Isnt that a Soviet hover craft ( I think it was called the Ekranoplan) that use ground effect stay airborne. I think read something about them a long time ago.
http://www.youtube.com/watch?v=xr8N0Z4Cl0U
Its not a hovercraft. Ground effect craft fly, but only in ground effect.Hovercraft do not fly. They only use the venturi effect in their rotors and props, where ground effect craft have a wing.