3D Printing an Electric Hydrofoil Surfboard for an English Project

The electric hydrofoil surfboard is by far my biggest 3D printing project. I got the idea off a forum I found and decided to make an electric hydrofoil surfboard for WISE. WISE is an English class for seniors at my high school where you have a regular English class for the first half of the year, and a large personal project for the second half of the year. One of the engineers from my robotics team agreed to be my mentor for the project. 

Testing the finished hydrofoil

I used a modified version of one of the builds on the electric hydrofoil forum when doing the project. This made the project a lot easier since someone had already tested most of the components such as the propellors, motor, motor controller, and gearbox. I learned a lot about o-rings and proper sealing procedures even just from building and modifying the designs other people worked on. 

This tiny motor has a peak power of 10hp

Test fitting the motor assembly

To make the hydrofoil wings I copied an airfoil shape from a database and used guided lofts and extrusions in Autodesk Inventor to get the shape I wanted. I made the wings swept back for additional stability and added mounts to integrate it to the rest of the hydrofoil. I also added aluminum beams to the center for extra support and used the Autodesk Inventor FEA to analyze the stresses in the beams.

Autodesk Inventor CAD model

Stress analysis of the larger support beam

Hydrofoil wing v1 

Printing and assembling the propellor duct

 

Gear assembly. I used thermal paste between the motor and the housing for motor cooling. 

Testing the motor

Making the surfboard was a really great experience because I had never one a composite layup before this project. I did some hand calculations to find the required volume and did a fiberglass layup over foamboard with the help of my mentor. We also put a layer on the hydrofoil wings for extra strength and rigidity. 

Similar to designs I saw online, I used one lifting wing and one downward wing for more stability. I also explored using a canard design for a slightly better lift/drag ratio but decided against it because it would make the hydrofoil a lot less stable. 

 
Prepping for the first test run

Throughout the project, there were a few setbacks. The first was the motor housing getting mangled in the lathe when I tried to take off a pass that was too large. Luckily I was able to get a new one for free from a guy I knew at a local shop. 

     

Another problem I ran into was the propellor duct snapped after the first day of testing. I reprinted it with more perimeters and infill and was out testing next week. 

After a few days of testing the motor controller caught on fire. This was caused by insufficient cooling and I got lucky it didn't burn the batteries or any other electronics. In later versions, I added a pump and water cooling and didn't run into any more problems. 

Burnt motor controller

Testing the cooling pump 

The last major problem I had was the original wings weren't large enough to lift the surfboard with me on it out of the water. I designed new hydrofoil wings with a more efficient airfoil and a much larger surface area. 

 

Left: new wings      Right: new wing size comparison

In the end I never quite got the hydrofoil working. I was able to get out of the water but a combination of me being inexperienced and me designing and 3D printing my own hydrofoil instead of buying an off the shelf solution made for a very unstable surfboard. I had a lot of test runs similar to the one above where the hydrofoil went up and then I fell back down. 

Overall, I'd say the project was still successful because of how much I learned. Before this project, I knew absolutely nothing about o-ring seals, fiberglass layups, airfoil profiles, brushless motor control, and how to properly spec out batteries and electronics.