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Abstract: The paper describes the interaction between the IMO instrument Energy Efficieny Design In-dex (EEDI) and the ability of a ship to be able to maneuver safely in adverse weather conditions. A method based on first principles is developed which can compute the equilibrium in yaw and sway if the ship is ex-posed to wind and waves. From the external and the steering forces, the power requirement to keep the speed can be computed. The results obtained with this method can be used to quantify the steering capability of a ship in heavy weather. The method was applied to some twin screw designs taking into account the future al-teration of propulsive power due to the EEDI. It was found that the EEDI had little effect on future steering abilities of the investigated ships, and as a result it can be concluded that properly designed twin screw ships will still have sufficient maneuverability in the future. This suggests that possible future regulatory attempts for safe maneuvering in adverse weather conditions should not focus on twin screw ships. It was also found that when then course keeping problem is to be investigated, the focus should be on following seas.