Wingsails permit aerodynamic efficiency and performance unthinkable with traditional sails, for they are made with innovative materials that guarantee great rigidity. But at the same time wingsails create great problems in logistical handling, for they are really rigid, and very different structurally from soft sails though they can be folded. For this reason they are exclusive to the America’s Cup and the less known International C-Class Challenge Cup, the so-called Little Cup. In both these races, though with very different budgets, research and development is free from regulatory constraints and an integral part of “fair competition”.A wingsail consists of an orientable leading-edge profile and mobile elements, like the flaps of an aeroplane wing. These consist of a structure of carbon ribs to which a plastic membrane, usually heat shrinking film created for industrial use, is applied. Although it is a crucial element for performance, so far the few users have been forced to use products conceived for other uses, adapted to the requirements of wingsails. The creativity and flexibility typical of small and medium-sized Italian enterprises today offers a specially studied solution, thanks to PROtect tapes, a company on the Adriatic Riviera (its headquarters are in Rimini) created to produce removable films for protecting friction points from where bylines on sailing boats. In 2012 the company was nominated for the METS Design Award for Loop X, an adhesive film extremely resistant to loads designed to substitute fabric in loops, used for example to fix rigging elements to the hull. On that occasion too the product was studied for the America’s Cup, for the extremely powerful 72 foot catamarans used (and probably will never see them on the water again, not even for a show) for the 34th edition in the waters of San Francisco. On that occasion the company, which was already supplying many products, propose to the team is the first version of the wing sails membrane. “We love challenges – PROtect tapes CEO Pietro Parmeggiani says. For the third generation of our wing membranes, we have decided to re-enginer completely the product and explore new paths instead of improving the current films. This radical approach, not shared by all the R&D members, is unusual for a company, but the Project Leader wanted something new, different and superior, a new product really making the difference in terms of performance and possibilities”.
A completely new membrane
The project leader wanted to make a wider film, lighter, stronger, wider, high shrink force despite there were additional risks because time to market was a critical factor and the resources required much higher. The idea was to revisit all raw materials, processes and surface treatments, additionally on top of the 75micron used on AC72 in San Francisco 34th America’s Cup. The project was to lower the gauge of the film to reduce the weigth and manufacture other films too to be used on smaller films. The wingsails are used not only in the America’s Cup, but also on the 25ft. C-Class catamarans used already from the Sixties of the XXth Century to contest the Little Cup, nickname for the International C-Class Challenge Cup were normally using 25 micron, the goal was to go down to 19 micron and eventually thinner than that.Even if PROtect tapes do manufacture the double sided tapes used for the application of the membrane to the wing and other tapes going with, one challenging target the company jointly set was the width of the product to reduce joints and the amount of tapes. At that time AC62 was still a reality so the product development was to reach a width of 3300mm. After several laboratory tests and production run, there had been selected a formulation of polyolefin shrink film that combines the best properties of polyethylene with those of polypropylene to produce a very high clarity film with good shrink in all directions. The film is stretched during its manufacturing process: when heated, the polyolefin film attempts to regain it’s original size and shape (memory) but is prevented from doing so by the wing membrane being tighted. The film thus shrinks tightly to the wing frame and cools. The blow film process was giving the possibility to reach the width required, eventually adding pigment but the really advantage of this process is the consistency of thickness profile and the possibility to produce a film made of several layers and for each layer selecting different formulations. PROtect tapes was testing films up to 9 layers to obtain a composite film with different mechanical characteristics. The change of boat for the next America’s Cup, moving to a smaller catamaran around 48/50ft from the 62ft initially settled, did not change the original plans because there will be a need for wider film, so the company kept the 3300mm as target.
Irradiation was also an option: it’s a method of “cross-linking” molecules to enhance film strength and literally irradiates the film with a beam of Beta radiation or electrons. This additional treatment if properly managed creates stronger film with a wider sealing and shrink dwell and temperature range. While irradiated film is nominal less clear, requires higher sealing and shrink temperatures but these were not critical issue for the application as long the higher shrink force was obtained. Shrink force is very important on films for wing membranes because it’s the only way to make sure that the “sail” does have the expected profile. If the film is weak the wind pressure is changing the windward profile with typical sags seen in San Francisco, but moreover changing the leeward profile, this means that the wing doesn’t have the designed profile. Shrink force was the first priority. Higher shrink forces require stronger double sided adhesive tapes so PROtect tapes had to improve that part of the package too.
The next America’s Cup
Actually, ACM (America’s Cup Management, the company owned by Oracle, the Cup Defender, to run the 35th edition) approved the 75micron Winglar membranes for the next America’s Cup. Some of the competitors started to test the membrane on the AC45F’s wingsail, the foiling catamarans used for the pre-event races, the America’s Cup World Series, held in Portsmouth and Gothenborg. The last regatta of the series in 2015 is in Bermuda (home of the next 2017 America’s Cup) in October 16-18.