The design of cooling water system is one of the important items for the marine machinery design. A simple and efficient cooling water system can greatly reduce the difficulty of the lofting design and the ships' operation cost. The cooling system with box cooler can be easily arranged without the cooling sea-water system in the ship, which can effectively save the machinery space and the power of power plants. The working principle and the installation of the box cooler for a 17 500 t chemical tanker are introduced in the current study, which can provide practical references for the engineer engaged in the detailed design in the shipyard.