Frame and board development
Differently from “regular” kiteboarding for which you may find for every level and morphology suitable equipment, before being able to go seated kiteboarding, you need to work on your equipment. I tried to shop the Internet, but no existing solutions were in my opinion satisfactory. They were all adaptation of existing equipment. Especially the existing frames (connection between the seat and the board) were derived from alpine ski frames with suspension or waterski cages.
I tried the seatkite machine developed by Tadeg Normand during a cold weekend in December 2012. As kite instructor, he developed a seat kite machine for a friend who was quadriplegic. It had some floaters in the backrest to make sure that you stay afloat up right. Very quickly I realized that safety is a serious issue when seated kiteboarding. This first experience told me that before even getting out of the water planning on the board, the forces of the kite pulling you horizontal through the water should be balanced with the resistance of the board- frame- seat combination.
When the frame and seat are correctly positioned on the board, then the kite pulls you naturally in a waterstart position, your head facing the kite. When the frame and seat are too much aft of the board or the board is too long in front of your feet, then the kite pulls you in a way that you are pulled backward with the tendency of also being pulled under water.
The weight and size of the machine was such that it was not at all suitable to use in waves from a beach, not mentioning the transport.
Back home in Scheveningen, with my friend and boardshaper Bram from Woody Cookie, we started the development of a frame that could be modified in order to try different settings. Marine multiply wood was the perfect material to shape and drill in order to experiment with different seat positions.
I was a total beginner in trying to develop at the same time my own equipment. Not an easy task.
Nevertheless, Bram and I went in January 2013 to Aruba to try my first sitkite-board, with a wooden frame. We decided to adapt a light weather twintip board as first support. Bram shaped some floatation volume in the nose and I put around 1kg of lead ballast in the back to help me float properly during waterstart maneuvers.
Unfortunately, the frame completely exploded after my first jump (see end of footage below). It was clear from that moment on that the challenge would be to build equipment that would be able to resist all forces and shocks.
And after 5 days of riding the adapted twintip board, I realized that I would have to design my own board with proper fins to be able to get upwind, with a proper rocker-scoop shape and outline to be able to ride and jump waves.
Back home, I went to Rob from Machinefabriek Krul to ask if it would be possible to make a frame from aluminum plates. Rob used to manufacture custom fittings for my 2.4mR (Paralympic Class sailboat) during my Paralympics campaigns. Plates are easier to ply and weld than tubes. We spent some time to imagine what would be the forces exerted on the frame and board while landing flat from a 5 meter high jump. After a first version, which folded after two sessions, Rob reinforced it with some profiles and thicker aluminum plates. We were always surprised that I never got hurt. The last reinforced model looked like the one on the picture below.
After two years of good services, due to fatigue and corrosion in salt water, some cracks appeared in the plates. Luckily Rob was always able to repair with some welding and reinforcements. At this stage, it was clear that the frame I developed was not suitable to be produced for commercial purpose.
Thanks to my contact with the Dutch Sailing Federation, I was able to make some measurements on the forces and accelerations while riding. The Innosportlab in The Hague placed an accelerometer on my board. Results are illustrated here below.
It produced some interesting results: the accelerations involved at landing with the board flat on the water are around 6G during a time laps of 0,2 seconds. With a body + equipment weight of around 80kg, it means a force of 500kg on the equipment!
Parallel to my own development program, some students from the Delft Technical University and The Hague University tried, with some academic approach, to design a frame following my requirements.
The results were very creative and ergonomic, but all of them were lacking robustness and reliability. I was always able to destroy the equipment the students and others technicians generously produced for my pleasure on the water. Here are some pictures of their ideas:
I tried many setups, even with suspension mechanisms. The rocking movement of the seat when landing jumps or edging upwind influenced negatively my board control. It was difficult to avoid bouncing in chop. The rocker-scoop line and shape of the outline of the board had a much larger influence on the shock and bouncing absorption than the suspension mechanism itself. Also, as my skills improved, I could reduce heavy shocks by controlling the side angle of the board during riding and landing jumps. I slowly abandoned the idea of having a suspension between seat and board. With an integral approach, where we designed together the frame and the board, we managed to build something light and robust without any moving parts. To create shock absorption for extreme wipeout situations, without losing stiffness of the frame, I placed some static rubber blocks between board and frame. The static rubber blocks work also as fuse. If they break, they are cheaper to replace than the board or the frame.
The final issue in the frame design has been the weight. I managed with the aluminum plate frame to build a strong and stiff frame, but it was rather heavy, around 3,5 kg. I was convinced that the performance goes also through weight reduction of the equipment. But it is not easy to increase strength without increasing moment of inertia, which means also volume, of the construction. For safety reasons, the board and frame should have as less volume as possible. While waterstarting, I need to float with my head outside the water; if you increase the board and frame volume, you have the tendency to float like a cork head down, which compromises the safety.
Parallel to the frame development, Bram and I worked on the shape of the board. Needless to say that we also learned the hard way: I broke many boards to come to the conclusion that a wood core between 12 and 16mm thickness was the best compromise between reduced volume and strength. Also multiple layers of multidirectional glass gave more flexibility and damping than a carbon layup. And since the beginning of 2015, the development on boards continued with the engineering team of F-One in France, which is now able to produce a board ready for the market. The state of the art production process and knowhow of F-One enabled to shape a woodcore board with a strongly curved nose, which enable a length reduction of the board in front of the feet. See picture below:
For 15 years I am now on wheels, I got Vanadium steel, carbon, titanium and Aluminum wheelchairs. All of them to heavy for my taste but none of them broke or rusted. A frame in high grade Aluminum or Titanium is therefore the solution, but difficult to manufacture in your garage.
As long as I was able to ride, I had the patience to put my ideas on paper. It was clear that before I contacted some wheelchair or handbike manufacturers, I needed to make construction drawings. Scott, a young industrial design engineer, helped me to draw a set of construction drawings in Solidworks.
The marketing and design team of Wolturnus from Denmark reacted very enthusiastically. Their knowhow in anodized high-grade aluminum (7020) racing wheelchairs and handbikes very much inspired me. After a few modifications on Scott’s drawings, they were able to produce a 25mm diameter tube frame with a weight of around 1600 gr, what an improvement!! Christian from Wolturnus even let me choose the color of the anodized coating. For the first time I was thinking esthetics for my equipment :-)
My new super light frame is also narrower which enables me to edge and carve more without the spray generated by the edges of the board hitting the frame. The reduced weight makes the handling in wave riding really improved. And finally I am now able to load the sitkite board alone in my van.
The frame is now available on the market, best in combination with a sitkite-board from F-One. There is a clear design synergy between the shape of the board and the dimensions of the frame.
The seat design is really depending on the ability / disability of the rider. As a complete paraplegic from vertebrae Th12, I still have all my abdominals. I use a seat from sitski frame manufacturer Tessier in France, size 1 with lowest backrest and without any side padding. The closed foam padding adds buoyancy to the system, which compromises safety (floating head down) as explain previously. My neoprene suit builds the padding between hip and seat. I only use a small foam padding under my butt to avoid pressure soars. The harness hook is the Multi Spreaderbar from Mystic strapped around the seat as shown below:
To summarize, it might be cheaper to start with adapting existing equipment and fixe yourself a frame with a handy friend in your workshop, but my experience is that as soon as you are able to ride and stay upwind, the adapted equipment might slow down your progression and ultimately your performance.
It took me three full years with different technical specialists to come to the actual design setup. I focused on reliability (which means safety), maneuverability (which means performance in wave riding) and light weight (which means self-sufficiency). For more technical information, do not hesitate to contact me, email: thierry@paralympicsailing.com.
For eventual price quotations, please contact directly:
- F-One
- Tessier
- Mystic
