Calculating safe design stresses for propeller s using available fatigue data is discussed in detail. It is noted that no procedure can be rigorously justified because of the considerable number of factors influencing propeller strength and the inherent variability of large castings and corrosion fatigue tests. However, a method is proposed which avoids relying on precise knowledge of the properties of materials. Service experience is used to arrive at correlation coefficients which are needed to calculate allowable stresses over a range of operating conditions. The trends shown are believed to be reasonable. It is observed that the fatigue strengths of the propeller bronzes must be several times the nominal design stresses. In addition, it is suggested that the most reasonable projections occur when it is assumed that fatigue strength drops toward zero as the mean stress approaches the yield strength.

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