| Abstract | In the past there has been very little available information on the drag and stability of Air Cushion Vehicles at low speed overwater. Hovercraft research has been more concerned with high speed (hump speed and above) operation, and while NPL and HDL et al have produced theoretical treatments of sub-hump wave drag and attitude, these are too complex to be convenient design tools.
Since one of the main interests in overwater ACVs in Canada is in large low speed towed or winched barges or ferries, i t seemed clear that design data in this area were urgently required. Early experiments were made with the 4 m long HEX-5 vehicle on a still pond, followed by a program of model tests, using 1.2 m models (ACF-1 and ACF-2) in a flume of flowing water, and the 4 m model ACF-3, again in the pond.
The importance of the work can be seen from the fact that the tow force required to move a typical AC vehicle ferry at 10 km/hour is in the order of 60,000 newtons (7 tonnes), needing about 200 kw winches. A proper method of predicting this drag is therefore needed, to avoid costly design errors. It is also possible for a vehicle to pitch and roll to an unacceptable degree, particularly when ferrying across a river having a strong current, if an unsuitable hull and skirt configuration is selected. These problems are intensified when the vehicle is operating in "shallow" water, (i.e. where the water depth is less than half the hull length) which is often the case with operation in rivers and lakes. |
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