To walk on water, to fly without wings—these are aspirations woven into the very fabric of human mythology. They represent a fundamental defiance of the physical world, a desire to transcend our limitations. For centuries, they remained squarely in the realm of gods and miracles. But today, silently gliding a foot above a glassy lake or a calm ocean bay, a new kind of craft is turning this ancient dream into an accessible reality.
This is the electric hydrofoil, or eFoil. And while it may look like a product of the distant future, its existence is a testament to the powerful convergence of a century-old principle of physics and a suite of bleeding-edge technologies that have only just reached maturity. To understand how it works is to embark on a fascinating journey through fluid dynamics, materials science, and extreme battery engineering. The eFoil isn’t a single invention; it’s a symphony of them.
The Science of Lift, Submerged
The magic of an eFoil begins with a concept that predates the airplane: the hydrofoil. The dream of lifting a boat’s hull out of the water to escape its immense drag has captivated inventors for over a century. As far back as 1906, Italian inventor Enrico Forlanini had a craft “flying” across Lake Maggiore. A decade later, Alexander Graham Bell’s massive HD-4 hydrofoil shattered water speed records. The principle they harnessed is the same one that keeps a 747 in the air, just applied to a different medium.
Submerged beneath the board is a wing. As it moves forward, water must travel a longer path over its curved top surface than its flatter bottom. According to Bernoulli’s principle, this faster-moving water exerts less pressure than the slower-moving water below. The result is a net upward force: lift. Simultaneously, as the wing angles slightly against the flow (its “angle of attack”), it deflects water downwards. By Newton’s third law, for every action, there is an equal and opposite reaction, so the wing is pushed upwards.
Once the craft reaches a critical speed, this lift becomes powerful enough to overcome gravity, hoisting the board, rider, and all its components entirely out of the water. The effect is profound. Surface friction, the primary source of drag that limits the speed of boats, vanishes. The ride becomes eerily silent and incredibly efficient, a sensation of gliding through air rather than plowing through water. A modern eFoil wing, like the Voyager C1500 found on a craft such as the Waydoo Flyer EVO, is a masterclass in this principle, its precise shape meticulously designed to maximize lift while minimizing turbulence.
The Power Dilemma: Taming Lithium on the Ocean
Creating lift is one thing; creating it silently, cleanly, and for over an hour is another challenge entirely. This is where modern battery technology enters the stage. The entire eFoil revolution is predicated on the phenomenal energy density of lithium-ion batteries—their ability to pack immense power into a small, lightweight package. A battery pack like the one powering the Waydoo EVO, with a capacity of 2,300 Watt-hours (Wh), holds enough energy to propel a rider for up to two hours, a feat unimaginable just 15 years ago.
But this power comes with a terrifying risk: water and high-voltage electricity are mortal enemies. Furthermore, lithium-ion batteries contain a volatile, energy-rich electrolyte. If a battery is punctured, overcharged, or overheats, it can trigger a catastrophic chain reaction known as thermal runaway, leading to fire or explosion. Now, imagine that risk sealed inside a watertight box, with nowhere for heat or pressure to escape.
This is why the heart of an eFoil battery is not the lithium cells themselves, but the sophisticated electronic brain that protects them: the Battery Management System (BMS). This unsung hero constantly monitors the voltage, current, and temperature of every cell. It prevents overcharging and over-discharging, balances the charge between cells, and can shut the entire system down at the first sign of trouble.
The engineering challenge is immense. The battery must be sealed to an IP68 standard, meaning it’s completely impervious to dust and can survive prolonged submersion. Yet it must also manage the intense heat generated during operation. It is, in essence, a self-contained, high-stakes ecosystem, and its safe operation is the bedrock upon which the entire experience is built. This contained power is then fed to an incredibly efficient brushless DC motor, a technology shared with high-performance drones, which converts electrical energy into near-silent propulsion.
The Material Compromise: An Engineering Showdown
When designing a craft for flight, every gram matters. The immediate instinct for any high-performance application is to reach for the ultimate lightweight material: carbon fiber. It’s incredibly stiff, strong, and has become synonymous with premium quality in everything from supercars to America’s Cup racing yachts. So it might be surprising to learn that many popular eFoils, including the Waydoo EVO, are made not from carbon fiber, but from a type of advanced foam called EPP (Expanded Polypropylene).
This isn’t a cost-cutting shortcut; it’s a profound engineering trade-off. Carbon fiber’s greatest strength, its rigidity, is also its weakness. It is brittle. A sharp impact can cause a catastrophic fracture. For a professional racer, this is an acceptable risk. For a beginner learning to ride—a process that inevitably involves falling and the board tumbling—it’s a recipe for a very expensive repair.
EPP, on the other hand, is defined by its resilience. It’s the same material used in modern car bumpers. It is designed to absorb impact energy by deforming and then returning to its original shape. It is extraordinarily durable and, while not as stiff as carbon, it is more than strong enough for the task. This choice reflects a mature design philosophy: engineering for the actual user experience, not just for the marketing spec sheet. It’s a pragmatic compromise that prioritizes durability and accessibility over the pursuit of ultimate, and often unnecessary, performance.
The Unseen Hand: The Brains Behind the Balance
The final piece of the puzzle is arguably the most subtle and the most crucial for making eFoiling accessible: the control system. Riding an eFoil for the first time is notoriously counter-intuitive. The dynamics of balancing on a single point of lift, several feet below you, are alien to our land-based instincts.
To ease this learning curve, advanced eFoils incorporate an Inertial Measurement Unit (IMU)—the very same technology that allows a drone to hover perfectly still or a smartphone to know which way is up. The IMU is a tiny chip containing gyroscopes and accelerometers that measure the board’s pitch, roll, and yaw with microscopic precision, hundreds of times per second.
This data is fed into the board’s main processor, which can then make micro-adjustments to the motor’s power output. If the board’s nose pitches up too aggressively during takeoff, the system can momentarily reduce power to help it level out. This “unseen hand” doesn’t ride the board for you, but it acts as a digital co-pilot, smoothing out the bumps and forgiving the small mistakes that would otherwise lead to a fall. It is the intelligent software layer that bridges the gap between raw mechanical power and fluid human control.
The Horizon
The eFoil is not the result of a single breakthrough. It is the beautiful, improbable culmination of decades of progress across a half-dozen unrelated fields. It is what happens when the hydrodynamics of the early 20th century finally meet the battery density, the motor efficiency, the material science, and the sensor intelligence of the 21st.
More than just a new water toy, it’s a powerful symbol of a broader shift towards personal electric mobility. It proves that when we combine and creatively apply our most advanced technologies, we can not only solve practical problems but also achieve things we once thought were impossible. We can, in our own small way, learn to walk on water.
