sail-world.com -- America's Cup: Oracle Team USA show off hull lifting foil developments
America's Cup: Oracle Team USA show off hull lifting foil developments
Mon, 25 Jun 2012
Oracle Team USA have released their first images of their L-Board daggerboards and T foil rudders, which have been used in a testing session in San Francisco.
The foils have been fitted into one of the four AC45's used by Oracle Team USA, the Defender of the America's Cup. The use of the foils is not permitted in the America's Cup World Series, but do provide an indicator as to what is likely to be seen on the team's first AC72, scheduled for launch in July 2012.
The effect of the foils is very dramatic, lifting both hulls completely clear of the water, increasing stability and reducing drag - both of which will substantially increase speed, providing the 'flying' can be controlled.
The function of both foils is obviously to generate lift, the L shaped foil is reasonably sizeable extending to at least half the beam of the hull.
The force on the daggerboards seems to be sufficient to cause the leeward one to bend under load.
Normally the L-daggerboard would provide the majority of the vertical lift and the rudder would provided a little lift but would be controlling the trimming angle.
The control mechanism to control the foiling/flight is not apparent. There is no wand as used in the foiling moths, and it may be that the angle is computer controlled. Certainly the crew don't look too pre-occupied with maintaining flight, and with three sails set in one of the shots, and at least one crew member on a winch, would not leave too many spare hands.
The purpose of the bulb on the base of the wingsail is unknown. It is maybe a more sophisticated wing sail control.
Remember to click on the expansion option in each shot to see the full screen view.
During last week’s training session in San Francisco, Oracle Team USA sailors were learning to fly on hydrofoils. An L-shaped daggerboard and T-shaped rudders were fitted to one of the team’s AC45s and the platform took flight.
Foiling is not a new phenomenon. Many high-speed ferries rely on hydrofoils for a smooth ride for their passengers. In sailing, the Moth class has experimented with foils since the early 1970s, about the same time that designers such as Rod Macalpine-Downey were experimenting with foils at Weymouth Speed Week. In 2009 the 60-foot foiling trimaran l’Hydroptere set the record at 51.36 knots.
Foils help reduce draft and increase speed. They are a very cost efficient way to gain performance. You can research them extensively in the computer before you build them, and they are small scale, compared with a wing. The foil project is a continuation of one started on USA 17, the team’s 90-foot trimaran that won the 2010 America’s Cup.