Driven by the maritime industry's need to reduce fuel consumption and emissions, developing lightweight yet strong structural materials is essential. This study investigates resin–talc sandwich core composites for shipbuilding materials. Composites of unsaturated polyester resin (UPR) and talc were fabricated via casting, with resin-to-talc ratios of 50:50 to 90:10 and catalyst concentrations from 0.1% to 1.3%. Mechanical properties were evaluated per Lloyd's Register standards. The 50:50 ratio with 0.1% catalyst achieved the highest tensile strength (22.11 MPa), while the 80:20 ratio offered optimal overall performance. Lower catalyst levels with 20% talc improved strength, ductility, and reduced voids.