SIX-DEGREE-OF-FREEDOM MOTION ANALYSIS OF A FLOATING SEAWEED HARVESTER UNDER WAVE-INDUCED LOADING IN SHALLOW WATERS

This study investigates the wave-induced motions of a floating seaweed harvester designed for deployment in Nigerian coastal and creek environments, with hydrodynamic conditions representative of Forcados Creek adopted as the case study. The vessel has a fully loaded mass of 19,860 kg, an overall length of 7.43 m, a beam of 3.68 m, and a draft of 0.34 m, making it suitable for shallow-water operations typical of Niger Delta creeks. Hydrodynamic excitation forces were evaluated using linear wave theory based on the Froude–Krylov formulation, while the vessel’s dynamic response was modeled as a coupled mass–spring–damper system to capture inertia, hydrostatic restoring forces, and damping effects. The analysis was performed for a representative wave period of 7 s, corresponding to a wave frequency of 0.89 rad/s, in a water depth of 22 m, reflecting realistic operational conditions. The computed responses indicate that the vessel’s motion is predominantly governed by translational modes, particularly in the horizontal plane. Maximum response amplitudes were found to be 0.315 m in surge, 0.90 m in sway, and 0.22 m in heave, while rotational motions were comparatively small, with roll and pitch limited to 0.03 rad and 0.10 rad, respectively. These relatively low angular responses suggest adequate transverse and longitudinal stability under the considered wave climate. Overall, the results demonstrate that the floating seaweed harvester exhibits stable and controlled dynamic behavior, confirming its suitability for shallow-water seaweed harvesting operations in Nigerian coastal and creek environments, where moderate wave action and limited water depths are dominant operational constraints.