To improve the slewing performance of kelp harvesting ships in the operation between aquaculture rafts and improve the mechanization level of the kelp aquaculture industry in China, the maneuverability simulation calculation of new kelp harvesting ship was studied. Using computational fluid dynamics technology and overlapping grid technology, the constrained model test simulation calculation of the kelp-harvesting ship's direct navigation motion, pure sway motion, and pure yaw motion is carried out, and the corresponding hydrodynamic derivatives are obtained. After the obtained hydrodynamic derivatives are dimensionless, a Matlab simulation platform is built based on the Abkowitz manipulation motion equation, and the motion prediction of the turning radius and turning cycle of the two types of kelp harvesting ship is carried out. The calculation results show that the turning capacity of the streamlined hull is the best. After installing the anti-net grid, the turning capacity of the ship decreases significantly and the installation of the side, pushing device can improve the turning performance of the ship. Comparing the simulation results with the real ship test results, the error of the simulation calculation is less than 15%, which proves the feasibility and validity of the simulation calculation, and it can be used as a reference for maneuverability motion prediction in the design of follow-up fishing vessels.