This section is designed as a knowledge hub to answer your most pressing questions about hydrofoils and their design principles.

The technology of hydrofoils, while rooted in history, is getting more popular since a few years. The reason: saving energy while increasing speed and comfort.

Hydrofoils or Foils are wing-like structures attached to the hull of a boat or ship that lift the hull out of the water as the vessel gains speed. Much like an airplane wing, these underwater wings function using principles of fluid dynamics. As the boat gains speed, water flows faster around the hydrofoil, creating a pressure difference between the top and bottom of the foil. This lifts the hull of the boat out of the water. And with no hull in the water, there is less water resistance. This significantly increases the speed and efficiency of the boat or ship.

Hydrofoils enable vessels to reduce water resistance by up to 80%, saving significant energy in the process. In essence, they allow boats to 'fly' over water, leading to a more efficient, smoother, and faster travel experience.

Moreover, modern technological advances have made the implementation of hydrofoils more practical than ever before. The decreasing costs of advanced control systems, sensors, and processing power have made it possible for us at Flying Fish to develop reliable, safe, and cost-effective hydrofoil systems.

Because hydrofoils generate more lift when water flows around them, they offer most benefits for vessels that need to sail fast. Also, if a vessel is more lightweight, it needs smaller hydrofoils and therefore will have even less water resistance. You can check these effects in the Hydrofoil Calculator.

Designing a hydrofoil boat or ship comes with some technical challenges that make hydrofoil design a professional craft of its own.

The first of these challenges has to do with the boat dynamics. A traditional boat or ship requires a propeller to move in longitudinal direction (forward and backward) and a rudder to steer (around the so-called yaw axis). In addition, a hydrofoil vessel also requires control over the flight height, the roll-axis and the pitch-axis. This means a foiling boat usually has 3 more degrees of freedom in its motion. It requires full understanding of flight dynamics, control systems, sensor filtering and mechanical actuation to make a hydrofoil fly as it should.

In addition to these degrees of motion, a second challenge is that the hydrofoils have to lift the weight of the entire boat out of the water at specific points, whereas a traditional ship is supported over its entire hull. This change causes material stress in the foils and introduces higher forces into the hull structure. A proper analysis of forces and deformations in the materials is required to guarantee the foils safely carry the loads they encounter.

So, developing an efficient hydrofoil system involves a balance of technical disciplines, from mechanical engineering to software development. At Flying Fish, our multidisciplinary team integrates these elements to create hydrofoils that can be easily applied to existing ship designs. This enables any shipbuilder to not only reduce energy consumption of their new boat, but also to improve comfort on board.

We design robust hardware following industry standards, to guarantee durability. This hardware stands up to the physical forces and corrosive effects of a marine environment. Furthermore, our background in mechatronics and onboard data ensures all parts of our hydrofoil system work together and reliably. Our hydrofoils are engineered for easy application to your vessel, robust performance and ease of maintenance.

There are three primary configurations for the placement of foils (or wings) on hydrofoil vessels: the canard, tandem and aircraft arrangements.

1) Canard Configuration: In the canard configuration, the smaller set of hydrofoils (referred to as canards) is placed forward of the main foils, towards the front of the boat. This setup is akin to the placement of small, forward wings on some aircraft. In nautical applications, canard configurations may offer better robustness against waves, but this depends on the design details.

2) Tandem Configuration: The tandem configuration involves two similar-sized hydrofoils positioned on the rear and front of the vessel. This setup distributes lift and weight almost equally between the front and rear foils. The advantage of this layout is that it potentially allows for better control, although it can be more structurally complex to design and implement.

3) Aircraft Configuration: The aircraft configuration places the larger main hydrofoils towards the front of the vessel, with smaller stabilizing foils at the stern, much like the layout of a conventional airplane. This setup may have advantages in terms of practical arrangment, because the smaller rear foil can be used for steering or propulsion with less exposure to floating objects in the water.

A crucial aspect to understand about hydrofoils is the concept of flight stability. Hydrofoil vessels need to maintain a steady 'flight' height above the water, requiring a delicate balance to prevent pitching or rolling. In the past, passive stability was often applied for calm waters. However, this leads to limited control over the entire range of speeds and sea states.

Luckily, modern control systems can actively monitor and adjust the hydrofoil's lift precisely to maintain this stability. Thanks to on-board software, the control system can account for factors like speed changes, wave conditions, and shifts in the vessel's load. This means that active control systems allow a hydrofoil to be used in a wide range of weather and wave conditions.

Besides requiring sensors and onboard controller, hydrofoil lift control requires a change in the water flow over the foil. This can be achieved through the use of flaps or full-wing control as follows:

1) Flap Control: Similar to the flaps on an airplane wing, these adjustable parts on the trailing edge of a hydrofoil can be manipulated to change the wing's lift characteristics. By altering the angle of the flaps in response to varying conditions and speeds, one can effectively manage the boat's lift and maintain an optimal ride height above the water. Control via flaps provides the most lightweight and power-efficient solution.

2) Full-Wing Lift Control: In contrast, full-wing control systems adjust the entire hydrofoil's angle of attack to regulate lift. This approach can require more energy and lead to more drag, but avoids the use of small mechanisms under water.

So, our applied expertise in control systems enables the hydrofoil to maintain balance by varying the lift forces on the wings. We can test our control systems before applying them, using our in-house developed hydrofoil flight simulator. This means we can test the flight experience of different hydrofoil configurations and control methods in various sea states.

The era of green propulsion with electric motors is here and hydrofoils are perfectly positioned to join that era. The inherent characteristics of electric motors - notably their high peak power and excellent efficiency - pair exceptionally well with the physics of hydrofoil boats.There are three primary propulsion options for hydrofoil vessels each with their distinct pros and cons:

1) In-Hull Motor with Driveshaft: This involves housing the electric motor within the vessel's hull. The motor's power is transmitted to a propellor via a driveshaft which extends through a vertical strut. A gearbox is typically required to match the high rotational speed of the electric motor with the lower optimal speed of the propeller. This option is known for its robustness and has the advantage of keeping the motor protected inside the hull.

2) In-Hull Motor with Waterjet System: Another approach involves using a waterjet system. The electric motor is located within the hull and drives a high-speed pump, which sucks in water and ejects it at high speed, creating thrust. This setup is mechanically simpler, as it does not require a driveshaft or gearbox. However, the efficiency is generally lower than a well-designed propeller system due to energy losses in the jet pump.

3) Underwater Pod with Direct-Drive Motor: In this configuration, the electric motor is housed in an underwater pod, directly driving a propeller without the need for a gearbox. The advantages of this system include improved efficiency due to the absence of a gearbox and driveshaft. However, it also presents its own challenges. The underwater location increases drag and can complicate motor maintenance. The motor and electrical connections must also be meticulously protected from the surrounding seawater.

As with all engineering solutions, the best choice depends on the specific use case, mission profile, and design constraints of the vessel. Each of these setups represents a viable path forward in the world of green propulsion. At Flying Fish, we use our extensive expertise in hydrofoil design and green propulsion technologies to help our customers make the best choices for their specific needs.

Because of the need for dramatic energy reduction in the maritime industry, the potential applications of hydrofoils are diverse and growing. From crew transfer vessels, passenger ferries, and water taxis to leisure yachts, we envision a future where hydrofoils become the standard in the marine industry. At Flying Fish, we aim to democratize this technology by offering a range of standardized hydrofoil modules, easily adaptable by shipyards and naval architects worldwide.

We are currently developing our Flying Fish Foil System (3FS): a comprehensive, fully-integrated solution to elevate your maritime vessels. Making your boat 'fly' will no longer be a distant dream but an accessible reality. Our foil system ensures seamless transition from conventional navigation to hydrofoil mode, offering the benefits of increased speed, exceptional energy efficiency, and smoother rides.

We invite you to join us in this exciting journey towards a future of zero-emission fast shipping. By making ships fly, we're helping shape a greener, more sustainable world that does not compromise on comfort or speed. Get in touch with us to discuss more or check out our Hydrofoil Calculator first to get a feeling for the energy you can save!