Extraordinary boats
The foiling IMOCA 60 Charal
In St Malo for the start of the Route du Rhum in early November, every inch of the IMOCA 60 pontoons was packed with fans trying to get a close up look at the huge variety of designs taking part.
But one boat needed serious crowd control around it – Charal, the aggressively styled foiling design launched just a couple of months earlier. The scale of Charal’s foils alone would have drawn attention, but videos of Beyou test sailing his new boat literally leaping from the water made Charal a hot topic in St Malo. We talked to designer Vincent Lauriot-prévost of VPLP about the concepts and technology behind it.
Charal is not just the newest IMOCA 60, she marks a ‘next generation’ step for the class because she is the first IMOCA 60 designed entirely around the foils.
Most of the IMOCA 60s carrying foils in the 2016 cycle were retrofitted with them. Even those that were built anew were designed to be competitive without the foils (Alex Thomson’s Vendée Globe 2nd place after shearing the starboard foil less than two weeks into the race proving the sense of this policy). In truth, nobody really knew if the foils would be reliable and effective across enough of the wind ranges experienced in a round the world solo race.
“In the last edition of the Vendée we proved foils on the conventional boats, which were on boats designed for power and righting moment,” explains Vincent Lauriot-prévost.
The results of the last Vendée Globe: 1st Banque Populaire, 2nd Hugo Boss, Maitre Coq 3rd, all Vplp-verdier foiling designs, proved conclusively that this was the future of the class. So for Charal, VPLP took a different approach.
“We have decided to make the new boat as a pure foiler. Instead of looking for a powerful hull we are looking for a less draggy hull, taking into account that the foils are going to be the element that gives the power.”
This means a big shift from trying to balance weight reduction and power, to working towards a lightweight and minimum drag hull form.
One of the challenges has been that the new generation foil packages – longer foils, and casings that are stronger and more complex – come with a weight increase.
“We know that all-in the package of the new foils, including the reinforcement of the hull and so on, are just about half a tonne extra weight [over the last generation foils],” explains Lauriot-prévost. “So how can we make the boat half a tonne lighter to compensate for this?”
Hull volume has been reduced wherever possible, retaining it forward and amidships but cutting away great angular sections of bow and topsides, then sloping down to a low transom to create what Lauriot-prévost describes as ‘a very bumpy sheer’.
Overall, the changes are significant and achieving them while remaining within the IMOCA stability rule was a challenge. “The hull is completely different. It’s a narrower waterline – we don’t want to be a cigar, but we accept to lose 15-20% of righting moment to be within the stability rule,” explains Lauriot-prévost.
During the design process they discussed with the Charal team whether they wanted the boat to remain competitive even if they lost a foil
(as did Thomson). The decision was made that the boat would not be have enough power to be seriously competitive in non-foiling mode – although it would be stable enough to be safe.
Wide load
The scale of Charal’s foils is impressive – they are wider than any other boat’s so far, with a long shaft and tip and an angled elbow. They are also surprisingly thick. The trade-off for the increased foil size and power is that they cannot both be retracted simultaneously.
“We accept [we can’t] have them fully up at the same time, because we want them big. We want to create the righting moment as far out of the hull as possible, and we want a foil which creates vertical lift but which creates side force at the same time,” says Lauriot-prévost. The shaft creates vertical force, while the oversized tip generates lateral and vertical forces.
The other key difference is that these latest generation foils have adjustable rake, using bearings fore and aft, which allow Beyou to alter the angle of attack by 5°.
How frequently the rake will be adjusted remains something to be explored but, says Lauriot-prévost: “You can imagine maybe that instead of playing with sail sheets you play with the foil controls, and tune the boat to the reaction in the water more than the reaction of the sail forces.”
There is one significant limitation to the power even the latest generation IMOCA 60 can generate: the class-restricted rig. “There is one fuse on the boat, which is the mast,” explains Lauriot-prévost. “The mast has
been designed for [loads of] 32 tonne metres (Tm) and fully foiled, fully canted, fully raked and fully ballasted we are more 43-45Tm.”
Finding the limits
To monitor these loads, Charal is covered with fibre optic sensors; five per foil with additional sensors in the foil rake adjustment bearings, as well as on the outriggers and backstay.
“During the trials it happened several times that we had alarms, because we were overloaded compared to the designed load,” says Lauriot-prévost.
Given that potential, the adoption of the IMOCA 60 class by the Volvo Ocean Race will be a serious test of restraint. “That’s a really strong discussion that we had with the Volvo teams, because the Volvo teams have not got the same approach as a single-handed sailor, and when they push, they push!”
The other limiting factor is of course the human on board. As with any IMOCA 60, Charal has been customised around her skipper, the hugely experienced Jérémie Beyou, and his personal preferences.
“One thing which is evident on this boat is that Jérémie doesn’t want to stack the sails inside,” says Lauriot-prévost. To make moving the sails on deck easier, there is a sloped scoop abaft the cockpit.
The cockpit is sheltered by a fixed cuddy made with Mylar film windows rather than a retractable coachroof – sliding components would be heavier. A pedestal grinder is placed under the cuddy, right in the middle of the pit.
To keep weight low all the lines coming from the bow or mast base are led through two tunnels to the pit area. The pit area has four inline winches, directly connected to the pedestal for the easiest transmission system possible, with no gearbox or T-junctions necessary. This offers big savings in weight and complexity, but does make for a very compact working area.
“You do end up with a cockpit that is not designed for crewed sailing, at all!” points out Lauriot-prévost. Down below was out of bounds – the inner workings of Charal’s foil controls are too new to be shared.
Many of the IMOCA skippers have talked about wearing helmets or body armour on the new foiling 60s, so extreme is the motion. Was protecting the skipper a factor in the design?
“It’s going to be the priority before the start of the Vendée,” says Lauriot-prévost, “But Jérémie needs to find out where it is important to protect. He needs to get a bit bruised first!”