the two 100-foot long backstays and by having a tidier rig all-round, they had about eight kilograms less rig drag in medium winds than we had. This is a lot of drag, and would equate that to about 1.5 square meters of wetted surface in a hull. We knew their hull had a bit more wetted surface than <EM>Luna Rossa</EM>'s because it was wider and a bit longer, but the reduction in rig drag more than made up for the extra hull drag."</P><P>The greater beam on NZL 60—about six inches at the waterline--gave her more stability, and this was part of her overall superiority in winds above 12 knots. When she was cracked off to gain speed, not only did she have the extra length to carry her along, but the additional stability meant that she would not heel over as much as <EM>Luna Rossa </EM>would under the same circumstances. She would squirt ahead instead.</P><P>The interplay of all these design features was almost endless. The hull was wider at the waterline than <EM>Luna Rossa </EM>, so in order to have the same displacement (both boats were at maximum rule displacement of 55,000 pounds) the sections of the hull were a bit shallower. Because the hull was shallower and the draft was at a rule maximum of four meters (13 feet), the length of the keel fin between the hull and the ballast bulb was a bit greater. And because the bulb was not round, but squashed into an oval section (to give it a lower center of gravity), the keel fin gained another few inches of length at the bottom. So the keel fin on the New Zealand boat—the part that gives lift when going to windward—was about five inches longer than the fin on <EM>Luna Rossa</EM>.</P><P>Therefore it would not be accurate to say the boat was faster because it was longer, or because it had more stability, or fuller sails, or a better rig, or a more sophisticated keel. They all worked together, and there is little doubt that there were at least as many ingenious features hidden from view below decks. </P><P>Topping it all off was a team of sailors who performed so well that finding any fault at all in several hours of competition was next to impossible. Peterson said that whereas <EM>Luna Rossa </EM>had one good tactician in Torben Grael, the entire New Zealand crew knew the gulf better than any of the Italians. There may have been some minor mistakes on board NZL 60, but none important enough for the eye or camera to pick up. Peterson, among others, has said that the New Zealanders would have won no matter which boat they sailed. Maybe so, but it would have been a much closer contest if the crews had exchanged boats, because there's no doubt that the speed on demand provided by the exquisite black boat was the key to one of the most astonishing sweeps in America's Cup history. </P><I>Peterson Photo Credit:</I> Carlo Borlenghi—PRADA Challenge for America's Cup 2000 </HTML>


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