A hydrofoil boat is a watercraft with wing-like structures mounted beneath its hull that lift the boat’s body out of the water as it gains speed. Once airborne above the surface, the boat experiences far less drag, allowing it to travel faster and more efficiently than a conventional hull plowing through waves. Hydrofoils have been used in everything from military vessels and passenger ferries to America’s Cup racing yachts and personal electric watercraft.
How Hydrofoils Create Lift
The foils underneath a hydrofoil boat work on the same principles as airplane wings, just in water instead of air. As the boat accelerates, water flows over and under each foil. The shape and angle of the foil forces water to move faster across the top surface than the bottom. Faster-moving fluid creates lower pressure, so a net upward force pushes the foil (and the boat attached to it) toward the surface.
At a certain speed, the total lift generated by the foils equals the combined weight of the boat and everything on it. At that point, the hull rises completely out of the water. This is the key advantage: a hull dragging through water creates enormous resistance, but a hull flying above the surface only has to overcome air resistance and the much smaller drag on the thin foils and struts still submerged. The result is higher speeds with less power.
Foil performance depends heavily on the angle of attack, which is the tilt of the foil relative to the incoming water flow. A small angle of attack increases lift rapidly while adding very little drag. Push the angle too far, though, and the foil stalls, much like an airplane wing that pitches up too steeply.
Surface-Piercing vs. Fully Submerged Foils
Hydrofoil boats generally fall into two design categories. Surface-piercing foils are angled so their tips break through the waterline during flight. This design is inherently self-stabilizing: if the boat rolls to one side, more of that foil dips into the water, generating more lift and correcting the roll automatically. The tradeoff is a phenomenon called ventilation, where air gets sucked down along the foil’s surface, suddenly killing lift and causing vibrations. Sharp-edged foil profiles and steeper angles make ventilation more likely.
Fully submerged foils stay entirely underwater during flight. They produce smoother, more consistent lift and avoid ventilation problems, but they can’t self-correct the way surface-piercing designs do. Instead, they rely on active control systems, sensors and mechanical actuators that constantly adjust the foil angle to maintain stable flight. This makes them more complex and expensive, but also more comfortable in rough water.
A Short History of Hydrofoil Boats
Italian inventor Enrico Forlanini built what is considered the first successful high-speed hydrofoil in 1906. Using a ladder-style construction with multiple small wings stacked on struts, his craft reportedly reached 36.9 knots (about 42 mph). Alexander Graham Bell, better known for the telephone, took keen interest in the concept and collaborated with engineer Casey Baldwin. Their HD-4 prototype, powered by two aircraft engines, set a marine speed record of 70.86 mph in 1919, a remarkable figure for any boat at the time.
Bill Boeing, founder of the Boeing aircraft company, pushed the technology further in the early 1960s with a hydrodynamic test craft that reportedly exceeded 124 mph. Boeing’s company later became one of the most significant commercial hydrofoil manufacturers, producing passenger ferries used in transit systems around the world.
Commercial and Military Use
From the 1960s through the 1990s, hydrofoil ferries operated routes across Europe, Asia, and parts of the Americas. These vessels typically carried over 200 passengers at cruising speeds far exceeding conventional ferries. The smooth ride was a selling point: because the hull clears the waves, passengers experience less pitching and rolling than on a traditional boat of similar size.
Militaries also adopted hydrofoils for patrol and fast-attack craft, valuing their speed advantage in coastal operations. The technology eventually lost ground commercially to large, high-speed catamarans, which could carry more passengers and vehicles without the maintenance demands of underwater foil systems. But hydrofoils never disappeared entirely, and recent years have seen renewed interest driven by new materials and electric propulsion.
Hydrofoils in Competitive Sailing
Modern racing has transformed hydrofoil technology from a niche curiosity into a headline feature. The AC75 class yachts used in the America’s Cup are fully foiling sailboats that fly above the water on curved, arm-like foils. These boats reach extraordinary speeds. During the 2024 Louis Vuitton Cup Final, INEOS Britannia hit 55.5 knots (nearly 64 mph) in winds gusting to only about 22 knots. That means the boat was traveling almost three times the speed of the wind pushing it, something impossible for a conventional sailboat hull sitting in the water.
The progression has been rapid. In late 2020, recorded top speeds hovered around 49 knots. By 2024, boats were consistently breaking 55 knots in race conditions. Active foil control, advanced composite materials, and sophisticated onboard computing make this possible, with the crew constantly adjusting foil positions to keep the boat stable at speeds where a small miscalculation can cause a dramatic crash.
The Speed Ceiling: Cavitation
Hydrofoils face a fundamental physics problem at very high speeds. When water flows fast enough over a foil’s surface, the pressure on the low-pressure side drops so far that the water essentially boils, forming tiny vapor bubbles. This is called cavitation. When those bubbles collapse, they release intense energy that can pit and erode the foil’s surface over time. More immediately, cavitation drastically increases drag (by roughly ten times) and can trigger a sudden loss of lift, similar to a stall.
For most foil shapes operating near the sea surface, cavitation becomes a real concern at speeds between about 20 and 30 knots, depending on the foil’s design and depth. Specialized foil profiles called supercavitating foils can operate through cavitation rather than being destroyed by it, but they sacrifice efficiency at lower speeds. This tradeoff is one reason hydrofoil boats haven’t simply replaced conventional hulls for all high-speed marine applications.
Electric Hydrofoils and Personal Watercraft
One of the fastest-growing segments is the eFoil, a personal electric hydrofoil board. Riders stand on what looks like a surfboard with a battery-powered propeller and foil mounted underneath. A handheld throttle controls speed, and once you’re moving fast enough, the board lifts out of the water for a quiet, smooth ride with no waves and no wake.
Current consumer models offer ride times of up to 2.5 hours on a single charge, though real-world duration depends on rider weight, speed, and conditions. The battery alone weighs about 27 pounds, and the full setup is manageable enough for one person to carry to the water. Prices remain steep, typically several thousand dollars, but the category has expanded rapidly since its introduction around 2018.
Beyond personal recreation, startups and established marine companies are developing electric hydrofoil ferries and water taxis. The energy savings are significant: lifting the hull out of the water can reduce energy consumption by 80% or more compared to a conventional hull at the same speed. For battery-powered vessels where range is the biggest constraint, that efficiency gain makes electric propulsion practical for routes that would otherwise require too large a battery pack.