The SR.N4 (Saunders-Roe Nautical 4) hovercraft (also known as the ''Mountbatten'' class hovercraft) was a combined passenger and vehicle-carrying 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

Saunders-Roe Saunders-Roe Limited, also known as Saro, was a British aero- and marine-engineering company based at Columbine Works, East Cowes, Isle of Wight. History The name was adopted in 1929 after Alliott Verdon Roe (see Avro) and John Lord took a c ...

. By the time that the vehicle's first trials took place in early 1968, Saunders-Roe had merged with

Vickers Supermarine Vickers was a British engineering company that existed from 1828 until 1999. It was formed in Sheffield as a steel foundry by Edward Vickers and his father-in-law, and soon became famous for casting church bells. The company went public in 18 ...

to form the British Hovercraft Corporation, who continued development. Power was provided by four

Rolls-Royce Proteus The Bristol Proteus was the Bristol Engine Company's first mass-produced gas turbine engine design, a turboprop that delivered just over 4,000 hp (3,000 kW). The Proteus was a reverse-flow gas turbine. Because the second turbine drov ...

marine turboshaft engines each driving its own lift fan and pylon-mounted steerable propulsion propeller. The SR.N4 was the largest hovercraft then built, 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 wheelhouse. The first design was long, weighed , was capable of and could cruise at over . The SR.N4s operated regular services across the

English Channel The English Channel, "The Sleeve"; nrf, la Maunche, "The Sleeve" (Cotentinais) or ( Jèrriais), (Guernésiais), "The Channel"; br, Mor Breizh, "Sea of Brittany"; cy, Môr Udd, "Lord's Sea"; kw, Mor Bretannek, "British Sea"; nl, Het Kana ...

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 cross-channel services, a single remaining Mk.III example, GH-2007 ''Princess Anne'', remains on static display at the

Hovercraft Museum The Hovercraft Museum, in Lee-on-the-Solent, Hampshire, England is a museum run by a registered charity dedicated to hovercraft. The museum has a collection of over 60 hovercraft of various designs. Situated at HMS ''Daedalus'' by the larg ...

Lee-on-Solent Lee-on-the-Solent, often referred to as Lee-on-Solent, is a seaside district of the Borough of Gosport in Hampshire, England, about five miles (8 km) west of Portsmouth. The area is located on the coast of the Solent. It is primarily a res ...

as of August 2021.

Development

Origins

In August 1962, the original concept for the SR.N4, which had been conceived at the same time as the SR.N2 was being designed, was abandoned.Paine and Syms 2012, pp. 131, 236. This original concept had effectively been a pair of elongated SR.N2 fixed together in a side-by-side placement and would have been powered by an arrangement of four pairs of

Blackburn A.129 The Bristol Siddeley Nimbus, later known as the Rolls-Royce Nimbus, was a British turboshaft engine developed under license by Blackburn Aircraft Ltd. from the Turbomeca Turmo in the late 1950s. It was used on the Westland Scout and Westland ...

turboshaft A turboshaft engine is a form of gas turbine that is optimized to produce shaftpower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust ...

engines. In its place, a new proposed hovercraft, which was referred to as the SR.N4 as well, was considerably larger and heavier, and powered by three pairs of

marinised

gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...

engine.Paine and Syms 2012, p. 131. However, during early 1963, work on the SR.N4 was put on hold due to a greater priority having been placed on the completion of the SR.N5 instead. In late 1964, it was decided to recommence design work on the proposed SR.N4.Paine and Syms 2012, pp. 131, 147. By the end of 1964, it had been concluded that, due to the improved projected performance of the craft's flexible skirt having lowered the power requirements involved, only two pairs of Proteus engines would be required instead of three.Paine and Syms 2012, p. 238. At this stage, the proposed design for the SR.N4 had a displacement of 165 tons and a payload of up to 33 cars and 116 passengers; this would not substantially differ from the final design adopted for the type. Experience gained from the SR.N5 and SR.N6 would contribute to the design of aspects of the larger SR.N4, which would be four times the size of any preceding hovercraft.Paine and Syms 2012, pp. 167–168, 202. This approach is credited with having been less expensive and having resulted in a more commercially viable hovercraft than would have been if it had been constructed as per the earlier incarnation of the SR.N4 and then required to perform modifications to improve the capabilities of aspects such as the skirt, which had been considerably advanced by development of the SR.N5 and SR.N6.Paine and Syms 2012, p. 236. Specific improvements included the adoption of triangular rubber 'finger'-like attachments to the curtain which provided for a better seal between the hovercraft and the water's surface as well as being cheaper and easier to maintain than previous configurations.Paine and Syms 2012, pp. 236–238. During the mid-1960s, some management figures within British Rail had become interested in the potential for operating a fleet of hovercraft for scheduled services that would link up to Britain's national rail system.Paine and Syms 2012, pp. 201–202. In November 1965, Frank Cousins, the Minister of Technology, announced that British Rail would participating in the development of the SR.N4 and would be a customer for the type. While orders had already been placed for the SR.N4 by this point, the

British Railways Board British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies. ** Britishness, the British identity and common culture * British English, ...

had decided to commit to taking delivery of the first craft to be produced; this was particularly convenient as the two orders which had been placed by Swedish operator Cross-Channel Hover Services specifically excluded accepting delivery of the first example.Paine and Syms 2012, pp. 202–203. By the end of 1965, having acquired three firm orders, it was now plausible for production of the SR.N4 to proceed.Paine and Syms 2012, p. 203.

Prototype and testing

Having realised that the market for large hovercraft was not yet large enough to sustain a number of competing companies at that time, in 1966, the hovercraft divisions of both

and

merged to form a new united entity, known as the British Hovercraft Corporation (BHC), which was headquartered on the

Isle of Wight The Isle of Wight ( ) is a Counties of England, county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the List of islands of England#Largest islands, largest and List of islands of England#Mo ...

.Paine and Syms 2012, pp. 165–166. In autumn 1966, production work commenced on the structure of the first SR.N4, which was internally designated ''001''. The vehicle was assembled in the same hangar in which the three

Saunders-Roe Princess The Saunders-Roe SR.45 Princess was a British flying boat aircraft developed and built by Saunders-Roe at their Cowes facility on the Isle of Wight. It has the distinction of being the largest all-metal flying boat to have ever been constructed. ...

flying boats had been constructed 15 years before. During 1967, as 001 was taking shape, it was announced that the SR.N4 had been named the ''Mountbatten-class''. Throughout the development and production of 001, both Hoverlloyd and Seaspeed carefully monitored progress on the project.Paine and Syms 2012, p. 295. In October 1967, the completed 001 was officially presented to gathered members of the press and to various representatives and dignitaries.Paine and Syms 2012, p. 249. On 20 November 1967, the first engine run was performed, after which 11 weeks of intense test runs on land were performed and the exposed faults were addressed. On 4 February 1968, 001 was launched onto water for the first time.Paine and Syms 2012, pp. 249, 297. The launch, while successful, had involved some risk due to the lack of space to manoeuvre with an untested control system. Later that same day, 001 conducted its

maiden flight The maiden flight, also known as first flight, of an aircraft is the first occasion on which it leaves the ground under its own power. The same term is also used for the first launch of rockets. The maiden flight of a new aircraft type is alw ...

.Paine and Syms 2012, pp. 249, 297–300. As experience with the prototype accumulated, the control arrangement proved to be quite effective even within confined spaces; incidents involving a loss of control did occur during the test programme, but these were mainly due to error on the part of the operator.Paine and Syms 2012, pp. 303–305. Ray Wheeler, BHC's chief engineer, was reportedly very pleased with the progress made during the initial trials. At the same time, 001 required substantial refinement and alteration in order to become a commercially viable craft.Paine and Syms 2012, p. 305. The air intakes had to be substantially modified in order to minimise

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

ingestion, and a revised skirt system was also developed.

Design

The Princess Anne Saunders Roe SRN 4 Mk 3

The SR.N4 was the biggest hovercraft to have been completed upon its introduction. Its primary structure comprised a large

modular Broadly speaking, modularity is the degree to which a system's components may be separated and recombined, often with the benefit of flexibility and variety in use. The concept of modularity is used primarily to reduce complexity by breaking a s ...

buoyancy tank, the internal structure of which being divided into 24 watertight compartments.Paine and Syms 2012, pp. 240–241. It had an identical platform shape to the smaller SR.N5, being rectangular with a semi-circular bow and a beam-to-length ratio of 1:1.66.Paine and Syms 2012, p. 241. Navigation wise, the SR.N4 had a dual radar system for navigation purposes allowing the craft to operate in zero visibility- Type Racal Decca Bridgemaster with GPS navigation system. The SR.N4 was powered by four

turboprop A turboprop is a turbine engine that drives an aircraft propeller. A turboprop consists of an intake, reduction gearbox, compressor, combustor, turbine, and a propelling nozzle. Air enters the intake and is compressed by the compressor. ...

engines.Paine and Syms 2012, pp. 238, 242. The Proteus engines each drove a set of diameter steerable

Dowty Rotol Dowty Propellers is a British engineering company based in Brockworth, Gloucestershire that specialises in the manufacture, repair and overhaul of propellers and propeller components for customers around the world. It is owned by General Elect ...

propellers, arranged in two pairs on pylons positioned on top of the craft's roof; upon the SR.N4's introduction to service, these were the largest propellers in the world. Six independent electrohydraulic systems, each driven from the main gearboxes, powered the movement of the

fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

s and pylons, while a further four units were used to actuate the variable-pitch propellers.Paine and Syms 2012, p. 244.

The control cabin of the SR.N4 resembled the flight deck of an aircraft, being relatively cramped in comparison with the

bridge A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...

of a typical vessel.Paine and Syms 2012, p. 353. It housed a crew of three, comprising a captain, first officer/flight engineer, and a second officer/navigator; the main role of the second officer was to avoid collisions, primarily using a Decca 629 radar to do so.Paine and Syms 2012, p. 353, 379. The flying controls appeared broadly similar to a typical aircraft, using an assortment of

rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally air or water). On an aircraft the rudder is used primarily to counter adve ...

pedals, joysticks,

yoke A yoke is a wooden beam sometimes used between a pair of oxen or other animals to enable them to pull together on a load when working in pairs, as oxen usually do; some yokes are fitted to individual animals. There are several types of yoke, u ...

s, separate propeller pitch levels, and engine speed controls; however, their functionality often differed substantially, such as the ability for the yoke to command the pitch of all four propellers.Paine and Syms 2012, p. 353, 366–367. The SR.N4 is fitted with a 12-ton skirt which runs under the perimeter of the whole craft and employs a complex structure.Paine and Syms 2012, p. 513. On the underside of the buoyancy tanks, a total of five 21-inch platforms (known as 'elephant feet') were positioned so that the craft could stably rest on three of them. Fuel was contained within flexible bags located at all four corners; the craft could be trimmed by intentionally redistributing fuel between the fore and aft tanks to better match the load and prevailing weather conditions. The craft would consume 1,000 gallons per hour at a cruise of 50 knots before refuelling with an approximate range of 150 miles. Maximum fuel capacity was 8068 gallons, 36,676 litres or 28.8 tons. The stern of the craft featured a sizeable set of doors for the loading and unloading of vehicles onto the car deck as well as all four of the exhausts for the Proteus engines, another set of loading doors were present on the front as well.Paine and Syms 2012, p. 242.

Weather limitations

The SR.N4 could operate up to

gale A gale is a strong wind; the word is typically used as a descriptor in nautical contexts. The U.S. National Weather Service defines a gale as sustained surface winds moving at a speed of between 34 and 47 knots (, or ).beaufort scale and 3.5m swell seas.

Operational service

Upon completion of the prototype SR.N4, Charles Anthony Brindle, the Managing Director of British Rail Hovercraft, 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. It was soon determined that Dover and Boulogne would be the preferable option for the maiden route, a decision that had been motivated in part by the local Chamber of Commerce having agreed to build a suitable hoverport to readily facilitate such operations.Paine and Syms 2012, pp. 230–234. 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.Paine and Syms 2012, pp. 309–310. In August 1968, the first SR.N4 entered commercial service with the GH-2006 ''Princess Margaret'' being initially operated by Seaspeed between Dover and Boulogne, but later craft also traversed the Ramsgate (

Pegwell Bay Pegwell Bay is a shallow inlet in the English Channel coast astride the estuary of the River Stour north of Sandwich Bay, between Ramsgate and Sandwich in Kent. Part of the bay is a nature reserve, with seashore habitats including mudflats and ...

) 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 car-carrying hovercraft was 22 minutes, achieved on 14 September 1995 by the SR.N4 Mk.III GH-2007 ''Princess Anne'' on its 10:00 a.m. service. SRN4Loading89

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 , increasing capacity to 418 passengers and 60 cars at the cost of a weight increase to roughly .Paine and Syms 2012, p. 595. To maintain speed, the engines were upgraded to four models, which were fitted with four diameter steerable

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 high and with winds.Paine and Syms 2012, pp. 595–596. The two main commercial operators (Hoverlloyd and Seaspeed) merged in 1981 to form

Hoverspeed Hoverspeed was a ferry company that operated on the English Channel from 1981 until 2005. It was formed in 1981 by the merger of Seaspeed and Hoverlloyd. Its last owners were Sea Containers; the company ran a small fleet of two high-speed Sea ...

, which operated six SR.N4 of all marks. The last of the craft was withdrawn from service in October 2000 and Hoverspeed itself ceased operations in November 2005.

Accidents

Most incidents were benign and resulted in little more than the vehicles towed back to shore. In 1978, the GH-2007 ''Princess Anne'' lost much of her air-cushion skirt in heavy seas 7 miles off Dover. However, in March 1985, 4 passengers lost their lives when GH-2006 ''Princess Margaret'' crashed into a pier at the entrance of

Dover Harbour The Port of Dover is a cross-channel ferry, cruise terminal, maritime cargo and marina facility situated in Dover, Kent, south-east England. It is the nearest English port to France, at just away, and is one of the world's busiest maritime pa ...

from Calais in force 6 to 7 heavy seas.

Military interest

The

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against ...

considered a mine sweeping version of the SR.N4, hovercraft being almost invulnerable to mines. A minesweeping version of the SR.N4 was thought to be capable of carrying the same equipment as a

Hunt-class mine countermeasures vessel The Hunt class is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an anal ...

, while being cheaper to purchase, although more expensive to operate. The use of hovercraft for minesweeping never got further than the concept stage, although an SR.N3 was used by the Inter-Service Hovercraft Unit for trials.

Surviving examples

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 were stored at

, next to the

. Haydon-Baillie is the owner of the super yacht ''Brave Challenger'' which 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 APUs had been removed from the craft. The SR.N4s were put up for sale and Hover Transit Services of

Bolton, Ontario Bolton (2021 population 26,795) is an unincorporated village that is the most populous community in the town of Caledon, Ontario. It is located beside the Humber River in the Region of Peel, approximately 50 kilometres northwest of Toronto. In r ...

, proposed putting the hovercraft back in operation (following a purchase and refurbishment) on

Lake Ontario Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York. The Canada–United States border ...

with service between

Rochester, New York Rochester () is a city in the U.S. state of New York, the seat of Monroe County, and the fourth-most populous in the state after New York City, Buffalo, and Yonkers, with a population of 211,328 at the 2020 United States census. Located in W ...

, and

Toronto, Ontario Toronto ( ; or ) is the capital city of the Canadian province of Ontario. With a recorded population of 2,794,356 in 2021, it is the most populous city in Canada and the fourth most populous city in North America. The city is the ancho ...

. 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 Homes England is the non-departmental public body that funds new affordable housing in England. It was founded on 1 January 2018 to replace the Homes and Communities Agency (HCA). HCA in turn was established by the Housing and Regeneration Act 2 ...

. The 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. In March 2018, GH-2006 ''Princess Margaret'' was broken up at Lee-on-Solent by her last owners, Homes England. GH-2007 The ''Princess Anne'' remains on site leased to the Hovercraft Museum.

Production

Built as Mk.I unless specified otherwise. *01 – GH-2006 ''Princess Margaret'' 1968, Seaspeed – originally the prototype, converted to Mk.III specification in 1979. Scrapped at

in March 2018 *02 – GH-2004 ''Swift'', Hoverlloyd – converted to Mk.II specification for February 1973, broken up in 2004 at the

*03 – GH-2005 ''Sure'' 1968, Hoverlloyd – converted to Mk.II specification in 1972, broken up in 1983 for spares *04 – GH-2007 ''Princess Anne'', Seaspeed – converted to Mk.III specification in 1978, on display at the Hovercraft Museum *05 – GH-2008 ''Sir Christopher'' 1972, Hoverlloyd – converted to Mk.II specification in 1974, broken up 1998 for spares *06 – GH-2054 ''The Prince of Wales'', Hoverlloyd – built as Mk.II, scrapped in 1993 following an electrical fire

Specification

Dimensions

Performance

*Max speed: Mark 1 – 65 knots (calm water, zero wind, at gross laden weight)
Mk.II – *Normal operating speeds: 40 – *Endurance: 4 hours (maximum power, 2,800 Imperial gallons of fuel) *Gradient: 1 in 11

In popular culture

Model kits

The plastic construction kit company

Airfix Airfix is a British brand and former manufacturing company which produced injection-moulded plastic scale model kits. In the U.K., the name 'Airfix' is synonymous with plastic models of this type, often simply referred to as "an airfix kit" even ...

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.

Film industry

The SR.N4 GH-2006 ''Princess Margaret'' featured in scenes from the 1971 James Bond film '' Diamonds Are Forever'' starring Sean Connery. The SR.N4 GH-2005 ''Sure'' starred in '' La Gifle'' with

Isabelle Adjani Isabelle Yasmina Adjani ; born 27 June 1955) is a French actress and singer of Algerian and German descent. She is the only performer in history to win five César Awards for acting; she won the Best Actress award for '' Possession'' (1981), '' ...

and in ''

The Black Windmill ''The Black Windmill'' is a 1974 British spy thriller film directed by Don Siegel and starring Michael Caine, John Vernon, Janet Suzman and Donald Pleasence. It was produced by Richard D. Zanuck and David Brown. Plot Two schoolboys are play ...

,'' starring

Michael Caine Sir Michael Caine (born Maurice Joseph Micklewhite; 14 March 1933) is an English actor. Known for his distinctive Cockney accent, he has appeared in more than 160 films in a career spanning seven decades, and is considered a British film ico ...

, both released in 1974. The SR.N4 is also featured in the 1980 film '' Hopscotch'' starring Walter Matthau and

Glenda Jackson Glenda May Jackson (born 9 May 1936) is an English actress and former Member of Parliament (MP). She has won the Academy Award for Best Actress twice: for her role as Gudrun Brangwen in the romantic drama ''Women in Love'' (1970); and again for ...

References

Citations

Bibliography

* *

External links

Hovercraft Museum: SR.N4 Mk.IBrave Challenger
{{DEFAULTSORT:SR.N4 Hovercraft Saunders-Roe