Issue: Volume: 22 Issue: 12 (December 1999)

CAD tools give America's Cup racing teams a competitive advantage




Since the beginning of the 150-year challenge, design innovation has played an important role in the competition's outcome-from the 1851 win of the swift schooner America over England's traditional fleet to the 1983 victory of the revolutionary winged-keel design of Australia II, which ended the New York Yacht Club's 132-year winning streak.

In fact, design innovation seemed to have been pushed a little too far in 1988, when the Stars and Stripes team protested New Zealand's fiberglass hull and its "big boat" design. The controversy led to the 1992 adoption of the International America's Cup Class (IACC) codes, which limit, among other things, boat length, weight, and mast size. Now, with all competitors building boats to the same general specifications, design innovation has become a struggle in minutiae, as the contenders try to find the optimal combination of fractional tweaks and changes, where a half inch here and a quarter inch there can provide the winning edge.

"The design work we're doing now is just as important as how the crew conducts itself on the water, because even a skilled crew can't make up for a boat that is slower than the competition," says Bob Billingham, chief operating officer of the San Francisco-based Amer ica One Team. "There's no question that the fastest boat will win this race-and you'll be talking about time differences of seconds."

During the last Cup challenge, held in 1995, Team New Zealand was the group that best capitalized on the benefits of computer-aided design technology-not only to draft boat specifications for various parts of its vessel, but also to test them by simulating real-world racing conditions. As a result of its innovative step in embracing digital design tools, the group will be defending the Cup during February in Auck land, New Zealand, against the winner of the four-month round-robin Louis Vuitton Cup, which determines the challenger.
The AmericaOne team was among several that employed state-of-the-art computer analysis and visualization to shave precious seconds from race times, which will likely make the difference in the world's most prestigious sailing competition.




"This time around, I believe there are quite a few other racing syndicates using CG analysis and visualization, so now we may well be one of the boys rather than the leader in this area," says Tom Schnack en berg, design coordinator for Team New Zealand. His prediction seems accurate, as many of the challengers are following in the defender's technological wake. Among them is Italy's Team Prada, whose designer, David Egan, is building on the expertise he gained as a member of the 1995 New Zealand team. "In 1992 and 1995, there were probably only one or two other syndicates, besides New Zealand, using things like graphic simulations. For this race, I imagine there isn't a single team that is not trying it," Egan says. "Those not taking advantage of this technology will be in trouble down in Auckland."

Yacht design has always been a traditional and conservative industry, and during the last race, people were still wondering where the technology fit in, says Egan. But now, most if not all of the 11 competitors for the America's Cup are using at least some type of CAD-related technology to design their multimillion-dollar boats. However, some syndicates-such as Prada, AmericaOne, and New Zealand-have been exploring the technology's outer limits in an attempt to secure an advantage.

The tide is now turning toward using design analyses-such as computational fluid dynamics (CFD) and finite-element anal ysis (FEA)-coupled with 3D visualization techniques, as the racing teams realize the advantages to be had. These tools become especially important to the design process when the actual racing begins, since the teams are permitted to alter their boat's design during the competition. In fact, many groups opt to build more than one vessel for the event.

Billingham estimates that during the last two Cup races, computer modeling was used far less than the expensive physical wind-tunnel and tow-tank tests (to measure the drag of a scale model as it is towed through the water). "In this Cup, I think you will see those roles reversed," he says. "We now trust computer modeling software so much that it is taking the lead, while physical testing is used to back up those results."

The catalyst for achieving buy-in to the various design technologies, Egan maintains, is 3D visualization. "CFD and FEA were almost exclusively the domain of the top automotive and aero space industries, not the yachting industry, so people re mained skeptical about their use," he says. "It's one thing for some one like me to use the tools to design what I think is a really fast boat, but it's another for a naval architect or sailor to be lieve me and want to make those design changes. With 3D vis ual ization, everyone can easily understand and trust the analyses."

Fluid flow, says Team New Zealand's Schnackenberg, is one area where 3D visualization becomes most useful in determining an optimal design. Without visualization, we cannot see the movement of air and water, just the effects of disturbance. But by coloring areas of high and low pressure, "we suddenly have some understanding of this complicated phenomenon," he says.

For Team New Zealand, using sophisticated volume-ren dering codes and tools, such as Fluent's 3D CFD software to model fluid flow, enables the team to visualize pressure maps over the hull, keel, wings, and even the sails, and then make changes to the boat de sign based on what is occurring. "We can make the wings bigger or move them backward or forward, and from the flow visualization, we can now understand how that may affect the boat's speed," says Schnack en berg.
AmericaOne used a varied tool set to visualize water pressures on the keel and bulb of one of its boat designs. The varying pressures on the appendages are represented by different colors.




The designers agree that almost any design change results from a combination of numerous minute tweaks that are measured in millimeters and fractional percentages, so it is virtually impossible to link a specific change to an increase in boat speed. Using analysis and visualization technology, however, enables the teams to test dozens of tiny changes and then determine whether the cumulative result improves overall performance, even if it's only by a second or two.

Perhaps the biggest challenge comes in analyzing the effects of both wind and water-two entirely separate phenomena. This crucial but difficult task requires a thorough understanding of hydrodynamic forces associated with the hull, keel, and ap pen dages, and aerodynamic forces associated with the sails and mast. Robert Hook, sail designer for AmericaOne, likens the overall yacht design to building an airplane that is half underwater and half above water. "The trick is to minimize the amount of drag being created under the water and to maximize the horsepower being created by the sails above the water," he says.

Unfortunately, outside of the yacht industry, there is little need to concentrate on these dual constraints, which has resulted in a dearth of high-end design and simulation tools that serve this purpose. Consequently, some teams, such as Prada, are taking advantage of the newer open CAD systems and engineering simulation packages-such as Parametric Technology Corp.'s Pro/Engineer, ICEM CFD software, and Computational Engineering International's (CEI) EnSight-and adapting them to their specific needs.

Even with these tools, determining fluid flow for a yacht design is extremely complex, because the amount of water touching the boat surface constantly changes with each wave. Further complicating this analysis is the fact that current CFD offerings work independently from the other programs used in the process, such as the CAD software to establish the boat's geometry. Prada, however, has overcome this obstacle by establishing a pathway so that its Pro/Engineer modeling data, Pro/Mechanica structural anal ysis information, ICEM CFD mesh generator, and EnSight post- processing software work together seamlessly without the manipulation usually required to share data between each program. "By combining 3D solid modeling with conventional CFD, we've been able to compute the aerodynamics to the accuracy demanded by the America's Cup race-something that's not typically done in the yacht-design process," Egan says.
Team New Zealand used computational fluid dynamics to identify regions of high pressure (shown in red) on the keel and bulb design of its boat.




This technique enabled Prada to accurately compute the area of the boat surface touch ing the water. "You're computing [the amount of water touching] the boat to within 1 sq. mm, which is necessary if you want to see the changes in drag that will make a difference," says Egan. In fact, just prior to the first round-robin, Prada designed a new keel that resulted in a change of 5 sq. mm of surface area, which may not seem like much, "but that's the level of detail that we were concerned with," he says.

AmericaOne, mean while, is using a variety of commercial CAD, CFD, and visualization software along with proprietary sim ulation codes that have been developed at companies such as Ford Motor Co., Pratt & Whitney, and Science Applications International Corp. "Although the sailboat simulation problem represents a unique combination of hydrodynamic and aerodynamic effects, we have developed a system that combines ex isting capabilities in each of these areas, instead of trying to develop our own single system that does it all," says Amer ica One de signer John Kuhn.

By using this approach, AmericaOne has created software that finds the operational equilibrium between hydrodynamic and aerodynamic forces, and "provides an indication of how a complete design performs for a specified set of environmental conditions that model the venue in Auckland," Kuhn says. This will play a key role during the lengthy racing period, when the group expects a general lessening of the wind strength. "So the design we want in the beginning is not the design we want to use at the end," AmericaOne's Billingham adds. This system also enables the team to examine the performance trade-offs between boat length and sail area, which are linked to each other according to the IACC rules.

And then there's Team New Zealand, which uses Yacht Research International's WinCup Velocity Prediction Program (VPP) to establish a relationship between the forces of wind and water. "When analyzing tank results, for instance, you can seldom consider the hull in isolation; different hull shapes may have different stabilities, and hence, affect the sail forces and resulting equilibrium," Schnackenberg says. The New Zealand team found the program so useful for analysis that, for this Cup defense, it invited the developer, Clay Oliver, aboard as a principal designer.

While Schnackenberg strongly emphasizes the importance of the program, he-like the other designers-declined to provide exact details concerning innovations uncovered during the design and analysis process, because competitors could use the information to alter their boat designs during the America's Cup racing period.

While simulation technology has not completely re placed physical testing, thanks to the software and hardware ad vances within the last few years it is providing teams with ad van tages never before seen in the history of the America's Cup, such as the ability to analyze the entire boat. In 1995, the New Zealand designers were using the technology to analyze parts of the boat-hull, keel, and ap pen dages. But now, Egan says, the design team at Prada is looking at the entire boat to answer questions such as, What kind of effect does wind angle have on the rudder angle? "Suddenly we are looking at the interaction of the whole design," he says. "We can drill down another layer and look at the secondary effects, and design an appendage, such as a rudder, not only to serve its primary purpose, but also to simultaneously benefit a different variable."

New Zealand, like Prada, is extending its analysis to the "sub-layers" of its boat design. Using team member Chris Mitchell's Access2 mast and rigging anal ysis program, for instance, gave New Zealand the con fidence to try a variety of rigging configurations, which re sulted in a new de sign. "A mast costs a half-million dollars, and if the rigging is wrong, it can bring down the mast very quickly," Schnackenberg says.
Critical details: Team New Zealand designed this tiny titanium rigging bolt in SolidWorks and CosmosWorks FEA to withstand forces of 4 to 5 tons.




AmericaOne is also analyzing numerous design variations of the boat's hull, rigging, and appendages as constrained by the IACC rules. For instance, when the designers chose to increase the sail area to provide additional aerodynamic horsepower to the boat, they had to compensate for it by reducing boat length or increasing total weight. Use of computer simulation to supplement field experiments now enables the group to analyze and evaluate more configurations that fit these constraints within a shorter time frame. "Instead of having a new design every month or two, we're now able to model fleets of boat designs in that same period," notes Billingham.

Team Prada is using the advances in analysis and visualization to concentrate on making countless minute changes, which, like loose change, add up. For example, by making about 25 minor tweaks to the size and shape of its keel design just prior to the start of the Louis Vuitton Cup, Team Prada cut about 40 seconds off its race time, which it then could test in a tow tank. "Without this technology," Egan says, "there's no telling how many years of testing it would take to figure out the right combination of so many tiny changes."

Team New Zealand is also concentrating on the smaller picture, using visualization and analysis to improve the tiniest portions of its boat. The failure of one little component can spell disaster, Schnackenberg says. If the sailboat cannot sustain the extremely heavy loads it incurs, a component will fail. Sails can tear, masts break, or worse, a boat can sink, as oneAustralia did after its hull split open during the 1995 regatta.
AmericaOne used proprietary simulation codes to analyze the various pressures on its spinnaker during a downwind course.




The key to using 3D technology successfully in the America's Cup, Egan maintains, is to have a strong initial design and the flexibility to make minor but necessary modifications once the racing begins. "The general assumption is that once the boat is designed and you're ready to race, that's the end of the computer design phase-which is far from true," Amer ica One's Billingham says. "Rather, the demands increase as you try to understand what you're witnessing and experiencing on the course."

According to Egan, you can start off strong with a good design, but if you don't make any changes to your boat when the racing starts, the whole fleet will overtake you. "During the previous Cup, from the day New Zealand started racing until the day it won, the team managed to increase the boat and crew speed by more than four minutes," he says. "So all the tuning Team New Zealand did on the yacht during the trials was as critical as all the design work we did up to that point."

Meanwhile, America One will rely on its base of Autodesk Auto CAD 2000 files to communicate with ven dors if a part breaks or must be re de signed during the race. "With AutoCAD 2000, we can describe a problem and distribute the files electronically so several vendors and engineers are working on the problem within a half hour," Bill ing ham says. "If you can't have the boat repaired and back out on the water the next day to go racing, you cannot be competitive."

Even though the advantages of making additional changes are apparent, not every team will commit to using active analysis when the racing begins. For those teams not taking advantage of this technology in Auckland, Egan predicts they will be in double jeopardy: They will fail to whittle seconds off their race times, and many will also turn down the wrong paths looking for a solution to create a faster design. "They will see that you've made a 40-second improvement, and they'll think that it is a result of a major design change, rather than a collection of small tweaks," he says. "So they begin to go in the wrong direction."
Using CEI's EnSight CFD software enabled Team Prada to visualize the CFD analysis of airflow around its spinnaker sail design.




According to AmericaOne's Kuhn, there is still a lot about Mother Nature that cannot yet be modeled on a computer. But he believes that visualization and analysis allow the team to visually interrogate everything it does. "We combine intuition, wisdom, and experience with our computer modeling. Without this ability, the various mathematical assumptions contained within even the very best modeling codes could lead us astray."

As computer-aided design and analysis technology becomes more robust, the designers expect that syndicates' reliance on it will become even greater in the future. "A hundred years ago, yacht de sign was 100% magic and 0% science," Egan says. "Over the years, those ratios became more balanced, and now, for the first time, computer simulation is helping us to understand that magic."

Karen Moltenbrey is an associate editor at Computer Graphics World.



Autodesk
San Rafael, CA
800-964-6432
www.autodesk.com

Computational Engineering International
Morrisville, NC
919-481-4301
www.ceintl.com

Fluent, Inc.
Lebanon, NH
800-445-4454
www.fluent.de

Hewlett-Packard
Fort Collins, CO
800-613-2222
www.hp.com

ICEM CFD Engineering
Berkely, CA
510-549-1890
www.icemcfd.com

SGI
Mountain View, CA
650-960-1980
www.sgi.com

Parametric Technology Corp.
Waltham, MA
781-398-5000
www.ptc.com

Yacht Research International
Annapolis, MD
410-267-7899
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