Hovercrafts

People have been building boats for a thousands of years, but engineers are still finding better ways to carry us over the water. One of the things that slows boats down is the choppy waves brushing underneath them so, if you want to go faster, you need to go over them. How can you make a boat do this? One way is to use a hydrofoil: a kind of underwater wing that makes a boat fly, very slightly, like a plane. Another option is to use a giant fan and ride your boat on a cushion of air. Boats that work this way are called hovercraft (or, in the military, as LCAC, Landing Craft Air Cushion vehicles).

How it works?

The hovercraft is a vehicle that can slide over the surface under it using a jet of air that makes an air cushion. It can go over every regular horizontal surface such as water, snow, sand or ice without being in contact with it. It is considered to be an airplane because of its way of moving on the air. They usually have two or three engines but some of them have just one.

In a hovercraft, a giant centrally mounted fan creates a massive down-draft of air that pushes the hull upward anything from a few centimeters/inches to a couple of meters (5-6 ft). A cushion of air is trapped underneath the craft by a flexible rubber skirt that can bend around obstacles on water or land. Smaller secondary fans mounted on top, and driven either by the same diesel engine (or separate engines), create a backward force that pushes the hovercraft forward. Rudders behind the fans swivel this backward draft of air from side to side to provide steering.

Small "fingers" of rubber attached to the bottom of the skirt improve the seal between the skirt and the waves beneath it. This maintains the cushion of air, keeping the hovercraft above the water and making the ride smoother for passengers.

HISTORY:

In the middle of the 1880s, the British engineer Sir John Thornycroft built a number of prototypes based on the idea of using air between the hull of a boat and water to reduce the resistance, but it did not found practical applications.

In 1952, the British inventor Christopher Cockerell proposed a practical solution, through simple experiments with a vacuum engine and two cylindrical cans showing the operating principle of a vehicle suspended on a cushion of air driven pressure, which makes possible to move on different surfaces. The most significant improvement was the development of a peripheral system jet to maintain the cushion of air under the vehicle. This sustaining air cushion would allow to operate over muddy and watery surfaces as firm ground on.

The British aircraft manufacturer Saunders Roe was the first person to develop a hovercraft able of carrying a person, the SR-N1, which was subjected to several test programs.

The bearing capacity of the boat was improved by adding a containing "skirt" made of rubber or flexible fabric under the hull, in order to contain the air under it and create an effect of "levitation".

The SR-N1 was equipped with a pistons engine, triggering a series of propellers, creating a direct flow on the surface; It was propelled by air expelled back and it could not be able to transport more than its own weight and the two persons weigh. This was one of the main problems for it sold.

The first passenger hovercraft was the Vickers VA-3, which was carrying passengers regularly along the northern coast of the country of Wales. It worked by two turboprops engines, moved by propellers and was led by a rudder.

During the Decade of the 1960s, Saunders Roe developed several designs for passengers, including the SR-N2, also developed by Cockerell, who added inflatable tubes, aeronautical propellers over aeronautic handles and a system of vents cylindrical to the hull to improve the bearing capacity. Later, the SR-N6 was developed, leading 38 passengers built by Saunders Roe and Vickers (which in 1966 join to form the British Hovercraft Corporation)

At the end of the 60s and beginning of the 70s, the French engineer Jean Bertin developed a hovercraft train called Aero train. Its prototype I-80 established the world speed record for an air cushion vehicle on dry land, wich had an average speed of 417.6 km/h and a maximum of 430 km/h.

In 1970, the largest english hovercraft were the best ones, the model SR-N4, which had four Proteus engines of Rolls Royce; they were driven on the “Canal de la Mancha”.

In the year 2000 the service was interrupted, after years of competing with the traditional boats, catamarans and the Eurotunnel; the reasons were the high cost of maintenance,  the fuel, and the lack of sponsorship State, which at that time was dedicated to large fleets in Europe .

The commercial success of hovercraft was dampened by rapid increases in the cost of the fuel, at the end of the 60's and 70's, what made the conflict in the Middle East; by the introduction of alternative ships, as the catamaran waves borers (marketed as Seacat in Great Britain), which use less fuel and can do almost everything that makes a hovercraft on water. However, elsewhere in the world has continued to develop the technology of the hovercrafts for military and civilian purposes ( the USSR and  the USA developed their own vehicles Hover giant, capable of carrying military arsenal under any weather conditions and in any field of battle), hovercraft practically disappeared from the British coasts, for being reintroduced as lifeguards, lifeboats by the Royal National institution of life boats.

Nowadays, the development of the kevlar and other polymers had made build transports of similar performance with innovative construction techniques and low operating costs such as the hydrofoils, catamarans, the trimarans and the seaplanes, as large as big as a Jumbo, which use the soil effect.