Hovercraft, SR.N4 Mk.III
Hovercrafts are capable of traveling at high speed above the surface of water.
hovercraft, water transportation, shipping, watercraft, air cushion, propeller, transportation, geography
On 25 July 1959, British engineer Christopher Cockerell crossed the English Channel with a unique vehicle, the SR.N1.
This vehicle hovered on a huge rubber skirt, held above water by an air cushion pumped under the skirt. It was characterised by high speed and the ability to travel both over land and water.
Originally designed for military purposes, it was the ideal vehicle to cross marshy areas, where boats and land vehicles could not be used, and to stop on sandy beaches. However, after about a decade of development, air cushion vehicles also appeared in public transport.
An improved version of the vehicle, the SR.N4, delivered passengers and cars between Dover and Calais from 1968 to the early 2000s. It could achieve a speed of 110 km/h over the water despite measuring 320 tonnes.
- rubber skirt
- air inlet
- steerable propulsion propeller
- car ramp
- gas turbine
- car deck
The SR.N4 measured 56.38 metres in length and 11.48 metres in height and had a gross weight of 320 tonnes. It was powered by four Rolls Royce gas turbine engines. These drove both the lift fans that blew air into the skirt, and the propulsion propellers. The propulsion of these vehicles is very similar to that of aeroplanes, since screw propellers cannot be used because no part of the hovercraft submerges in the water at all during a journey.
The latest version of the world's largest hovercraft, the SR.N4, was able to transport 60 cars and more than 400 passengers. Since then, hovercraft even larger than the SR.N4 have been built, but only for military purposes.
- rubber skirt
The high-performance fans continually pump air below the rubber skirt from above, forming a thin air-cushion between the rubber skirt and the water (or the land). This compressed air holds the vehicle above water. Since hovercraft do not touch the water, the drag does not slow them down, so their cruise speed is much higher than that of traditional ships. Moreover, it is very comfortable to travel on a hovercraft during storms because waves do not affect its locomotion.
The only disadvantage of hovercraft is the bad directional control due to the fact that these vehicles freely 'slide' above water and any cross-wind can make their manoeuvering very challenging. Likewise, over land, a hovercraft is not able to climb up even gentle slopes moving sidewards.
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