By Michelle Slade
February 6, 2003
Source: www.rnzys.org.nz

Alinghi's Jim Bungener is the team's resident CFD expert.

The orange lines that run horizontally across Alinghi’s jib and main are by no means an attractive addition however they are extremely functional, playing a major part in a complex operation used by the crew for perfect sail trim.

The system is called Sail Vision and was used by Team New Zealand in 1999, with prototypes under development back in 1995 in San Diego. It has been widely adopted as the standard to manage sail trim in this Cup event. Simply, the Sail Vision system uses cameras in the mast that take images down the mast at the angle of the sails, the resulting data helps the crew perfect their sail trim.

Alinghi team member Jim Bungener is a specialist in the area of computer simulation of fluid flows across air and water and is the main guy in the Swiss design team working in the complex field of CFD – computational fluid dynamics.

Watching Team Alinghi training in the lee of Rangitoto Island this week in a very light 6-8 knots of breeze, Bungener described the Sail Vision system and the complex process used to improve sail shape.

Images are taken from the cameras located atop the mast. Images are taken down the mast at the sails then sent automatically to a computer on board the Alinghi chase tender. The computer analyzes the line detail on the images, and that in turn provides the algorithm that defines the orange lines and performs a perspective correction on each line - providing the 3 dimensional shape of the line.

This information is relayed back to both SUI-64 and SUI-75, and the crew are able to deduce the important numbers which help define the twist of the sail, the depth of the sail and the camera location of the draft fore and aft. The result is that crews can tweak and trim until sail trim on both boats is equal, the goal of two-boat testing. With two identical sets of sails powering the boats, it’s much easier to remove one parameter at a time in the training process.

Said Bungener, “We are trying to make as many things as possible equal and the great thing now is that we can quantify the detail required, both for the jib and main.”

Bungener works very closely with the EPFL University in Lausanne, often sending data to their Alinghi research partners at the university for more detailed analysis. While it may seem that we are already at the height of technical innovation Bungener says there’s still a way to go.

“Computers are just starting to become powerful enough to manage requirements of sail programs,” he explained. “The precision of hull simulations can also be improved and even with subtle details, there are still gains to be made, in building materials that will result in lighter boats and stiffer sails for example.”