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For only the third time in its 162-year history, the ’s Cup was decided by a final race where the winner took all. The took place in San Francisco, and it was the US Oracle Racing that won the title on the 15th day of racing © ACEA/Photo Gilles Martin-Raget HIGHSPEED SAILING THE DESIGN PRINCIPLES BEHIND THE DEVELOPMENT OF THE 2013 AMERICA’S CUP RACING

A new breed of lightweight contested the 34th America’s Cup in San Francisco. The were created through a complex process that involved several disciplines including marine hydrodynamics, aerodynamics, structural mechanics and advanced composites. Matthew Sheahan, racing and technical editor of World, writes about recent developments of these racing .

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At the core of the new design was the issue of stability – righting moment – the ability to resist heeling and the key driving force of any

Since the inaugural race around Compared to the more familiar Apart from the vessel’s greater As always, winning the Cup put broader range of wind a large proportion of its weight important factors in this the Isle of Wight in 1851, the 82’ America’s Cup single-hulled, size, the black was the victors in a strong position to conditions, originally set at 3-33 acting as a lever to windward. newfound performance was the world’s oldest international heavyweight yachts with their notable for its giant 203’ wingsail define the rules for the next knots, but later scaled back to This weight times the horizontal 40m tall wingsail. COMPONENTS OF FORCE sporting trophy has represented traditional lead keels, the new mast, taller than the full wingspan event, and as Coutts revealed around 6-26 knots. distance from the hull that ON MAINSHEETS the leading edge in breed of lightweight catamarans of a Boeing 747, in place of a the details, it was clear that remains in the water is what WIND design and technology. In 2013, were less than a third of the more conventional mast and ‘soft’ multihulls would be the boats of generates the high righting WINGSAILS DESIGN BASICS Looking more like an aircraft’s the 34th America’s Cup delivered weight of the monohulls. . The use of a solid wingsail, choice. The move was a moment. More righting moment Speed was at the heart of wing than even the most the biggest leap in yacht racing The previous America’s Cup, only the second time in the controversial one. Only twice and a lighter means Oracle’s vision for the new look advanced soft sail and mast MAINSAIL LEECH performance of any previous held in in 2010, had history of the Cup, was to become before had multihulls been used considerably higher performance America’s Cup, as were the new combination, wingsails are rare match throughout its 162-year been a major departure from the one of the key features of the next in the America’s Cup. sophisticated television images – see Righting moments. but they do present several history. Hosted in San Francisco norm, an event that set a new generation of America’s Cup-class At just 72’ long, the new and live audio from crew But while multihulls levelled advantages. The first is the ability during September 2013, this agenda for the 2013 Cup. The boats. Shortly after winning, AC72 machines would be members, both part of a larger the playing field as far as righting to maintain an efficient aerofoil America’s Cup saw two 72’, winning boat was BMW Oracle Oracle Team USA’s CEO and five- significantly shorter than their package designed to attract a moment was concerned, there shape without inducing the high $10 million carbon fibre Racing, a 135’ trimaran owned by time America’s Cup winner Russell 2010 predecessors but could sail bigger audience. Upping the were other drawbacks with HORIZONTAL catamarans rise above the sea’s American billionaire and founder Coutts announced the new vision considerably faster, hitting top loads that are required when COMPONENT pace meant abandoning slow this type of boat for America’s REQUIRED TO using control lines to achieve PULL SAIL IN surface to achieve unprecedented of the Oracle Corporation, for the 34th America’s Cup and speeds of 47knots (54mph). They single-hulled boats with their Cup racing. the required shape on a soft sail. speeds around the course. . the radical new boat. could also handle a much heavy lead keels in favour of Catamarans may be quick in a One example is the lightweight, high speed straight line but they are slow to mainsheet that controls the multihulls. Bringing the racing manoeuvre. The America’s Cup is MONOHULL RIGHTING MOMENTS angle of attack of the wing to close to the shore was also part a match race, a simple two-boat HIGH VERTICAL The previous generation of Cup monohulls weighed around 24 the wind. Here the sheet doesn’t LOAD TO KEEP CENTRE OF BUOYANCY affair where nimble MAINSAIL LEECH tonnes. A modern AC72 weighs around 6 tonnes, yet of the new template, again, MAINSHEET something that suited shallow- manoeuvrability is a key part of need to pull down vertically to STRAIGHT has a similarly sized sail plan. Given such fundamental differences, maintain the shape of the it is easy to see how big the difference in power-to-weight ratios draft multihulls better than the game, as crews jostle to deep-keeled monohulls. outsmart their opponents by trailing edge as it does on a RIGHTING LEVER is. One major downside for the , however, is that beyond CENTRE OF GRAVITY At the core of the new pushing their boats through conventional sail. Instead, the a certain angle of heel, the multihull will not recover and a capsize sheet simply needs to pull the is unavoidable. design was the issue of stability – tight turns. Multihulls would be On a solid wingsail, leech profile sail in laterally. This makes the is maintained through physical But there was another reason why the architects of the new righting moment – the ability to slower and less nimble than their RIGHTING MOMENT mainsheet easier to adjust shape in the wing. Therefore there rule wanted to see multihulls rather than monohulls. resist heeling and the key driving monohull counterparts and is no vertical load in the mainsheet, quickly by the crew as they are and horizontal load only Establishing an opponent’s potential performance starts with force of any yacht. A monohull therefore weak in this area. At not having to haul on such high establishing their boat’s righting moment. The precise shape generates its righting moment least this was the consensus in loads. This in turn means that CATAMARAN of the hull is key, and therefore why teams guard such details through a combination of the the sailing world during the slower to operate but physically the boats do not require such carefully. A high righting moment generated by a relatively wide position of the hull’s centre of buildup to the event. impossible for the crew to highly geared, heavy and hull will be powerful in strong winds but have the disadvantage buoyancy and the righting effect However, by the time the perform as many tacks and tight slow winches. of greater wetted surface area and hence greater drag in lighter of the keel. In broad terms, the racing got under way, the manoeuvres as they did during The AC72 wingsails were CENTRE OF GRAVITY conditions. A narrower hull would have lower drag and therefore heavier the keel, the higher the innovative configurations aboard the racing. around twice the weight of a CENTRE OF BUOYANCY perform better in lighter winds, but would have less righting righting moment. That said, a both challenger Emirates Team The wingsail also presents conventional mast, but the sheet moment and therefore less power in stronger conditions. heavier keel also means a heavier New Zealand and defender lower drag than a conventional loads of a soft sail would have Calculating, and indeed limiting, the righting moment for a and potentially slower boat. Oracle Team USA had convinced sail plan through manoeuvres multihull is much easier, as this is less influenced by the hull shape By contrast, a multihull even the most sceptical that this been eight to ten times more. and will therefore decelerate less. RIGHTING LEVER and more influenced by the basic dimensions, predominantly that generates its righting moment new breed of multihull had With 8-10 tonnes of load on the Conversely, the more abrupt of weight times distance. To limit boats’ power, the rules for the through its wider beam rather challenged conventional wisdom conventional mainsheet power delivery of a wingsail RIGHTING MOMENT defined a maximum weight and maximum beam. At a than with a keel slung beneath. and that catamarans could compared to 1 tonne on the means that crews can also stroke, everyone had close to the same potential power output. At the point that one hull is lifted provide exciting, closely fought wingsail mainsheet, the sail de-power more easily with a clear of the water, a multihull has . One of the would not only have been wingsail than with a soft sail and

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IMPROVING FOILS included both upwind and forgiving but higher-drag foils as downwind legs, entirely on the team learned to sail the giant HIGHER CENTRE OF EFFORT Hydrofoil technology has been Less twist in middle section their foils. machine, the new designs around for a long time. Its early generating more power The lessons learned on the became more refined in their development started over 100 Moths have been valuable in the shape and required more years ago when Italian Enrico development of the foiling accurate sailing from the crew. Forlanini achieved 36.9 knots AC72s. Indeed, many of the Throughout the early sailing (42.5 mph) with his 60hp design engineers and sailors in trials, the approach seemed to airscrew-driven boat in 1906. America’s Cup teams have been pay off as the team sailed more Achieving speeds on water to drawn to Moth sailing to learn confidently in stronger winds and rival those of many of the cars of the tricks and technology more awkward sea states. Ideally, the day made several engineers firsthand. Yet to do so for the Cup the team would have built and sit up and take notice, among catamarans meant overcoming trialled the widest range of them the Wright Brothers and several fundamental issues. daggerboards across a broad LOWER CENTRE Alexander Graham Bell, both of Hydrofoils work well on range of conditions, but with OF EFFORT whom experimented with foil- Trailing edge of sail is powered vessels where the each foil taking between 1-3 more twisted here than borne craft. But it wasn’t until engine can provide sufficient months to produce and costing on Oracle. This reduces 1938 that a sailing boat got up Rudder with ‘T’ foil drive at top of wingsail speed for the boat to rise up onto Canted daggerboard $450,000, time and cost limited and keeps power low onto foils with Americans Robert its foils. To get to this point, the this development. down Rowe Gilruth and Carl William Windward daggerboard vessel needs to push through retracted as only one Their opponents, Oracle Team As boat raises up on foils Price, who managed to achieve high levels of drag. Once over the allowed to be down except Underwater ‘L’ becomes USA, started with a more refined tip just breaks surface the same feat, albeit more ‘hump speed’, (named after the when manoeuvering ‘V’ when canted looking boat that suggested slowly, under sail. typical shape of the speed vs At speed on foils © ACEA/Photo Gilles Martin-Raget lower aerodynamic drag and Yet despite the breakthrough, drag curve), the hull is raised clear lower-drag foils from the outset. sailing hydrofoils have been rare above the water and the overall machines were capable of foiling controlling the ride height was heel and therefore reducing the Their first breakdown resulted and mainly the domain of speed drag reduces dramatically. On a downwind 5-6 knots faster in the next issue for designers. This power available. from a daggerboard failure, but record attempts rather than sailing boat, however, it is harder typical racing conditions than if was particularly tricky given that The answer was to use just eight days into their testing mainstream yachting. The French to guarantee sufficient wind to their hulls were in the water, the the rules prohibited any moving hydraulic rams powered by the programme, the American boat 60’ trimaran L’Hydroptere is one get the boat to rise. If it can’t then question was whether this surfaces on the foils such as the crew winding handles on suffered a major setback when of the best-known modern there is a big drag penalty when additional speed would be flap and elevator type devices grinding pedestals, to angle the the cat tripped up, capsized at Centre of effort © ACEA/Photo Gilles Martin-Raget foiling yachts, having set the compared to a non-foiling boat sufficient to deliver a net gain that are common aboard foils in towards the centre of speed and suffered serious outright speed because of the additional around the course if the boats the Moths. the boat, known as canting. By structural damage. Miraculously, stop the boat more quickly if strengths, it is raised in order to record in 2009, sustaining a resistance caused by the extra didn’t foil on the upwind legs. To achieve this, teams varying the amount of cant, the no one was badly hurt, but the required. In match racing, create more heeling force to lift speed of 52.86 knots (60.83 hydrofoil surface area. Emirates ’s developed self-levelling systems proportions of vertical to accident was a major setback. decelerating is as important as one of the hulls out of the water mph) for 500m in 30 knots Sufficient power-to-weight original calculations suggested to control the ride height – see horizontal lift could be changed Three months of testing were lost being able to accelerate and early, thus halving the total hull of wind. ratio and righting moment are that the minimum wind speed at At speed on foils photograph. to suit different points of sail as the team rebuilt its damaged manoeuvre quickly. drag – see photo labelled Centre At the opposite end of the essential to lift the boat clear of which the boat would foil Riding too high would mean less and weather conditions – first boat while reconsidering The final key advantage is one of effort. size scale, the International Moth the water. In addition, to take full downwind would be 14 knots. As of the vertical part of the see Canting. some of the design issues for the of lowering the sail plan’s centre The wingsail was still only one Class, a 10’ racing dinghy advantage of the big potential testing and crew training daggerboard would be in the Learning how to handle second, more refined boat in its of effort. By adjusting the various side of the high performance weighing just 30kg has been speed gains, Cup boats needed progressed, this limit was to water and therefore less sideways these new, highly powered campaign. flap elements that make up the equation for the new breed of leading the way in small sailing to foil on all legs of the course come down to below 10 knots of force would be generated. hydrofoiling machines was a In the end, it was this lower trailing edge of the wing, the America’s Cup class boats. Lifting hydrofoils. Today the fleet, which and not just some. In the early wind. In addition the team Pushed too hard, the boat would big challenge for designers and drag design that won through as height of the centre of effort of the entire boat vertically out of has minimal class rules in order stages of design this was thought started to learn how to foil skip sideways. Riding too high crew, yet despite the the Oracle crew learned how to the sail plan can be altered. In the water on hydrofoils to reduce to encourage development, is to be the stumbling block for upwind. At this point foiling was also raised the sail plan further complexity, it was clear to the handle its sprightly machine. stronger winds, the centre of the hydrodynamic drag of the dominated by foiling boats. In the AC72s. now definitely part of the game. above the water’s surface and Kiwis that foiling would be a Success came at the eleventh effort is lowered to reduce the hulls was the second major addition, the class was the first While it was clear that these Given the range of speeds increased the heeling lever, crucial part of the campaign. hour for the defenders but heeling moment. In lighter wind step forward. to race around a course that highly powered, lightweight that the boat would be sailing at, making the boat less stable in Having started with more provided some of the most

40 INGENIA INGENIA ISSUE 57 DECEMBER 2013 41 HIGH-SPEED SAILING PROFILE AN ELITE dramatic racing that the Cup has However, lessons in control ever seen. systems and even foil section But there was also a stark design could have an influence in reminder as to the risks involved other areas of yacht design, be it and the level at which the new the methods of draft reducing technology was being pushed. lifting keels on cruising boats, or ENTREPENEUR Seven months after Oracle’s more refined high-lift/low-drag capsize, tragedy struck when foil sections for keels, rudders and British Olympic sailor Andrew even roll stabilisers. RETRACTED CANTED NO CANT Simpson was killed aboard When it comes to the solid wing , it is less likely that this Artemis Racing, one of the Retracted Wind David Braben FREng technology will trickle down into position other challengers, when the Downwind boat capsized and broke up mainstream yachting. Despite position their impressive efficiency and Wind during training. Windward hull Upwind their ability to reduce loads in the position A multi-million pound business that develops computer control lines, the wings are Wind games had its origins in David Braben’s schoolboy hobby FOILING AND complex and expensive to build. Leeward hull WINGSAILS Stepping (taking down) and of programming a simple PC. Three decades later, his The future for sailing hydrofoils is removing such wings is also an exciting one. The fast-paced difficult and potentially risky, company, Frontier Developments plc, has successfully Under America’s Cup rules: racing of the America’s Cup not particularly in windy conditions - No moving surfaces allowed floated on the London Stock Exchange. Braben has only highlighted the thrill and when the wing still wants to fly - Foil cannot extend outside maximum beam, hence the ‘L’ configuration - Boats are not permitted to have both daggerboards lowered for more than 30 seconds speed of sailing on foils, but it has whether it is attached to the boat been instrumental as a co-founder of the Raspberry Pi also enabled a greater or not. Stepping an AC72 wing Foundation, helping to bring to thousands of schools a understanding of how such takes around 30 people, and like BALANCING ON FOILS configurations may work without modern equivalent of the hobbyist computer that got him other teams, Emirates Team New The curvature helps to align the ‘L’ shaped foil into more of a ‘V’ as conventional moving control Zealand have had several the daggerboard is lowered, but this can be increased by canting started. He talked to Michael Kenward at Frontier’s HQ surfaces. There is also a greater alarming moments when the the daggerboard in towards the centre of the boat as well. In the understanding of how much in Cambridge. wing has overpowered them absence of any control surfaces on the foil, this ‘V’ configuration more stable a fast-moving boat is during the stepping process. provides a self-levelling effect. when it is riding on its hydrofoils. For the future of wingsails, As the boat accelerates, the hull rises and the amount of foil As a schoolboy, David Braben loved writing The company, Frontier Developments Given the problems of practicality is the limiting factor. in the water reduces as does the amount of vertical lift that is programs on an Acorn Atom. This was a plc, employs more than 250 people, encountering waves at high Throughout the history of the generated until an equilibrium between the downward force of time before personal computers provided with around 100 programmers working speed with conventional, non- America’s Cup, technology has the hull and the upward lift of the hydrofoils is reached. sophisticated programming packages to alongside 100 designers. The business foiling boats, hydrofoiling always played an important part For controlling the ride height when the self-levelling effects manage all aspects of life. It was certainly develops computer games that sell in continues to offer the possibility elsewhere in the sport. From before computer games rivalled feature films their millions. of increased speeds in otherwise electronic wind instruments of the ‘V configuration’ were not available, the angle of attack of in their visual effects and complexity. These games have large and devoted challenging sea states. developed in the 1930s to the the bottom ‘L’ section of the foil could be altered by raking the The Acorn’s attraction for this youngster followings. Last year, nearly 27,000 fans But foiling is not the future for wing keels and Kevlar sails of the daggerboard fore and aft, again using hydraulic rams manually with an interest in science and engineering opened their wallets on Kickstarter, the all. While the America’s Cup has 1980s, the America’s Cup has operated by the crew. The boat maintains its fore and aft trim was that he could easily teach himself how to crowdsourcing site, to raise £1.25 million for always provided a trickle down always had a greater influence with the T-foil on the rudders, which hold the stern down. Under write programs as all the tools and languages the development of the latest version of the for technology, foiling is unlikely than has at first been apparent. the rules, these were only adjustable when not racing. were provided with the machine, from BASIC Elite game, now one of Frontier’s flagship to be used on typical cruising For all its radical changes, the to full assembly language programming. products. It will cost a lot more than that boats of the future. The heavy immediate benefits of this BIOGRAPHY “I found the whole learning process extremely to develop the game, says Braben, but keels of monohulls and even the America’s Cup cycle may be Matthew Sheahan is racing and technical editor for Yachting compelling,” he says. These days, Braben runs crowdsourcing also offers “a fantastic, novel relatively heavy structure of difficult to see at present, but the World magazine and has covered every America’s Cup since a software business based in the Cambridge opportunity for bringing a game to market cruising multihulls, make it 34th America’s Cup will doubtless 2002. He previously worked in the marine industry at Proctor Bell and Braben’s Elite broke new ground when Masts before which he had studied yacht and boat design at it was published in 1984. It was published by Science Park with a game development without using a publisher and building a extremely difficult to generate provide key developments and Acornsoft for the BBC Micro and the Acorn studio in Halifax, Nova Scotia. community around the game.” sufficient power-to-weight ratios technologies for the wider sport what is now Solent University. A keen racing sailor himself he Electron computers and the necessary righting in the future, just as it has during has sat on various main and technical committees in the sport. moments. the last 162 years.

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