The effect of shape of afterbody on propulsion 1

Abstract

The boom in high-powered tanker-building after the last war led to many cases of vibration troubles and cavitation-erosion damage on the propeller blades. For this reason an extensive systematical investigation into the effect of shape of afterbody on propulsion has been carried out at the NSMB. The basic ship type was a 39,000 ton deadweight tanker, the maximum size that can pass the Suez Canal in loaded condition. The variations in afterbody which were studied follow: I–Optimum shape from an efficiency point of view, based on statistical data of the NSMB (moderately U-shaped sections). II–Extremely V-shaped sections. III–Extremely U-shaped sections. IV–Cigar-shaped stern with Mariner rudder arrangement (Hogner afterbody). V–Extremely U-shaped sections combined with a screw in a nozzle. VI–Extremely U-shaped sections combined with two screws, each fitted in a nozzle, one above the other. VII–A twin-screw arrangement. Resistance and self-propulsion tests were carried out with four- and five-bladed propellers in the loaded and ballast condition. Wake measurements with pitot tubes and flow observations with tufts have been made. Cavitation tests in the tunnel with adjustable frow were carried out. Finally the variations in the propeller thrust and torque during one revolution were recorded and analyzed.