hovercraft, also known as a ground effect machine and air cushion vehicle. It supports its own weight by generating and containing an air cushion beneath its hull. The air cushion, usually generated by fans, is created by blowing air beneath the hull. This air hits the surface the vehicle is travelling over and, because it cannot escape, it turns back upwards which lifts the hull clear of the surface. More air coming in keeps the hull off the surface, and air escaping from under the hull ensures an equilibrium is maintained. Flexible skirts contain the cushion of air and raise the hull higher to allow it to clear obstacles.
Although there were experiments in the air cushion principle in Europe in the late 19th century, it was not until Dr Christopher ( Sir Christopher from 1969) Cockerell (1910–99) patented his ideas in December 1955, and then approached the British Ministry of Supply for funding, that work on building the first hovercraft began. Called the SR-N1, it was built by Saunders-Roe on the Isle of Wight, weighed 4 tons, and had a maximum speed of 25 knots. In 1959 it crossed the English Channel with its inventor and a crew of two, proving the practicability of fast amphibious travel.
Improvements in the hovercraft's skirt resulted in bigger versions being possible and by 1966 a regular service across the English Channel had started. Various types were built, the largest and most commercially viable being the SR-N4 that came into service in 1968. It weighed 177 tonnes and was powered by four Proteus
gas-turbine, and two Rover turbine, engines. In 1978 it was stretched to double the capacity and was driven by the world's largest
propellers, 6.4 metres (21 ft) in diameter. These were mounted on swivelling pylons and were used to manoeuvre the 300-tonne craft. Its 30-tonne skirts lifted the hull between 3 and 4 metres (12 ft) clear of the water at the bow and nearly 3 metres (9 ft) at the stern, and it carried up to 61 cars and 426 passengers across the 34-kilometre (21-mls.) wide channel at 112 kph (70 mph). In total the SR-N4s conveyed over 70 million passengers and 15 million cars, and continued in service until October 2000 when they were withdrawn in favour of the
Seacat. However, hovercraft still maintain services between the mainland and the Isle of Wight, and Oita Hoverferries still operate around the shallow coastal waters of Japan. Russia and the USA built large numbers of hovercraft and many have been built for export in Britain.
Sidewall hovercraft have also been developed. These have rigid sides which contain the air more efficiently. Though non-amphibious they have the advantage of using screw water propulsion, and remain popular passenger vessels in many parts of the world such as China and the Mediterranean.
Without the friction of a hull travelling through water, the hovercraft is one of the world's fastest
ferries and two SR-N4s amassed over 44,000 operational hours each. However, the real advantage of the hovercraft is its ability to operate where no other vessel can, in shallows, on mud flats and
ice, and across
shoals. This gives it a unique potential which can be exploited for survey work, for exploration,
lifesaving, and military purposes. Nowadays, they tend to be built more like boats than aircraft, often constructed with welded hulls and
diesel engines, rather than riveted airframes and gas turbines. This makes them cheaper to build and buy, and they are more robust and cheaper to operate. The US Navy has almost one hundred 100-tonne hovercraft some of which were used in the 2003 Iraq War. Britain's Royal
Marines also operated them there, and many
coastguards and other paramilitary organizations use them worldwide. The Greek Navy operates the world's largest hovercraft, the 350-tonne
Zubr (buffalo class), employing them to guard the Adriatic coastline.
The future for hovercraft is secure, albeit in a niche market. Once regarded as overly sophisticated, they are now reliable workhorses that perform specific duties throughout the world. The word hovercraft is the same in the plural and the singular. See also
surface effect ship.
www.hovercraft-museum.org
Warwick Jacobs
