Behind the design of the Foil range

Welcome to behind the design. Today we speak with foil designer Jerome Bonieux and Foil product manager Max Pajank to talk through the new SPIRIT and SPIRIT SLS foil range. Welcome guys, Jerome, could you tell us what is new and what we can expect with the new Spirit and Spirit SLS.

Hear the Full interview

Hear the Full interview

Jerome. We started development with the aluminium foil, we’ve got a new mast for this year and the idea was to optimize the designer profile because, as you know, the aluminium mast is an extruded profile so the thickness of the profile the quarter length is really important that’s going to give you sort of the rigidity, torsion and bending that you can expect from your mast, which are super important characteristics for a mast. So we spent quite a long time working on different profiles, different thicknesses for the walls and we came up with this new mast that we have which is, I can’t remember the exact numbers, but something like 15% stiffer in bending stiffness and torsion while still being 15% lighter than last years model and also being 5% more efficient.

So we’ve managed to win everywhere, drag, torsion, bending stiffness, weight and hydrodynamic efficiency. Once we were happy with this profile we took the same profile onto the Spirit SLS carbon range as we decided to make a similar construction to the hollow aluminium mast. Everything that worked well for the aluminium worked well for the carbon mast so it was also very stiff and very light, even lighter than the aluminium.

There’s also a new fuselage to go along with the new mast, can you tell us a little bit about that?

Jerome. Sure, starting with the aluminium fuselage, we decided to shorten it by 3cm. We brought the front wing a little closer to the mast making the whole foil a little more manoeuvrable. We knew we already had a really stable platform, bringing the front wing closer to the mast loses a little stability but we had such a stable platform we could get away with bringing it closer.

The gain we got from this design change in terms of manoeuvrability and just overall feeling as you go faster, you feel like you have more control over the foil, whereas before we used to get quite a lot of front foot pressure as speed increases and now with the new position of the front wing we have a more linear front foot pressure with speed. The only drawback is a little bit less pitch stability but we are still one of the most stable platforms out there if we compare with our competitors.

Moving onto the wings, are they cross-compatible with previous spirit fuselages and are there any new additions to the range?

Jerome. We kept all the same mounting for the front and back wings, so you can use all your existing wings with the new mast and fuselage system. We’ve done some small tweaks to the wings. We’ve added a small recess in the front wing so the fuselage sinks inside the wing, this makes the connection more streamlined and hydrodynamic.

We had a few prototypes for the launch but we felt the wings we had were working super well and by just doing this small change to the fuselage by bringing the front wing closer we achieved an improved feel for our foils. The few prototype rounds we did weren’t a significant step forward so we decided to use the time to work on more wings and come up with something that is relevant in terms of change and feeling.

Moving over to you Max, tell us about the feedback you received going into the product development phase and what goals were you trying to achieve with the new Spirit and Spirit SLS range?
Max: The main reason we decided to make the new profile more beefed up and stronger, was to give it more stability and bending stiffness. Another reason was the fact foil winging has become more popular and we received feedback from dealers and customers that it’s not ideal for foil winging. Our main target was to make a set-up that was perfect for kite foiling but also working for foil winging.

On the aluminium Spirit fuselage, there are two mounting points for the rear wing, what does this change and what was the thinking behind this design?
Max: As Jerome mentioned earlier, we have quite a stable hydrofoil when compared to other wings out there on the market. Advanced riders often want a high level of playfulness for wave riding or carvy turns for improved manoeuvrability, that’s why we decided to add an extra insert that gives a better turning behaviour and more advanced foil.

So a more agile foil?
Max: Exactly

Do we still see the wedges being used with this year's system?
Max: Yes, each foil can be tuned to deliver more or less lift and more stability at higher speeds based on their preference.

You also work closely with ixent. Could you explain what they bring and what areas do they assist in the design process?
Jerome: They are a German engineering company, with experience in the America’S Cup. They help us with all the layups and calculations when it comes to lift, drag, coefficient of moment; all the important design parameters when you are making a foil. So when I have a design in mind I will first do a 3D model and send all the measurements to ixent and they then run the calculations based on what I have sent them. They then come back to me and say, we suggest you move the wing further forward, or you twist the tip, or let's de-camber the profile here and there to achieve what we had in mind to start with. So I’ll then take these recommendations, change my design to fit the changes and then send it back for a final confirmation, then we go ahead and make a mould and then test the wings before they are production-ready. Most of the time there are still a few minor changes we do after the first round of testing, because as good as the simulations are, they are never 100% perfect, there is always a little margin of error let’s say and there’s always room for us to tweak it more after riding the prototype. So that is what we do, after testing we come back and say, what about adding a little something here and there and then eventually we get to the stage where we are ready to produce a final mould, still test that to make sure all the changes are perfect and then once everything is verified the wing comes out on the market. It’s quite a long process but it's the right way to do it. Starting with calculations, building a database so we know what works and what doesn’t. For example, pitch stability and we want to keep this design parameter the same, we can make sure the new wing we build will match that stability, even if we tweak the profile or angle of attack, we know we can expect the same stability if that would be an important parameter we want to keep for example. So having this database as we continue to build more and more wings allows us to fine-tune the result better and more efficiently. Every time we come up with new designs they are closer to what we had in mind.

Let’s compare the Spirit and Spirit SLS mast and fuselages, one is available in Carbon and one in Aluminum. I imagine the Carbon would be lighter, but is the stiffness the same for the two models and for people looking into both, what kind of riders have each of the ranges been designed for?
Max: The Aluminum Spirit range is more targeted towards beginners to foiling and those who may have not begun foiling yet. With the two back wing mounting options on the fuselage, the riders have the perfect set-up to tune their foil to make it more agile and playful once they have reached a certain level of foiling. The Spirit SLS is targeted towards the experienced and ambitious riders who already have some level of foiling, those looking for the best lightweight option we are offering. Also not only does the weight-saving come from the fact it’s carbon, only having one back wing mounting point on the fuselage helped us reduce as much material as possible.

Is the stiffness comparable between the two models or is it mainly the weight savings?

Jerome: The carbon one is lighter as you would expect and in terms of stiffness, the mast in terms of torsional stiffness they are pretty much identical, aluminium being a very good material to resist torsion, but in bending stiffness the carbon is a bit stiffer. When it comes to the fuselage the advantage the carbon has is in the weight, I think the carbon is about half the weight of the aluminium fuselage. This becomes interesting when doing jumps, spinning the foil. The fuselage is the furthest part away from your board, this is where you are going to notice the most effect when you reduce the weight, in a rotation or when you are trying to swing the board over the top of your head in an inverted rotation, then the carbon mast and fuselage system will give you a definite advantage here.

The Fanatic and Duotone mast and fuselages are different shapes, thicknesses and strengths, would there be one set that would recommend to someone who foil wings more than kites or visa-versa?
Max: I think the first point in deciding whether to go for a carbon Fanatic or Spirit SLS Duotone set-up is the planned use. If someone knows that he is mainly out for foil winging, prone foiling or wake surfing then they should choose the Fanatic set up, in order to have a wider range of possible wings for different waves and wind conditions, but if you want to do mostly kite foiling we would recommend the Duotone Spirit SLS range. The Duotone Spirit SLS has been built, designed and developed for kitesurfing and kite hydrofoiling so that’s the main purpose for this set-up.

Jerome: The one exception might be for really light riders, say for example you weigh 40kgs you would want to pick the Duotone set up as you’ll require smaller wings in general and that’s where you’ll find the smaller wings. The Duotone wings start at 500 sqcm, whereas the Fanatic range starts at 900 sqcm. The fact that the mast and fuselage are a little bit softer isn’t going to be an issue if you are lighter, you won’t be able to apply enough load into the system anyway to flex, so this is the only case where we would recommend the Duotone for dedicated wing foiling. Also, the Duotone set-up will be lighter so being a lighter rider, you will benefit from this lighter set-up. If we bring up two examples of our foil wing team riders out here with us in Mauritius, Henning is going for full-on freestyle moves, using big kicker waves to go huge and do big jumps and even then riding waves, he is using the Fanatic set up to have the stability and strength for hard landings and take-offs and on the other side we have Olivia here who is on the lighter side, she is mainly using her foil for riding waves here and also in Maui, so she is using the Duotone set up because of her body weight and riding style.