The SR.N4 (SaundersRoe Nautical 4) hovercraft (also known as the Mountbatten class hovercraft) was a combined passenger and vehiclecarrying class of hovercraft. The type has the distinction of being the largest civil hovercraft to have ever been put into service.
Work on the SR.N4 was initiated in 1965 by SaundersRoe. By the time that the vehicle's first trials took place in early 1968, SaundersRoe had merged with Vickers Supermarine to form the British Hovercraft Corporation, who continued development. Power was provided by four RollsRoyce Proteus marine turboshaft engines each driving its own lift fan and pylonmounted steerable propulsion propeller. The SR.N4 was the largest hovercraft then built, designed to carry 254 passengers in two cabins besides a fourlane automobile bay which held up to 30 cars. Cars were driven from a bow ramp just forward of the wheelhouse. The first design was 40 metres (131 ft) long, weighed 190 long tons (193 t), was capable of 83 knots (154 km/h) and could cruise at over 60 knots (111 km/h).
The SR.N4s operated regular services across the English Channel between 1968 and 2000. In response to operator demands, stretched versions of the SR.N4 were developed, culminating in the Mk.III variant, which had almost double the capacity for carrying both cars and passengers as the Mk.I. While interest was expressed in military applications for the type, no vehicles were ultimately used for such purposes.
Following the fleet's withdrawal from crosschannel services, a single remaining Mk.III example, GH2007 Princess Anne, remains on static display at the Hovercraft Museum at LeeonSolent.
.Upon completion of the prototype SR.N4, Charles Anthony Brindle, the Managing Director of British Rail Hovercraft, was responsible for establishing the first crossChannel route for scheduled services by the type.[31] In October 1966, Brindle and several engineers surveyed several potential sites on both the British and French sides of the English Channel using an SR.N6 to determine their suitability for the hovercraft service, which had been given the name Seaspeed. Amongst the most suitable candidates had been Dover or Folkestone on the English side and Calais or Boulogne on the French side.
In August 1968, the first SR.N4 entered commercial service with the GH2006 Princess Margaret being initially operated by Seaspeed between Dover and Boulogne, but later craft also traversed the Ramsgate (Pegwell Bay) to Calais route as well. The journey time from Dover to Boulogne was roughly 35 minutes, with six trips per day being conducted at peak times. The fastest ever crossing of the English Channel by a commercial carcarrying hovercraft was 22 minutes, achieved on 14 September 1995 by the SR.N4 Mk.III GH2007 Princess Anne on its 10:00 a.m. service.
Princess Anne loading in 1989
In 1972, the first SR.N4s were temporarily withdrawn for conversion to Mk.II specification which would provide for seven further car spaces and 28 more passengers. The first of the enlarged craft, the Swift, entered service at the beginning of February 1973.[36] The capacity increase was achieved by removing an inner passenger cabin in order to accommodate the extra cars and widening the outer passenger cabin: this was achieved without changing the overall footprint of the craft.[36] New aircraftstyle forwardfacing seats created an atmosphere of enhanced sophistication, and a redesigned skirt was intended to reduce window spray, enhancing the view out for passengers, and to give a smoother ride in rough seas: contemporary reports nevertheless commented on the "unsprung" nature of the ride.
After 1976, a pair of SR.N4s were refitted with new deep skirts and stretched by almost 56.1 ft (17.1 m), increasing capacity to 418 passengers and 60 cars at the cost of a weight increase to roughly 320 t (315 long tons).[37] To maintain speed, the engines were upgraded to four 3,800 shaft horsepower (2,834 kW) models, which were fitted with four 21 ft (6.4 m) diameter steerable Dowty Rotol propellers. The work cost around £5 million for each craft, and they were designated Mark IIIs; the improvements allowed them to operate in seas up to 11 ft 6 in (3.5 m) high and with 57.5mileperhour (92.5 km/h) winds.
The two main commercial operators (Hoverlloyd and Seaspeed) merged in 1981 to form Hoverspeed, which operated six SR.N4 of all marks.[39] The last of the craft was withdrawn from service in October 2000 and Hoverspeed itself ceased operations in November 2005.