Will AC72 foil design win the America's Cup?

Foil shapes on AC72's

Boat development continues right up to the America's Cup Match. Foil shapes are getting a lot of attention.

The Protocol for the 34th America's Cup limits teams to 10 AC72 daggerboards (paragraph 29.7). All four teams launched their first AC72 with the same shape boards on port and starboard. Now they test different shapes in each hull - so they will be able to test more designs.

Emirates Team New Zealand

The second AC72 for ETNZ has curved boards and there is no line on the outboard side to pull it down. Photo: Chris Cameron

Their first AC72 launched with S-shaped foils with winglets on both hulls. When they launched their second AC72, the S-shaped boards were replaced by C-shaped boards and the board on starboard has a gentler curve. Team New Zealand used a pair of SL33 catamarans for testing while they built their AC72. They put wing sails on the SL33s and modified the daggerboard cases so they could test foils and learn to foil.

AC72 number 2 has curved boards

ETNZ launched their first AC72 with S-shaped daggerboards. Note the line outboard of the foil to pull it down.


ETNZ tested in SL33 catamarans while building their AC72. Image ETNZ Video

Luna Rossa

Luna Rossa launched their AC72 with straight boards with winglets and has tested S-shaped boards and boards with a kink rather than a smooth curve.

Note the line to pull the board down and compare with ETNZ's S-board in boat 1 and the curved board in boat 2. ETNZ seems to have gone to a different system to lower the boards in their second AC72.

Testing S-foil in Luna Rossa AC72. Image: Luna Rossa video

Straight board, sharp bend at winglet

AC72 Luna Rossa straight board with winglet. Photo: Pierre Orphanidis

Curved board with upturned winglet in Luna Rossa AC72


Artemis designed their first AC72 for "skimming" not "foiling." The daggerboards were J-shaped with no winglets and were designed to carry about 80% of the weight of the boat. This reduces drag but not nearly as much as in full foiling with the hull completely out of the water.

AC72 "Artemis" with J-shaped daggerboard and no winglet. Photo: Sander van der Borch

After speed testing with OTUSA in February 2012 they began modifications to increase foil lift (but not enough for full foiling) and to reduce aerodynamic drag. They have announced that their second AC72 will launch in late May and will be able to foil. Even before beginning modifications, they added a winglet to their rudders, visible in the photo below.

AC72 with J-shaped board with no winglet. Image: Artemis Video

Oracle Team USA

OTUSA launched their AC72 with straight boards with winglets. They broke one on their first day sailing. They modified a board from their trimaran that won the America's Cup in 2010 since it would take 3 months to build a new board.

OTUSA AC72 launched with straight boards with winglets.

After repairing damage from their October 2012 capsize, OTUSA relaunched boat 1 with different foils on each hull - a straight board with an upturned winglet on starboard and a curved board with a horizontal winglet on port. Videos usually show them foiling on the port board, so perhaps the starboard board is better suited to upwind sailing.

OTUSA relaunched their first AC72 with new daggerboards

Winglet shape - starboard daggerboard OTUSA AC72

Winglet on port daggerboard of OTUSA AC72

Updated 22 March 2013 by Jack Griffin