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Aviation History
1964
1964 - 0821.PDF
SR.N4 general arrangement HOVERCRAFT CHANNEL LINK . . . the technical progress made in engineering of long flexible skirts. the Size of Hovercraft to Meet Channel Sea States Analysis of the sea states which occur in the English Channel show that: (i) On 90 per cent of occasions wave heights are equal, or less than 4-5ft with associated wind speeds of 15-20kt. (ii) On 5 per cent of occasions wave heights reach 6-8ft with associated windspeeds of 25-30kt. (iii) On one or two days per year wave heights reach 13ft with 40-45kt winds. To run a scheduled hovercraft service in these sea states it must be capable of operating at: (a) 70kt in 4~5ft seas, (b) 45-50kt in 6-8ft seas, (c) 15-2Okt in 13ft seas. It has been established that the minimum size of craft to meet the above requirements has a length of approxi- mately 140ft—about double that of the SR.N2. With a payload primarily made up of passengers and cars the all-up weight is approximately 150-165 tons, and the power requirement in the order of 10,000-15,000 h.p. This is the basis upon which the proposed SR.N4 is being designed. Details of the SR.N4 The principal features of SR.N4 are given below, and Air-Cushion Vehicles its external features are illustrated in Figl. Weights, Gross, 150-165 tons, disposable load, 60-75 tons, normal fuel load, 10 tons (2,800gal). Dimen- sions, Length, 128ft, beam, 83ft, height, 41ft 3in. Powerplants, Main engines, four Bristol Siddeley Marine Proteus rated at 3,400 max cont s.h.p. each. Auxiliary power units, two Rover 2S/I50 gas turbines. Performance, endurance, 2.6hr, typical cruise range, 190 n.m., overwave capability, 77kt in calm seas, 65-70kt in 4-5ft seas, 4S-50kt in 6-8ft seas, l5-20kt in 13ft seas. Internal Arrangement The SR.N4 is being designed specifically as a passen- ger/car ferry. This is particularly evident from the disposition of the machinery at the sides of the craft which allows a drive-on/drive-off layout for the main vehicle deck. Built-in power- operated loading and unloading ramps in association with this arrangement ensure a rapid turn-round. In order to cater for heavier traffic, in particular touring coaches and light commercial vehicles, the headroom along the centre of the main deck has been made lift 3in and about half the vehicle deck has been strengthened to take heavier wheel loadings associated with such vehicles. To cater for heavier vehicles, a modification can be made to the craft superstructure which would enable it to take three 16-ton lorries which would have to be loaded and un- loaded through the aft ramp only. The modifications would involve raising the central roof aft of the control cabin to give a headroom of 14ft and reinforcing the floor to carry vehicles up to a maxi- mum laden weight of 26 tons. The following table gives details of the alternative payloads that can be carried and makes clear the flexibility of the design. It should be noted that freight (particularly on pallets or in containers) can be carried in lieu of passengers or vehicles. Internal arrangements of sever- al versions are illustrated in Figs 2, 3, 4 and 5. Case Basic craft 1 2 3 4 5 6 7 Modified craft 8 9 Type of payload All-passenger (seated) All-passenger (com- muter—476 seated,184 standing) Passenger/car (stan- dard) Passenger/car (maxi- mum car capacity) Passenger/car (inter- mediate ratio)Passengw/car/coach Freight Heavy vehicles + pas- sengers (say 3x16 tons laden weight)Heavy vehicles -f cars + passengers (say 3x16 tons laden) No of items* 566 pass. 660 pass. 228 pass.. 27-32 cars 116 pass., 33-40 cars 170 pass., 31 cars228 pass.. 15-18 cars.3 coaches — 228 pass., 3 lorries 50 pass., 2 lorries, 12 cars Pay- load (tons) 50.5 58.9 51.3 52.3 51.8 59.1 60-65 60.5 59.8 * Notes: (A) Passengers are assumed to have baggage which gives an average weight/passenger of 2001b. (B) The number of passengers quoted includes those in the cars and coaches who are assumed to occupy seats for the crossings. (C) Where two numbers are given for the cars carried, the first refers to a load of medium/large European cars as found on the cross-Channel routes, average size 14ft 6in x FLIGHT International supplement, 26 March (964 5ft 6in. The second applied to the "average" European car, size 13ft x 5in. The first (smaller) number gives the highest weight and this is quoted in the last column. Where only one number is given, this refers to the larger size only. Versatility of SR.N4 One of the most important features of the hovercraft fitted with flexible skirts is its ability to make transitions from sea to land and so enable it to operate, independently of tides, from bases which can be located outside normal congested ports at almost any point along coastlines or rivers above the high water mark. The variety of internal layouts des- cribed in the previous section allows the ratio of cars to passengers carried to be varied to suit the particular needs pre- vailing at given times of the year. The high cruising speed and overwave performance will enable average journey speeds of at least 1 n. mile per minute to be achieved for 90 per cent of the year. This means that the classic Dover- Calais Channel route will take as little as 22min transit time. On a longer route such as Southampton-Cherbourg the journey will take only an hour and a quarter. All these factors emphasize the potential of the SR.N4 to operate rapid services from a variety of coastal ports on the South Coast of England, thereby providing links to the Continent from ports more convenient to the traffic emanating from Northern and Western England. Proposals for such services as Harwich - Calais, Southampton - Cher- bourg, Newhaven-Dieppe, as well as the Dover-Calais route, are given in Part 2 of this report. Terminal bases Consideration has been given to the layout requirements of both hovercraft terminals (hoverports) and maintenance bases, which could be situated conveniently outside normal congested ports. Hoverport Fig 6 shows our concept of a sophisticated hoverport capable of handling up to 20 arrivals and 20 de- partures an hour, i.e., a craft leaves the terminal every three minutes. Such a schedule would cater for half the peak hourly traffic predicted by the Ministry of Transport White Paper for 1985 onwards. An artist's impression of the same layout is also given. In all, it covers approximately 30 acres and the total cost is estimated to be in the region of £2m. From Fig 8 it will be seen that it is as large as the present station and boat terminals in Dover Harbour, but it includes the extensive car parking and fuel storage tank areas A railway station could be added to the layout, preferably linked by subways to the main hall, but this has not been illustrated since the hoverport was laid 40a
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