Abstract
For the application behind ships two different types of ducted propellers are considered; the ducted propeller where the nozzle accelerates the flow at the propeller and the ducted propeller where the nozzle decelerates the flow at the propeller. The first type of ducted propeller is now extensively used in cases where the ship screw is heavily loaded or where the screw is restricted in diameter. The accelerating nozzle offers a means to increase the efficiency of heavily loaded propellers. The second type of ducted propeller is used to increase the static pressure at the impeller. This nozzle may be used if retardation of propeller cavitation is desired. This paper deals with the first type of nozzle. The open-water test results of ducted propeller systems suitable for application on pushboats and tugs are given. In addition the results with a nozzle specially suited for astern operation are supplied. The effect of the appendages (rudders, struts etc.) on the characteristics of ducted propeller configurations suitable for pushboats and single-screw tugs has been studied. The optimum value of the flanking rudder angle has been determined. Finally, the results of open-water tests with ringpropellers, ringpropellers in nozzles and a multiple nozzle-ringpropeller system are discussed.
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