Behind the Design of Duotone’s 2019 Spirit Foil Line

What was the vision for the Spirit Line?

Ken: We wanted a complete range of kite hydrofoils which were fun, easy and durable for all types of rider.

Sky: Foiling is going in many different directions and there are many different styles. We wanted to offer a range of wings to cover freeride and surf, which is the style of riding I’m personally most interested in and practice on a daily basis.

How did you achieve this and how does it translate into performance?

Ken: We had great success with the aluminum mast of 2019, so we refined that a bit without changing the basic idea.  It’s really hard to beat an aluminum fuselage for strength, weight, low drag and real durability.  We needed good strength because we were planning to put some sizeable wings on it. We kept the cross-section as small as possible and consistent with strength constraints. For our most affordable wing set, Freeride wings, we wanted to stay with our Carbon 30 wing material that was so successful last year. The Carbon 30 delivers a very affordable and durable foil, something everyone can enjoy without being too precious. The back wing is similar to 2019, but has a lower aspect ratio and thinner profile. The winglets provide a nice amount of directional stability.

Sky: Ken and I have worked on a lot of surf and SUP foils over the past year and a half. We’ve found that there are many design parallels to be drawn between the big surf foils and kite freeride/surf foils. Surf foils need to be very tolerant of big changes in the angle of attack, stable and easy to use. These same qualities also make for really fun and accessible kite surf foils.

What were the challenges you faced and how did you overcome them?

Ken: We wanted to make our 950sqcm wing in Carbon 30. The challenge there was to create a fairly big wing but keep it within volume constraints imposed by the moulding process  I have three pre-production samples of this wing in Carbon 30 and I love them because they perform well and are nearly bombproof – great for riders that hit reefs and rocks, which is most of us from time to time. Unfortunately, the surface finish of these samples aren’t great, so I’m not sure where we stand with that wing. In addition, we have an all-carbon version of this wing and it’s a bit faster, which is nice, but not as bomb-proof. We also ran into the issue that our GT version of the Spirit line is almost too fast. It’s very competitive with the Daytona all-carbon foil set.

What are the qualities, characteristics, and purpose of each foil in the range?

Sky: The Spirit Freeride is a nice all rounder that is good for people getting into foiling for the first time. It has a big speed range and is stable and easy. The front and back wings are constructed using our Carbon 30 Compound, which is a super strong, molded material that doesn’t scratch or ding easily. It’s great for schools or riders who want something easy and durable.

The Spirit Carve and Spirit Surf foil wings are made of uni-directional per-preg carbon with a foam core and are light and stiff. These two wing sets are inspired by pure surf foils and share many of the same qualities we look for when surfing without a kite like early take off speed, great carving abilities, low stall speed and maximum glide. All of these performance characteristics make them easy and playful, with the ability to use a very small kite if desired, to achieve that magic surf feeling on a kite.

What was your role in the development of the Spirit line?

Ken: I did a lot of the initial design work. I researched different wing shapes then working with CAD software and drew up some wing models. I ran some of the wing models through computational fluid dynamics (CFD) software so I could evaluate their likely performance. Finally, I worked with my CNC guy and shaped wings to the precise design shape.For the fuselage shapes, I didn’t do CFD analysis. Instead I used CAD software to model prototypes which were then shaped by my CNC guy. Once that was done, Sky Solbach and I were ready to take the wings for testing.

How has the Duotone foil range evolved over the years?

Ken: When we first became interested in foiling, few people were doing it and lot of them were getting hurt. We thought that maybe there should be more emphasis on safety, so we made the safest foil on the market. As the sport has developed, there’s better information at the beach, in shops and online, so people are able to get into kite foiling without as much risk as before. In response to this change, we went for more conventional shapes and put greater emphasis on affordability and durability. That’s what the Carbon 30 wing material gave us.  This year we have retained the emphasis on affordability and durability with a Carbon 30 wing set, but have gone to even higher performance levels with our full-on carbon wings.

Sky: Our foil range is much more diverse now and we are offering different types of foils for different conditions and riding styles. As foiling evolves we will continue to offer foils for all facets of kite foiling.

Max: This foil range is the best we’ve ever had at Duotone. Besides the optimized mast profile, our Carbon 30 wing material makes them more robust, leads to better performance and gives them the perfect look.

In your opinion, what makes the perfect foil?

Sky: Personally, I am looking for a pure surf feeling. For me there’s nothing better than laying into a turn on a surfboard and feeling the fins and rail engage, accelerating through the turn. I want my foil to translate that type of feeling so that I can achieve a similar sensation in tiny waves or even on flat water. I also know that other riders might say the perfect foil is one that goes 35 knots around a race course in 10 knots of wind. But there lies the beauty of foiling, it offers something different to each user and it’s up to you where you want to take it.

What makes foiling so exciting?

Max: Foiling offers new possibilities and challenges. There is no better feeling than flying over the water with little wind in your kite. Although foiling is challenging in the beginning, it allows you to enter a new world of kitesurfing and surfing.

What dictates performance trends in foiling?

Sky: I have always believed that if something is fun and accessible, then people will want to do it. We are always finding new ways to have fun on foils and things are still evolving. It’s exciting that so many people are interested in foiling and that so many brands are putting effort into making it better, easier, more diverse. It’s all about where riders want to take it and it will only continue to improve.

Tell us about the manufacturing process.

Sky: All of our fuselages are CNC milled out of high-grade aluminum, so the precision is perfect. Our aluminum mast is glued to the base plate in a process used by Formula One, that fuses aluminum parts and is additionally screwed with two M8 bolts for the most bombproof connection in the industry. Our wings are manufactured using high-grade pre-preg uni-directional carbon with optimized fiber orientation for maximum stiffness and strength. We have done the hard work to source our own manufacturing rather than doing the one-stop-shop solution in Chinese factories of other brands. It shows in the quality of our foils.