This paper presents a systematic approach for designing the hydraulic mechanism as a part of the gripper system employed in offshore wind turbine monopile installation. Traditionally, such equipments used in marine operation are designed based on deterministic approach, selecting actuators and power pack by applying a safety margin which is not explicitly derived from a systematic load/load effect analysis, or a reliability based method. The method in this article offers a systematic way of designing the hydraulic power system, actuators and supporting structure to overcome extreme and fatigue loadings during operation. The design starts with a global analysis and modelling of monopile and installation vessel. The forces and motions from global analysis are then employed for designing hydraulic actuators and power system. A dynamic model of hydraulic system is built to analysis dynamic response in hydraulic system. The results from this local dynamic model can be used in power management and system optimization. The proposed method is a step forward to apply reliability-based design on mechanical components in marine applications through a systematic long-term load and load effect analysis.