After Cockerell left the Marconi Company, he bought Ripplecraft Ltd., a small Norfolk boat and caravan hire company, with a legacy left by his father-in-law. The firm made little money, and Cockerell began to think how the craft could be made to go faster. He was led to earlier work by the
Thornycroft company, in which a small vessel had been partially raised out of the water by a small engine. Cockerell's greatest invention, the
hovercraft, grew out of this work. It occurred to him that if the entire craft were lifted from the water, the craft would effectively have no drag. This, he conjectured, would give the craft the ability to attain a much higher maximum speed than could be achieved by the boats of the time. Cockerell's theory was that instead of just pumping air under the craft, as Thornycroft had, if the air were to be instead channelled to form a narrow jet around the perimeter of the craft, the moving air would form a
momentum curtain, a wall of moving air that would limit the amount of air that would leak out. This meant that the same cushion of high-pressure air could be maintained by a much smaller engine; and for the first time, a craft could be lifted completely out of the water. Cockrell tested his designs across the village green opposite his house in the
Broadland village of
Somerleyton in Suffolk. He tested his theories using a vacuum cleaner and two tin cans. His
hypothesis was found to have potential, but the idea took some years to develop, and he was forced to sell personal possessions to finance his research. By 1955, he had built a working model from
balsa wood and had filed his first patent for the hovercraft, No. . Cockerell had found it impossible to interest the private sector in developing his idea, as both the aircraft and the shipbuilding industries saw it as lying outside their core business. He therefore approached the British Government with a view to interesting them in possible defence applications. The leaders of the defence groups were not interested in providing funding and put the idea of the hovercraft on the government's secret list. Being on the secret list stopped Cockerell from making his design public. It remained classified until 1958, upon news of similar developments on the continent, it was declassified, and Cockerell was introduced to the NRDC (
National Research Development Corporation). In the autumn of 1958, the NRDC placed an order with
Saunders-Roe for the first full-scale hovercraft. This
prototype craft was designated the
SR.N1 (Saunders-Roe – Nautical One) and was manufactured under licence from the NRDC. On 11 June 1959, the SR.N1 was first shown to the public, which was capable of carrying four men at a speed of 28 miles per hour. Weeks later, it was shipped over to France. It successfully crossed the
English Channel between
Calais and
Dover on 25 July 1959, 50 years to the day after the historic crossing by
Bleriot. In January 1959, the NRDC formed a subsidiary called Hovercraft Development Ltd. Cockerell was the Technical Director and the company controlled the patents which it used to license several private sector firms to manufacture craft under the registered trademark of Hovercraft. Cockerell received an
Honorary Doctorate from
Heriot-Watt University in 1971. ==Later life==