Power boats and work boats operating primarily in coastal areas have traditionally been constructed using fiber-reinforced plastic (FRP). However, since the 2000s, stricter environmental and maritime safety regulations have limited the use of FRP due to its non-recyclability and prolonged degradation period exceeding 100 years. In contrast, high-density polyethylene (HDPE) offers a sustainable alternative because it is lighter, more buoyant, highly impact-resistant, and fully recyclable with no harmful emissions during disposal. Given these advantages, HDPE is gaining recognition as an eco-friendly material for small vessels, particularly in domestic coastal waters. This study evaluates the structural strength and safety of HDPE hulls according to high-speed light-duty shipbuilding standards. A detailed finite element model was developed to assess both yield strength and buckling strength under external forces. Structural analysis, including a 150% increase in bottom plate thickness, provided insights into hull integrity. The buckling strength of each panel was analyzed for various load combinations. The findings and methodologies presented here offer valuable guidelines for future structural safety assessments of small to medium-sized HDPE vessels.