The risks associated with the navigation of large tankers in restricted waterways have resulted in continuing development of routing measures such as Traffic Separation Schemes (TSS). This is generally subject to discussion between the administration and ship operators which may find some navigational rules and regulations unnecessarily restrictive. Motivated by the need for an objective and scientific method to determine the vessel characteristics and environmental conditions for a safe passage through a restricted waterway, this paper presents an optimized routing procedure based on maneuvering simulations and non-linear direct search techniques which can be used to determine the best attainable route for large tankers in restricted waterways and specified environmental conditions. The mathematical model for predicting the maneuvering performance is based on a modular approach in which the hydrodynamic, propeller and rudder forces are computed separately, while environmental forces are estimated by semi-empirical methods. The objective of the optimization procedure is to determine the required number and magnitude of rudder control commands for remaining within a specified TSS and minimizing a grounding or collision possibility.