I thought I would share some pictures of a recent project to build a hydrofoil for a kitesurf board. Public awareness of hydrofoils has increased since their adoption by Americas Cup catamarans but very simply they are just a wing which is designed to lift in water. For this project, the aim is to generate enough lift to raise the board and rider out of the water, allowing a completely smooth and almost frictionless ride. This means that you can kitesurf in very light winds at up to 3 times the windspeed. Kite foilboards are increasingly being used for racing, but my interest was more in its freeride potential for exploring the flat waters around Oban.
I decided to modify a kite surfboard to suit the foil, but wanted to retain the ability to remove the foil and use it as a regular board when the conditions suited. Consequently the foil is mounted using a strong carbon plate attached to the board by 4 bolts. To spread the load a little more, a glass-fibre plate is also mounted top and bottom.
The forces through the vertical mast are huge, so for this version I bought a pre-made aluminium mast online. The baseplate and wings bolt on to this. I thought this modular approach might come in handy if I decide to build higher performance wings at some point.
As of writing this article I’ve had six sessions with the board and am now reasonably confident at flying it on both tacks. The initial learning curve is very steep and involves a lot of crashes, but it’s been worth the effort. When you get up on the foil the feeling must be similar to a seabird skimming the surface; completely smooth and silent. It’s also very clear that you’re flying a tiny, sensitive airplane through the water, and the muscle memory to control the height takes some getting used to. But it’s very addictive!
Edit: Now have a short clip of it in action: https://www.youtube.com/watch?v=VLkVU4_AP7M