The sit-down hydrofoil, first developed in the late 1980s, is a variation on water skiing, a popular water sport. When towed at speed, by a powerful boat or some other device, the board of the hydrofoil 'flies' above the water surface and generally avoids contact with it, so the ride is largely unaffected by the wake or chop of the water and is relatively smooth. The air board is a modified hydrofoil where the skier stands up.