Full scale wave and whipping induced hull girder loads

One year full scale measurements available from Victoriaborg, a general cargo/container vessel with hull flare and bow flare, were analyzed to determine the effect of whipping on fatigue. The measurements utilized comprise the global strains in the midship region. From the global strains and ship’s geometric properties the hull girder bending moments were determined using a simple beam model. The wave and whipping induced hull girder bending moments and stress records were analyzed in detail.
In order to distinguish the wave frequency loads and the whipping loads, Fast Fourier Techniques were applied in order to obtain a high frequency part (whipping response), a low frequency part (wave frequency response) and the original response. Various sailing speeds up to 20 knots with a step of 4 knots were also considered. Information on the contribution of whipping to the wave induced vertical hull girder bending moment was obtained. The horizontal hull girder bending moment with respect to the vertical hull girder bending moments was also determined.
This paper addresses the full scale monitoring campaign. Furthermore it describes the calculation methods of the measured data applied to obtain the fatigue damage originating from whipping and the wave frequency loads. Assuming the low amplitude cycles contribute to fatigue, due to whipping the fatigue damage induced by the vertical hull girder bending moment increases with about 30%.