A year ago, Emirates Team New Zealand lost the America’s Cup by just one second. That won’t happen again, if naval architect David Le Pelley has his way.
Le Pelley and the team at the University of Auckland’s Yacht Research Unit have developed a computational testing system to shave seconds off the speed of the next America’s Cup yacht.
Its purpose is Computational Fluid Dynamics (CFD)— in non-geek speak, that’s a numerical way of working out how fast the sails are.
Typically, wind flow on sails has been tested with smoke and mirrors—figuratively speaking. A camera mounted on the mast films how smoke behaves around the sail. But this technique is only really effective for upwind sailing, as when travelling downwind the sail obscures the camera. The highly curved surface of the sail also makes measurement difficult. “It’s been completely unfeasible to do CFD in an affordable way on downwind sails so far,” says Le Pelley. “The geometry hasn’t been possible.”
The new system works by scanning the sails using a mirror, a rotating motor and a laser, then sends the data to a computer 1,000 times per second for analysis. The laser scanner sits inside a scale model of the boat and determines the shape of the flying sail. It allows designers to analyse the flow of wind on the sails and test changes made on the boat.
“For instance, you can take the information back to sail designers and say, ‘You need to take depth out of this seam or that seam,’ and then you can retest and see the difference it’s made,” says Le Pelley.
When used with the twisted flow wind tunnel, the laser will be one of the only full sail scanning technologies available in the world, and used for Team New Zealand. “It will be a fundamental jump in sail technology for downwind sailing,” says Le Pelley.
The new system will be of key interest at the international High Performance Yacht Design Conference hosted by the university in December.
When the twisted flow wind tunnel opened in 1994 it was the only facility of its kind in the world. It’s also used to test aerodynamic pressure for cyclists and model Auckland city buildings to predict drafts.