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While maritime vessels typically float on water, there are exceptions such as hovercraft and wing-in-ground effect vessels (WIG craft) that float above the water surface.
Large seabirds and several species of waterfowl can glide for extended distances above water, and their wing profile during gliding served as the template behind the development of WIG craft. At present, there are builders located in South Korea (Wing Ship Technology), Malaysia, Singapore and Australia.
While aircraft flight depends on a vacuum effect occurring and being sustained on the top surface of the wing, WIG craft flight is very different. When gliding above water, the wing profile of seabirds and waterfowl scoops air and generates a downdraft along the outer edges of the wing tips. A percentage of that downdraft flows inward and develops into an updraft near the WIG craft mid-section. That updraft carries most of the weight of seabirds and WIG-craft.
The IMO classifies WIG craft as a maritime vessel, and they can typically fly at an elevation of 10 percent to 20 percent of the wingspan distance.
Climbing High
Wing Ship of South Korea has recently developed a ground-effect wing that can carry a WIG craft to an elevation of 90 percent of wingspan, meaning that a craft built with a wingspan of 120 feet (36 meters), could climb to an elevation of 108 feet (33 meters) above sea level and above small and medium size maritime vessels.
A WIG craft of 200 feet or 61 meters wingspan could cruise at an elevation of 20 to 40 feet (six to 12 meters) above ocean while consuming a third of the fuel of an equivalent size commercial airliner. When needed, it could climb to an elevation of 180 feet (55 meters) above ocean.
During testing on the Caspian Sea, the Russian built Ekranoplan could fly at an elevation of 30 feet (10 meters) above water. However, pilots discovered that wingtips struck the water surface during severe turns.
The development from South Korea allows pilots to climb future WIG craft to higher elevation before making a severe turn. However, prolonged operation at high elevation would also increase fuel consumption. Pilots would climb the craft to high elevation when encountering a ship or when approaching a runway at a coastal airport and also operate the craft at high elevation after take-off from such an airport.