In the design of a screw propeller, the thickness of blade is determined to have sufficient strength in accordance with stress calculation. Nevertheless, blade fracture rarely happens from various causes, and some are considered from fatigue failure. The investigation on fracture-section of these propellers reveals that the fatigue starts at a different point from the point of maximum stress calculated by conventional method. Therefore, the author has calculated, for a typical propeller, the radial distribution of stress of blade section and the distribution over a section of a given radius more reasonably than conventional method. The result is that the point of maximum stress calculated by the author's method is nearer to the starting point of fatigue, not coinciding with the point of maximum stress calculated by conventional method.
