Artemis Racing unloading in San Francisco with the daggerboard aperture visible below the mainbeam
While the sailing world is still coming to terms with the concept of seeing 72ft America's Cup catamarans charging at 30kts plus, while fully out of the water on foils, the design teams are several steps further down the path.
So far only one style of foil has been seen - an S-shaped dagger board with a tip at right angles to the main part of the board, however a new type of hinged foil has been approved.
New diagrams released in a public interpretation by the Measurement Committee for the 34th America's Cup, show that a second style of foil could be used - and would be legal under the class rules.
The new foil style is similar to that seen on the high performance French trimaran, l'Hydroptere which at one stage was the world speed record holder with a run of over 50kts.
But instead of being contained within the hull of the AC72, as with the daggerboards seen so far, the new board is external and is just attached to the hull by a bearing, and supported by an external strut.
When raised it comes completely clear of the water.
Hinged Hydrofoil, with external strut, in the raised position. The 7metre radius is the maximum permitted by the class rules
The overall concept is within the maximum 7 metre length permitted for daggerboards by the America's Cup Class Rule.
Two options were put to the Measurement Committee for interpretation, one shows an external support, the second shows an internal control on the daggerboard similar to a canting heel.
In the decision dated September 6, 2012 Nick Nicholson, Chairman of the Measurement Committee stated: 'Nothing in the AC72 Class Rule explicitly prohibits the daggerboard concept shown in Figures 1a and 1b, provided the constraints of Rule 9 (Daggerboards) are met and the daggerboard and its installation otherwise comply with the limits and requirements of the Class Rule.'
Hinged Hydrofoil, with external strut, in the lowered position.
In a second string to its decision the Committee stated the same phraseology in response to the second concept.
In the America's Cup, there has been a long standing practice where a team can submit an idea for interpretation as to its legality by the Measurement Committee or International Jury - even though the matter may be hypothetical. The reason for the practice is that it avoids later measurement protests, which at that stage are acrimonious and avoidable with this advance warning procedure.
Once the interpretations are usually made public so that other teams can see them, and can make their design decisions accordingly.
It is not known which team has lodged the interpretation request. Both the two sailing AC72's seen to date have through hull daggerboards. Although Artemis has not been sailing the aperture for the daggerboard can be seen in one of her hulls as she was unloaded in San Francisco. Whether that is an aperture for a push-through daggerboard, or a location for a hinged foil remains to be seen. She also has what appears to be a sanded piece of hull topside above the daggerboard aperture.
Hinged Hydrofoil, with internal control strut, in the raised position.
Hinged Hydrofoil, with internal control strut, in the lowered position.
Les 5 corsaires de l'Hydroptere pour le record du monde du Pacifique. Jacques vincent, Jean Le Cam, Yves Parlier, Alain Thebault et Luc Alphan .
Close up of the hinged foil as used in l’Hydroptere. A different concept along the same theme using hinged daggerboards has been raised in the context of the 34th America’s Cup
L foil and rudder foil - AC72 - First Sail - August 31, 2012 San Francisco
Emirates Team NZ AC72 sailing on the Hauraki Gulf, Auckland NZ September 6, 2012