In most cases parametric hull optimisation is preformed considering flat water conditions. In some cases, added resistance in waves can have significant influence on operational costs of the vessel, while at the same time the optimum hull shape in waves might not be equal to that in calm water. In these cases, it is prudent to consider wave resistance within the parametric optimisation study. In this test case, a parametric bow optimisation in waves is conducted for a container feeder vessel. The bulbous bow geometry is varied, as well as the stem profile. Different bow designs are evaluated using CFD in calm water and in regular waves. Resistance in calm water and in waves is combined into a signle weighted resistance, where the corresponding weights represent relative frequency of different sailing conditions. The regular wave characteristics are determined by considering the most frequent sea state that the vessel encounters. Three parameters are used to describe the modifications of the bow:

1. Stem profile factor: This parameter controls the profile of the bow stem, ranging from a conventional slanted stem to a vertical stem.

2. Width of the bulb,

3. Height of the bulb.

Table below shows the variation of the hull geometry with different parameters.

The optimisation yielded a hull form shape that reduced resistance in waves by 6.6 %. Weighted resistance is reduced by 2%, where calm water resistance increased by 0.6%. Hence, the hull form was modified in a way that does not affect calm water resistance to a significant extent, while reducing resistance in waves.

Follow the link below to download the complete semi-displacement ship optimisation study for more information.