In today's marine industry, high-density polyethylene (HDPE) material has gained popularity due to its recyclability that relieves the concerns for sustainability of the products and its lightweight, resistance to environmental effects, such as moisture, corrosion, organisms, UV, etc. its sufficient mechanical properties. HDPE material may be combined with other light materials for structural optimisation. In this work, the performances of three joints - one T-joint and two L-joints - designed by the authors and representing the assembly of HDPE hull and Glass Reinforced Polyester (GRP) composite sandwich superstructure were studied experimentally and numerically. Adhesively bonded, bolted and welded joints were subjected to tensile load. Due to the maximum strain and the failure loads, Type A shows promising performance followed by Type C and B. Type C is more cost-effective while providing a moderate strength followed by Type B and A. Results also affirm the utility of the 2D-FE models for the strain distribution in such joints.