The proposed new oil berth at Jawahar Dweep Island, Mumbai, is planned adjacent to the approach channel leading towards Pir Pau and Jawaharlal Nehru Port. The width of the channel is around 200 m and straight at the location. An existing berth J4 which is located adjacent to the new berth had in the past some incidences of breaking of mooring lines during monsoon season. The present study was done to study the effect of passing vessel effect and the environmental loading on a vessel berthed at that location. The study includes a complete simulation of mooring line forces due to wind, wave and current for the vessel ranges from 150,000 DWT to 250,000 DWT and arriving at the quick release mooring hook capacities. The passing vessel effect on the selected mooring hook capacities was reviewed by carrying out the combined effect of wind, wave and current together with the passing vessel effect. A critical review of the existing methods including OPTIMOOR simulation has been carried out to determine the suitable method for the present situation. The study indicated that the mooring hook capacities selected for the environmental loads shall be increased by 25% to cater for the combined effect of passing vessel. Several parametric studies have been carried out to include the distance between the passing vessel and the moored vessel, vessel speed, and vessel sizes, and the results are presented and discussed.