Do Propellers Sing?
Yes, sometimes they sing: Some propellers in service produce a high-pitched noise, often referred to as Singing. This sound typically is a clear harmonic tone much like a humming or ringing wine glass.
More of an annoyance than anything harmful, the causes of singing are not completely understood. Many theories have been put forward to account for the phenomenon of Singing, but it appears to be affected by critical factors for which the theories make no allowance. For instance, in some cases when a twin-screw vessel has one propeller that sings, the noise is eliminated just by switching position of propellers. Or had been replaced by an identical spare Propellers which were found silent. Also the less number of blades the less cases of "singing".
Mitigation of Singing: Antisinging Edge
The singing is in function of propeller diameter and Rpm's, Boat speed and Trailing-edge size (thickness) and roundness. In most of the cases not much can be done on Diameter, Rpm's or speed, but we can modify the Edge Geometry. This has been the Strategy for all efforts to eliminate singing
Most Propeller professionals (and others) are familiar with the Antisinging Edge – a Chamfering of the Trailing edge, typically on the Suction side. The intent of this shape is to avoid the creation of curving flow eddies by cleanly separating the flow off of the blade.
The following graphic shows the Chamfering that goes from a 0.5 or 0.4 Radius to the tip of Suction Side.
However the adoption of unduly thin edges can result in erosion or fracture of the blade near the edges, it is advised that Antising Edge may be considered as a last resort to minimize the Singing of an existing Propeller.
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