34 BREEZE MAGAZINE Gomboc: A design high-flier for ETNZ By Ivor Wilkins Among the many talents and skills brought to bear on the design and development of Emirates Team New Zealand’s winning boat for the 35th America’s Cup was an extremely valuable but highly secret contributor called Gomboc. Wikipedia devotes considerable space to guiding us through the arcane world of physics and mathematics to define a notion first imagined in 1995 by Russian mathematician Vladimir Arnold. However, Dan Bernasconi, who presided over ETNZ’s design brains trust, obliges That aggression applied across for example, the cycling decision was with a simplified definition: “Gomboc is the the board to create the features that adopted early and Ashby refused to name of a mathematical shape which has distinguished the Kiwi campaign, including employ grinders to prevent any threat exactly two positions of equilibrium, one of the cycling system, appendages and foil of reverting to traditional thinking. As an which is stable and the other is unstable.” and wing control systems. aside, Bernasconi revealed that the cycle In the world of foiling, the search is Reinforcing that aggression concept, system, which proved so beneficial not for equilibrium against an array of team managing director Grant Dalton just in delivering more power but in freeing forces constantly threatening instability. added: “We knew we couldn’t outspend more hands to help control the boat, might Appropriately then, Gomboc was the name them, so we had to out-think them. We have gone even more radical. given to a highly sophisticated in-house had a saying that we wanted to throw the The team looked hard at having the software program aimed at overcoming design ball out as far as we could and see cyclist lie prone to further reduce windage, those hostile forces and achieving the high- if we could get to it.” but just could not find the space to make speed equilibrium that enabled the team to Crucially, stretching the performance that work. There was also concern that soar to victory. frontier had the full endorsement of Ashby, in Bermuda’s tropical conditions, the In the post-match euphoria of the Peter Burling, Blair Tuke, Ray Davies and cycle-grinders could overheat if they were triumph in Bermuda, skipper Glenn Ashby the rest of the sailing team. It came to completely out of the airflow. said, “We knew we had to be extremely rule every decision across the boat. Once In identifying where the biggest design innovative and aggressive with our design adopted, decisions were pursued with total opportunities lay it was clear that foiling philosophy. We knew we would have to risk commitment. would occupy the most attention. “The big to win the America’s Cup.” With hydraulic demand at a premium, trade-off with foiling,” says Bernasconi, BREEZE MAGAZINE 35 “is between a boat that is easy to sail but design package,” Bernasconi explains. by stall at low speeds and by cavitation slower, versus a boat that is hard to sail, “From a hydrodynamics design point of at high speeds, how the flow of the wake but can deliver more performance. We view, 90% of the America’s Cup is about from the foil would affect the rudder.” took a decision right at the beginning that developing the best analytical tools. In Bernasconi started developing the early we would ignore the easy-to-sail options the end, whoever has the tools that most version of Gomboc in the aftermath of and would go all-out for performance.” accurately predict lap times is going to be the Deed of Gift Match in 2010. He was Traditional reliance on VPP gave way able to produce the best boat. part of Ernesto Bertarelli’s design team to a much more complex analysis of “A huge effort on the performance and, with time on his hands following the performance – taking account of the wide side of the design team is devoted to match defeat, thought he would turn his range of dynamics that come into play developing those tools. The actual shape attention to developing software that would when yachts engage in close combat. of a foil comes very late in the process. hopefully be useful in the future. “VPP tends to push you down an Months of investigation and analysis take Since then, with inputs from design team optimal path of straightline speed. We used place before the final foil shape is produced members and others, it has undergone VPP remarkably little in this campaign and just days before the build deadline. considerable refinement with full-scale put much more emphasis on measuring “Making sure the tools are telling the validation and experimental testing. “You how fast you could get the boat around truth is where the big effort is required.” can look at the real loads on the foil the track, taking account of acceleration, Operating in a largely virtual realm, how through fibre optics and compare them manoeuvres and so on.” is accuracy assured? “A lot comes back to with the prediction. The same with take-off Perhaps reflecting Bernasconi’s the first principles of the physics. That is speeds versus prediction, and angles of background in Formula One, lap times our job as engineers, to make sure we are attack; for example, when you are sailing trumped straightline speed. The lap time modelling the important aspects well. That at 32 knots, is the rake angle the same as approach forced a global consideration of is something which is always developing. the simulator predicted? everything on the boat – the appendages, “When we started this years ago we “There are lots of avenues to explore. appendage control system, wing control, would model a foil shape with simple lift When you see something that doesn’t crew functions, hydraulic demand. and drag characteristics at various sections match, you hunt it down and figure it out “Gomboc was the key to predicting along a rigid structure. Then later, we were and improve the simulation.” lap times. It is a combination of a VPP, able to model how the foil would bend and For the 2017 campaign, the tools were real-time simulation and an appendage twist under load, how it would be affected pretty well advanced and improved further 36 BREEZE MAGAZINE through the process. “We developed a pretty full tool set for analysing and modelling foils. The appendage group of Bobby Kleinschmidt, Guillaume Verdier and Nick Hutchins collaborated closely with other designers and sailors to feed shapes and structures into those tools and simulations. “We also used commercial RANS and FEA programs for more detailed evaluation of fluid flow and structure, but the primary design tool was the in-house simulation software.” The first test of the process came when, at last, the sailors could move off the simulators and onto sailing the test platform. Their verdict? “Pretty good,” says Bernasconi modestly. “The comments from the sailors after we launched Boat One was Dan Bernasconi – ETNZ Design Co-ordinator it was just like sailing the simulator.” That was only the beginning, however. less surface area than Oracle’s. This area control system and the method of trimming “If you looked at the foils on our test boat, reduction was achieved by using higher for twist played a significant role as did you can see continuing development. The aspect-ratio foils with shorter chord lengths rudders and elevators, which represented foils with which we won the America’s Cup – something Oracle tried to move towards a late part of the ETNZ development. – we called them seven and eight – were by modifying their foils in the five-day A lot of development went into considerably different from the test foils. break between the first and second Match maximising the 3° rudder rake differential “That showed confidence in our tools, weekends which enabled the windward rudder to because those would become one of only Having opted for very high performance exert considerable downforce, adding two pairs of race foils. To commit to them, foils, the next challenge was getting the to the righting moment of the boat. On even though they were quite different from most out of them on the water. Here arriving in Bermuda, ETNZ spotted that anything we had actually sailed with, did the design team came up with a fully Oracle were sailing with slack lower require great confidence in our simulation automated test system where computers shrouds and soon realised that this would that they would be sailable and fast. flew the boat on an autopilot named Polo. allow the hull platform to twist more under “How we got there was a process of “This was useful to prove where we load, dropping the windward bow and multiple iterations. For the five test foils and could get to with control of the foils, to consequently increasing the rudder rake by four race foils we had on the water, we set the bar if you like. The sailors could as much as 0.5° – enough for a significant must have done laps on the simulator of at see what the computer could achieve and increase in righting moment. least 500 test foils and 400 race foils. challenge themselves to match it.” Reconnaisance photos of the Oracle “That is the beauty of simulation. It takes And to a large extent they did. “Through boat confirmed this increased ‘racking’, only five minutes to try a new shape.” the manoeuvres, the sailors could actually and a war of words ensued between the With the sailors driving the simulators, do a better job, but in a straight line teams and the Measurement Committee: they could also contribute ideas about foils the computers had a slight advantage.