This report is based on the achievement of the 5 year research project 'Drift prevention of disabled ships in rough sea' which was sponsored by the Ministry of Land, Infrastructure and Transport. The project continued from the year of 1998 to 2003. After the oil leakage incident of 'Nakhodka', same kinds of incidents like 'Erika' and 'Prestige' occurred almost every 3 years. The purpose of the project is to establish the technology to prevent disabled ships due to an engine trouble, damage, breakage and capsize from drifting and to tow them to the safety area in rough sea in order to prevent the secondary disaster caused such as collision and explosion. The computer simulation system to provide the information for the drift motion prediction, towline tension, maneuvering method and needed horse power has been completed. This is called OTSS (Optimum Towing Support System) and can be a useful tool for the optimum towing operation in emergency situation.
