 In 1972, Mike Murphy and Bob Woolley added a bi-wing hydrofoil to a surfing kneeboard, then reduced the bi-wing to a single wing.Murphy and Bob Woolley then applied the concept to sit-down hydrofoil, with Woolley riding the first "Sit Ski" in 1984.After various material changes, including the addition of a seat belt to keep rider and ride together and prevent separation collisions, they sold their first "Air Chair" in 1990.