You probably know that the AC Class yachts that will race in 2017 are largely one design – the shape of the wing, the hulls, the pod under the wing and the crossbeams are all fixed by the class rule. The same is true for cockpits and grinding pedestal positions. This leaves aerodynamic fairings, daggerboard shapes, rudder shapes, wing internal structures and control systems as the area for the designers to work their magic. The teams have been testing design ideas on their “AC45X” experimental boats – sometimes called “turbo” or “sport” boats.
In light air the boats will need longer wings on the daggerboards to provide enough lift for foiling. In stronger winds teams will use shorter wings with lower drag. Crossover conditions will be challenging to decide whether to use the high lift or the low drag boards. There has been a lot of talk about upwind foiling and foiling tacks, but those techniques require sailing longer distance over a less direct course.
You can see the long wing and the reverse curve of the daggerboard on the port side of Emirates Team New Zealand’s AC45X test boat. On the starboard side you can see how the reverse curve gets the board out to the maximum beam to increase righting moment. (The sea otter seems to want a close look.)
In a New York Times article, Oracle designer Scott Ferguson talks about longer daggerboard wings for light air and shorter daggerboard wings for medium to heavy air. Like the Kiwis, Oracle has been testing longer foil wings as this photo shows:
Rudders and boat building strategy
Groupama Team France mounted their rudders in the hulls so they can save money by using the rudders from the test boat in their race boat.
Land Rover BAR and Emirates Team New Zealand wanted to test the geometry of the slightly longer AC Class race boat, so they built special rudders that could be hung on gantries off the stern.
Team France and ETNZ will use most of the components of their test boat to build their race boat, saving money. Essentially, they will just change the hulls. Like Oracle, Artemis and Team Japan, BAR will have a test boat and a race boat in Bermuda so they can do two boat testing.