Lightweight detection methods are frequently utilized for unmanned system sensing; however, to tackle the challenge of low precision in detecting small targets on the water’s surface by unmanned surface vessels, we present an enhanced method for ship target detection tailored specifically to this context. Building upon the mainstream single-stage Yolov8 object detection model, our approach involves the integration of the Reparameterized Convolutional Spatial Oversampling Attention (RCSOSA) module, replacing the traditional Classic 2D Convolutional (C2f) module to bolster the network’s feature extraction capabilities. Additionally, we introduce a downsampling module, Spatial to Depth Convolution (SPDConv), to amplify the extraction of features relevant to small targets, thereby enhancing detection accuracy. Finally, the Focal Modulation module, based on focal modulation, replaces the SPPF (Spatial Pyramid Pooling with FPN) module, leading to a reduction in channel count, parameter volume, and an augmentation of the network’s feature representation. Experimental results demonstrate that the proposed model achieves a 3.6% increase in mAP@0.5 and a 2.1% improvement in mAP@0.5:0.95 compared to the original Yolov8 model, while maintaining real-time processing capabilities. The research validates the higher accuracy and stronger generalization capabilities of the proposed improved ship target detection method in various complex water surface environments.

The purpose of this paper is to conduct a seakeeping analysis of planing craft under regular wave with large wave height. To obtain a reliable numerical method to simulate the sailing of planing craft in waves, Reynolds-averaged Navier–Stokes (RANS) solver and overset method are adopted. The motion response and resistance of the planing craft USV01 in regular wave were numerical predicted and compared with the corresponding seakeeping experimental tests. The results show that the numerical method has high accuracy. For further study, a new planing craft whose name is improved vessel is selected for simulation, the low steaming of the USV01 and improved vessel in regular wave with large wave height was simulated, and the seakeeping of the two vessels was studied. The analysis about the influence of wave length on the motion response and navigation configurations of the improved vessel under regular wave was carried out. Meanwhile, the influence of speed on different navigation configurations of the improved vessel was also analyzed. The improved vessel can provide better seakeeping, and a reduction in the speed of the vessel will benefit its seakeeping, irrespective of its navigation configuration.

A comparative analysis of the hydrodynamic performance of a planing craft in the monomer-form state (MFS) and trimaran-form state (TFS) was performed, and the inhibition mechanism of twin side-hulls on porpoising instability was evaluated based on the numerical method. A series of drag tests were conducted on the monomer-form models with different longitudinal locations of the center of gravity (L_cg); the occurrence of porpoising and the influence of L_cg on porpoising by the model was discussed. Then, based on the Reynolds-averaged Navier–Stokes (RANS) solver and overset grid technology, numerical simulations of the model were performed, and using test data, the results were verified by incorporating the whisker spray equation of Savitsky. To determine how the porpoising is inhibited in the TFS, simulations for the craft in the MFS and TFS when porpoising were performed and the influence of side-hulls on sailing attitudes and hydrodynamic performance at different speeds were analyzed. Using the full factor design spatial sampling method, the influence of longitudinal and vertical side-hull placements on porpoising inhibition were deliberated, and the optimal side-hull location range is reported and verified on the scale of a real ship. The results indicate that the longitudinal side-hull location should be set in the ratio (a/L_m) range from 0.1 to 0.3, and vertically, the draft ratio (D_d/T_m) should be less than 0.442. Following these recommendations, porpoising instability can be inhibited, and lesser resistance can be achieved.

In order to improve seakeeping performance of the slender catamaran, Semi Submerged Bow (SSB) anti-pitching techniques is applied. Based on CFD method to forecast the longitudinal motion of the original catamaran (without SSB) in regular waves, and the calculation results and the ship model test results were compared, results show that the numerical method can effectively predict the longitudinal motion of the slender catamaran in regular waves. Semi Submerged Bow is added to the bottom of two demi-hull respectively, and the longitudinal motion in regular waves is predicted. The results show that the longitudinal motion amplitude of catamaran with SSB is smaller than the catamaran without SSB. The installation of SSB reasonably can effectively improve the seakeeping performance of the catamaran.