This paper presents a methed to estimate an actual load on ship structural members and proposes an allowable stress for fatigue strength of the members. The method for evaluation of the load was developed by fatigue analysis of the following conditions, that is, period of service years, crack length and stress concentration factor at the crack initiated position etc. Equations for the allowable stresses under various enviromental condition (in air and in sea water) were proposed, using ordinary S-N_c curve (N_c; crack initiation life) of notched specimens, S-N_p curve (N_p; crack propagation life) of cracked specimens and modified Miner rule for both of crack initiation and crack propagation, and assumed exponential distribution for wave bending stress. These equations can be applied not only to the crack initiation life but also to the crack propagation life for any limited survice period.
