For Imoca 60s, lifting the boat out of the water is one thing but the knock-on effects to the design, engineering and construction have seen significant changes elsewhere that have required a much closer cooperation between designers, builders and material suppliers than ever before.
‘The introduction of foils has changed the load conditions as the leeward foil works with the fin of the canting keel to lift the boat at speed,’ Manganelli explains. ‘So not only do we need to deal with the support structure of the foil itself but we now have to consider the additional loads that are put into the boat’s structure. ‘The structure around the foil is pretty complex and some of the design loads are of the same order of magnitude as those we have in the keel. So in effect we've added an extra righting moment producing appendage that puts a big additional moment into the boat. The result is that you've got a second major structural element to deal with on a similar scale to that of the keel and yet we are not really doubling the weight of the keel support structure in these boats. Instead, we're integrating the foil support structure into the keel support structure so that some of the elements are serving a double purpose in order to avoid
62 SEAHORSE
adding more mass to the boats.’ ‘The structure elsewhere in the boat has evolved too as we have several additional challenges to deal with. For instance, in the event that the foils hit something we need to make sure that the boat isn’t torn to pieces. The Hugo Boss collision in last year’s Transat Jacques Vabre is a good example where the boat suffered serious damage but made it back to shore.
‘To achieve this, we're making use of the experience that we've gained through a number of a foil support structure designs for projects involving Maxis, Imoca 60s, Volvo Ocean Race boats and others. So, it’s a complex design challenge, but it's not an unfamiliar one.’
But that isn’t the end of the issue. Just as changing the power delivery in a car will affect various other areas from the gearbox, brakes, chassis and so on, changing load paths and loading conditions will affect almost every component aboard the boat. ‘With this last generation, the combination of ballast tanks, canting keel and rake adjustment on the foils, there's so much to tweak and learn and adjust and so many parameters; it's a constant and fast-paced evolution. If you consider the performance progression of Charal from when she was launched up to
Above: the structural engineering version of the Rorschach test. Where a casual reader might see an abstract kaleidoscope of colours, structural
engineers see the pressures, stresses and strains in the hull shell of a foiling Imoca 60. The lay-up of materials within the hull and its supporting structures is designed accordingly with a very high degree of precision
now, the improvement is pretty extraordinary as it has been for others in the fleet. There was already some difference between the performance that was expected of the boat at the design stage, against what she actually delivered when she went sailing. And then there was another step forward between what she was doing a year and a half ago and what she's capable of now. The bottom line is that the pace of change has been incredibly quick and the learning curve steep. So the challenge for us is staying ahead of that curve. Working closely with teams is what makes this possible. ‘As performance increases, slamming is another critical area and while Corecell has become the material of choice for the core in the underside of the hull, we have been able to further optimise its usage thanks to the improved understanding of its dynamic behaviour. In the recent years we have gained extremely valuable insight into the properties of Corecell at high strain rates through extensive testing performed by our New Zealand office in collaboration with the University of Auckland. Some of that knowledge has trickled into our designs. Close collaboration with the teams is key to further improve our understanding of the new loading
GURIT
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