Sensor Warns of Yacht’s Breaking Point

A new fiber Bragg grating sensor system that measures the forces acting on a yacht’s sail could help to detect weak points in time to warn yachtsmen when a boat has reached its breaking point.

In the world of racing, tiny details can make the difference between victory and defeat. The urge to break new records has turned boat building into a high-tech business, and the racing yachts that compete at international regattas today are sporting machines designed to reach top speeds. The process to optimize such boats has been ongoing for decades; until recently, it looked as if a limit had been reached.

Now, scientists from the Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute (HHI) have developed “nerves of glass” sensor technology that can measure the forces that act on hulls, masts and sails to detect points of weakness on yachts. The technology originally was created to monitor wind turbines, where rotor blades and cables are exposed to high loads.

To measure the forces acting on the sail, researchers have fitted it with a web of glass fibers. (Image: © Fraunhofer HHI)

At the center of the new technology are fiber Bragg gratings — microscopic structures integrated into the glass fiber at defined intervals that alter the refractive index. Light racing through the glass fiber is reflected by these lattice points. The wavelength of the reflected light depends on the distance between the microscopic structures: Every stretching or compression of the glass fiber alters the wavelength.

“With fiber optic sensors, we can detect delaminations and even cracks at any early stage — long before a part breaks or fails,” said professor Wolfgang Schade. “All you need is a fiber optic cable, in which dozens of sensors can be fitted.”

To measure the reflectance spectrum quickly and cheaply, the Fraunhofer team developed a mini-spectrometer consisting of a chip that splits light into various frequencies. They were able to draw conclusions about the forces currently acting on the glass fiber by analyzing the frequency spectrum.

The idea for the sailboat measurement technology came to Schade during a sailing voyage in the fall of 2010.

“Sailing is all about making best use of the win and being as fast as possible,” he said. “At the same time, you also have to avoid pushing the equipment beyond breaking point. Fiber optic sensors can help to determine the forces acting on hulls, masts and sails during the journey in real time.”

In collaboration with sailcloth manufacturer Dimension-Polyant, the team fitted a web of glass fibers containing 45 measuring points onto a mainsail and a genoa. On a test journey, measurements were conducted on the sails.

“It turned out that the tension in the head, right at the top of the sail, was greater than assumed,” said Jens Nickel, who runs the a sail workshop in Stade. “However, the strain on the clew, the lower aft corner of a sail, and on the entire leech area, the aft edge of a sail, was smaller than had been thought.”

He used this data to optimize the sail by reinforcing the areas that were subject to greater stress and using lighter material in the areas that were less stressed.

“We have now fitted sail battens with fiber optic sensors, which will help competitors in future to find the optimal trim, i.e., the sail position at which the boat travels the fastest under specific wind and wave conditions,” Schade said.

The results from the sensor technology are accessible anywhere onboard at all times, and Schade’s team is developing an app that allows crew members to access this real-time data from their smartphones. The new measuring system will soon launch under the name NextSailSystem.

For more information, visit: www.fraunhofer.de