CLASS40 - DERNIERES EVOLUTIONS DANS LA CLASS40

DERNIÈRES ÉVOLUTIONS 

DANS LA CLASS40

Petit rappel nécessaire, la longueur de la coque est limitée à 12,19 mètres, le bau à 4,50 mètres, le tirant d’eau à 3 mètres. Le bout-dehors démontable ne doit pas dépasser 2 mètres et le franc-bord moyen doit être au moins égal à 1,08 mètre. Le déplacement minimum est de 4,5 tonnes, plusieurs ballasts totalisant 1500 litres sont possibles, la quille est fixe, pas de dérive ou de foils, pas de gréement sophistiqué, et les matériaux exotiques, carbone, Kevlars ou autres sont interdits. Le tirant d’air de la grand-voile est au maximum à 19 mètres, et la surface des deux voiles, solent et grand voile, limitée à 115 mètres carrés. Enfin, deux mesures, qui devaient empêcher de concevoir un scow, prise à 20 centimètres et deux mètres de l’étrave, limitent la largeur de la coque à 45 centimètres et 3,15 mètres.

Le premier à tenter une solution adaptée à la jauge pour créer une carène proche des scows est celle d’Eric Levet pour le cabinet Marc Lombard, qui, dès 2016, travaille dans cette direction. Carac, n° 150, un Lift 40, mis à l’eau en 2017, possède une coque pleine sur l’avant, avec un flanc vertical qui contourne le voilier. La carène est résolument à fond très plate, avec des sections eu U très ouvertes et un bouchain résolument vif. Il n’y a plus de transition entre le bordé et la carène, le bouchain crée une cassure franche. L’étrave est relevée, ce n’est déjà plus la longueur de la flottaison à l’arrêt qui compte, mais la capacité de la carène à planer, et à escalader les vagues au lieu de s’y planter.

1 – CARAC

Carac est le premier de la série des Lift 40 du cabinet Marc Lombard. Le dessin du bouchain sur la moitié arrière est plus haut en réalité. L’angle d’attaque de l’étrave est un début de révolution dans le dessin des carènes des Class40.

2 – Carac, lines

Le plan général montre une nette évolution vers une version scow. D’ailleurs, certains scows américains présentent ce genre d’étrave pincée. Les lignes d’eau sur l’avant sont proches du bouchain et très courbes. À la gîte, le voilier prend appui sur un plan pratiquement plat, de l’avant à l’arrière, favorisant le planning.

 

L’arrivée dans le circuit des Class40 de David Raison, par Ian Lipinski (14 victoires sur son Mini entre 2016 et 2017), et le Crédit Mutuel, n° 158, bouleverse toutes les solutions précédentes, et va au-delà des idées préconçues. 

3 – CREDIT MUTUEL

La révolution David Raison, qui nous avait pourtant habitués à ses nez ronds depuis dix ans, s’est imposé dans la Transat Jacques Vabre 2019 avec son premier Class40, en écrasant la concurrence, pourtant réputée de haute volée. Le nez rond, rendu pointu par obligation de jauge, fait un pied de nez à toutes les traditions.

 

La moitié arrière du voilier est au maximum du bau autorisé, et l’avant est le plus large possible, dans la limite de la fameuse mesure à 20 centimètres de l’étrave. Comme sur le Lift 40, la coque est entourée d’un ruban vertical ; la carène, aux formes douces, vient se rapporter sous le bouchain. L’étrave est très fuyante, et la flottaison commence bien au-delà du couple un. Le but est clair, le voilier doit planer en permanence, et lever le nez ! Afin d’améliorer les performances au près, le voile de quille est en avant par rapport au bulbe du lest, et pour assurer une plus grande raideur de la coque, et assurer un volume en cas de retournement, le roof est prolongé jusqu’au premier couple.

4 – Crédit Mutuel, lines

Sur les derniers Class America, on parlait de boîte à chaussure, on est de nouveau en plein dedans. Il y a une certaine symétrie dans les lignes d’eau sous la flottaison, qui correspondent à la carène immergée. Dès que le voilier gîte, la surface de flottaison diminue drastiquement.

 

La mise à l’eau tardive de la dernière version des Mach 40 de Sam Manuard, le Mach 40.4 n°159, Banque du Léman, pour la Transat Jacques Vavre 2019 n’a pas permis à Simon Koster et Valentin Gautier de monter sur le podium. 

5 – BANQUE DU LEMAN

Sam Manuard n’a pas hésité à reculer le pied de mât, le centre de flottaison et le voile de quille. La silhouette est hyper puissante. En réalité, avec de la brise, la tête de mât se courbe et la sustentation opère, soulevant l’étrave pour mieux surfer sur les vagues.

 

Manuard reprend les idées de David Raison, mais en arrondissant le bouchain, avec une carène plus ronde et des lignes plus tendues en générale. Le bouchain, assez haut, est conservé sur le tiers arrière. La flottaison est un peu plus longue que sur Crédit Mutuel, mais la volonté de se hisser sur les vagues est la même, même si le voilier pousse un peu plus d’eau que son concurrent. 

6 – Banque du Léman, lines

Une coque tout en rondeur, creuse et tendue, avec un avant bien plein, des sections très en rondeur. Les sections longitudinales, en rouge sur la vue de profil, montrent une différence importante avec le plan David Raison, alors que les deux plans de coque sont très proches, étant obligés de rentrer dans la mesure de jauge proche de l’étrave.

 

Les deux Mach 40.3, qui accompagnent Crédit Mutuel sur le podium en 2019, montrent que la solution scow n’est pas un gage de victoire, mais un vent nouveau flottait déjà sur la Class.

7 – CROSSCALL

Précurseur de cette nouveauté dans la Class avec son Lift 40 en 2016, le cabinet de Marc Lombard, avec Eric Levet aux premières loges, n’a pas hésité à chercher comment exploiter l’espace qui existe entre les deux mesures de jauge.

8 – Crosscall, lines

Le raisonnement normal du designer, sur son écran, consistait à tirer une ligne droite de l’étrave à la première mesure, soit un angle de 96 degrés, puis d’arrondir en passant par la seconde mesure pour terminer tangentiellement (c’est-à-dire doucement) au bau maximum de 4,50 mètres. Dans la première génération, les architectes ont hésité à créer une ligne droite sur la moitié de la longueur, et préféré arrondir légèrement cette ligne en favorisant un bau maximum en arrière du pied de mât de la descente. 

Or, dans cet espace, entre la ligne d’étrave et la tangente au point de mesure des deux mètres, le cabinet a formé une bosse de 35 centimètres d’épaisseur, qui écarte la carène à un endroit crucial, et prolonge la flottaison à la gîte de près de 90 centimètres. En effet, l’inconvénient de l’étrave-scow pointue est de diminuer drastiquement la longueur de flottaison à partir de 10 degrés de gîte. Tant que la brise souffle, les formes sont suffisamment tendues pour que la longueur de flottaison ne soit pas un souci, mais dans le petit temps, la longueur est primordiale, autant que la réduction de la surface mouillée. Cette protubérance aurait pu être un handicap sur le plan de l’augmentation de la surface développée de coque, mais la bosse a pu être circonscrite en incurvant le flan à cet endroit et en augmentant le plan incliné du livet qui plonge vers l’étrave. 

Les formes des sections de la carène sont fidèles aux idées du cabinet qui favorise un fond plat, avec un arrière légèrement incurvé, pour un meilleur planning, et des côtés en V pour réduire la surface mouillée à la gîte, en s’appuyant sur le bouchain. Des sections moins caricaturales que sur leur premier Lift 40, une étrave qui rebique un peu plus, mais des lignes plus tendues sur l’avant, le Lift 40 V2 d’Aurélien Ducroz et David Sineau, Crosscall (N° 166), a tout pour décoller. Le voile de quille a été avancé pour le près, alors que le mât est en arrière du milieu du voilier, le safran, lui est maintenant en arrière de la jupe, gage d’équilibre aux grandes allures.

9 – EMILE HENRY - HAPPY VORE

Si les architectes de l‘agence VPLP sont connus pour avoir fait avancer les choses en Imoca, ils sont tous nouveaux venus dans la Class40 avec leur Clak 40. Deux voiliers ont été mis en chantier, et malheureusement, seul le bateau de Nicolas d’Estais et Erwan Le Draoulec, Emile Henry - HappyVore (N° 167), partira dans cette Transat. Comme sur le trimaran d’Ellen MacArthur B&Q – Castorama, avec lequel elle a détenu le record du monde en solitaire en 2005, chaque côté du voilier reçoit un décor totalement différent. Le côté tribord est noir, aux couleurs d’Emile Henry, et l’autre est blanc et vert pâle. J’ai eu toutes les peines du monde à reconstituer ces plans, le voilier étant encore en chantier au moment du bouclage.

10 – Emile Henry – HappyVore, lines

Le parti pris architectural est relativement sage, avec un centre de carène assez reculé et un livet qui reprend la forme de leurs 60’, ce qui réduit la surface développée du pont. L’étrave est suffisamment haute pour pouvoir descendre l’arrière du pont au maximum, affinant la silhouette du voilier et diminuant l’effet boîte à chaussure. Le bouchain inférieur est un peu plus haut que sur les Max 40 de David Raison et la forme générale de la carène est assez proche, avec un tableau arrière un peu moins large. Le gréement est le plus reculé de tous les Class40 pour favoriser le planning.

11 – SERENIS CONSULTING

Pour le dernier Pogo, le Pogo 40 S4, le chantier Structures dirigé par Erwan Tymen a choisi Guillaume Verdier pour renouveler sa gamme. Sur les trois voiliers commandés, deux participent à la Transat Jacques Vabre. Serenis Consulting(N°163) de Jean Galfione et Eric Péron, et Seafrigo-Sogestran (N° 172) de Cédric Château et Jérémie Mion. Ce qui frappe sur ce plan, c’est l’assiette du voilier, résolument enfoncé sur l’arrière, avec un voile de quille en avant du lest, qui lui est très reculé, et avec un centre de gravité du lest très en arrière. Le profil de carène rebique au niveau de l’étrave, s’enfonce en ligne droite jusqu’au-delà du voile de quille, remonte avec un point d’inflexion pour terminer à l’horizontale quinze centimètres sous l’eau. Le voilier semble cambré, et près à décoller.

12 – Serenis Consulting, lines

Les sections de la carène sont douces, sans cassure, avec un bouchain bas assez près de l’eau et plus étroit que le bouchain supérieur. Visiblement, la priorité n’a pas été donnée à la raideur. En effet, le bau maximum, vue en plan, est inférieur à celui de la jauge, de 8 centimètres, c’est-à-dire 4,42 au lieu de 4,50 mètres et il est rectiligne à partir du pied de mât, et le bouchain inférieur ne dépasse pas 4,15 mètres de large. Les formes rondes correspondent à une recherche de surface mouillée, même si l’arrière peut traîner un volume d’eau important. Compromis entre recherche de vitesse par petit temps, moyennes élevées au portant dans la brise et efficacité au près dans la mer formée, Guillaume Verdier nous a concocté un cocktail original qui ne manque pas d’atout. 

 

Pour compenser le volume d’un roof assez court, le pont avant présente un bouge important. Tous les Class40 ont la particularité de ne pas rester à l’envers, grâce à un règlement qui impose beaucoup de volume au-dessus du livet de pont.

13 – Sections x6 Class40

Les sections des trois premiers Class40 mettent en évidence leurs différences. Un voilier taillé à la serpe pour Carac, une boîte à chaussure sur une carène tendue pour Crédit Mutuel et des courbes bien pleines pour Banque du Léman. 

La première chose que l'on remarque en observant les six sections des Class40 en forme de scow, c'est que sur les trois derniers, les flancs ont été considérablement réduits en hauteur, afin de diminuer la résistance latérale au vent, particulièrement néfaste dans les petits airs. Cela permet également de réduire la surface développée de l'ensemble de la coque, et de transférer le poids gagné dans le lest.

 

Cette classe est décidément vouée à un bel avenir.

François Chevalier

Class40

Longueur hors tout : 14,19 m

Longueur de coque : 12,19 m

Bau : 4,50 m

Tirant d’eau : 3,00 m

Tirant d’air : 19 m

Solent et Grand-voile : 115 m²

Déplacement : 4,5 t

Ballast : 2 x 750 litres

LATEST EVOLUTION IN THE CLASS40 - 2021

 Latest evolution in the Class40

A quick reminder: the length of the hull is limited to 12.19 meters, the beam to 4.50 meters and the draft to 3 meters. The removable bowsprit must not exceed 2 meters and the average freeboard must be at least 1.08 meters. The minimum displacement is 4.5 t, several ballast tanks totaling 1500 liters are possible, the keel is fixed, no daggerboards or foils, no sophisticated rigging, and exotic materials, carbon, Kevlar or others are forbidden. The air draft of the mainsail is limited to a maximum of 19 meters, and the surface area of both sails, solent and mainsail, is limited to 115 square meters. Finally, two measures, which should prevent the design of a scow, taken at 20 centimeters and two meters from the bow, limit the width of the hull to 45 centimeters and 3.15 meters.

The first Class40 to attempt a solution adapted to the rule to create a hull close to the scow is that of Eric Levet for the Marc Lombard firm, which, as of 2016, is working in this direction. Carac, n° 150, a Lift 40, launched in 2017, has a full-hull forward, with a vertical side that goes around the boat. The hull is resolutely flat-bottomed, with very open U-shaped sections and a resolutely sharp chine. There is no longer any transition between the planking and the hull, the chine creates a clear break. The bow is raised, it is no longer the length of the waterline at rest that counts, but the ability of the hull to do some planning, and climbing the waves instead of crashing into them.

1 – CARAC

Carac is the first of the Lift 40 series from Marc Lombard. The drawing of the chine on the rear half is actually higher. The angle of attack of the bow is the beginning of a revolution in Class 40 hull design.

2 – Carac, lines

The general plan shows a clear evolution towards a scow version. In fact, some American scows have this kind of pinched bow. The water lines on the front are close to the chine and very curved. When heeled, the yacht leans on an almost flat plane, from front to back, making it easier to plan ahead.

The arrival in the Class40 circuit of David Raison, by Ian Lipinski (14 victories on his Mini between 2016 and 2017), and the Crédit Mutuel, n° 158, overturns all previous solutions, and goes beyond preconceived ideas. 

3 – CREDIT MUTUEL

The David Raison revolution, which had been accustomed to its round noses for the last ten years, has won with its first Class40 in the Transat Jacques Vabre 2019, which crushes the competition, even though it is reputed to be top class. The round nose, made pointed by the obligation of a rule, is a thumbnail to all the traditions.

The aft half of the boat is at the maximum of the authorized beam, and the front is as wide as possible, within the limit of the famous 20 centimeters from the bow. As on the Lift 40, the hull is surrounded by a vertical ribbon; the hull, with its soft shapes, comes to rest under the chine. The bow is very elusive, and buoyancy begins well beyond frame one. The goal is clear, the sailboat must glide permanently, and raise the nose! In order to improve upwind performance, the keel sail is forward in relation to the ballast bulb, and to ensure greater stiffness of the hull, and to provide volume in case of overturning, the roof is extended to the first couple.

4 – Crédit Mutuel, lines

On the last America's Cup Class boats, we talked about a shoe box, but we're back in it again. There is a certain symmetry in the water lines below the waterline, which corresponds to the hull underwater. As soon as the sailboat heels, the water surface decreases drastically.

The late launch of the latest version of Sam Manuard's Mach 40, the Mach 40.4 n°159, Banque du Léman, for the Transat Jacques Vavre 2019 did not allow Simon Koster and Valentin Gautier to reach the podium. 

5 – BANQUE DU LEMAN

Sam Manuard didn't hesitate to move back to the mast step, the center of buoyancy and the keel sail. The silhouette is very powerful. In reality, with the breeze, the masthead bends and the lift operates, raising the bow to better surf the waves.

Manuard took up David Raison's ideas, but rounded the chine, with a rounder hull and tauter lines in general. The chine, quite high, is kept on the rear third. The waterline is slightly longer than on Crédit Mutuel, but the will to ride the waves is the same, even if the boat pushes lightly more water than its competitor. 

6 – Banque du Léman, lines

A hull all in roundness, hollow and taut, with a very full bow, sections very in roundness. The longitudinal sections, in red on the side view, show an important difference with the David Raison plan, whereas the two hull plans are very close, being obliged to fit in the rule measurement close to the bow.

The two Mach 40.3s that accompany Crédit Mutuel on the 2019 podium show that the scow solution is no guarantee of victory, but a new wind was blowing on the Class.

7 – CROSSCALL

A forerunner of this novelty in the Class with its Lift 40 in 2016, Marc Lombard's firm, with Eric Levet in the front row, did not hesitate to look for ways to exploit the space that exists between the  two rule measurements.

8 – Crosscall, lines

The designer's normal thinking, on his computer screen, was to draw a straight line from the bow to the first measurement, an angle of 96 degrees, and then round off through the second measurement to end tangentially (i.e., gently) at the maximum beam of 4.50 meters. In the first generation, the architects were reluctant to create a straight line for half the length, preferring to round it off slightly by favoring a maximum beam aft of the mast step.

However, in this space, between the bow line and the tangent at the two-meter measurement point, the firm formed a 35-centimeter-thick protuberance, which pushes the hull apart at a crucial point and extends the waterline at heel by almost 90 centimeters. Indeed, the disadvantage of the pointed bow scow is that it drastically reduces the waterline length from 10 degrees of heels. As long as the breeze is blowing, the shapes are tight enough that waterline length is not a concern, but in light airs, length is essential, as is the reduction in wetted area. This prominence could have been a handicap in terms of increasing the developed hull area, but the bulge was contained by curving the sidewall at this point and increasing the inclination of the planking which falls towards the bow. 

The shape of the hull sections is faithful to the ideas of Marc Lombard's office, which favors a flat bottom, with a slightly incurved stern for better planning, and V-shaped sides to reduce the wetted surface area at the helm, by leaning on the chine. With fewer caricatured sections than on their first Lift 40, a bow that bounces fairly more, but straighter lines up front, Aurélien Ducroz and David Sineau's Lift 40 V2, Crosscall, n° 166, has everything it takes to take off. The keel sail has been brought forward for upwind sailing, while the mast is aft of the middle of the boat, and the rudder is now aft of the transom, providing balance on long reaching. 

9 – EMILE HENRY - HAPPY VORE

If the architects of the VPLP agency are known for having made progress in the Imoca class, they are newcomers to the Class40 with their Clak 40. Two boats have been built, and unfortunately, only Nicolas d'Estais and Erwan Le Draoulec's boat, Emile Henry – HappyVore, n° 167, will be taking part in this Transat. As on Ellen MacArthur's trimaran B&Q - Castorama, with which she held the solo world record in 2005, each side of the boat is given a totally different decoration. The starboard side is black, in the colors of Emile Henry, and the other is white and pale green. I had great difficulty in reconstructing these plans, as the boat was still being built at the time of writing.

10 – Emile Henry – HappyVore, lines

The architectural approach is relatively reasonable, with a fairly aft center of gravity and a top side that follows the shape of their 60', which reduces the deck area. The bow is high enough to lower the aft end of the deck as much as possible, thus slimming the silhouette of the boat and reducing the shoebox effect. The lower chine is fairly higher than on David Raison's Max 40s and the general shape of the hull is quite similar, with a slightly narrower transom. The rigging is the furthest back of all the Class40s to improve planning.

11 – SERENIS CONSULTING

For the latest Pogo, the Pogo 40 S4, the Structures shipyard directed by Erwan Tymen selected Guillaume Verdier to renew its range. Of the three boats ordered, two are taking part in the Transat Jacques Vabre. Serenis Consulting, n°163, owned by Jean Galfione and Eric Péron, and Seafrigo-Sogestran, n° 172, owned by Cédric Château and Jérémie Mion. What is most noticeable about this plan is the boat's trim, which is resolutely sunken at the stern, with a fin keel in front of the ballast, which is very far back, and with the center of gravity of the ballast very far back. The profile of the hull bends at the level of the bow, sinking in a straight line to beyond the fin of the keel, rising with a point of inflection to end horizontally fifteen centimeters under water. The boat seems to be cambered, and ready to take off.

12 – Serenis Consulting, lines

The sections of the hull are smooth, with no breakage, with a low chine close to the water and narrower than the upper chine. Clearly, stiffness has not been the priority. Indeed, the maximum beam, seen in drawings, is 8 centimeters less than the rule, i.e., 4.42 instead of 4.50 meters, and it is straight from the foot of the mast, and the lower chine does not exceed 4.15 meters in the beam. The round shapes correspond to a search for wetted surface, even if the stern can drag a large volume of water. Guillaume Verdier has concocted an original cocktail of speed in light airs, high average speeds downwind in a breeze and efficiency upwind in heavy seas. 

To compensate for the volume of a rather short roof, the foredeck has a lot of deck camber. All Class 40s have the particularity of not staying upside down, thanks to a rule that imposes a lot of volume above the deck.

13 – Sections x6 Class40

The sections of the first three Class40s highlight their differences. A sailboat cut to size for Carac, a shoe box on a taut hull for Crédit Mutuel and full curves for Banque du Léman. 

The first thing you notice when you look at the six sections of the scow-shaped Class40s is that on the last three, the sides have been drastically reduced in height, to reduce the lateral wind drag, which is particularly harmful in light airs. This also reduces the developed surface of the whole hull, and puts the weight gained into the ballast.

This class is definitely destined for a great future.

François Chevalier

Class40

Overall length: 14.19 m (46,55’)

Hull’s length: 12.19 m (40’)

Beam : 4,50 m (14,75’)

Draft: 3.00 m (9,85’)

Air draft: 19 m (62,33’)

Solent and Mainsail: 115 m² (1 237,85 sq. ft.)

Displacement: 4.5 t

Ballast: 2 x 750 litres

36th AMERICA'S CUP: ANALYSE de la VICTOIRE de TE RUHATAI

 Analyse de la Victoire de TNZ

Avant de démêler ce que sera la prochaine America’s Cup, il est indispensable de comprendre pourquoi Te Rehutai a été le plus rapide, sur le plan architectural, et je n’ai pas vraiment vu d’explications dans la presse. 

 

Tout d’abord, Guillaume Verdier, l’initiateur des AC75, a une vision globale du voilier idéal plus homogène, dans la mesure où il en est l’inventeur. Premier point, l’AC75 doit voler dès que le vent permet le départ des régates. Second point, la coque doit avoir une fonction d’aile d’avion à basse vitesse, et près du sol. Aussi le navire est traité comme un hydravion devant décoller et se maintenir au-dessus de l’eau à basse vitesse. 

L’étrave de Te Rehutai est particulièrement découpée comme celle d’un Catalina. Seuls les deux cockpits émergent de l’aile, le plus étroit possible. Le pont est abaissé au maximum en tenant compte des points de mesure minima, le fond de la coque est en aile de mouette et le plus plat possible sur l’arrière pour assurer l’effet de sol. Résultat, une surface frontale de 10 à 15 % inférieure aux challengers. Enfin, les foils ont deux fonctions, raideur par le lest, et la portance, donc le poids sera dans un obus, et les ailes sont longues, fines et horizontales, pour un maximum de portance et un minimum de traînée. Peut-être pas autant de portance que son proche concurrent qui a opté pour de larges ailes qui contiennent le lest, mais les Néo-Zeds remontent le vent avec un VMG légèrement supérieur.

Le cocktail est inédit, étonnant, un peu tarabiscoté, mais gagnant !

36th AMERICA'S CUP: ANALYSIS of TE RUHATAI's VICTORY

 Analysis of TNZ's Victory

Before unraveling what, the next America’s Cup will be like, it is essential to understand why Te Rehutai was the fastest, in yacht designing terms, and I haven’t really seen an explanation in the press.

 

First, Guillaume Verdier, the initiator of the AC75, has a global vision of the ideal sailboat that is more homogeneous, as he is the inventor. 

The first point, the AC75 must fly as soon as the wind allows the start of the regatta. 

The second point, the hull must have a function of an airplane wing at low speed, and near the land. Also, the ship is treated like a seaplane that must take off and stay above the water at low speed. The bow of Te Rehutai is particularly cut out like that of a Catalina. Only the two cockpits emerge from the wing, as narrow as possible. 

The deck is lowered as much as possible, considering the minimum measurement points, the bottom of the hull is seagull-winged and as flat as possible on the stern to ensure the land effect. The result is a frontal area 10 to 15% smaller than the challengers.

Finally, the foils have two functions, stiffness through ballast, and lift, so the weight will be in a bullet, and the wings are long, thin, and horizontal, for maximum lift and minimum drag. Maybe not as much lift as its close competitor who has opted for wide wings that contain the ballast, but the Neo-Zed goes upwind with a slightly higher VMG.

The cocktail is new, surprising, a little convoluted, but a winner! 

America's Cup - AC75 designs February 2021

 LATEST AC75 - DEVELOPMENTS - ANALYSIS

AC75 DESIGNS

(End January 2021)

The first four AC75s built in 2019—we have already featured them on the blog—have had their share of surprises. Built in view of the 2020 regattas in Cagliari and Portsmouth, they are now destined to be scrapped (!) as these races have been canceled.

 

As we could see, the design teams had come up with very different architectural solutions in answer to the new rules. As a result, it was not easy for them to be sure about what the second boat would look like. However, everyone retained that it was essential to design a slim hull under the main hull, a kind of long keel, to facilitate the take-off.

         

It’s never obvious to redraw the shape drawings of a boat for which we have no documents from the designer’s office. The design teams are increasingly comprised of hydrodynamic and aerodynamic engineers, and the amount of creative work left to the designers is increasingly reduced. For our own part, we’ve never spent so much time understanding and reproduce the lines of these yachts. It is difficult to reference, as usual, the designers’ personality. If it’s impossible to mistake a William Fife’s drawing with a Nat Herreshoff, from now on the ideas fly, as much as the crafts! And each one builds on a powerful idea to avoid slowing down in maneuvers or wind changes, and quickly recover speed.  

 

Britannia 2

Back to the first Britannia.

This one looked almost like a semi-trailer, with a bow as a cap and back boards that could help with beam wind propulsion. Another, more interesting feature was to dig a central tunnel in order to increase the surface area of the lower part of the mainsail. Consequently, the mast support was positioned higher on a console. Indeed, the rule stipulates that the mast base must be at least 1.50 m above the measurement waterline, at the same height as the sheer line. The rule also specifies the longitudinal location of the spar step. Amazing, by the way, these rules, where the characteristics are not called by name. We talk on a reference line or plane, but never about “hull length” or “freeboard.” By going down the central section of the deck, it’s possible to save more than two square meters of sail. However, this option has some disadvantages. Thus, this sailboat would win the prize for the largest hull development and, in general, this is not the purpose. From an aerodynamic point of view, the semi-trailer solution is not a panacea. The hull, very wide at the aft end, with a fairly round hull, adheres before take-off and slams during water landings. Very soon, it became obvious to add a central edge to soften the hull’s fall in the water.

            

For the latter yacht, Britannia 2, the design team has completely reviewed its copy. Exit, the wind tunnel. A large, flat-bottomed keel, which extends from under the bowsprit, quickly widens to end, deep enough, in a tapered position, ahead the rudder. The hull itself is lined with a second one, narrower, which begins in front of the foils to stop on the stern. It is designed for trim adjustments. In fact, the boat is made up of three superposed hulls. Britannia 2 is cambering while losing height. This prevents the hull from undergoing a violent rise in wetted surface area.

As all competitors have found, the AC75 does not need width at the waterline when at rest. Arms and foils operate as stabilizers. This is a feature that was little taken into consideration in the first generation, but that everyone has integrated since then. A great deal of aerodynamic work has been done to ensure good aerodynamic leak. However, the priority seems to have been given to a better penetration of the sea spray, with a freeboard diving well below the bowsprit. The outline of the Britannia 2’s bow appears to create less buoyant lift than its rivals, notably in light airs, when lifting onto its foils. When forced to increase the curve of the foils’ flaps, the British lose speed, especially in tacking. To make this set flying, wide foils have been retained, with initially wings “Stuka type,” allowing self-stability, then broad V-shaped wings, with a spoiler at the tips. The ballast is positioned in the central part of the wings, without creating a bump. Tricky choices, but which have been carefully fine-tuned by a outstanding staff and a continuously progressing development.

 

Patriot

 

The first version of the New York YC Challenger AC75 focused on “aerodynamics.” The result was a big soap worn to cross the limits of the rule in a shape that provided less resistance. 

When some observers realized that the next Cup monohulls would fly, they thought that only the foils would be decisive. So, farewell to the naval architects! But it’s not so easy to stay stable and up in the air, sea and the wind are by definition unstable. On the water—and above it—nothing is obvious. 

For their second racer, Patriot, the Americans have opted to refine the front shapes considerably while maintaining a broad deck but remaining below the allowed width. There’s not a single spot where the hull or the underbody would be flat. All surfaces are perfectly rounded. The forward sections are in a very open V-shape, which creates a figure suitable for lift at the beginning of speeds. The keel—thin—starts under the bowsprit and dips almost straight down to the arms of the foils. Then it climbs beneath the hull at the last part. The deck is slightly recessed to gain sail area, favor the wind acceleration in the lower part of the sails and increase the plaque effect by reducing its inclination. In this way, the center of gravity is dropped.

 

AC75s tend to tip forward during tacking, losing speed, going from 40 knots to 30 knots, even 25 knots if the hull contacts the water, and to 18 knots when the hull plunges deeper in water.

On the three views of the line plan, the hull is shown in the boat’s measurement position, i.e., at rest. In this configuration, the mast is inclined five degrees aft. However, when flying, the pitch changes and the yachts heel forward, often by about one point five degrees. Sometimes the curve can be as much as five degrees. However this doesn’t last. Only Luna Rossa 2 leans fairly less. In fact, the boat is in its trim when the bands on the sails become horizontal. On the other side, all the sail planes are represented in the highest-flying position. But this difference in display is not a problem for designers who only work with computer programs.

 

On Patriot’s water lines (see drawing view), the narrowness of the waterline, and therefore its thinness, can be clearly discerned, with particularly pinched water entrances. The foils are wide V-shaped, slim, with a shell in the center and two small spoilers folded down at each end. At the peak right from the first trials, it was without considering the progress made by the other teams.

 

Luna Rossa 2

 

Right from the beginning, the Italians had decided on a long keel and a symmetrical silhouette, with the freeboard measurement point culminating at the very foot of the mast. Below the waterline, the water lines were nearly balanced. The fact that cockpits are lateral is a result of multihull habits in which the central section has become the indispensable mainsail base plate, following the theory that the ideal plate perfectly reflects the sail above, like a mirror, with all its strength.

The version #2 of Luna Rossa doesn’t show any radical change, but the keel, still V-shaped, is deeper and the cut of the freeboard on the front is more marked. The front water lines are more pronounced. The foils remain in an inverted V shape, with a fairly large surface area, and the ballast is incorporated in the arms and foils, which are fitted with spoilers at the wingtips, with an almost straight trailing edge.

 The double mainsail is kept in a battened position, without a boom at its foot. These winglets are known to reduce air or water turbulence at the ends. On airliners, the fuel saving is about 3.5%. With a relatively conventional concept, Luna Rossa focused its energy on maximizing its advantage and has enjoyed the benefits.

 

Te Rehutai

 

The initial departure of the defender boat, Te Aihe, had surprised: inverted multihull bow, canoe hull under a lightened TP52 hull, wide wing foils, without bulbs. The audacity of the New Zealanders had impressed.

With Te Rehutai, the amazement is still full. A broad bow wafer with rounded edges, a keel that starts in the axis of the bowsprit, widening to the horizontally, while a true keel, curved, comes to stick underneath to die on the transom in the shape of a reversed cake mold. This emphasizes the two functions of the hull: to control the wind at deck level and, for the hull, to manage changes in trim and hull height. It can also be added that the aerodynamic problem is crucial, and that the design of the bow and the entire forepeak can play an important role in its ability to rise in the air. These shapes would still be basic on Te Rehutai if on the bridge, the channel did not start so early, from the tack of the Solent—rule obliges—so that the official support of the mast is carried by a 60-centimeter-high pylon. As a result, the jib and mainsail areas are increased, and the plate slope is decreased. Below, the flat hull flared at the stern to end in a very wide V at the transom.

What is for sure is that all the ingredients that seemed to give an advantage over the first boats launched were found on this machine, whose design is innovative, to say the least. As on Britannia 2, two horizontal V-shaped rods at the masthead are used to trim the mainsail opening. The arms of the foils have a protrusion on the back, before the part left open to each contestant, which increases the buoyancy of the arms and thus the stability of the boat. The foils have a prominent, seamless bulb with slim, flat, chopper-shaped wings with winglets. Their newest design is just as thin, but less curved.

 

If the first flights seemed quite stationary, and some flights in light airs were amazing, the control of these monohulls is a matter for specialists who admit to spending a lot of time behind the screens. The America’s Cup has often been contested with a wide range of skills and disparate sailboats. The winning team will be the one that will have found the most multi-purpose racer, between technology and a sense of the sea, in such a way as to be able to explore the full potential of these monohulls of the future.

 

AC75 DATA

AC75

Foil monohull

Overall length: 22.86 m

Hull’s length: 20.70 m

Beam: 5 m maxi

Beam foils out: 16 m

Draft: 5 m

Air draft: 28 m

Surface of the mast: 17.2 m².

Mainsail: 142 m².

Solent: 90 m².

Genoa: 205 m².

Sail area upwind with Solent: 232 m².

Sail area downwind: 347 m².

Foil weight: 2 × 1,175 t

No-load displacement: 6,195 t

Crew members, weight: 1.12 t

Team members, number: 10 + 1s