The goal of this project was to create a functioning prototype of a hydrofoil that would be attached to the bottom of a surfboard and used to ride ocean waves. The device had to provide enough lift to elevate the user and a surfboard above the water while riding a wave and had to be created in such a way that it would be able to withstand the forces exerted on it by the user and the wave. To accomplish this, the shape main wing was optimized using XFLR5, and the hydrofoil was constructed using wood, fiberglass, unidirectional carbon fiber, and epoxy resin.
I began by designing the shape of the main wing on a program called XFLR5, which is normally used to design airplane wings. After trying out several different shapes and airfoils, I decided to go with the outline shown to the left using the Aquila 9.3% smoothed airfoil. Thanks to XFLR5, I was able to get an estimate as to the amount of lift the wing would give going at the speed of an average ocean wave. However, I didn’t spend too much time trying to perfectly optimize the main wing shape since ultimately I would be sculpting it by hand, and it would not be the exact same shape as the one I had modeled on my computer.
I built the main wing by gluing together several panels of thin plywood and letting them dry while clamped on a curved surface. Afterward, I cut out the profile with a handheld jigsaw and shaped the foil with an angle grinder and an orbital sander. Once the shape was finished, I covered it in fiberglass for extra strength.
I made the stabilizer wing the same way I made the main wing (by gluing together several layers of thin plywood and sculpting them to the desired shape). On top of the wing, I fixed a small piece of plywood plated with carbon fiber and fiberglass that would be used to attach the wing to the fuselage. An elongated hole in the plate allowed the angle of the wing to be adjusted.
Again, the mast was made in a similar way to the wings, except instead of just being reinforced with fiberglass, I used multiple layers of unidirectional carbon fiber. Since its so long and thin, it seemed like the mast would be the part of the hydrofoil that would be most prone to breaking, which is why I added several layers of carbon fiber and fiberglass. Holes were drilled into one end of the mast and threaded rods were glued into the holes. Those threaded rodes allowed the mast to be secured to the fuselage.
The fuselage was made out of a 1 in. by 2 in. red oak board reinforced with several layers of unidirectional carbon fiber and fiberglass. I put a slot in the rear to receive the stabilizer wing and in the front I inserted three coupling nuts that would be used to attach the main wing. In order to make a tight fitting attachment point for the mast, I poured a mix of epoxy and milled fiberglass into a slot on the fuselage, then inserted the mast, which was covered in a thin layer of beeswax. The beeswax allowed me to remove the mast after the epoxy hardened, leaving a slot that fit the mast perfectly. I then drilled holes in the slot so that the mast could be secured from underneath.
To mount the hydrofoil to the board, I decided to use two longboard fin boxes side by side, which would allow me to secure the mast at four points. To provide a stronger base for the attachment, I routed out a section of the board and filled it with fiberglass and epoxy. This way, the forces of the hydrofoil would be less likely to ruin the board or pull out the fin boxes.