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Aviation History
1964
1964 - 1632.PDF
w FLIGHT International supplement, 28 May 1964 will be the manufacturing cost of the craft. A high-speed passenger-carrying hovercraft will have installed power of about 100 s.h.p./ton and, to minimize size, a cushion pressure as high as "hump" drag considerations allow, say 60-851b/sq ft for craft 160ft long. Drawing upon the various aspects reviewed it is possible to set up a picture of the hovercraft ferry. An efficient hovercraft is the smallest craft, and hence the cheapest product, which will carry the load and perform as desired. Since headwinds and waves have a marked effect on hovercraft speed and range it is essential to take the perfor- mance in the average sea condition. If water is shallow over significant parts of the route, engine power may have to be increased and there could be a minimum size or maximum cushion pressure to permit the craft to accelerate satisfactorily. Fig. 10 illustrates the trend of costs with increasing cushion pressure for a single deck craft of 150 tons displace- ment weight. Data refer to a passenger ferry carrying about 500 passengers and their luggage and capable of maintaining 65kt in 5ft waves. If it is to carry a large proportion of cars, 28 cars and 140 passengers for instance, the craft must be larger to accommodate the motor cars, and thus the cushion pressure is lower. For minimum operating cost this is not necessarily a disadvantage. Air-Cushion Vehicles Hovercraft first costs are high compared with ferry boats and series production aircraft in terms of work capacity, payload and cruising speed. This state of affairs may be expected to change with technical develop- ment and the establishment of a design from which a number of substantially similar craft may be built; however, at the moment the first cost makes a considerable contribution to hourly operating costs by way of interest on capital, deprecia- tion, and insurance. The method of costing is similar to that used for aircraft since no suitable form- ulae are available for ship costing. Using this procedure, direct operating costs of two to three shillings per ton mile are obtain- ed for short journeys, e.g., ferry stage length of 50 miles, which limits utilization to about 1,500 hours. Operating costs are marked up by a factor of 2.5 to give a real- istic fare after paying for the establishment to operate, publi- cize, and profit from the ferry operation, and allowing for a load factor. These levels lie between those charged by ship and air ferries, Fig 11. Fares are shown per unitweight based on five passengers and one 05- 1 0-4- 0-2- WAVES 5 FEET —1— 3 e 4 0 —I— 5 0 —I— 60 —1 70 DISPLACEMENT WEIGHT CUSHION AREA Fig. 9 Structure weight CONSTANT PAYLOAD TOTAL FIRST COST (LB/FT2) EQUIPPED STRUCTURE DISPLACEMENT WEIGHT CUSHION AREA CUSHION PRESSURE 50- AIR FARES PASSENGER5 ONLY Fig. 11, left economics Hovercraft - \ n i > o o: Z XV) SHIP FERRY FARES PASSENGERS & CARS [I ENGLISH CHANNEL) Fig. 12, below A practical layout for a ferry ACV. o £ For control, the driver adjusts the propeller blade pitch for differential thrust, and over hard ground re- tractable wheels are lowered to prevent side drift. Such a craft can be built using data available now but it is hardly big enough for all- year-round cross-Channel operation Fig. 10 Economic size car. In terms of a fare stage of 25 miles the fares are £5 10s Od per car and £1 18s Od per passenger. These fares can be maintained if 60 per cent of the overall capacity throughout the year is main- tained, and with seasonal traffic varia- tions this may be difficult. An illustration of a practical layout follows in Fig. 12. Fig 11 shows a larger craft can be available in the next year or two. This will have substantially better economics; sea and air ferries have a formidable contestant imminent. 71
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