In aerodynamics, ground effect refers to the lifting force under the wing of an aircraft in proximity to the ground. It plays a big part in the landing and takeoff.
For fixed-wing planes, ground effect is the result of a reduction in the amount of induced drag - a function of the lift generated at the tip of a wing. When the craft is traveling close to the ground, air vortices become elliptical as the airflow is pushed outwards.
A ground-effect vehicle (GEV) takes advantage of the namesake effect to sustain flight over a level surface, often over a body of water. Among the best known is the Soviet Ekranoplan, also known as the Caspian Sea Monster.
Although they may look like seaplanes, ground-effect vehicles are not supposed to fly out of ground effect. They are sometimes characterized as a transition between a hovercraft and an aircraft.
They possess obvious advantages over some traditional transportation means. Given the similar size and capacity, a GEV has better fuel efficiency than an airplane. A GEV also is much faster than a surface vessel because it travels without touching the water, except during takeoff and landing.
However, due to the lack of control over altitude, GEVs can only move horizontally to avoid a collision. And they have a higher risk of damage when coming into direct contact with other vessels and objects, because of their aircraft-like body construction. In traveling during high winds, GEVs often get the heavy pounding by waves, which causes significant wear-and-tear on the craft and discomfort in passengers.
Source: Curious Droid via Youtube