Structural desin of a bulbous bow with regard to collision safety

Dimensioning of bulbous bows is based on conservative and usually empirically developed Classification Rules. Furthermore their structural design is subordinate to manufacturing aspects. Thus bulbous bow structures are mostly overdimensioned and could be regarded as rigid in case of a ship collision. Weakening bulbous bows stiffness results in noticeable influence on absorbable collision energies. Anyhow this approach is limited because usual operating loads like hydrostatic pressure or slamming loads are still to be considered. The paper describes a design approach for bulbous bows that aims at the best compromise between preferably weak regarding collision load on the one hand and preferably stiff under operating load on the other hand. Linear and nonlinear FEM-calculations based on ultimate load theory are combined in order to estimate stability of weakened designs. Examinations are accompanied by nonlinear explicit FEM-calculation of a ship collision scenario taking into account stiffness of striking and struck ship