A Note on the Singing of Propeller

Abstract

This report outlines the result of our investigation on the typical singing of propeller, conducted on a ship recently built in our yard. This investigation confirmed Dr. Kito's theory that the singing phenomenon of propeller is the coincidence of frequency of the exciting force to the natural frequency of the propeller blade, which is periodically excited by the Karman Vortices induced from the trailing edge. Singing phenomena measured on our ship were as follows. 1. Singing appeared at about 100 r/m and disappeared at 210 r/m, and no singing above this revolution. 2. Peak frequency of the singing was 655 c/sec, which was independent to propeller revolution. 3. 655 c/sec was found to be one of the natural frequencies of the propeller blade in water. 4. By, so-called, Karman Vortex theory, it was calculated that the effective edge thickness of 2.3 mmφ constantly causes 655 c/sec at the revolutions between about 100 r/m and 210 r/m. 5. It was found during the docking that the edge was about 2 mmφ. 6. The initially designed edge was 1.0 mmφ. At the sea trial conducted after the correction of the edge to 1.0 mmφ, sinig was completely diminished. 7. As the general conclusion, the edges of small diameter propellers must be more accurately finished.