bending moments are greatest, while the fore and aft areas are quite shallow – which by the way is good for stability. We really pushed to simplify the lines, to have a streamlined design by avoiding angles and steps wherever possible.’
Surely a scow in all but name? The immensely powerful forward sections on Charal are further exaggerated by the more slender waterlines of the latest Imoca 60 launch. For the present there is no restriction on the length of Imoca foils but this will be changed after the 2020 Vendée Globe in anticipation of the classʼs entry into the Volvo arena
the hull that take the appendages-gener- ated efforts fully into account.
‘It’s striking, when you look at the superimposition of the digital prediction and the actual picture of the boat under sails, to see how spot-on the hypotheses were. Thrust, longitudinal balance, heel… everything so far seems to be as envisaged. And that can be put down to that “whole system design” approach.
‘If we go back to 2016, though, we quickly realised that skippers did not use the boats exactly as we thought they would: I was genuinely surprised by what I saw compared to what I had imagined and we fed those learnings into our thought process this time around. Therefore we have a more informed, refined view, one that is closer to “real life’’.’
‘That’s undeniable’, adds Daniele, ‘but it’s a bit early to say we got it totally right predictions-wise, since sailors will most probably end up making their own user’s manual and surprise us again.
‘Having said that, we had to imagine the behaviours of these machines which are essentially unprecedented, so it would have been easy to be way off with our pre- dictions. But that has not been the case at all, at least not for the moment.’ ‘For example, we foresaw that with these much longer foils the working heel angles would be dramatically less pro- nounced than on the previous generation; our first outings clearly proved us right.’ Another important factor to consider is the fact that both CFD and VPP tools benefit from a wealth of data that has been built up over the years, and they are now at a maturity level that greatly enhances the designers’ ability to make subtle choices. This notably helps when it comes to imple- menting Jérémie’s and the team’s require- ments with a good degree of precision. ‘You can see the beginning of our re- think around hull shapes with the 2016
42 SEAHORSE
generation Hugo Boss, St Michel and Banque Populaire, but it was all rather timid because of course we still did not know how foilers would fare on a racing lap of the planet,’ continues Quentin. ‘Now, between the hull of Boss 2016
and Charal 2018, there has been a whole- sale step change.’ Something that is obvi- ous when, for example, looking at the dramatic bow shapes on both boats; Alex Thomson’s previous Imoca, second in the 2016 Vendée Globe, may have initiated the now familiar sliced-away topsides for- ward but with Charal the same designers have gone much, much further. The basic idea is to reduce windage, according to Daniele, as well as to reduce weight: ‘The problem we have in this instance of course is that deck design is greatly influenced by the stability con- straints imposed by the class rule. The radical removal of upper hull volume neg- atively impacts stability at 110º, so we had to find the right weight loss/stability ratio.’ Quentin joins in: ‘It’s also down to the skipper’s choice, of course, and his level of comfort in terms of working on the foredeck, stability of course, plus some windage and hydro considerations. When the boat hits a wave at 30kt, would we rather pierce it, or have buoyancy? ‘Multihulls clearly evolved towards the former option, but for Imocas some ques- tions remain and intuition still plays a big role here. Bearing in mind of course that the objective for these boats is to sail with the bow clear of the water, so volume is still affordable and Imocas have rather full front sections. Finally, the structural solu- tions are just as crucial, and we worked closely with Gurit on that, particularly as deck shape now influences the definition of the hull girder so dramatically. ‘On Charal, seen from the side elevation what is striking is the relative bulge in thickness around the mast area where the
Which means that, if freeboard is lim- ited in the cockpit area, skipper protection becomes a conundrum in itself. ‘Yes,’ says Daniele, ‘with the added factor of ease of stacking on deck, which is something Jérémie is quite adamant about, something he took away from his Volvo experience.’ The ballast configuration is also of course another parameter, which is largely dictated by the skipper and his team according to the preferred sailing style. In this instance we won’t be able to reveal much since Beyou and his troops had rather particular requirements which shall remain classified at this stage. ‘Suffice to say,’ notes Quentin, ‘that penalising upwind performance was not something they were willing to do too much.’ So let’s leave it at that for now, as we will for the next chapter of the Charal story be examining the structural task much more carefully: ‘A lot of thinking has gone into the “high-intensity” zone, which sits at the interface between foils, mast and keel,’ says Quentin.
‘The level of effort developed by these big foils is unprecedented. We’re into a totally new game. It’s not a question of simply defining a mast bulkhead plus keel area reinforcement, like it’s been the case so far… Those days are behind us.’ Next month: Part II – putting (as well as keeping) it all together
CHARAL DESIGN TEAM Vincent Lauriot-Prévost Senior naval architect Quentin Lucet
Senior naval architect Daniele Capua
Principal naval architect Guillaume Dupont Junior naval architect Antoine Lauriot-Prévost Junior naval architect Adrien Letourneur
Performance engineer VPP/foils Paul Kerdraon
Performance engineer VPP/foils Nicolas Baral
Structural engineer Giorgio Provinciali
Hydro performance consultant
GURIT STRUCTURAL ENGINEERING Paolo Manganelli
Principal engineer/technical guidance Katia Merle
Lead engineer and project manager Yoan Stephant
Design engineer/analyst Raphael Gerard
Design engineer/FEA specialist Thomas Letanche
Project engineer/FEA specialist
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