Following a short review of the ship classification principle, of the cyclic fatigue in ship structures, the deterministic format based on S-N curves is reviewed. First, the probabilistic format for fatigue verification using S-N curves is presented with emphasis on the uncertainties and limits of use versus ship structures design. Then the semi-probabilistic format, as used in the new Bureau Veritas BV2000 rules for steel ships is presented. Particular attention is given to the selected partial safety factors versus the other failure modes. The calculation of those partial safety factors is also analysed, based on practical cases. As a conclusion, the interest of the probabilistic approach versus the deterministic one is outlined. Then the limits of practical applications, semi-probabilistic for design and drawing approval, probabilistic for rule developers and RBI are discussed. To end, the research and development needs for future are pointed out.