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In HSVA’s medium-sized cavitation tunnel, an LDV-service (Laser Doppler Velocimeter) was used to measure the three-dimensional flow field in the slipstream of different model propellers. Three propellers were investigated with the same main dimensions except for different skew. The propellers were designed especially for this investigation. The skew angles were 0 degrees, 21 degrees and 62 degrees. Most measurements were done at a distance of 0.3 D behind the propellers at uniform inflow.

Recently, several additional devices and unconventional aftbody shapes have been applied to improve the overall efficiency of ship propulsion. These are Grothues spoilers, wake ducts, vane wheels, and asymmetric aftbody shapes. The paper describes the different physical mechanisms and specific features of the devices and configurations. Furthermore, theoretical and experimental data are presented regarding the gain in efficiency, based on calculations and model tests. Finally, experience with full-scale applications is reported.

No abstract

Over a period of 1.5 years roughness measurements ani other observations were made on more than 100 used marine propellers. The most surprising result was to find that the surfaces of the majority of these propellers had become smoother in service than they had been when originally delivered. In sea water propellers made on Mn Bronze produced clearly different, and less satisfactory, results than those made of Ni-Al Bronze. In fresh water, on the other hand, Mn Bronze propellers produced results that were virtually equally as good as those achieved by Ni-Al Bronze in sea water. Investigations of the surfaces of new and used propellers by means of a scanning electron microscope revealed that a definite change occurs in the surface structure. The scratched finish on the surface of a propeller that is produced by grinding during manufacture disappears, leaving a surface having a smooth appearance.