SR.N4 The Princess Anne
The SR.N4 (Saunders-Roe Nautical 4) hovercraft (also known as the Mountbatten-class hovercraft) was a large passenger and vehicle carrying hovercraft built by the British Hovercraft Corporation (BHC). BHC was formed by the merger of Saunders-Roe and Vickers Supermarine in 1966. Work on the SR.N4 began in 1965 and the first trials took place in early 1968. Power was provided by four Rolls-Royce Proteus marine turboshaft engines each driving its own lift fan and pylon-mounted steerable propulsion propeller.
The SR.N4 was the largest hovercraft built to that date, designed to carry 254 passengers in two cabins besides a four-lane automobile bay which held up to 30 cars. Cars were driven from a bow ramp just forward of the cockpit / 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 services across the English Channel between 1968 and 2000.
Upon completion of the prototype SR.N4, Charles Anthony Brindle, the Managing Director of British Rail Hovercraft Ltd, was responsible for establishing the first cross-Channel route for scheduled services by the type. 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 would be most suitable.
It was soon determined that Dover and Boulogne would be the preferable option for the maiden route, a decision which had been motivated in part by the local Chamber of Commerce having agreed to build a suitable hoverport to readily facilitate such operations. As there was no funding available for pre-service passenger trials, the opening season of active operations effectively served as a continuation of the trials activities as well. Brindle was aware that BHC would not be paid until the SR.N4 was in service, and thus there was a considerable emphasis placed on getting the craft ready for commercial use right at the point of delivery.
In August 1968, the first SR.N4 entered commercial service with the 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. In 1971, the Princess Margaret featured in the James Bond film "Diamonds Are Forever". The journey time from Dover to Boulogne was roughly 35 minutes with a total of six trips per day being conducted at peak times. The fastest ever crossing of the English Channel by a commercial car-carrying hovercraft was 22 minutes, which had been achieved by the SR.N4 Mk.III Princess Anne on 14 September 1995 during the 10:00 a.m. service.
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. 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. New aircraft-style forward-facing 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). 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 57.5-mile-per-hour (92.5 km/h) winds. The stretched SR.N4s (Super-4's) held the distinction of being the world's largest hovercraft, and continued to hold this title until the Russian Zubr class LCAC hovercrafts' arrival early in the 21st century.
The two main commercial operators (Seaspeed and Hoverlloyd) merged in 1981 to form Hoverspeed, which operated six SR.N4 of all marks. In all operations, while the craft were occasionally damaged, there was loss of life only once when on 30 March 1985 the Princess Margaret was blown onto a breakwater at Dover and four passengers were killed. The last of the craft was withdrawn from service in October 2000 and Hoverspeed itself ceased operations in November 2005.
The Royal Navy considered a mine sweeping version of the SR.N4, hovercraft being almost invulnerable to mines. This never got further than the concept stage, although an SR.N3 was used by the Inter-Service Hovercraft Unit for trials.
The two remaining Mk.III examples of the craft (GH-2006 Princess Margaret and GH-2007 Princess Anne) were bought by Wensley Haydon-Baillie for £500,000 and reside at the Hovercraft Museum. Haydon-Baillie is the owner of the super yacht Brave Challenger and uses the same Rolls-Royce Proteus Marine engines as the SR.N4s. The purchase included seven years' worth of spares including engines. As of winter 2015 all engines and APU's have been removed from the craft. The SR.N4s were put up for sale and Hover Transit Services of Bolton, Ontario, proposed putting the hovercraft back in operation (following a US$10 million purchase and refurbishment) on Lake Ontario with service between Rochester, New York, and Toronto, Ontario. The plan did not come to fruition, with government officials concluding that the organisation lacked the experience necessary to be viable.
The land on which the Hovercraft Museum stands is owned by the Homes and Communities Agency. Proposed redevelopment of the site has led to the two craft being threatened with scrapping, but a petition was launched with the aim of preserving one of the craft, which led into a 3-year lease of the hovercraft to the museum in August 2016 with the intention of subsequently permanently handing over the hovercraft to the museum, The Princess Anne was the craft chosen to be kept and will be restored in a former Seaspeed livery.
The plastic construction kit company Airfix produced a 1:144 scale model of the SR.N4 in the early 1970s, with a clear plastic top decking to show the detailed interior.