This paper is concerned with evaluating the effect of heavy weather avoidance on the long-term wave-induced loads on ships. Two hydrodynamic codes, VERES based on a 2D strip theory and WASIM based on a 3D Rankine panel method, are employed to calculate the wave-induced loads and motions on various vessels. Two models for heavy weather avoidance are envisaged. The first one is based on the assumption that operational criteria relevant to vertical acceleration, green water, and bottom slamming are fulfilled. The second one is based on the assumption that the sea state forecasts are available to the shipmaster and that rerouting is made. Based on the first model, the effect of the heavy weather avoidance on the long-term wave-induced hull girder loads is evaluated. In particular, the effect of hydrodynamic analysis methods and wave scatter diagram are also assessed. The calculated values are compared with those given in ship rules. The results show that several factors should be critically assessed in evaluating the accuracy of the ship rule values.