Hydrofoil Design and Build

Hydrofoiling is a super cool concept! It looks as if you are just gliding seamlessly above the water. That’s why I decided to design and build my own hydrofoil.

This was a huge project and I learned a lot from it!

Hydrofoil Design Basics

First off, the basics of hydrofoiling. A hydrofoil works by a wing running through the water and producing lift. This lifts a person standing on the board out of the water. This is exactly how an airplane works! Hydrofoils can exist in many forms: large yachts hydrofoils, sailboat hydrofoils, and surfing hydrofoils. In essence, they all work the same but, this article will be focusing surfing hydrofoils.

Components

The main components of the hydrofoil are the connector plate, mast, fuselage, front wing, rear wing, and the board (not pictured). It’s important to break these down and understand the importance of each feature.

Connector Plate: This is what connect the entire hydrofoil to the board. This means all of the force generated from the hydrofoil will go through this plate. Hence, it needs to be super strong.
Mast: This is simply a vertical board curved to be hydrodynamic (pretty much just smooth edges).
Fuselage: Connects the mast and wings together. This needs to be strong as this translate the force from the wing to the mast.
Front wing: Generates almost all lift necessary to get the boarder out of the water. The biggest emphasis in designing this is the hydrodynamics.
Rear wing: Along with generating lift, this is the stabilizing factor for the hydrofoil.
Board: Simply something to stand on when riding. Not much thought needed here.

Designing the Hydrofoil

Hydrofoil design is very complex and all of the different design choices greatly depend on the use case of the foil. Foils for surfing may be bigger for more lift at slower speeds and foils meant for towing behind a boat may be smaller and less stable, etc. This preliminary design will outline key design points and show the design and built hydrofoil.

Front Wing Size and Shape

The size and shape of the wing directly determine the use case of the hydrofoil. The wing size is commonly measured by the wing reference area in cm². The two plots on the right will help you determine what size wing you need.

Large hydrofoil manufacturing such as Slingshot and LiquidForce have their foils around 1000 – 1500 cm².

The shape of the foil is dependent on the aspect ratio of the wing, which is the ratio of length to width of the wing. The higher the aspect ratio, the more efficient the wing is, but the smaller the ratio, the more stable the wing is. As a beginner, I would choose a aspect ratio less than 5.

Hydrofoil front wing design — 3D plot for hydrofoil front wing sizing

hydrofoil front wing design and sizing — Hydrofoil front wing sizing for varying velocities

aspect ratio for hydrofoil design — Definition of aspect ratio

hydrofoil front wing design and build — Design for front wing

Fuselage and Rear Wing Design

The fuselage and rear wing are less important to the design. The rear wing controls the stability of the foil, and the fuselage has the most structural stress on it. Without getting too much into the math behind it, a good choice for the rear wing is a larger option for more stability and a good choice for the fuselage would be a 1″ x 1″ aluminum bar or a wood fuselage wrapped in carbon fiber. My design for the rear wing and the fuselage can be seen below.

Mast and Connector Plate

The mast and connector plate are extremely hard to machine. For this reason, they were bought off of Slingshot’s website. The mast is 62 cm, as to make falls less harsh. If the intent is to ride the foil in the ocean, I would recommend the 82 cm or even the 92 cm version to counteract larger waves. You can look around for these items, and can get them cheap for less than $100 each. The connector plate is the industry standard and can connect with almost every board and the track system.

For more detailed information on the design, see this research paper I wrote.

Building the Hydrofoil

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