Land Rover BAR
British Challenger in the 35th America’s Cup
The America’s Cup is considered the pinnacle of yacht racing. Countries compete for the oldest trophy in international sport in yachts that represent the cutting edge of yacht design and technology. The America’s Cup match is held between only two teams, the defender and one challenger. Cape Horn Engineering was proud to be at the core of the design team of Land Rover BAR, the British Challenger in the 35th America’s Cup. The ultimate goal is to #BringTheCupHome, where it all started in 1851.
Cape Horn Engineering was responsible for providing CFD analysis to the design team and was involved in the overall concept design of the boat and the performance prediction.
CFD analysis was required for multiple aspects of the design of the solid winged foiling catamaran and the CFD team spent a substantial amount of their time producing comprehensive aerodynamic and hydrodynamic models to feed the velocity prediction programs or VPPs and on the man-in-the-loop simulator. Thousands of simulations were required each time. In order to do this, all processes had to be streamlined with extremely efficient workflows and simulation setups.
One key benefit about working for America’s Cup teams is having access to large resources, in terms of thousands of licenses and computer cores. Our main tools were Simcenter STAR-CCM+ for the simulations and NX for CAD, but across other departments, we also used additional Siemens products, such as Teamcenter, HEEDS, and Fibersim.
Rudder in Wake of Daggerboard
The simulations with the rudder in the wake of the daggerboard were free-surface simulations of the catamaran foiling on one daggerboard and the two rudders. The leeward rudders inevitably is in the wake of the daggerbord in front and is much influenced by its wake. In these simulations, which were run for different boat speeds, 4 degrees-of-freedom were allowed, and these 4 motions were adjusting during the simulation until they balance 4 target forces or moments coming from the VPP. The target side force from the wing or sail plan was balanced by the yacht drift or leeway. The yacht vertical force, mainly the yacht displacement, was balanced by the rake of the board. Target pitch and yaw moments from the VPP were balanced by the rudder base rake and rudder angle respectively.
For the output, we processed a myriad of information. The total drag and righting moments of the whole system were the main results we needed to achieve our objectives.
Data was also processed for the individual forces and moments on the board, leeward and windward rudders, blades and elevators, leeway of the yacht, board rake, rudder base rake, rudder angle, rudder shaft torques, bending moments on blades and elevators, areas prone to cavitation ( for instance on the board elbow or rudder to blade junctions ) and many more details of the flow such as the flow angles in planes in front of the rudders.
The main outputs were the total drag and heeling/righting moments. These were combined with derivatives coming from the VPP to obtain the VMG gains and losses. The VMG is the velocity made good or combination of boat speed and course angle relative to the wind. The end result of these simulations were a direct measure of the ability of the yacht to complete the race in the quickest manner, comparing different board candidates.
