Oil and gas operators have taken considerable amount of measures to prevent offshore service vessel collision with risers, especially in the wake of the Mumbai High North disaster. One of the measures taken is the installation of steel riser-guards on fixed offshore jacket platforms. The conventional riser-guard however, has been associated with several design related issues, which provide room for further design optimisation, or even a potential replacement with other alternatives. Quantification and selection of appropriate design load for riser-guard system is highly desirable for design improvement and optimization. This study attempts to investigate and establish the impulse loads equivalent to the broadside collision of a 2500 tonne displacement vessel with the conventional riser-guard. Parametric study was performed to investigate the effects of varying width to the resulting impulse load equivalent to vessel collision forces. General purpose finite element modelling software was used to perform dynamic analysis and establish the equivalent impact loads.