The primary roof body of a subsea manifold dropped object protection structure consists of protective plates, welded at each edge, arranged in a suitable pattern to protect various components within a manifold from any external damage. The protective plates should be able to absorb impact caused by accidental dropped loads. The aim of the project is to determine the optimum thickness of the roof plate, maximum deflection and energy absorption of the roof plate using theoretical equations which was developed. The theoretical results were compared with simulated finite element analysis (FEA) results for the maximum deflection and energy absorption of the roof plate under designed impact load. The effects of parametric variation in plate thickness and impact loadings on the roof plate were investigated. The study was concluded with theoretical formulas for energy absorption and maximum deflection of the plate upon impact loadings. It was observed that the optimum thickness of the roof plate under designed impact loadings is 12.7mm. Protective plate with 12.7mm thickness is recommended for the primary protective roof structure. Bachelor of Engineering (Mechanical Engineering)