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Was racing technology report too generalized?

Jan 1, 2003

I enjoyed the recent article by Sven Donaldson on technology in the America's Cup and Sydney/Hobart Race ("Trends down under," March/April 2000, Issue No. 104). It was very informative and interesting. However, Donaldson did generalize a bit too much and left out some very important tidbits, which leads the unknowing reader to false conclusions.

For example, on the subject of computer-aided design, I'm not sure Donaldson's conclusions are right. Yes, the America's Cup is loaded with computer-aided technology, but something needs to be mentioned about the Kiwis' Black boats, both designed from the brain of Laurie Davidson, and not from a computer. In fact, both this Cup and their last Cup designs came off Davidson's drafting board, then went to computer modeling (which disagreed with his design) and then to a tank test (which agreed with Davidson's design) and so they have found that, in the big picture, there is still not enough data in computers for the nuances of hull design, and so computer-aided design is mostly relegated to appendages and foil testing. The fact that the Kiwis' program is the least computer oriented, combined with the fact that they won the Cup last time around and have just won it again, says much about the skill and experience of Mr. Davidson, and gives less credit to the wonders of computer-aided design.

I also disagree with some of his comments on narrow beam. If this article was only about the America's Cup boats I would not have brought this up, but since it encompasses the larger realm of sailing, the Sydney/Hobart, I must speak up.

The conclusion drawn that narrower beam is faster is again a false generalization. For an upwind and less planing-oriented boat like the America's Cup class, yes, generally narrower is faster (although the Kiwis' latest winning black boat is wider in the stern section than the Italians' Luna Rossa). On a bigger and broader spectrum of sailing, many wide-beam boats are faster than narrower completion. The BOC racers and Whitbread 60s are two examples of very beamy boats, designed to blast along on beam reaches with the aid of water ballast, faster than narrower boats of similar dimensions could.

Donaldson's re-cap of the Sydney-Hobart race really hits this point home as the relatively beamy Whitbread 60 Nokia almost stole line honors from the very high-tech, lightweight, and narrow-beamed 146-foot Mari Cha III, which finished the Sydney-Hobart Race only one hour and 20 minutes ahead of Nokia but had nearly twice as long a waterline! Also, at Key West Race Week this year, the narrow and light Synergy 1000 was badly beaten boat for boat by the much beamier and non-water ballasted Henderson 30s. So narrow isn't always faster. Mr. Donaldson knows better; he just left out a few important notes.

Sven Donaldson responds:

Your letter raises interesting points that I'd like to address in some detail.

Of course, my remarks about computerized flow modeling were not meant to suggest that America's Cup yachts are literally designed by computers. But there's no question that computers played an important role, even in the Kiwis' camp. New Zealand's design team, led by ex-physicist Tom Schnackenberg, included not only Laurie Davidson with his celebrated seat-of-the-pants approach, but fluid dynamist Richard Karn and Annapolis-trained naval architect Clay Oliver, a dedicated "numbers man" by his own admission. Team New Zealand spent four years preparing for the defensealmost twice as long as Prada. Because the team philosophy was to leave no stone unturned, they invested quite heavily in both flow modeling and tank testing.

More than anything else, New Zealand's dominance over two Cup cycles resulted from an unusually flexible management approach that fully involved all 86 team memberssailors, designers, and shore crewin every aspect of the program. Their style was conspicuously different from the compartmentalized, top-down administrative structures of the other syndicates. In 1995, it was the close working relationship between Kiwi sailors and tech guys that created the first ultra-stiff rigsa counter-intuitive development that yielded an overwhelming speed advantage in San Diego. At that time, everyone else was striving for the minimum mast size and weight under the IACC rules, because "everyone knows you need to minimize weight and windage aloft."

No question, New Zealand brought an excellent hull to the 2000 America's Cup match, and Laurie Davidson certainly deserves a substantial share of the credit. By the same token, the Kiwis had outstanding sails and a very clever rig that worked in perfect concert with the bottom half of the boat. It's interesting that the lion's share of technical questions and comments in the open forum section of Quokka's America's Cup web site concerns hull design, but the designers and sailors themselves always put top priority on the rig and the sails.

Those at the forefront of America's Cup development seem to agree that the speed differences between a pair of good hulls, keels, masts, or whatever are too small to be detected using either tank testing or computer modeling. Only painstaking, two-boat testing can resolve these issues, and even then results are often less than clear-cut. This raises an important question: did NZ-60 really demonstrate superior speed over Luna Rossa? Considering that the Kiwi's won a huge advantage in three out of five pre-starts, and secured the favored side for all five opening beats; I'm not convinced we can really tell. Some of the experts claim that NZ-60's bow and stern configurations should give her an edge upwind, especially when tactics call for sailing fast and low. But in the Cup races, almost every time the Kiwis footed down to square up a cover on Luna Rossa, they were simultaneously benefiting from more pressure and a favorable shift. While there's no question New Zealand decisively outsailed Italy in the Cup match, in terms of pure boat speed, the two contenders appeared very closenothing like 1995, when NZ-32 blew away Young America with obviously superior upwind speed.

Computational fluid dynamics (CFD) is a tool that allows aircraft and yacht designs to evaluate shapes more quickly and at far less cost than either model testing or full-scale experimentation. However, the margin of error for both CFD and tank testing remains large enough that very expensive, time-consuming two-boat testing is indispensable to a competitive America's Cup or Volvo Ocean Race program. Nevertheless, the CFD and tank-testing programs are also extremely helpful, because even the richest Cup programs can only build and test a couple of new boats. Ideally, it becomes a matter of evaluating two hulls that appeared equally promising at the design stage. Later, when one proves better on the water, real-life sailing data can be used to fine-tune the CFD programs, thus improving their predictive value.

Over the long run, I am convinced that better computerized design tools will enable talented yacht designers to do superior work in less timewhich ultimately means better value to the boat buyer. On the other hand, it's inconceivable that computers will ever take the place of imaginative designers. This month's Ocean Racing column provides more evidence to this effect.

Regarding your remarks about narrow vs. wide beam, my comment on the trend toward narrower IACC boats was by no means a blanket generalization to the effect that narrower is faster. I actually said that the performance benefits of form stability are often overrated, and that many handicapping rules, open class rules, etc., have artificially encouraged beamy shapes.

Admittedly, the IACC rule was deliberately formulated to encourage exceptionally slender shapes. When a task force of the world's top designers got together to develop a new America's Cup class, its mandate included preserving the slim, graceful look of the Cup racers from bygone eras. A maximum beam of 16 feet was imposed, and some of the early boats approached this limit. Californian Doug Peterson, working for Team New Zealand in 1995, is credited with recognizing the advantages of going much narrower than the 1992 norm. By now, the narrow boat trend may have "self-limiting" at around 11 feet due to stability and volume distribution constraints. On the other hand, the ultra-slim French boat showed bursts of great speed despite a severe cash shortage.

Other design rules encourage very different solutions. Open 60s are 19 feet wide, specifically because the class limits static heel induced by moveable ballast to a maximum of 10° per side. Despite their very light displacement, these ultra-wide hulls produce high resistance, especially upwind in a seaway or when heeling less than about 15°. Wide beam works here because these boats are allowed enormous rigs; and, as you pointed out, they frequently race off-wind in heavy air. When open class fleets must beat to windward, the advantage often shifts to the more conservative, narrower designs such as True Blue (Class II Around Alone record holder) and Balance Bar. Since the days of the IOR, analytical handicapping systems have always treated beam as a speed-reducing feature provided it's evaluated separately from lateral stability (an unambiguous speed generator).

Volvo Ocean Race 60s such as Nokia are designed to a "box rule" that establishes most design parameters including beam within fairly narrow limits. Typical LOA is 64 feet with a beam of 17 feetproportions shared by many modern cruisers from Beneteau, Catalina, etc. Compared to open 60s, V.O. 60s have more fixed ballast, at least 40% greater displacement, and fairly moderate rigs. Generous water ballasting and an exceptionally low center of gravity give V.O. 60s the raw sail-carrying power to sustain very high speeds when reaching or running in heavy weather. However, they are also exceptionally potent all-around performers thanks to a favorable combination of stability, rig efficiency, and, yes, moderate beam.

Is the relatively slender Synergy 1000 inherently slower than the Henderson 30? Maybe, but it's tough to say for sure, considering the Synergy was a brand-new boat at Key West, while the Hendersons have been working up for several seasons. Historically, some highly successful race boats have debuted at Key West with rather indifferent results, including, if memory serves me, the Melges 24. As with the recent America's Cup match, I think it's risky to infer too much from what amounts to a confounded (i.e., multi-variable) experiment.