Computational fluid dynamics predictions of draught and trim variations on ship resistance in confined waters

Adjusting a vessel's trim and draught to enhance resistance characteristics is a promising strategy to improve the energy efficiency of maritime transport. However, the vast majority of scientific effort has been directed at such gains in deep, unrestricted waters. Shallow and confined waters modify the flow and pressure distribution around a ship, altering considerably the resistance curve. This study aims to elucidate trim and draught increase effects on a ship's resistance while advancing through a restricted waterway using Computational Fluid Dynamics. The results show that increasing the draught of a benchmark hull magnifies the hydrodynamic resistance by approximately 10% to 15% depending on the ship speed. This added hydrodynamic resistance may be compensated by adjusting the vessels’ trim, but the ability to compensate the added hydrodynamic resistance is sensitive to ship's speed. At low speeds, the numerical model predicts the increase in resistance due to a 10% higher draught can be reduced by varying the trim angle leaving the total resistance 0.87% higher than at the design draught and zero trim angle condition. On the other hand, higher speeds offer a greater potential for resistance reduction through trim.