Friday, April 17, 2009

Single kayaker seems outmanned against Olympic-style K4 craft with four oarsmen

At the outset, the race seems lopsided. A single kayaker is outmanned against an Olympic-style K4 craft with four oarsmen. As expected, the foursome achieves an early lead. What happens next, however, is miraculous—what onlookers could only explain in terms of deus ex machina. The kayak accelerates to triple its speed. The kayak wins by more than a length.

Einar Rasmussen arranged the informal 200-M challenge as a demonstration. The four-time Norwegian kayaking champion and physics expert and his partner, kayakbuilder Peter Ribe, have created what they hope will become the fastest human-powered craft in history—the Flyak.

There’s nothing supernatural about the Flyak’s acceleration, as the name implies, the Flyak “flies.” Its wings are underneath the water, in the form of front and rear hydrofoils. The more the surface area of a hull touches the water, the greater the vehicle’s resistance.

Once it reaches a certain speed, the Flyak’s hull does not touch the water at all.

The two aluminum foils are positioned at a slight tilt. The Flyak begins the race at a disadvantage, with its hull in the water and its underwater foils creating even more drag. As a result, paddling the Flyak is more inefficient than a normal kayak during the initial strokes.

But once the rider works the speed up to roughly 10 KMH (6 MPH), the Flyak is ready for take-off. The energy on the oblique foils propels the hull up above the water’s surface. Once airborne, the velocity gained from paddle strokes increases dramatically. Theoretically, the Flyak can achieve speeds nearly twice as fast as conventional championship-level racing kayaks.

Not everybody can fly, unfortunately. The big limitation of the Flyak is cardiovascular. “You can’t go very long distances with this craft,” says Fredrik Wenstøp of Pivot, the Oslo firm that formulated the commercial design. “It takes very intense energy for the paddler to keep up on the foils.”

Rasmussen, too, emphasizes that the Flyak is a highly specialized racing vessel that requires a good deal of skill and endurance from the kayaker: “The total weight of the kayaker and hull dictate the area of the foil pair. Kayakers with a high level of fitness can use smaller foils, and thereby reach higher speeds,” he says. “You could say that the Flyak is like a Formula One car—fast, and just as practical.”

The foils are removable and interchangeable through a hand-screw apparatus behind the seat. By removing the foils, the craft can be maneuvered like a conventional kayak. The bottom surface of the boat’s 17’ carbon-fiber hull, says Wenstøp, is not dramatically different than other racing kayaks. Wenstøp’s firm is familiar with creating curves, more often for aesthetic, rather than aerodynamic purposes. Pivot specializes in building 3-D models of complete forms.

Wenstøp used a MicroScribe digital scanner to record points directly off the inventors’ hand-sanded prototype. The 3-D points were imported into the surface modeler Rhinoceros, where Wenstøp could flesh out a wireframe surface.

“The biggest challenge was to get the shape to conform exactly with the scanned 3-D points,” says Wenstøp. “Products like the foil kayak are dependent on good surface modeling to achieve both functional and aesthetic requirements. We needed 100 percent control over every curvature in the model. Controlling curves can be done with pinpoint accuracy in Rhino, which also has many measuring tools to check tolerances and dimensions. By using Rhino as our main modeling application, we have the kind of control needed. Rhino also shortens the time it takes to make all digital documentation: mockups, rapid prototypes and then the final production-ready models.”

The top of the design is fairly unique, with the rider seated on top of the boat, rather than inside it. “The Flyak is a completely water-tight body that cannot take in water or sink. This makes it much easier to learn the technique, as the paddler can just climb back on without having to get the boat out of the water to empty it,” explains Wenstøp.

The position of the seat was adjusted iteratively during modeling and prototyping. “In developing the sit-on-top cockpit, several hand-built models were digitized and reconstructed in Rhino,” says Wenstøp. “We used the MicroScribe digitizer and a haptic modeling device from Sensable for the sculpting of soft shapes. When we were satisfied with the results, we CNC-milled a plug and molded the cockpit with vacuum bagging.”

The other departure from convention lies in the steering. Riders keep the Flyak on course with a foot on a steering pin, which controls the front foil like a rudder. Riders wishing to master the art of kayak flight will have to get accustomed to some unfamiliar elements, including steering, seating and balance, not to mention the athleticism needed for the intense sprints.

“It has a thin racing hull, which is by design unstable, and the front steering and foil maneuvering does not make it much easier. There are no flaps or any other mechanisms that sense the surface to keep the Flyak level,” says Wenstøp. “It’s a difficult craft to learn.”

One of Rasmussen’s long-term goals is for the Flyak to replace racing kayaks in Olympic competitions. Along the way, there are other milestones for which to reach. One is to break the world record, which achieved a speed of 32 KMH (20 MPH). In the race against the K4, the Flyak was clocked at around 27 KMH (16 MPH). Through training of the rider and tweaking of the design, Rasmussen is confident the Flyak will eventually surpass the current benchmark.
The invention is now in production in Portugal, and will soon become commercially available from NELO, one of the world’s largest kayak producers. The inventors’ Oslo-based company, FoilKayak AS, will offer the foils and accessories.


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