ON LOAD FLUCTUATION ACTING ON A PROPELLER BLADE (ON CONDITION THAT A BLADE RISES PARTIALLY TO WATER SURFACE)

The load fluctuation acting on a propeller blade in waves was investigated experimentally using a device to measure the load acting on a blade. The load fluctuation acting on a blade where the propeller blade rises partially to the water surface was also investigated using the same apparatus. Tank tests were carried out where the open propeller boat was restrained and the propeller revolution was controlled at a constant rate in the still water to make the fundamental characteristic of the blade load fluctuation clear. The experimental results were examined with the simplified estimation model. The following results were obtained 1) where a blade rises partially to the water surface, the load acting on the blade fluctuates severely. It can be inferred that the torque acting on the blade is negative. 2) The reason for this result is considered to be that the force caused by the change of the added mass periodically through the water surface acts on the blade along the rotational direction. 3) The effects of the change of the added mass upon the blade thrust is small. SO, the thrust acting on the blade is positive even on the blade passing through the water surface.