Editing SR.N4 (section)

==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]]]]

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}}

[[File:SR.N4 interior.jpg|thumb|The interior of The ''Princess Anne'' in 2019]]

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 50 knots 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}}