(Almost) a clean sheet of paper
Moving from Archimedean craft to foilers – and particularly to foils – demands a new mindset as much as it does a new approach to composite construction and engineering
Persico Marine is a name associated with the building of cutting-edge race craft, having been deeply involved with the Volvo Ocean Race boats, the America’s Cup and many more. This year the boatyard delivered 20 foils alone, and Persico’s order books are filling fast for more.
When sailing boats literally take off, it naturally changes the game quite a bit. Not only the sailing, but also the design and construction. Especially so when we look at larger racing yachts. We have become used to foiling dinghies of the International Moth class, which has always embraced new ideas and technology almost in a pioneering manner. But designing and building foiling sailboats of substantial sizes like the AC catamarans, last seen racing in Bermuda at speeds well in excess of 40 knots, is quite a different story. So what are the technical challenges in building these foils? After all, appendages like keels, rudders or centreboards are basically all foils. Now, however, we are talking about profiles more akin to aircraft wings than traditional sailboat keels. ‘Boats without foils are probably around 40 per cent slower,’ says Mark Somerville, general manager of Persico Marine’s racing unit. ‘This changes the whole way of sailing. Yesterday, it was all about VMG,
76 SEAHORSE
now it is the apparent wind. During the last America’s Cup regatta, the general public could not really tell if these boats were going upwind or downwind. And more and more classes are now changing to foils.’ As different classes and types of boat switch to foiling, from the Moths to the extreme racing machines for the America’s Cup, many different types of foils are designed. ‘These are all made with different technologies, different processes’, Somerville explains. ‘We work very closely with designers and engineers. We have a wealth of experience to share with designers. This close collaboration is necessary to keep failures down. All the loads of the entire boat must go through the foils. You can’t have any flaws here. The level of expectation and precision is much higher here than in any other part of the boat. Also, at the same time, foils are designed to be as light and small as possible.’ Marcello Persico, CEO, adds: ‘This is a lot of responsibility. The quality of the part they are flying on actually ensures the safety of the crew and the boat. Because of this, we develop ever more steps of quality control.’ This is especially true when Persico is not building the entire boat, but “just” delivering the foils to another builder. Another crucial part,
The Italian America’s Cup team Luna Rossa launched their first Persico built AC75 at
their base in Cagliari on 2 October. A particularly notable
commission for Persico is the contract to supply all of the foil arms for all the teams in the next America’s Cup. The foil arms are built to a strict one-design standard at 300kg each with a weight tolerance of just 1kg
obviously, is the connection of the foil to the hull. For the last generation of Volvo Ocean Race yachts, Persico points out that they were in control of the tolerances of all foil-bearings in the hulls. Progressing from this experience, Persico now often also supplies the bearings for the hulls together with the foils – otherwise, this could be a potentially weak spot. What about other weak spots? ‘Foils are basically just another form of appendage,’ Somerville says, ‘but they are different today, keels are much stronger. Some are hollow and some have solid carbon stocks. These are very difficult to manufacture, especially as size increases. In a thicker laminate you must know exactly how to deal with, for example, thermal effects. Things literally get hot when making big laminates. We are dealing with thermal expansion and resin reaction – resin can become too hot, begin to boil and even burn in the process! Then there is also distortion during the curing process as resin shrinks when cooling down. All this is quite complex, but needs to be fully understood to manufacture these parts. The foil itself is stiffer and stronger than the tooling made for it and can, if the process is not accurately controlled, distort the tooling and its own shape. However,
LUNA ROSSA/STUDIO BORLENGH
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