The new norm – Part II
Lead designer Renaud Bañuls digs a little deeper into the design philosophy behind Thomas Coville’s spectacular new Sodebo 3 Ultim with a look at a new generation of foils and the essential part being played by numerical simulation as the Ultim class moves deeper into full foiling
As was touched upon in Part 1 last month, a major innovation on Sodebo Ultim 3was to improve drastically the Passive Speed (the inherent speed of a yacht before applying any sailor inputs) of the chassis and the sail plan. The big challenge in the latest generation
of Ultim came from the larger foils that must be designed, engineered and then suc- cessfully manufactured if we are to achieve the performance gains of up to 25 per cent that we identified are available depending on wind speed and angle. On the previous generation of Ultim,
including the former Sodebo 2 (ex-Geron- imo), the curved foils fitted were still prim - arily assisting the buoyancy of the floats to
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deliver what we call the ‘skimming’ mode with the outer hulls each just kissing the sur- face of the water. They were only efficient at relatively high speed, and only started to make the boat fully flying when Thomas later installed rear foils on the rudders. When full foiling was achieved it was still a compromise between two technologies. The latest generation of larger foils start
to be efficient and make the boats fully flying far earlier. However, this huge potential doesn’t necessarily make the new Ultim a ‘fully flying boat’. Even if they can fully fly at a relative low boat speed no one knows today how long a solo skipper will be able to make his Ultim fly around the planet in reasonable safety.
Foils and the Passive Speed approach To design the foils of Sodebo Ultim 3 we enjoyed a strong collaborative partnership with Thomas [Coville] and his Sodebo in-house design team (in particular Yves Mignard and Jean-Mathieu Bourgeon), together with the renowned foil expert Martin Fischer and structural engineer Steven Robert. Foiling requires a lot of work from the
sailor. We all saw during the 35th America’s Cup the AC50s foiling with the crew constantly grinding or cycling to
provide a consistent level of power to the helmsman (or flight controller) as he continuously adjusted the foils and rear rudder and elevator pitch to stabilise the flight. This human input is what we dubbed Active Speed in Part I. Trimming the foils and the rear foils
requires time and energy. It is easy to understand that it is much more demand- ing for a solo skipper on a huge and very powerful trimaran. An America’s Cup team will conceive
fast foils with maximum operating effi- ciency, getting the expected lift for the minimum drag. But this approach will of course require active control from the crew to keep the boat stable. On Sodebo Ultim 3, mainly dedicated
to solo racing, such stability will not depend upon active control from Thomas. Nor can it come from an automated flight- control system as this is not allowed by the current Ultim class rule. So the flight stability on Sodebo 3 has to be passive, being derived inherently from the design.
Stability vs performance In other words, fast foils for our purposes require active stability. But that passive dynamic stability in the design of the foil necessarily impacts its performance. Meanwhile, sailing an Ultim single-
PHOTOS FRED MORIN/SODEBO
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