were also a consideration.
‘Chris Mitchell analysed the short- to-tall configurations with varying amounts of twist to balance the joint loads, shroud loads and stability,’ Drummond notes. ‘When the wing is untwisted, the head falls off to leeward; with maximum twist, the head is lifting to windward and the upper leeward shroud carries a higher load.’
Within the modular framework of the new three-configuration rig, the biggest changes are internal. Gone are the mechanical rope and pulley control systems, replaced entirely by hydraulic and electronic controls. ‘Wing camber is controlled at five heights with hydraulic rams pushing or pulling directly on the flap,’ says Drummond. ‘The accuracy is expected to be 0.2° and the process of calibrating the fleet is simplified.’ At CBC, enormous effort has gone into establishing a production line that will ensure repeatable precision in the construction process. More than 300 components go into each wing, with the carbon fibre elements produced on graphite tooling board or carbon shell tools and assembled on CNC jigs.
The finishing and detailing of the internal structure is outstanding with 3D printed titanium fittings for the ram attachments and bearings and custom manifolds for the hydraulics. Extensive tooling means that many of the carbon frame elements are standardised square hollow sections as opposed to nomex cored. Intense optimisation by Paul Bieker and Pure Design & Engineering was required to mitigate against buckling of the thin walls.
‘Flap flexibility has also been a big focus with this generation of wings,’ says composite engineer and CBC general manager Susan Lake, pointing out the absence of shear webs. ‘During the America’s Cup, we were building less and less stiffness in the shear, so the flaps could generate more twist.
Above: the new wingsails were tested rigorously to ensure that they really are all identical. The old sailsʼ rope-and- pulley control systems have been replaced by hydraulic and electric controls. Camber is adjusted at five different heights by a series of hydraulic rams which are expected to achieve an accuracy of about 0.2°. Right: the production line at CBC has been
very carefully designed to guarantee repeatable precision at all stages of the (very complex) construction process.
More than 300 components go into each wing including 3D-printed titanium fittings and bearings,
custom-made manifolds for the hydraulics and precisely tooled carbon fibre elements
‘The designers have pushed that further this time, resulting in the removal of shear webs altogether.’ Separating the sections to
reconfigure the wing is achieved by undoing three bolts and unplugging the hydraulic and electronic lines. ‘Making that change would take about an hour,’ says Nathan Libby, who is charged with the electronic systems. ‘It is pretty much a case of plug and play with connectors at each joint. It is quite an intelligent set-up. You do not have to recalibrate the whole system every time you change the rig configuration. The yacht will know automatically which configuration is in play.‘This is a massive step forward from the old system of ropes and strops and pulleys. The wing is much more controllable and much more accurate. ‘It moves a lot of hydraulic oil very quickly. Tack to tack is about two seconds at the moment. It has the potential to be even faster, but we are taking it gently at first. The range of movement is also greater, about 40° compared with about 25°, providing a lot more twist than before.’ The hydraulics involve three carbon fibre accumulators, two at the base and one at the top to maintain even oil pressure over a vertical span of up to 29m. Each hydraulic line has its own manifold and control system. ‘A lot of the refinement is based on the efficiency of the system and how the individual control lines interact with each other and how power is managed and distributed around the system,’ says Brad Webb. Like most of the people involved in this project, Webb is a veteran of multiple America’s Cup campaigns. He notes that the F50 project has required a distinct change of mindset from single solutions for a one-off campaign, to series production for a fleet of one-design yachts competing in multiple events at multiple venues over an extended timeframe. ‘After 20 years of working in an America’s Cup environment, it is quite hard to change that thought
process where the focus is on finding the lightest and most efficient solution and reliability considerations only come at the end,’ he says. ‘With this project, reliability choices have to be made at the beginning or we are not going to get through the season. ‘It is like having a devil and an angel on each shoulder, one saying you have to make it as light as you possibly can and the other saying it has to last through five or six events, with only so much time and resource to get things done. When you are a couple of days out from a regatta and you have six or seven boats all having the same issue, you have a real scramble on your hands.’ Susan Lake agrees: ‘The big difference is in the tooling. Because we are building eight of everything, you can invest in time and tooling. There are decisions you can make when you have a production run that are more efficient.’
Notwithstanding the mindset shift
towards greater margins of reliability, the new wing – with all the electronics and the hydraulic accumulators, rams and oil lines – weighs in at less than 12kg over the minimum weight specified in the 2017 America’s Cup Rule. ‘Everyone is pretty comfortable with that,’ Lake smiles.
www.corebuilderscomposites.com q SEAHORSE 71
CHRIS CAMERON
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