View source for SR.N4

{{Short description|Hovercraft built for English Channel services}}
{{Use dmy dates|date=November 2016}}
{{Use British English|date=November 2016}}
{|{{Infobox ship begin}}
{{Infobox ship image
|Ship image            = SRN4 Hovercraft Mountbatten Class.jpg
|Ship caption          = Mark III SR.N4 arriving in [[Port Dover|Dover]] on its last commercial flight October 2000
}}
{{Infobox ship class overview
|Name                  = SR.N4 ''Mountbatten'' class
|Builders              = [[British Hovercraft Corporation]]
|Operators             = {{unbulleted list
  | [[Hoverlloyd]]
  | [[Seaspeed]]
  | [[Hoverspeed]]
  }}
|Class before          =
|Class after           =
|Built range           =
|In service range      = 1968–2000
|Total ships completed = 6
|Total ships active    =
|Total ships scrapped  = 5
|Total ships preserved = 1
}}
{{Infobox ship characteristics
|Hide header           =
|Header caption        = (Mark III)
|Ship class            =
|Ship type             = [[Hovercraft]]
|Ship tonnage          =  320 t 
|Ship displacement     = 
|Ship length           = {{convert|56.38|m|ftin|abbr=on}} 
|Ship beam             = {{convert|23.77|m|ftin|abbr=on}}
|Ship height           = {{convert|11.48|m|ftin|abbr=on}} on landing pads
|Ship draught          =  
|Ship draft            =
|Ship depth            =
|Ship hold depth       =
|Ship decks            =
|Ship deck clearance   =
|Ship power            = 4 x {{convert|3,800|shp|abbr=on}}
|Ship propulsion       = 4 x [[Bristol Proteus|Rolls-Royce Marine Proteus]] gas turbines for lift and propulsion, each driving a single four-bladed variable-pitch propeller
|Ship speed            = {{convert|70 |kn|mph km/h}}
|Ship range            = 
|Ship endurance        =
|Ship boats            =
|Ship capacity         = up to 60 cars and 418 passengers 
|Ship crew             =
|Ship sensors          =
|Ship notes            =
}}
|}

The '''SR.N4''' (Saunders-Roe Nautical 4)<ref>{{cite web |url= http://www.jameshovercraft.co.uk/hover/html/srn4.htm|title= James' Hovercraft Site: SRN4|accessdate=2008-03-22}}</ref> hovercraft (also known as the '''''Mountbatten'' class hovercraft''') was a combined  passenger and vehicle-carrying class of [[hovercraft]].<ref>{{cite book |title=A Dictionary of Aviation |first=David W. |last=Wragg |isbn=9780850451634 |edition=first |publisher=[[Osprey Publishing]]|year=1973 |page=250}}</ref> 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]]. By the time that the vehicle's first trials took place in early 1968, Saunders-Roe had merged with [[Vickers]]' hovercraft division to form the [[British Hovercraft Corporation]], who continued development. Power was provided by four [[Bristol Proteus|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 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 {{convert|40|m|ft|0}} long, weighed {{convert|190|LT|t|0|lk=on}}, was capable of {{convert|83|kn|mph km/h|0|lk=in}} and could cruise at over {{convert|60|kn|mph km/h|0}}.

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 cross-channel services, a single remaining Mk.III example, GH-2007 ''Princess Anne'', remains on static display at the [[Hovercraft Museum]] at [[Lee-on-Solent]] as of August 2021.

==Development==
[[File:Hovercraft.ogg|thumb|Hovercraft landing in [[Port of Calais|Calais]]]]
[[File:Boarding.ogv|thumb|Boarding a Hovercraft with a vehicle]]
===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.{{sfn|Paine|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 [[Bristol Siddeley Nimbus|Blackburn A.129]] [[turboshaft]] 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 [[Bristol Proteus|Rolls-Royce Proteus]] [[Marinisation|marinised]] [[gas turbine]] engine.{{sfn|Paine|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.{{sfn|Paine|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.{{sfn|Paine|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.{{sfn|Paine|Syms|2012|p=238}}

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.{{sfn|Paine|Syms|2012|p=167–168}}{{sfn|Paine|Syms|2012|p=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.{{sfn|Paine|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.{{sfn|Paine|Syms|2012|p=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.{{sfn|Paine|Syms|2012|p=201–202}} In November 1965, [[Frank Cousins (British politician)|Frank Cousins]], the [[Minister of Technology]], announced that British Rail would participate 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]] 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 [[Hoverlloyd|Cross-Channel Hover Services]] specifically excluded accepting delivery of the first example.{{sfn|Paine|Syms|2012|p=202–203}} By the end of 1965, having acquired three firm orders, it was now plausible for production of the SR.N4 to proceed.{{sfn|Paine|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 [[Saunders-Roe]] and [[Vickers Supermarine]] merged to form a new united entity, known as the [[British Hovercraft Corporation]] (BHC), which was headquartered on the [[Isle of Wight]].{{sfn|Paine|Syms|2012|p=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]] [[flying boat]]s had been constructed 15 years before.{{sfn|Paine|Syms|2012|p=236}}{{sfn|Paine|Syms|2012|p=238}} During 1967, as 001 was taking shape, it was announced that the SR.N4 had been named the ''Mountbatten-class''.{{sfn|Paine|Syms|2012|p=238}} Throughout the development and production of 001, both Hoverlloyd and [[Seaspeed]] carefully monitored progress on the project.{{sfn|Paine|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.{{sfn|Paine|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.{{sfn|Paine|Syms|2012|p=249}}{{sfn|Paine|Syms|2012|p=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]].{{sfn|Paine|Syms|2012|p=249}}{{sfn|Paine|Syms|2012|p=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.{{sfn|Paine|Syms|2012|p=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.{{sfn|Paine|Syms|2012|p=305}} The air intakes had to be substantially modified in order to minimise [[salt]] ingestion, and a revised skirt system was also developed.{{sfn|Paine|Syms|2012|p=305}}

==Design==
{{expand section|date=January 2017}}
[[File:The Princess Anne Saunders Roe SRN 4 Mk 3.jpg|thumb|''Princess Anne'' at [[Port of Calais|Calais]]]]
[[File:SR.N4 interior.jpg|thumb|The interior of The ''Princess Anne'' in 2019]]
The SR.N4 was the biggest hovercraft to have been completed upon its introduction. Its primary structure comprised a large [[Modularity|modular]] buoyancy tank, the internal structure of which was divided into 24 watertight compartments.{{sfn|Paine|Syms|2012|p=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.{{sfn|Paine|Syms|2012|p=241}} The SR.N4 had a dual radar system for navigation, allowing the craft to operate in zero visibility - Type Racal Decca Bridgemaster. A GPS navigation system was fitted.{{sfn|Investigation of Heavy Weather Damage |loc=Annex 1}}

The SR.N4 was powered by four [[Bristol Proteus|Rolls-Royce Proteus]] [[turboprop]] engines.{{sfn|Paine|Syms|2012|p=238}}{{sfn|Paine|Syms|2012|p=242}} The Proteus engines each drove a set of {{convert|19|ft|m|abbr=on|1}} diameter steerable [[Dowty Rotol]] 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.{{sfn|Paine|Syms|2012|p=241}} Six independent [[Hydraulics|electrohydraulic]] systems, each driven from the main [[Transmission (mechanics)|gearboxes]], powered the movement of the [[fin]]s and pylons, while a further four units were used to actuate the [[Variable-pitch propeller (aeronautics)|variable-pitch propeller]]s.{{sfn|Paine|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 (nautical)|bridge]] of a typical vessel.{{sfn|Paine|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 Radar|Decca 629 radar]] to do so.{{sfn|Paine|Syms|2012|p=353}}{{sfn|Paine|Syms|2012|p=379}} The flying controls appeared broadly similar to a typical aircraft, using an assortment of [[rudder]] pedals, [[joystick]]s, [[Yoke (aeronautics)|yoke]]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.{{sfn|Paine|Syms|2012|p=353}}{{sfn|Paine|Syms|2012|p=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.{{sfn|Paine|Syms|2012|p=513}} On the underside of the buoyancy tanks, five 21-inch{{clarify|height? width? |date=June 2023}} platforms (known as 'elephant feet') were positioned so that the craft could stably rest on three of them.{{sfn|Paine|Syms|2012|p=244}}

Fuel was contained within flexible bags located at all four corners; the craft could be trimmed by redistributing fuel between the fore and aft tanks to better match the load and prevailing weather conditions.{{sfn|Paine|Syms|2012|p=241}} The craft would consume 1,000 gallons per hour at a cruise of {{convert|50|kn|mph km/h}} before refuelling with an approximate range of {{convert|150| mile|abbr=on}}.  Maximum fuel capacity was {{convert|8068|impgal|L|abbr=on}}; about 29 tons.<ref>{{Cite book|first1=Liang |last1=Yun |first2= Alan |last2=Bliault|title=Theory and Design of Air Cushion Craft|publisher=[[Elsevier Science]]|year=2000|isbn=9780080519067|page=13}}</ref>

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 was located at the bow.{{sfn|Paine|Syms|2012|p=242}}

The SR.N4 could operate up to [[gale]] force 8 wind on the [[beaufort scale]] and 3.5m swell seas.{{sfn|Investigation of Heavy Weather Damage|page=9}}

==Operational service==
[[File:Hovercraft in Dover.jpg|thumb|''Princess Margaret'' at the mouth of the [[Port of Dover|Western Docks in Dover]], 1998]]
Upon completion of the prototype SR.N4, Charles Brindle, the managing director of British Rail Hovercraft, was responsible for establishing the first cross-Channel route for scheduled services by the type.<ref>[https://web.archive.org/web/20160718010656/http://www.nrm.org.uk/railwaystories/railwayvoices/charlesanthonybrindle Charles Anthony Brindle] [[National Railway Museum]]</ref> 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 [[Port of Dover|Dover]] or [[Folkestone Harbour|Folkestone]] on the English side and [[Port of Calais|Calais]] or [[Boulogne-sur-Mer|Boulogne]] on the French side.{{sfn|Paine|Syms|2012|p=230}}{{sfn|Paine|Syms|2012|p=234}}

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.{{sfn|Paine|Syms|2012|p=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.{{sfn|Paine|Syms|2012|p=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.{{cn|date=July 2024}} Rival operator [[Hoverlloyd]] built the world's first purpose-built hoverport at [[Ramsgate Hoverport]], specifically designed for the SR.N4, to also serve the Calais route.{{cn|date=July 2024}}

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&nbsp;a.m. service.<ref>{{cite news |url=https://news.bbc.co.uk/onthisday/hi/dates/stories/june/15/newsid_3025000/3025267.stm |title=Hovercraft Facts |work=1966: Hovercraft deal opens show |publisher=[[BBC News]] |date=15 June 1966 |access-date=9 April 2010}}</ref><ref>{{cite web |url= http://www.dover-kent.co.uk/transport/hovercraft.htm |title= Hovercraft |access-date= 2008-01-23 |work= Dover – Lock and Key of the Kingdom |publisher= www.dover-kent.co.uk |url-status= dead |archive-url= https://web.archive.org/web/20120917130412/http://www.dover-kent.co.uk/transport/hovercraft.htm |archive-date= 17 September 2012 |df= dmy-all }}</ref>
[[File:SRN4Loading89.jpg|left|thumb|''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.<ref name=Autocar197302>{{cite magazine| title =Hovering along on the Crest of a Wave |magazine=[[Autocar (magazine)|Autocar]] |page=6 |date = 8 February 1973}}</ref> 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.<ref name=Autocar197302/> 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.<ref name=Autocar197302/>

After 1976, a pair of SR.N4s were refitted with new deep skirts and stretched by almost {{convert|56.1|ft|m|1|abbr=on}}, increasing capacity to 418 passengers and 60 cars at the cost of a weight increase to roughly {{convert|320|t|LT|0|abbr=on}}.{{sfn|Paine|Syms|2012|p=595}} To maintain speed, the engines were upgraded to four {{convert|3800|shp|kW|0|lk=in}} models, which were fitted with four {{convert|21|ft|m|1|abbr=on|adj=on}} diameter steerable [[Dowty Rotol]] [[Propeller (aircraft)|propeller]]s. 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 {{convert|11|ft|6|in|m|1|abbr=on}} high and with {{convert|57.5|mph|km/h|1|adj=on}} winds.{{sfn|Paine|Syms|2012|p=595–596}}

The two main commercial operators (Hoverlloyd and Seaspeed) merged in 1981 to form [[Hoverspeed]], which operated six SR.N4 of all marks.<ref>{{cite news |first=Justin |last=Parkinson |url=https://www.bbc.com/news/magazine-34658386 |title=What happened to passenger hovercraft? |work=BBC News Magazine |location=UK |date=9 November 2015 |access-date=2023-06-18}}</ref> The last of the craft was withdrawn from service in October 2000 and Hoverspeed itself ceased operations in November 2005.<ref>{{cite news |url=https://news.bbc.co.uk/2/hi/uk_news/england/kent/4406224.stm |title=Many jobs lost as ferries stop |work=BBC News |date=4 November 2005 |access-date=2023-06-18}}</ref>

===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, resulting in a [[Marine Accident Investigation Branch]] investigation.{{sfn|Investigation of Heavy Weather Damage}} However, in March 1985, 4 passengers lost their lives when GH-2006 ''Princess Margaret'' crashed into a pier at the entrance of the [[Port of Dover]] from Calais in force 6 to 7 heavy seas.<ref>{{Cite book|last=Hollebone|first=Ashley|title=The Hovercraft: A History|publisher=[[History Press]]|year=2012|isbn=9780752490519|page=26}}</ref><ref>{{cite web |url=https://discovery.nationalarchives.gov.uk/details/record?catid=8419462&catln=6 |title=Report of the inquiry into the accident to hovercraft 'The Princess Margaret' |work=[[National Archives (United Kingdom)|National Archives]]|location=England}}</ref>

===Military interest===
The [[Royal Navy]] considered a [[mine sweeping]] version of the SR.N4, hovercraft being almost invulnerable to [[Naval mine|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]], 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.{{sfn|Brown|Moore|2012|p=140–141}}

==Surviving examples==
[[File:SRN4 Hovercraft The Princess Margaret.jpg|thumb|''Princess Margaret'' at the [[Hovercraft Museum]] in May 2008]]
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 [[Lee-on-Solent]], next to the [[Hovercraft Museum]]. 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]], proposed putting the hovercraft back in operation (following a {{USD|10 million}} purchase and refurbishment) on [[Lake Ontario]] with service between [[Rochester, New York]], and [[Toronto]], Canada.<ref>{{cite news |url=http://www.citytv.com/toronto/citynews/life/money/article/22191--can-fast-hovercraft-service-between-u-s-and-toronto-stay-afloat|title=Can Fast Hovercraft Service Between U.S. And Toronto Stay Afloat?|work=[[CityNews]]|date=9 April 2008|accessdate=10 September 2010}}</ref> The plan did not come to fruition, with government officials concluding that the organisation lacked the experience necessary to be viable.<ref>{{cite news |url=https://www.thestar.com/news/gta/2008/07/15/has_fast_ferry_ideas_time_passed.html |title=Has fast ferry idea's time passed? |work=[[Toronto Star]]|date=15 July 2008 |accessdate=29 March 2013}}</ref>

The land on which the Hovercraft Museum stands is owned by [[Homes England]]. 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,<ref>{{cite news|url= https://www.bbc.co.uk/news/uk-england-hampshire-35449474 |title= Petition to save last cross-Channel hovercraft |work= [[BBC News]]| date= 30 January 2016 |accessdate= 4 February 2016}}</ref> 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.<ref name="BBC_15Aug2016">{{cite news | url=https://www.bbc.co.uk/news/uk-england-hampshire-37082509 | title=Cross-Channel hovercraft Princess Anne 'to open to public' | work=BBC News | date=15 August 2016}}</ref>

In March 2018, GH-2006 ''Princess Margaret'' was scrapped at Lee-on-Solent.<ref>SRN4 Hovercraft Demolished ''[[Ships Monthly]]'' June 2018 page 7</ref><ref>Regional News ''[[Rail (magazine)|Rail]]'' issue 857 18 July 2018 page 27</ref> GH-2007 The ''Princess Anne'' remains on site leased to the Hovercraft Museum.<ref>{{cite web |url = https://www.bbc.co.uk/news/uk-england-hampshire-44236076 |title = Cross-Channel hovercraft Princess Margaret scrapped |publisher = BBC News |date = 24 May 2018}}</ref>

==Production==
[[File:BHC SR.N4 GH-2004.jpg|thumb|SR.N4 GH-2004 ''Swift'', 1974]]

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 [[Lee-on-Solent]] in March 2018
*02 – GH-2004 ''Swift'', Hoverlloyd – converted to Mk.II specification for February 1973, broken up in 2004 at the [[Hovercraft Museum]]
*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===

{|class="wikitable"
|-
|+
|-
!
!Mark 1
!Mark 2
!Mark 3
|-
!Length
|colspan=2|{{convert|39.68| m|ftin|abbr=on}}
|{{convert|56.38| m|ftin|abbr=on}}
|-
!Beam
|colspan=3|{{convert|23.77 | m|ftin|abbr=on}}
|-
!Height
|colspan=3| {{convert|11.48 | m|ftin|abbr=on}} on landing pads
|-
!Gross weight
|165 [[tonne|t]]
|200 t
|320 t
|-
!Powerplant
|colspan=2|4 x 3,400 [[Horsepower#Shaft horsepower|shp]] [[Bristol Proteus|Rolls-Royce Proteus]] [[gas turbine]]s
|4 x 3,800 [[Horsepower#Shaft horsepower|shp]] [[Bristol Proteus|Rolls-Royce Proteus]] [[gas turbine]]s

|-
!Load:
|30 cars and 250 passengers
|36 cars and 278 passengers
|up to 60 cars and 418 passengers<br/> (112 tonnes maximum)
|}

===Performance===
*Max speed: Mark 1 – {{convert|65|kn|mph km/h}} (calm water, zero wind, at gross laden weight) <br/> Mk.II – {{convert|70|kn|mph km/h}}
*Normal operating speeds: 40 – {{convert|60|kn|mph km/h}}
*Endurance: 4 hours (maximum power, 2,800 Imperial gallons of fuel)
*Gradient: 1 in 11

==See also==
*[[N500 Naviplane]]

==References==
===Citations===
{{Reflist}}

===Bibliography===
{{Refbegin}}
* {{cite book |last1=Brown |first1=David K. |last2=Moore |first2=George |title=Rebuilding the Royal Navy: Warship Design since 1945 |location=Barnsley, England |publisher=[[Seaforth Publishing]]|year=2012 |isbn=978-1-84832-150-2}}
* {{cite book |last1=Paine |first1=Robin |last2=Syms |first2=Roger |url=https://books.google.com/books?id=hXuAevQ3SS0C |title=On a Cushion of Air: The Story of Hoverlloyd and the Cross-Channel Hovercraft |publisher=Robin Paine |year=2012 |isbn=978-0-95689-780-0}}
* {{Cite tech report |title=Report of the Investigation of Heavy Weather Damage to Hovercraft GH2007 The Princess Anne.|publisher=[[Marine Accident Investigation Branch]]|url=https://assets.publishing.service.gov.uk/media/547c715140f0b6024400011b/the_princess_anne.pdf |date=2000-06-05 |ref={{sfnref|Investigation of Heavy Weather Damage}}}}
{{Refend}}

==External links==
{{Commons category|SR.N4}}
*[http://hovercraft-museum.org/mk1.html Hovercraft Museum: SR.N4 Mk.I] {{Webarchive|url=https://web.archive.org/web/20070312080927/http://hovercraft-museum.org/mk1.html |date=12 March 2007 }}
*[http://hovercraft-museum.org/mk2.html Hovercraft Museum: SR.N4 Mk.II] {{Webarchive|url=https://archive.today/20041211093224/http://hovercraft-museum.org/mk2.html |date=11 December 2004 }}
*[http://hovercraft-museum.org/mk3.html Hovercraft Museum: SR.N4 Mk.III] {{Webarchive|url=https://web.archive.org/web/20070312104420/http://hovercraft-museum.org/mk3.html |date=12 March 2007 }}
*[http://www.bravechallenger.com Brave Challenger]

{{BHC}}

{{DEFAULTSORT:SR.N4}}
[[Category:Hovercraft]]
[[Category:Saunders-Roe]]
[[Category:Ferries of the United Kingdom]]