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CNC helps windsurfers improve performance
John Lewis, Northeast Technical Editor -- Design News, April 23, 2001
New Hyde Park, NY —A more efficient airfoil design combined with low-cost computerized manufacturing technology is helping professional windsurfer racers, such as Anders Bringdahl, improve their performance and win races.
According to George Klein, general manager at Techno-Isel, five of the top 10 windsurfers use boards designed by Gerhard Opel and his group. Opel has combined his 14 years of experience as an aeronautical engineer with his fondness of board sailing, and now designs rudders for windsurfing boards. And thanks to a Techno CNC router, the group produces fins to precise aerodynamic profiles at a cost that is less expensive than hand-production.
In the past, sporting goods manufacturers typically used duplicators or power tools to build complicated wood, plastic, and composite components in volumes too low for expensive automated machines. But now, more companies are modeling their products in CAD software and then producing them on a new generation of low-cost CNC routers that duplicate the computer-aided design geometry used to define the part to an accuracy of ±1 mm.
Often, this makes it possible to improve the performance of the product by increasing its geometric complexity. It also allows systematic changes and experiments to improve product performance. Yet the new machines cost as little as $20,000 and can run without operator attention except for setup, which keeps costs low.
For example, Opel's high-performance rudder fins are critical to windsurfing board performance. Boards are generally 7-ft 8-inches to 9-ft 4-inches long, and normally operate in a planing condition with only the rear one-fourth to one-third of the board touching the water. The small fixed fin at the rear of the board provides counterforce and operates in much the same manner as an airplane wing. But unlike the wing of a conventional airplane, the fin must work symmetrically in both directions—similar to fighter and aerobatic airplane wings that are designed to function equally well upside down.
While racing windsurfing fins have traditionally been designed by trial and error, it occurred to Opel that optimized airfoil designs developed for aircraft could be transferred to sailboard fins with little or no modification. The problem in implementing this idea was how to produce these airfoil designs to the required level of accuracy.
Fins for mass-produced windsurfing boards are produced from injection molded plastic. These fins are not used for high-performance boards because the injection-molded fins change their shape slightly as they cool.
Fins for high performance boards are traditionally produced by far more expensive manual methods. Typically an experienced craftsman will first build a series of templates describing the fin's contours. Then the craftsman uses these templates as guides in producing the final form with a hand grinder. It usually takes approximately one day to complete a high-performance fin, according to Opel. However, the accuracy of manual production leaves much to be desired. Consequently, it's necessary to test the fins in the water to determine whether or not they are effective. And top-name competitors typically accept only two out of every 10 fins produced by these methods, Opel adds.
"When I originally developed the idea of building fins according to optimized aerodynamic profiles," Opel explains, "I assumed that it would be necessary to build them using conventional manual techniques. I knew we could achieve much greater accuracy with CNC machining, but I couldn't consider it seriously because I assumed it would be a $100,000 investment, which unfortunately couldn't be justified because the market for high performance sailboard fins is just not large enough to justify such a large expenditure."
Then Opel discovered the Techno CNC router. "Now it takes only 4 hours to produce each fin," explains Opel, "and I get better accuracy and part-to-part consistency than with the more expensive and time consuming manual methods."
The CNC router concept is clearly an idea whose time has come in the sporting goods and recreation equipment arena. It makes it possible to improve the performance of such products by allowing complex geometries to be produced to a high level of accuracy and repeatability at a fraction of the cost of traditional CNC machining equipment.
For more information about CNC routers from Techno-Isel: Enter 539
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