A hovercraft, or air-cushion vehicle (ACV), is a vehicle or craft that can be supported by a cushion of air ejected downwards. It can travel over any relatively smooth surface, such as gently sloping land, water, or ice, while having no almost no contact with it.
The first recorded design for a vehicle which could be termed a Hovercraft was in 1716 by Emanuel Swedenborg, a Swedish designer, philosopher and theologian. His man-powered air cushion platform resembled an upside-down boat with a cockpit in the center and manually operated oar-like scoops to push air under the vehicle on each downward stroke. No vehicle was ever built, no doubt because it was realised that human effort could not have generated enough lift.
In the mid-1870s, the British engineer Sir John Isaac Thornycroft built a number of ground effect machine test models based on his idea of using air between the hull of a boat and the water to reduce drag. Although he filed a number of patents involving air-lubricated hulls in 1877, no practical applications were found. Over the years, various other people had tried various methods of using air to reduce the drag on ships.
Col. Melville W. Beardsley (1913-1998), an American inventor and aeronautical engineer, along with Dr. W. Bertelsen worked on developing early ACV's in the USA. It was not until 1952 that the inventor Christopher Cockerell designed a vehicle based on his 'hovercraft principle'. This was the missing link everyone else had not seen and made a commercial craft possible. He was knighted for his services to engineering in 1969 for his work on the Hovercraft. Sir Christopher even invented the word 'Hovercraft' to describe his invention.
Cockerell used simple experiments involving a vacuum cleaner motor and two cylindrical cans. He proved the workable principle of a vehicle suspended on a cushion of air blown out under pressure, making the vehicle easily mobile over most surfaces. His significant advance was developing a peripheral jet system to retain the air cushion under the vehicle. The supporting air cushion would enable it to operate over soft mud, water, and marshes and swamps as well as on firm ground.
The British aircraft manufacturer Saunders Roe which had aeronautical expertise developed the first practical man-carrying hovercraft, the SR-N1, which carried out several test programmes in 1959 to 1961 (the first public demonstration in 1959), including a cross-channel run. The SR-N1 was powered by one (piston) engine, driven by expelled air, and could carry little more than its own weight and two men,and did not have any skirt at first trials. It was found that the craft's lift was improved by the addition of a 'skirt' of flexible fabric or rubber around the hovering surface, to contain the air. The skirt was an independent invention made by a Royal Navy officer who worked with Sir Christopher to develop the idea further.
The first true passenger-carrying hovercraft was the Vickers VA-3, which in the summer of 1961 carried passengers regularly along the North Wales Coast from Wallasey to Rhyl. It was powered by two turboprop aero-engines and driven by propellers. During the 1960s Saunders Roe developed several larger designs which could carry passengers, including the SR-N2, which operated across the Solent in 1962 and later the SR-N6, which operated across the Solent from Southsea to Ryde on the Isle of Wight for many years. Operations commenced on 24th July 1965 using the SR-N6 which carried just 38 passengers. Two modern 98 seat AP1-88 hovercraft now ply this route, and over 20 million passengers have used the service as of 2004.
As well as Saunders Roe and Vickers (which combined in 1966 to form the British Hovercraft Corporation), other commercial craft were developed during the 1960s in the UK by Cushioncraft (part of the Britten-Norman Group) and Hovermarine (the latter being 'sidewall' type hovercraft, where the sides of the hull projected down into the water to trap the cushion of air).
In the late 1960s and early 1970s, Jean Bertin developed a hovercraft train dubbed the Aérotrain in France. His I-80 prototype established the world speed record for overland air cushion vehicles with a mean speed of 417.6 km/h (260 mp/h) and a top speed of 430 km/h (267 mp/h).
By 1970 the largest British hovercraft were in service, the Mountbatten class SR-N4 model, each powered by four Rolls-Royce Proteus engines, regularly carrying cars and passengers across the English Channel from Dover or Ramsgate to Calais. This service ceased in 2000 after years of competition with traditional ferries, catamarans, and the opening of the Channel tunnel.
In 1998, the US Postal Service began using the British built Hoverwork AP.1-88 to haul mail, freight, and passengers from Bethel, Alaska to and from eight small villages along the Kuskokwim River. Bethel is far removed from the Alaska road system, thus making the hovercraft an attractive alternative to the air based delivery methods used prior to introduction of the hovercraft service. Hovercraft service is suspended for several weeks each year while the river is beginning to freeze to minimize damage to the river ice surface. The hovercraft is perfectly able to operate during the freeze-up period, however, it could potentially break the ice creating hazards for the villagers using their snowmobiles for transportation along the river during the early winter.
The commercial success of hovercraft suffered from rapid rises in fuel prices during the late 1960s and 1970s following conflict in the Middle East. Alternative over-water vehicles such as wave-piercing catamarans (marketed as the Seacat in Britain) use less fuel and can perform most of the hovercraft's marine tasks. Although developed elsewhere in the world for both civil and military purposes, except for the Solent Ryde to Southsea crossing, hovercraft disappeared from the coastline of Britain until a range of Griffon Hovercraft were bought by the Royal National Lifeboat Institution.
There are an increasing number of small homebuilt and kit-built hovercraft used for fun and racing purposes, mainly on inland lakes and rivers but also in marshy areas and in some estuaries.
Hovercraft typically have two (or more) separate engines (some craft, such as the SR-N6, have one engine with a drive split through a gearbox). One engine drives the fan (aka the impeller) which is responsible for lifting the vehicle by forcing air under the craft. One or more additional engines are used to provide thrust in order to propel the craft in the desired direction. Some hovercraft utilise ducting to allow one engine to perform both tasks by directing some of the air to the skirt, the rest of the air passing out of the back to push the craft forward.
Hovercraft - the History and Development
The word "hovercraft" was probably coined by a newspaper, or even by Christopher Cockerell himself, to try to capture the essence of the vehicle. The more accurate modern description "air-cushioned vehicle" is more similar to the German Luftkissenboot.
As with any new idea it is fuelled by need, finance, and curiosity, and motivated often by the need to improve an existing product; the word development covers all this and more.
In view of Vosper Thorneycroft's involvement in military hovercraft in the 1960's, it is probably ironic that they were making use of an idea patented by Mr.Thorneycroft, a boat builder in the 1870's who suggested that by pumping air under a boat of a certain design it would help to lift the hull, reducing draft and thereby the drag of the vessel would be reduced. There is a patent to this concept taken out in 1910.
Later in the 1920's a Swede developed an improvement on the ice sledge by propelling it with an air propeller in such a way as to get ram airlift on his platform. Further development was not continued.
The hovercraft as we know it today has largely been credited to Christopher Cockerell, a lateral thinker of his day who, after developing crucial components for use on British radar during the war, retired to a boatyard in Norfolk, where in the interest of making a faster powerboat that would plane at lower speeds came up with a similar idea to that of Thorneycroft; what goes around comes around!!! He took the idea further by the skilful use of vectored air to make the whole vehicle hover, thereby removing the drag from any part of the hull which might have been in contact with the surface, be it land or water.
It is worth mentioning at this point that I do not think Cockerell ever intended his craft to be anything more than an amphibious marine vehicle. Where insurance underwriters and others get the idea that a hovercraft is some sort of low flying aeroplane says much about their lack of understanding of the concept.
At a similar time in the late 1950's a Doctor William Bertelsen in the USA was looking at alternative forms of transport in order to reach his patients when the roads were impassable. He continued to develop various hovering vehicles and roadways for hovercraft over the next 50 years. He is probably best known for the use of fans mounted on gimbals, but as with all things it is not necessarily the product, but the marketing of it, that makes the difference to its success or failure. In the case of Cockerell with his military contacts he was able to head up a British military development group, which with some time, reluctant government funding finally produced SRN1 which successfully crossed the Channel from England to France on the eleventh of June 1959, fifty years to the day after Bleriot did the same crossing in his aeroplane.
As with all things if there is the possibility of a military use money is found to further development from which civilian side-products are often developed.
The Russians built a fleet of very large military craft for use in the upper Baltic, particularly useful over the ice and snow, while the Americans were later to see the military advantages of hovercraft under the Reagan administration: when they did they invested heavily in both amphibious landing craft and rigid sidewall designs as the basis of their hundred miles an hour navy. But as with most things political, the military investment is usually in proportion to the perceived threat, and as the USSR was coming apart at the seams the investment was reduced. But the US Navy now has a fleet of vastly powerful air cushion landing craft, which, with their mother-ships, are now an integral part of the US Marine structure.
Some very successful craft that evolved from the military development work were used on civilian ferry designs, culminating in the large cross-Channel craft.
The small or light [a British government definition of under one tonne] hovercraft of today were originally built, some of them by people in the commercial industry, but mainly by people inspired by the concept. Some of the early craft can be seen at the Hovercraft Museum at Lee-on-Solent. As one would expect many of the designs were scaled down versions of the larger commercial types of the day.
Largely by virtue of the commercial industry being based around Southampton Water, the largest grouping of like-minded people was in that area and so the Hover [later Hovercraft] Club of Great Britain and the Hovercraft Society were formed.
At the Browndown hovercraft event in 1976, which took place on the 10th anniversary of the first Browndown event, Christopher Cockerell told me of the reluctance of his team to the idea of fitting "a ring of Mackintosh" around the SRN1 after its cross-Channel trip. In retrospect the comment is quite interesting because the use of a flexible seal or skirt was possibly the single most important step forward in making the hovercraft a practical transport vehicle, and secondly highlights the difficulty of working with a team of aircraft engineers trying to produce a marine product for military use.
As the British Isles are a relatively small area making interaction between individuals relatively easy, it is not surprising to me that craft produced by the home-builder or small company rapidly evolved and have continued to do so long after the larger military/ commercial designs appeared to consolidate their basic idea's. A lot of time was taken up in the early development of the larger commercial craft in the improvement and refinement of the skirt. Companies such as Hovercraft Development Ltd [HDL] were specifically involved in making skirts more efficient, which gave the craft improved handling. This work made use of and added to the skirt patents, which were held by the British government.
Some development on propulsion systems was also noticeable. Again, in my view, commercially the breakthrough came when the industry stopped trying to make hovering aircraft with aero-engines etc, and started to make air-cushioned boats, both amphibious and non-amphibious [rigid-sidewall]. The rigid-sidewall craft were made using Glass Reinforced Plastic [GRP] technology for use where a shallow draught boat was required, or where there was a lot of water debris, in harbours etc. As these craft were normally diesel-powered driving both lift fans and water props, it was a natural progression to build diesel-powered amphibious hovercraft - e.g. the AP 188.
This rather simplifies the case for the commercial development, but against the same period of 20 to 30 years the light hovercraft had gone from craft that would barely move to ones that could race in tight formation over land and water courses in groups up to 25 at the same time at speeds in excess of 50 miles an hour. On the light leisure/commercial side, craft are being used as viable forms of transport on a day-to-day basis, as well as for just plain fun. At the same time development on small craft often being built with limited resources has been innovative in squeezing the best results out of the often limited materials available. When they were then used competitively or in groups it was inevitable that the better concepts prevailed.