Left: Team New Zealand technical director Dan Bernasconi raises the Cup with a mixture of euphoria… and relief. A questionable advantage of training alone in Auckland up to the very last moment and with only one test boat was it made it harder for watching rivals to measure progress. Against that was the stress of not knowing if you are even on the pace until you meet your first opponent for real. Achieving such a performance edge working remotely is surely one of the technical achievements of America’s Cup history?
decision right at the beginning that we would ignore the easy-to-sail options and would go all out for performance.’ Traditional reliance on a VPP gave way
to a much more complex analysis of perfor- mance – taking account of the wide range of dynamics that come into play when yachts engage in close combat. ‘A VPP tends to push you down an
optimal path of straightline speed. We used VPP tools remarkably little in this cam- paign and put much more emphasis on measuring how fast you could get the boat around the track, taking account of accel- eration, manoeuvres and so on.’ So, perhaps reflecting Bernasconi’s back-
ground in Formula One, lap times trumped straightline speed. The lap time approach forced a global consideration of everything on the boat – the appendages, appendage control system, wing control, crew func- tions, hydraulic demand. ‘Gomboc was the key to predicting lap
times. It is a combination of a VPP, real- time simulation and an appendage design package,’ Bernasconi explains. ‘From a hydrodynamics design point of view, 90 per cent of the America’s Cup is about developing the best analytical tools. In the end, whoever has the tools that most accurately predict lap times is going to be able to produce the best boat. ‘A huge effort on the performance side of the design team is devoted to developing
those tools. The actual shape of a foil comes very late in the process. Months of investigation and analysis take place before the final foil shape is produced just days before the manufacture deadline. Making sure the tools are telling the truth is where the big effort is required.’ Operating in a largely virtual realm, how
is accuracy assured? ‘A lot comes back to the first principles of the physics. That is our job as engineers, to make sure we are modelling the important aspects well. That is something that is always developing. ‘When we started this years ago we
would model a foil shape with simple lift and drag characteristics at various sections along a rigid structure. Then later we were able to model how the foil would bend and twist under load, how it would be affected by stall at low speeds and by cavitation at high speeds, how the flow of the wake from the foil would affect the rudder.’ Bernasconi started developing the early
version of Gomboc in the aftermath of the Deed of Gift Match in 2010. He was part of Ernesto Bertarelli’s Alinghi design team and, with time on his hands following the Match defeat, thought he would turn his attention to developing software that would hopefully be useful in the future. Since then, with inputs from design team members and others, that software has undergone consid- erable refinement with full-scale validation and experimental testing.
‘You can look at the real loads on the foil
through fibre optics and compare them with the prediction. The same with take-off speeds versus prediction, and angles of attack; for example, when you are sailing at 32kt is the rake angle the same as the simu- lator predicted? There are lots of avenues to explore. When you see something that doesn’t match, you hunt it down and figure it out and improve the simulation.’ By the time of the 2017 campaign the
tools were quite well advanced and improved further 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 col- laborated closely with the other designers and sailors to feed shapes and structures into those simulations. ‘We also used com- mercial RANS and FEA programs for more detailed evaluation of fluid flow and struc- ture,’ says Bernasconi, ‘but the main tools were 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 it was just like sailing the simulator.’ That was only the beginning, however. ‘If
you looked at the foils on our test boat you can see a continuing development curve; the
SEAHORSE 39 w
CHRISTOPHE FAVREAU/DPPI
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88
