Designing kites for a world record

October 20 2024

Our boat for the world record is powered by a kite instead of a conventional sail. Before thinking about take-off procedures or control systems, we first had to design and produce much larger kites than traditional ones, that can withstand extreme loads: instead of pulling an 80 kg humain being, our kites have to pull a boat weighing around a ton! It’s not something you can find in local shops, so we had to design custom kites to meet the very specific needs of our record-breaking boat. We tell you more in this article. 

Why use a kite?

While it’s rather unusual to see a kiteboat attempting to break the world sailing speed record, the potential of kites is unquestionable: the second highest speed ever recorded on the water is held by Alex Caizergue (57.97 knots / 107 kph average on a 500m run).

For SP80, the kite was the obvious choice:

– A kite is easily interchangeable: depending on the conditions of the day, the team can adapt and use a 25m2 kite as easily a a 40m2 one.

– Regarding safety, the boat can slow down in a few seconds, simply by releasing the kite, which is impossible on a conventional sailboat. This is reassuring for our pilots who have to launch our rocket at 150 kph!

– From a more technical standpoint, the kite’s traction is centralised in a single point on the boat, which enabled us to “easily” create a mechanical system that constantly balances the kite’s force with the boat and its foils. We’ve already talked about it here: our entire boat is designed around one key concept : stability!

The challenge: designing world record kites

The mission was clear: our kites have to tow a one-ton boat up to 80 knots (150 kph), while remaining fairly easy to control. We have to guarantee a giant kite will take-off in difficult wind and wave conditions, with a record-breaking boat on the other side of the lines that just wants to move forward, and fast. 

A kite combining performance, strength and ease of use is not something easy to find! The team spent years in R&D testing ideas, with some developments still in progress…

Inflatable or Ram-air kite, finding a compromise

Two types of kites exist on the market: ram-air or foil kites, with a similar structure to that of paraglider, and inflatable kites.

The main difference is that the former, like a paraglider, will inflate solely thanks to wind power, whereas an inflatable kite will be inflated before sailing.

Inflatable kites are way easier to handle, especially for the take-off! On the other hand, they are also thicker and heavier: an inflatable kite will be significantly less performant than a ram-air kite.

When focusing only on performance needs during a run, it seems logical to use ram-air kites to propel our boat. However, when including the take-off stages, this choice is not so obvious! Keep in mind that we need to take-off huge kites (between 25 and 45m2) in strong winds (with gusts up to 45 knots), with waves that can rise up to 80cm… and all of this from the sea!

We therefore made the choice to use inflatable kites, while optimizing them as much as possible to bring their performances closer to that of ram-air kites. By “optimizing”, we’re talking about working on a kite’s shape or its bridles: for example, we can design a kite that has a longer shape, which is more efficient, but which will also be more complicated to handle on the water and will have more bridles, increasing the kite’s drag. In short, it’s a matter of finding the best possible compromise!

Our current kites

When we launched our boat a year ago after years of design work, we knew we’d need as much time on the water as possible as we still had a lot to learn:

– Logistics: getting the boat out of the harbor, towing it to the best sailing spot, getting it into the right position for the start of a run, recovering it after a run, etc.

– Boat steering: learning to control a one-of-a-kind boat combining sailing and kiting, that behaves in a unique way on the water.

– Safety: for the pilots, to be able to release the kite and get out of the boat quickly in the event of a crash. For the team, ensuring an obstacle-free run (animals, O.F.N.I, other users of the water), knowing the safety procedures for the pilots, knowing how to recover them in case of need, etc.

– Kite management: finding a take-off procedure that works regardless of kite size, knowing how to recover it after a release, knowing how to fly it in a closed cockpit with reduced visibility, etc.

To train as quickly as possible in all these areas, our first priority was to design kites that were powerful enough to pull the boat, but not too complex to handle. If you’d like to know more about one of our sailing days,we encourage you to read our previous article!

We first designed a 25m2 kite with designer Bryan van Ostheim. After testing it extensively on the water with the boat, we gradually refined the profiles of subsequent kites. Today, we have 3 custom-built inflatable kites at our disposal: our “small” 25m2 kite, which we use in heavy conditions, a more versatile 40m2 kite, and a 55m2 kite which enables us to train in light wind conditions. In theory, these kites are strong enough to take us to the world record!

OUR KITES FOR TOMORROW (?)

If our current kites are capable of taking us all the way to the record, we have lots of ideas for doing better, and are working hard on R&D alongside our sailing.

Why continue R&D if our current kites can get us to the record  Designing a more efficient kite would enable us, for example, to make runs in lighter (and therefore more manageable) wind conditions and achieve the same speed. In terms of safety for the team, the pilots and the boat, this is a significant gain! Similarly, having more efficient kites would enable us to sail with smaller kites, and having a few square meters less to take off would greatly simplify our take-off logistics…

Looking at Vestas Sailrocket II, the current world sailing speed record holder since 2012, or at the America’s Cup boats (AC75s), you’ll notice that they don’t use traditional sails. The former uses a rigid wing, while the latter are sailing with “double skin” sails. In terms of performance, this is the absolute best in the world of sailing.

Representing a major innovation in the sailing competition sphere, rigid wings are more powerful and produce significantly less drag than traditional sails. The disadvantage is that they are logistically much more complicated to set up (impossible to fold or store on the water) and much more expensive. Pushing this idea further, sailing a rigid kite would, in terms of performance, be far superior to our current inflatable kites. On the other hand, it’s extremely complicated to implement in our sailing conditions!

Double-skin sails, on the other hand, are very efficient, but again require a lot of logistics: they’re complicated to control, to tension, etc. From a kite perspective, double-skin inflatable kites haven’t yet seen widespread use, but this is an exciting development to watch at the moment – not only for kite-surfers but also for our boat…

To sum up, we know that our inflatable kites are very efficient, but we also know that ram-air kites, or even rigid kites, would be much better! In the real world on the water, it’s currently too complicated to implement… but perhaps we could create a hybrid kite that would take the best of both worlds? In other words, a kite that would take off easily thanks to a bladder, but which would perform much better in the air thanks to elements used in ram-air kites, or even rigid kites? That’s what we’re working on when we’re not sailing!

We’re currently testing 10m2 custom hybrid kites which could then be ordered in larger sizes to tow our boat at 150 km/h. For the moment, we’re still at the prototype stage…to be continued!

© Copyright: Guillaume Fischer

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