Jan Termöhlen got his start in the business of composites at a very young age. Recalling his earliest memories, he would work beside his father crafting windsurfing boards in their home in Duisburg, Germany. Living two hours from the ocean, Jan followed his father’s conversion from windsurfing to kiteboarding in 2007. Soon after, he began building his own boards, starting with a surfboard and then focusing his skills on kiteboards, developing a particularly strong obsession with fish shapes. Directing his studies towards mechanical engineering, Jan obtained a master’s degree in composites, the art of building machinery out of resin and fibers. During his studies, he was always building surfboards on the side, but eventually, his hobby’s focus shifted to handmade hydrofoils. Transitioning from a college graduate to a self-employed mechanical engineer, Jan designed bike components until he connected with Core Kiteboarding’s design team, who enlisted him to work on their new foil platform.
What does a ground-up design process for a complete foil collection look like?
It starts with the goals of the program, and for Core’s SLC platform, the aim was to build a kite foil that would suit kiters of all levels. Beginners appreciate its intuitive handling and nice control, while experienced foilers like how its playful dynamics help them step up their game; we made control and stability the key variables in every design decision. There are so many dimensions of foil performance to balance as you’re experimenting with shapes and materials, but its ease of use was always at the top. One of the other key design goals was to create a foil that was resistant against turbulence. This makes the wing slice through the water like butter with no vibrations, and ultimately that’s where the product’s name SLC came from—it refers to the silence you experience while riding our foil setup.
The process itself was very intensive, with feedback from the entire design team that took us through about 25 prototypes from rough early versions to the fine-tuning of the mature, finished product. I started with a section of the wing that came from my studies in engineering; the shape was influenced by theoretical performance and mathematical concepts. We took that initial shape and began experimenting with real-world results. I’ve always built my own prototypes, and because of Core’s affiliation with Carved custom boards, the organization is well versed in composite construction. There was this immediate synergy between my experience with composite bike parts and Core’s in-house knowledge of carbon twin tip construction. With instant access to a CNC machine and 3D printer, our lead time was never longer than 72 hours. In-house 3D printing and laminating allowed us to get our ideas onto the water quickly and test many different factors needed to fine-tune each aspect of the wings.
What was the hardest part of the R&D process?
I had a strong grasp of the theoretical and mathematical principles behind what we wanted in our product, but the hard part was figuring out how to validate these concepts in reality. You can take concepts like hull design, turbulent and laminar flow principles and punch in Reynolds numbers to simulations of various sections, but these calculations are worthless if you can’t find a path to reality. Good engineers are inherently lazy; we try to calculate as much as possible ahead of time because it saves time and effort if you can minimize the hard work of hand-building models in a workshop.
Early on in the process, we had achieved a very stable prototype that we tested in the smooth waters in Fehmarn, where Core’s headquarters are located. I began testing with Sebastian Witzleben and we achieved incredible control and stability, but perhaps the first prototypes could be considered too stable. We then headed to Cape Town to test with Steven Akkersdijk in the rough winds and beautiful waves. While Steven was impressed with our first efforts, we ended up having some intense conversations, not quite arguments, but he was very honest about wanting to see prototypes with more speed and glide. Steven has had a lot of experience with other foil products, and he’s been focused on advanced riding, mastering complex maneuvers like the around the world. Over the next few months, we continued to talk on the phone, and when he came back to Fehmarn to test our improvements, he got off the water with this huge smile, totally satisfied with our changes.
There were many little challenges along the way. Everyone on the team gave input; for instance, we wanted every screw on the fuselage to be the same length. Having used other foils with confusing screw lengths, the goal was to use a single tool, a P30 Torx wrench, and to have all bolts interchangeable. This seemingly simple request actually presented quite the challenge because the fuselage has a geometry that is optimized for efficiency. The foil wing is in a constant stream, and we had designed the fuselage to not disrupt that stream, but with variable thicknesses, it is hard to design uniform bolt lengths for both the mounting of the stabilizer and the front wing. Eventually, sitting on the beach in Fuerteventura, the solution came to me. There were a lot of little challenges, but the process was certainly a team effort. The SLC platform is the product of several heads coming together to identify problems and then figure out creative ways to solve them.
If the foil’s steering is broken down into the three axes, how do you approach the balance between roll, pitch and yaw?
First, you have to evaluate each axis for its stability which is a balance between looseness and stiffness or the delay between your inputs and movement. Each axis is linked; for instance, if you roll the foil, it also has to yaw while the pitch has to steer up to catch you. If it doesn’t do this right, then the foil feels really uncomfortable. Linking the three axes is key to having a nicely behaved foil. One of the critical inputs that we worked on was stabilizing the front foot pressure needed at different speeds and during turns. Often you will experience foils that require more front foot pressure going down a face of a wave or when hitting its upper speeds, but we ended up doing something very special that equalizes your foot pressure throughout turning and acceleration, giving you the same output in different water conditions. I can’t reveal our tricks, but it’s one of the unique features that make this foil so smooth to ride and easy to use.
You ended up with two specialized kite foiling wings; how do you explain the type of riding for each?
Starting with the 1250 wing, we tuned it to make light wind starts easier with equal acceleration amongst the different axes. Since this wing is aimed at progressing foilers, you have to allow it to speed up instead of just accelerating out of control. The wing requires you to put extra pressure on your front foot to accelerate, which is very important for beginners. For those just getting used to the body movements and speed control in foiling, the predictability of the 1250 gives you a comfortable feel with good performance.
The 1000 wing is designed for people who are looking for higher speeds and more glide. The 1000 is a bit looser on every axis, which works really well for wave riding and more advanced maneuvers. Steven has been pulling double around the worlds with this wing because it has a lot more glide, and you don’t need as much power to accelerate. Even if the SLC’s wings behave a bit differently, they both have the same purpose; ease of use for their intended speed and performance.
In addition to the foil setup, you are releasing a foil deck as well. What was the key to this board’s development?
The clear task with the SLC board was to achieve early planing and good control in flight as well as easy relaunch on accidental touchdowns. Sebastian Witzleben started with the bottom shape, focusing on a deep spine and a double concave. The spine gives you easy release for foiling up and soft touchdowns, while the double concave provides early planing. The rails have reduced volume making for clean takeoffs and the angle of the beveled rail reduces the wetted area, which means less friction and equates to less suction. The step in the tail contributes to a clean release and higher board speeds. While we focused much of our attention on how the board performs during waterstarts and landings, you have to keep in mind that most of the time, the board is ridden above the water. Basically, the board behaves like a gas pedal for 90% of the time you are riding, and if it bends or flexes, you get delay and loss of performance. We used a carbon PVC sandwich to deliver stiffness that transfers your body’s input directly into your foil wing, so you get a precise feel for every type of riding.
What have you learned about the larger picture through the foil development process?
Foiling is having a big impact on the whole water scene and there is so much momentum across kite foiling, foilsurfing, SUP and now wingsurfing. It feels like there’s this new spirit of innovation that is flooding the market. It’s nice to see people wanting to try new things, and in response, there’s more space for experimenting. As kite design has matured, we have seen a bunch of consolidation in designs and development has shifted towards improvements on the materials side. Yet, a niche like foiling is young and there’s so much variety and room for innovation—it’s a very exciting place to be as a designer and mechanical engineer.