The basic principles of the hovercraft were discovered by Christopher Cockeral in 1953. He discovered that a substantial load could be lifted on a cushion of air.
Looking nothing like an ordinary boat the hovercraft resembles a very large rubber dinghy. Requiring no hull it rides out of the water on a cushion of air. Freed from the drag of the water it can therefore travel at great speeds typically up to 65 knots/120 kilometres per hour.
A hovercraft is supported by slightly compressed air which is driven downwards by air jets, Because the air is constantly escaping it has to be replenished by the engines continuously. To minimise this loss a flexible rubber skirt is fitted around the hovercraft base. This `air skirt' traps air and causes the solid bottom of the craft to lift almost clear of the water. The small air gap beneath the craft is not seen as a problem, as the flexible skirt will bend over waves and solid objects with only a slight increase in surface drag.
Controlling the speed of the craft is achieved by altering the pitch of the driving fan blades increasing thrust so pushing the craft forward. The pitch of the blades can be turned right around reversing the thrust, this allows the craft to travel in reverse or can be used as a brake slowing the forward motion of the craft. Steering a hovercraft is a problem simply because of the lack of contact with the ground. Any tight turning merely results in the craft sliding sideways. Larger hovercraft get around these problems by using swiveling driving fans allowing for sideways travel if necessary. Devices are also fitted to the fans which alter the thrust to one or the other engines depending on the direction required. Even with all these devices fitted hovercrafts are notoriously difficult to handle in windy conditions.
Travelling on a cushion of air allows the hovercraft to traverse not only water but also roads, swamps or deserts and as such are used to great effect by the military to transport troops and equipment over terrain not suitable to other forms of ground transport.
