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The Imoca class can be said to be in a period of transition. Rudder elevators are (still) prohibited so designers and teams have been putting maximum thought into achieving steady flight without a key control device normally deemed essential. Compromises explored in turn generate increased demands on the engineers to allow seemingly unnatural solutions to perform well. Jocelyn Blériot discussed some of these left-field challenges with the engineering team at Gurit including structural engineer Paolo Manganelli

As we were watching a small number of Imocas battling it out around the globe fully crewed for the first time, a new generation of 60s was being launched and put through its paces. To try to understand the latest thinking in structural design, and to evaluate how far the most recent boats had evolved from the previous generation, we spoke to Gurit’s Paolo Manganelli, Yoan Stephant and Nicolas Poidevin. The firm has been involved in three of the most recent projects, in each case with a different set-up: directly contracted by Jérémie Beyou’s Charal team, in collaboration with VPLP for Malizia, and coming in to doublecheck the work for Eric Bellion and Jean Le Cam’s efforts. Three configurations, three different philosophies… and a host of new parameters to play with.

For Malizia the focus was firmly on reliability, with a ‘clear demand from the team’ on that aspect, stresses Paolo. Compared with the previous generation of boats this meant significantly pushing the requirements in terms of structural strength.

Main picture: Boris Hermann’s Malizia team knew what they wanted from the start, an unbreakable – within reason – Imoca 60 that they could push harder than their competition, particularly through the long Southern Ocean leg 3 of The Ocean Race. They got what they wanted and sure enough the toughest leg of the race was theirs for the taking. As well as adding both structure and laminate to the worst slamming areas, Malizia also features that old big-seas favourite… extra freeboard.

The Gurit team readily admits that they went into the discussion trying to take a bit of that edge off, which led to some in-depth discussions before landing on compromises that today feel like the right balance. ‘Malizia wanted to put the emphasis on the boat’s ability to deal with rough seas, which had an influence on hull shapes, notably in terms of freeboard height,’ says Manganelli. The idea was also to be able to launch without running the risk of having to return to the yard soon afterwards – and if that meant a bit more weight from the outset, well, so be it.

Reliability was also, naturally, an objective for Charal but the team in this case did not set precise minimum requirements. ‘Sam Manuard, Dimitri Nicolopoulos and ourselves were around the table,’ says Poidevin, ‘and we agreed on thresholds based on the experience acquired on L’Occitane and Charal 1.’

The group knew that hull bottom strength would need to receive special attention, and this guided structural considerations, but the brief was not as prescriptive as with Malizia.

It comes as no surprise that all teams want a boat that can endure what a Vendée or Ocean Race can throw at it, but the ways in which that criterion expresses itself are contingent on the skipper’s experience(s). ‘Part of the input comes from structural engineers, based on past projects’ learnings and data, but the client has the final say,’ notes Paolo Manganelli.

‘We have limits beneath which we do not want to go, but where the cursor is placed above this minimum is down to the racing team. We saw that with Malizia, who were keen to go well above our limit – in a sort of belt and braces approach. Others can be more… shall we say playful? ‘And of course when thinking about reliability trade-offs, the worry is always about being heavier than the competition.’

Load inflation all around
Interestingly, Poidevin stresses that ‘experience does not necessarily make discussions more straightforward’, as perhaps the temptation to experiment is greater, and with it comes a new flurry of questions.

Younger teams tend to stick to their guns and know precisely what they want to avoid – in other words, not being able to finish due to gear failure. Structure is a key weight factor, and weight has an impact on performance, ‘but, having said that, accepting a sacrifice on structure weight can also allow you to take risks elsewhere, it’s definitely not a binary choice’, Manganelli muses.

Whether the weight impact is greater on foiling boats than on their predecessors is an interesting question: it’s clear in transition and pre-flight phases, but because the loads are also greater in foiling mode teams that have heavier (hence stronger) boats may be less hesitant to put their machine under stress when things get rougher.

Poidevin weighs in: ‘This probably plays out more on a RTW race than on a Rhumtype transat, and to look at the big picture what we’re talking about is a 150-200kg difference on an eight or nine-tonne yacht.

‘Add just that and you’ll make a quantum step in terms of toughness. On a fully loaded boat of this size and weight it’s not that significant.’ To conclude on this specific issue, suffice to say that these different starting points between Malizia and Charal did not generate vastly different risk profiles, both sitting comfortably in a safe zone.

Above: maybe a little colour would help? Jérémie Beyou blends in nicely with the all-black operating centre of Charal 2. The jury is currently out on the latest Charal, but with its unwieldy-looking combination elevator/rudder system it may be that the underlying potential of the Sam Manuard design itself has yet to be fully revealed

‘In Jean Le Cam’s and Eric Bellion’s case, working with their designer David Raison a choice was made early not to foil, but the question of loads around the hull bottom is still critical in a context of increased performance compared with the previous generation of non-foilers. Loads rise roughly to the square of speed, which means a 10 per cent speed increase equals 20 per cent more effort,’ says Poidevin. ‘It’s a simplification but it gives a pretty good idea of what’s at stake.’

Hull design has also evolved steadily towards scow shapes, with flatter sections around the bow, meaning more and harder slamming. Between the 2016 generation Vendée boats and their 2024 counterparts some loads have gone up 150 per cent.

Anticipating what the next generation is likely to bring is also part of the thinking needed, and something that the Gurit team pays specific attention to. This has a direct implication in terms of design and calculation hours, which keep on creeping up due to a higher number of hypotheses and scenarios being formulated with each new iteration. ‘And this,’ says Manganelli, ‘despite the declared simplification and cost-reduction objectives and the relative maturity of the class…’

The variable that does not seem to inflate is the time horizon between the decision to build a new boat and its launch – yet design programmes are getting longer as the yachts are getting more and more complex. To resolve that tension, simply adding manpower to bump up design hours is not an option: the sequencing of work streams (one decision determining specific next steps) requires extremely careful project management, with precise weekby- week forward planning.

As racing teams grow in numbers and integrated skills the volume of questions sent Gurit’s way also follows an inflationary trend – respecting timelines depends on agreeing with the teams which ones to dig into… and which ones to nip in the bud.

Complex systems and their environment
If the new generation of boat does not appear to drastically depart from the previous one in terms of overall design, some key systems are becoming either more innovative or more complex, or both. An illustration of this phenomenon is Charal’s inverted-V steering gear architecture, with its long rudders meeting at the centre of the transom.

‘This was a hefty file to deal with,’ says Manganelli, ‘as the considerable angling of the rudders introduced efforts we have never seen on previous boats.’ Usually this is a pretty straightforward area of the boat to deal with, but Charal’s solution threw up a lot of new questions.

There is a central node of efforts where the two rudders meet, and all reinforcements have therefore to be concentrated around a small area – so much so that everybody was surprised by the actual quantity of material necessary to add to that high load zone. ‘We needed to envisage a lot of different scenarios,’ continues Nicolas. ‘With such large surfaces due to the rudders’ length, for example, sideways wave impacts on the windward appendage when out of the water need to be considered as a bigger risk factor than with more conventional systems.’

The solution was conceived to stabilise the boat in flight mode, in the context of class rules banning T-rudders, and this choice (based on preliminary studies) had such an impact on the overall structural work that it could not be a reversible trial. Once approved, when the team felt confident enough, it created a lock-in, ‘and so far it seems to work very well’, says Paolo. But in any case the boat would not accept a simple switch back to a more traditional set-up without some major work… which would mean months of yard time.

Charal 2’s design work started a week before Jérémie Beyou set off on the 2020 Vendée Globe on the first boat, with the aim to launch in time for the subsequent Route du Rhum which overall led to approximately 45 extra design days compared to Charal 1.

Things that go bump (and avoiding ‘crack’)
Concerning the keel area, following Hugo Boss’s heavy grounding in the 2019 Transat Jacques Vabre, data was fed back to the class regarding the loads that his boat had been subjected to. ‘It was about twice the magnitude of what we’d seen so far,’ says Manganelli, ‘and that forced everyone back to the drawing board.’

It also prompted a change in build regulations, a new requirement mandating that a boat needs to be able to withstand 6G should it come to an abrupt stop with the bulb colliding with an obstacle. Add to this the fact that the keel bearing needs to be able to cope with a longitudinal force of 100 tonnes, which equates to about 10 times the boat’s weight. ‘Here it’s not just about adding layers to the bottom of the hull,’ notes Stephant, ‘plus the one-design nature of the keel fin and fittings means that structurally your options are already reduced: the longitudinal position of the ram relative to the bearings cannot be a variable parameter, for example.’

All the questions revolving around dynamic loads have led to more investment in monitoring equipment to try to prevent a cascade of failures due to a non-detected initial weakness. Teams cannot perform regular inspections of all compartments at sea so it is more important to have reliable alarm systems; something that Malizia in particular was keen to push hard on.

Boris Hermann’s team adopted a colourcoded system coupled with sound: orange when loads are getting significant, red when the level of stress requires the crew to slow down and black when something may have given way and mandates an immediate inspection.

Above and below: Once again Charal was one of the first teams to launch a new design for a new Vendée Globe cycle, the extra lead time allowing them space to risk exploring a radical alternative solution to achieving level flight – given that an Imoca relying for lift on an angled keel fin plus a single immersed foil invites comparisons in balance with a two-legged stool. As 1997/98 Whitbread Race winner Paul Cayard observed during the last Vendée, dragging your a**se around the world with the bow in the air is not a good look for a modern sport

Malizia also chose to invest heavily in data acquisition; there are about 60 sensors spread over the bottom of the hull (30 on each side) plus many on deck as well. This increase in focus results directly from wanting to prevent a PRB-style catastrophic failure: knowing the compression loads in the deck allows the crew to always keep within a safe operating range. ‘It’s also about building a knowledge base,’ says Manganelli. ‘Each outing brings additional data, and this gradually leads to either validating or going against a design hypothesis.’

Should specific areas require reinforcement the information gathered by the sensors should allow work to be carried out in a preventive manner rather than following a breakage… whether in training or, worse, during a race. This type of monitoring is commonplace on America’s Cup boats as well as on big multihulls, but it’s still not the norm in the Imoca class. Apart from when it comes to the foils…

‘Financially, it’s not a massive investment relative to the cost of a campaign,’ explains Stephant, ‘but it’s costly in terms of manhours to first rig the whole system, then to analyse all the data which requires a dedicated person.’ From Gurit’s perspective it’s nevertheless a no-brainer given all the advantages such knowledge brings: being able to evaluate choices that were somewhat empirical and to know precisely at what percentage the boat actually operates.

‘Even as we speak,’ says Manganelli, ‘I’ve logged onto the Malizia dashboard [during The Ocean Race] where they send data in real time… Looking good!’

Material concerns
Beyond sheer performance the class – and to an extent the sport as a whole – is working on its sustainability credentials which naturally raises a lot of questions for materials experts such as Gurit. ‘It’s an important area of development,’ says Manganelli, ‘and our impression is that there is plenty of low-hanging fruit still to be picked.’

The team concedes that there can be a cost in terms of weight, which they can quantify and share with the designers who then evaluate trade-offs. Yet if the Imoca class decided to take a further step in this direction (a question of political will) at its disposal there is already a range of existing solutions. ‘It’s about materials but also very much about build techniques and processes,’ Manganelli continues.

‘But imposing a proper, class-wide constraint would level the playing field and generate genuine, interesting progress, unlike isolated efforts to integrate a few kilos of bio-materials here and there as we see today,’ says Poidevin.

Concretely, simplifying the ingredients list would be a good start (reducing the number of different pre-pregs, for example), as well as thinking about alternatives to carbon fibre where possible.

Going towards less energy-intensive processes (lower cure temperatures) as well as limiting the number of moulds that are disposed of after one use are other avenues, according to the Gurit team, who acknowledge that their expertise should inform that discussion with the intention of allowing the class to make fact-based choices… should it decide to legislate.

As Stephant points out to emphasise the feasibility of such measures: ‘Class40 races are as exciting as Imoca ones, despite the absence of exotic materials.’

One question at the heart of this discussion is the discrepancy between sailing’s image as a clean sport and its material reality: will there come a point of lesser acceptability from the public’s perspective (and therefore the sponsors) due to the environmental impact of the build phase?

Technology’s evolution already makes it realistic to envisage ‘hybrid fibreglass/ carbon infusion boats which in less than a couple of Vendée cycles could be as fast as today’s Imocas,’ says Manganelli.

‘But the real issue is how progress is defined: is it about shaving two days off a round-the-world race or halving the associated emissions?’ An interrogation that reaches far beyond our sport… which in the meantime promises us many more epic moments.

The Gurit Imoca team Nico Poidevin and Yoan Stephant: engineering and project lead. Gregor Borstnar, David Thompson, Simon Everest and Thomas Basset: engineering design and FEA. Thomas Grinsted, James Ledingham, Vittorio Mostosi: FEA. Sergei Kuzmin, Robert Horne, Douglas Mullins, Lauren Rutherford, Mark Saunders, Tim Smyth: 2D and 3D modelling. Paolo Manganelli: technical guidance and final sign-off…

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