1. Hovercrafts or cushion crafts are vehicles that support themselves a small distance above the ground or water surface on a cushion of air forced downward by vertical fans. Unlike road vehicles and boats, hovercrafts have no physical contact with the surface over which they float and, unlike aircraft, they are incapable of rising above this surface much over a foot or so.
2. As a vehicle the hovercraft requires three or four times as much power as an automobile or truck to operate. The same is true in comparison to boats and ships. On the other hand, cushion crafts require one half to one quarter the power needed to support an airplane or helicopter in flight.
3. Hovercrafts find application in those surface transportation tasks that cannot be done efficiently by automobiles, trucks, buses, trains, or boats. A hovercraft could ferry troops from conventional troopships to the shore at speeds over 60 mph. It would not be obliged to stop at the beach but would continue inland. Hovercrafts are used as ferries, taking passengers, cars and goods to and from the continent. Another application is for inter-island transportation in arctic waters, where winter ice often makes the waterways impassable for ships and where the ice is not solid or smooth enough to permit the passage of trucks or sledges.
4. Hovercrafts are propelled in forward flight by various methods. The most efficient method is propulsion with air propellers, but the rotating propellers may form a serious hazard to passengers and operators. Another method is by tilting the machine as a whole in the direction of intended motion so that a part of the high-pressure becomes available for the forward movement. Sometimes a combination of various methods is used.
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