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Photograph of a marine ducted propeller

A ducted propeller is a propulsion device consisting of a conventional open propeller surrounded by a duct or nozzle. Ducted propellers find extensive applications in both marine and aeronautical fields. The duct surrounding the propeller may be used either to accelerate or to decelerate the flow in the propeller plane. In marine applications the flow accelerating duct is known as the "Kort Nozzle" and the flow decelerating device is generally referred as the "pump-jet"

The concept of surrounding the propeller by a shroud is very old. Kort Nozzle ducted propellers have been widely used in tugboats and trawelers where the propeller is small and heavily loaded. The advantage of using a ducted propeller for these vessels is that the flow is accelerated and thus an improvement in propulsive efficiency is obtained In addition the duct shares a fair proportion of the thrust and thereby reduces the propeller loading. The flow accelerating pump-jets find considerable applications for the propulsion of submarines and torpedoes since the lower velocity in the propeller plane helps to delay the cavitation induced noise. The duct itself however will produce a negative thrust.

Table 1

NSMB Expt 0.4321 0.7470 3.5090 0.065 0.8897
Ryan/Glover Theory 0.4321 0.7790 3.3700 0.0546 0.7454
Gibson/Non Iterative 0.4321 0.7790 - 0.0610 0.8350
Gibson/Iterative - 0.7560 - 0.0627 0.8550
Vortex Element Method - Iterative - V. Balabaskaran 0.4321 0.7470 3.5090 0.0633 0.8637

Comparison of measured and predicted duct thrusts


Aerodynamic Studies on Kort Nozzle Ducted Propeller Aerodynamic studies of a Kort Nozzle Ducted Propeller



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Updated on 11 Sep 2001