SR.N6 Class (Winchester Class) British Hovercraft

The Saunders-Roe (later British Hovercraft Corporation) SR.N6 hovercraft (also known as the Winchester class) was essentially a larger version of the earlier SR.N5 series. It incorporated several features that resulted in the type becoming one of most produced and commercially successful hovercraft designs in the world. While the SR.N2 and SR.N5s operated in commercial service as trials craft, the SR.N6 has the distinction of being the first production hovercraft to enter commercial service. In comparison to the SR.N5, the SR.N6 was stretched in length, providing more than double the seating capacity. Some models of the craft were stretched further, enabling an even greater capacity. Experience gained in the development of the SR.N6 has been attributed as heavily contributing towards the design and production of the largest civil hovercraft to be ever produced, the SR.N4. Several major design features of the SR.N6 appeared on both the SR.N4 and further hovercraft designs by Saunders-Roe and its successor, the British Hovercraft Corporation. The Saunders-Roe SR.N6 (also known as the Winchester class) is a medium-sized hovercraft primarily designed for passenger service. The initial models of the type were capable of accommodating up to 38 passengers, which was greater than the maximum capacity of 18 that could be carried by the smaller SR.N5. The SR.N6 was subsequently further stretched to accommodate a further 20 passengers; this capacity upgrade let to it being considered to be more viable for commercial operations than any previous hovercraft design. By eventually increasing the capacity to 58 seats, the SR.N6 Mk.1S became the first hovercraft to be capable of transporting a typical coach load of people. In a military configuration, the SR.N6 is capable of carrying up to 55 fully equipped troops, or alternatively up to 6 tons of equipment. The SR.N6 was powered by a single marinised model of the Bristol Gnome turboshaft engine; this drove both a single rear-facing 9 ft (2.74 m) diameter 4-bladed Dowty Rotol variable-pitch propeller along with a 7 ft (2.13 m) diameter centrifugal lift fan. The Gnome engine was an expensive component for operators, leading to some establishing their own internal overhaul facilities and making arrangements with other Gnome operators, including the Royal Navy, to reduce costs from relying on costly services from Rolls-Royce Limited.[9] Around 20 per cent of the operating costs of the type have been attributed to maintenance of the 4 ft flexible skirt, which reportedly lasted for up to 500 hours, while similar cost levels have been reported for fuel. Early on, the SR.N6 was outfitted with an improved skirt, featuring fingers and forward puff ports, which resulted in improved forward control and reduced skirt wear; fingers had not been present upon the initial version of the skirt used prior to 1966. The endurance of the fingers would be progressively improved over time, issues with salt spray negatively affecting both the engine and propeller were also encountered early on. An initial experience of some components having short overhaul lifespans or being unreliable was encountered during early days. During the early years of not only the SR.N6 but other hovercraft as well, the hovercraft skirt remained an unresolved area of difficulty during this era. The SR.N6 was piloted from a forward-seated position at the front of the main passenger cabin. The pilot would exercise control over the direction of the craft via a series of control surfaces that was located immediately behind the variable pitch propeller. Early on, pilots were normally aviators which had been recruited from the Royal Air Force and Fleet Air Arm, however it has been claimed that experienced mariners would often be more skilled at operating the type, if not taking more time to adapt to its atypical form of propulsion, in part due to their familiarity at safely navigating within uncontrolled maritime environments. For navigation purposes, some SR.N6s were outfitted with onboard radar; multiple radar arrangements were used with the type, including pilots receiving radio guidance from on-shore radar operators in some circumstances.