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Inside the mind of Xavier #1 | What if making boats fly is a dead end ?

November 18th, 2020

In this new article series, Xavier Lepercq, SP80 co-founder and technical manager, shares his thoughts on boat design, speed sailing, and the World speed record. Reaching 80 knots on the water with the wind as sole source of power is an incredible technical challenge. His pursuit to break the world speed record has led him to question architectural codes that are currently the standard within the sailing world.

From concept to mature technology, the development of foils and foiling boats spans 139 years. The French engineer Emmanuel Denis Farcot was the first, in 1869, to imagine boats able to lift off the water. The first successful foiling boat however was not realized until 2008. The Hydroptère broke the World sailing speed record along with the mythical 100km/h barrier. This achievement opened the development floodgates. The 2013 America’s Cup put foiling boats in regattas on the world stage, and the 2017 edition led to the maturity of the technology.  The 2021 Cup will enable the experimentation of a novel foil configuration however this will not provide a significant speed advantage over its predecessor, the AC50. 

The limits of foiling technology have been clearly identified: exceeding 50 knots (93 km/h) is difficult, however reaching 55 knots (102 km/h) is near impossible due to the onset of cavitation. It has taken nearly 150 years for foiling technology to reach its full potential, largely due to the spike in innovation that has occurred over the last 20 years.

From left to right: the Hydroptère (©Hydroptère), which beat the world sailing speed record in 2009 / Emirates Team New Zealand’s AC50 (©Emirates Team New Zealand), Challenger of the 35th America’s Cup / American Magic’s AC75 (©American Magic), Challenger of the 36th America’s Cup

When it comes to records, where speed is the ultimate goal, foils will be inadequate

Does this mean the end of foils? Surely not! The diversity of classes in sailing is phenomenal and lends beauty to the sport. In the same way that flying boats will never replace Archimedean boats, they cannot be substituted for by “something else”. However, when it comes to the “record”, where speed is the ultimate goal, foils will be inadequate.

Tired of hearing the status quo “foils = innovation”, in spite of their technical limitations, we have created SP80 with the purpose of shattering established codes of boat design and forging new routes. You’ve guessed it, there will be no foils on board our boat, we will truly be using “something else”!

WE CREATED SP80 WITH THE PURPOSE OF SHATTERING ESTABLISHED CODES of BOAT DESIGN

But let’s not get ahead of ourselves; first, some mathematics that allow us to understand how foils came to be synonymous with speed. By definition:

Speed = Power / Drag

So to go faster, there are two solutions:

1 – Reduce the drag
There are a multitude of possibilities to reduce the drag of a boat, but the most efficient remains the use of foils. By lifting the hull above the waterline, foils reduce the surface area in contact with the water which in turn reduces drag. However, foils inevitably experience cavitation around 55 knots. Bubbles generated by cavitation produce instability and large amounts of drag, limiting boat speed. The foil is therefore a dead end if your goal is to go very fast.

Cavitation bubble on a foil – Experimental study realized by EPFL for the Hydroptère ©Article: L’Hydroptère: How multidisciplinary scientific research may help break the sailing speed record.

2 – Increase the power
The architects have done it before: they invented the catamaran, the trimaran, the ballast, the tilting keel, etc., in order to increase the uprighting moment of boats, as well as their driving force. But in the end, increasing the power has always translated to building larger, longer, and heavier boats that generate more drag. Mindlessly increasing the power is a poor strategy, seeing as the fastest boats are not the biggest.

A foiling moth (left – ©Martina Orsini) is much faster than a Class J (right – ©Carlo Barenghi), though the latter is much more powerful

The World sailing speed record offers incumbents considerable potential for innovation: there are very few rules. Nearly everything is permitted, engineers and architects can let their minds roam free. Today, I believe that the speed of boats is not limited by the physics of our world but rather by our own imagination! With SP80, we took advantage of the absence of barriers. We brainstormed for two years and thousands of hours to get to a concept we believe in. Thereafter it took another year to refine our design.

TODAY, THE SPEED OF BOATS IS LIMITED NOT BY THE PHYSICS OF OUR WORLD BUT RATHER BY OUR OWN IMAGINATION!

After taking the time to test many ideas, we developed a concept that enabled us to increase the power without sacrificing or compromising stability, and maintaining a relatively small boat size. Our weight/ power ratio resembles that of racing motor speedboats. After all, they attain speeds well above 80 knots without having to fly!

NO, WE WILL NOT FLY, WE WILL STAY IN CONTACT WITH THE WATER, AKIN TO A FORMULA 1 ON A BEND!

Xavier Lepercq, co-founder & technical manager
Photo in header: ©Maxime Horlaville / Apivia

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