In this blog post, we’ll explore the characteristics of WIG craft—which overcome water resistance and move close to the water’s surface as if flying—and the principle of ground effect.
Most people have probably heard of magnetic levitation trains. They’re famous for traveling not by rolling on wheels along the tracks, but by using magnetic forces to hover just above the tracks. But have you ever heard of a boat that hovers above the water? You might say, “Aren’t boats supposed to float on water?” But this type of boat actually hovers above the water, just like an airplane. That’s right—a wing-in-ground (WIG) craft is a flying boat.
In fact, it’s difficult to reach high speeds on the water due to water resistance. For example, when “Swimming Emperor” Phelps swims in a pool, an average person could easily outpace him just by jogging lightly. That’s precisely because water resistance is that significant. As this example shows, water resistance is much greater than one might think. The appearance of a wing-in-ground (WIG) craft is actually closer to that of an airplane than a conventional boat. Through this reverse thinking, WIG crafts have been able to significantly reduce the drag caused by the hull’s contact with the water and travel at high speeds by moving primarily through the air.
Generally, boats are modes of transportation that float on water using buoyancy. However, breaking the stereotype that they must float on water using buoyancy, WIG crafts are vessels that fly close to the water’s surface by utilizing the ground effect. Ground effect is a phenomenon in which, as the wing of a flying object approaches a boundary surface such as the water’s surface or the ground, the airflow around the wing changes, increasing lift and reducing induced drag. For a wing-in-ground (WIG) craft to rise above the water’s surface, it fundamentally requires lift generated by airflow; near the water’s surface, ground effect enhances the efficiency of this lift. Here, lift refers to the force acting vertically on an object moving through the air, caused by airflow and pressure distribution; it is the force that causes the object to rise. On a wing, lift is generally generated by the pressure difference between the upper and lower surfaces of the wing. As the pressure beneath the wing becomes relatively higher and the pressure above the wing becomes relatively lower, a force is created that lifts the wing upward. WIG craft utilize this principle of lift and, because they operate their wings close to the water’s surface, can fly even more efficiently through ground effect.
Since ground effect is the most unique and important principle of WIG craft, I will explain it in a bit more detail. When a WIG craft flies close to the water’s surface, the airflow around the wings is influenced by the water’s surface. In particular, vortices and downdrafts generated at the wingtips are suppressed, reducing induced drag, while the pressure beneath the wing increases, boosting lift. Consequently, the craft can fly more efficiently with the same amount of thrust, which is a key reason why wing-in-ground (WIG) craft can travel at high speeds close to the water’s surface. You can observe changes in airflow similar to the ground effect through a simple experiment at home. If you place an A4 sheet of paper on a dining table and push it quickly with your hand, you can observe a change in the airflow around the paper. However, the ground effect observed in actual wing-in-ground (WIG) craft cannot be explained solely by air colliding with the water’s surface and being reflected back toward the wing; rather, it is a complex aerodynamic phenomenon resulting from the combined effects of changes in the pressure distribution between the wing and the water’s surface, along with the suppression of wing-tip vortices and downdrafts. A wing-in-ground (WIG) craft is a vessel that utilizes this principle to move as if it were continuously flying above the water’s surface.
WIG craft were developed not merely to reduce water resistance, but through a counterintuitive approach aimed at drastically reducing the drag generated when the hull comes into contact with the water. While large-scale commercialization was previously limited due to issues such as economic viability, stability, operation, and certification, there has recently been a resurgence in efforts to utilize WIG technology.
In 2026, China’s NAVEE unveiled the “WaveFly 5X,” a two-seater consumer-grade wing-in-ground aircraft, and successfully conducted test flights; in the United States as well, tests are underway to develop and commercialize ground-effect-based watercraft such as REGENT’s “Seaglider.” Therefore, while it is difficult to view wing-in-ground craft as merely experimental concepts, it is still too early to say they have become widely commercialized modes of transportation like conventional passenger ships or aircraft. Consequently, for wing-in-ground craft to establish themselves as practical modes of transportation, ongoing research and development is necessary not only regarding economic viability but also in areas such as safety, operational environments, certification and regulations, and technical reliability. I hope that someday people will actually be able to travel to Japan or China aboard commercial wing-in-ground craft.
