<p>Large floating rafts with variable cross-sections and perforated sandwich layers are extensively used for mechanical noise control, yet simplified modeling methods that preserve the intrinsic mechanical properties of the sandwich structure for marine applications have received limited attention. This study proposes a novel semi-analytical method that establishes a simplified computational model (3D-MHM) for large floating rafts using a multilevel homogenization model, enabling efficient and highly accurate static and vibrational predictions of static and vibrational characteristics. This approach addresses the computational challenges of traditional numerical methods while accurately capturing key structural responses including structural displacement, strain, and natural frequency. A comparative analysis with 3D-FEM and 2D-traditional equivalent model (2D-FSDT) shows that 3D-MHM is superior to 2D-FSDT in terms of accuracy and superior to 3D-FEM in terms of computational efficiency. The perforation geometry of the wall is described parametrically using Bézier curves, enabling more efficient analysis of the effects of perforation geometry and quantity on vibration performance and mechanical properties. Further comprehensive bending and natural frequency analyses were performed on variable-section floating rafts featuring typical openings. The results show that when the sandwich parameters are consistent, the proposed method remains well adapted to floating rafts with variable cross-sections and typical openings. The 3D-MHM achieves high accuracy (errors &lt; 5%) for cores with high equivalent modulus, but for low-stiffness cores the error can become significant (up to ~ 35%); thus applicability should be judged based on core properties. These findings provide design guidance for deformation mitigation and vibration attenuation in marine engineering applications of floating raft systems.</p>