Farewell to Gautier Sergent, visionary sail designer for North Sails

The sailing world and that of the North Sails family mourns the passing of one of the most brilliant and visionary sail designers there has been internationally in the past decade, Frenchman Gautier Sergent, 47 and father of three, from a heart attack.

America’s Cup, Imoca 60, Ultim, Gautier-designed sails have won regattas and toured the world, and he is also credited with many of the technological developments put in place by North Sails, such as the research carried out to make sails with structural inference like the jibs seen on the AC 75s in the America’s Cup.

Gautier Sergent had worked on the last America’s Cup with Ineos Team UK for which he was the sail designer, while in this campaign he was involved with Alinghi Red Bull Racing. After working extensively in the United States developing North Sails 3Di technology, Gautier had been one of the supervisors of the sail loft in Lorient, near La Base, the nerve center of European ocean sailing.

Ken Read, president of North Sails, said of him, “He was a visionary sail designer and embraced new challenges with enthusiasm and dedication. Gautier leaves an irreplaceable hole in the sailing world and a legacy that North Sails will be proud to honor.”

The Newspaper of Sailing had interviewed him in 2016, in a long chat with our Mauro Giuffrè themed Imoca 60, with a special focus on Imoca foil projects.

Gautier Sergent and the Imoca 60s

How have the sail plans of the latest generation of Imoca foilers changed?
There is one less sail allowed in the regulations than last time. So up to 8 sails in total, including the storm jib. This in itself forces a review of the sail inventory. If you add the new foils design that drastically changes the boat’s polars, the new sail inventories are drastically different from last time. Then each skipper makes the specific choices based on his boat, but if we try to summarize the differences for new foilers:
– Generally there are no more symmetrical spinnakers
– the so-called J1 (masthead jib walled at the extreme bow) has disappeared. That sail generated high loads by being masthead. The rig, which is of the One Design type and limited to 30t.m of righting moment, has become the fuse or weak link in the chain now that foils can generate a huge dynamic righting moment (close to 40t.m launched at tight slack).

So the trend is to favor fractional sails. This also helps the stability of the boat when foiling(lowering its center of gravity and center of effort). As you can imagine the boats are quite unstable in pitching by not having elevators on the rudders. Just like a rocking chair! And because boats start foiling very early, they will have to reduce sail area much earlier, so as to shift the various “crossovers” between sails to lower limits of the true wind.

What is the difference, and why, with the sail shape of an older generation Imoca?
In general, the sails have become flatter especially at the top. Boats need the square footage to take off but then you try to “unload” aerodynamic power as the boat rises on the foils and accelerates (with the apparent soaring). Because you are racing solo, you will not always have perfect sail trim, so making the topsails flatter means they “automatically” depower when boats accelerate. The shape curves are also more advanced to maintain the balance of the boat and realize fast airfoils.
All sails that are not jibs use “load sharing technology” (Helix) (there is no anti-twist cable, but the sail has “structural” reinforcements that replace it and absorb the loads by lightening the rig ed.). This helps to reduce crushing of structures and to project forces forward rather than sideways. It also reduces loads on the rig, which is a key element, as explained above, as the rig is the limiting factor in terms of power.

What are the maximum speeds that a new Imoca can reach?
Maximum speeds are limited by sea state. What is impressive is what we call sustained speed. The previous generation could reach high speeds on a surf along a wave. These new foilers are most impressive in the medium breeze, where they can really use the full power of the foils and sails and be stable. For example, in TWS15 (TWS is the real wind ed.) and in reasonable sea conditions we will have a boat at 25kts speed 120 real angle to the wind. We have had cases where guys have been able to sustain a boat speed of 25kts for a very long time. Hours, not seconds.

Mauro Giuffrè