Impact of aft deformation with wedge and step on performance and stability of high-speed hard chine monohulls via experimental and numerical assessments

This study examines the stability and performance of three types of boat models: stepless, wedge-mounted, and two-stepped, across different movement conditions—displacement, semi-planing, and planing (or skiing). Parameters like trim (the angle of the boat), rise-up (how the boat lifts out of the water), and resistance (drag) were experimentally measured. Spray patterns were examined at various speeds. Notably, this study focuses on chined models (a chine in boat design is a sharp change in angle in the cross section of a hull), which have not been compared before. The tests were conducted at speeds of 2, 4, 6, and 8 m/s. The results showed that the models were stable in displacement and semi-displacement conditions. However, the bare hull (without any steps) was unstable in planing conditions. In contrast, vessels with two transverse steps were stable and had less drag across all conditions. Additionally, both trim and rise-up were lower in the stepped and wedged models compared to the bare hull. At higher speeds, the two-step model had less drag than the other models. For further analysis, different wedge-mounted and two-stepped vessels were selected for numerical studies using simulation of turbulent flow in arbitrary regions—computational continuum mechanics (C++ based) software. The findings indicated that optimizing the position of the first step can reduce resistance at speeds above 8 m/s; moving it farther from the stern decreases the drag. However, increasing the distance of the second step from the stern can actually increase the drag.