Topic summary
Kort nozzle
Extracted from the Wikipedia article Ducted propeller.
Advantages and disadvantages
Kort nozzles or ducted propellers can be significantly more efficient than unducted propellers at low speeds, producing greater thrust in a smaller package. Tugboats and fishing trawlers are the most common application for Kort nozzles as highly loaded propellers on slow-moving vessels benefit the most. Nozzles have the additional benefits of reducing paddlewheel-effect (e.g. the tendency of a right-hand propeller to back to the left) and reduce bottom suction while operating in shallow water.