Since the early 70's ship maneuvering simulators using fully equipped bridge structures are being used to study the real-time behavior of ships in open water and in ports and to train ships crews to carry out maneuvers safely and efficiently. The number of simulators in use bears testimony to the need for insight in ship behavior and the successes reached in training crews to sail ever larger ships in existing and new ports. Besides training of crew members, simulators are used to judge maneuvering characteristics of new, as yet unbuilt ships, efficiency and safety of new harbours and the effects of new propulsion systems and maneuvering aids. The basic process of a real-time maneuvering simulator is the mathematical model which represents the behaviour of a vessel sailing at variable speeds in deep or shallow water, in current, at high and at low speed without or with the effects of port structures, bottom irregularities and of other ships included. At the present, probably all simulators make use of mathematical models based on Newton's equations of motion for a body moving in the horizontal plane or , in some cases, in all 6 degrees of freedom. Hydrodynamic forces due to flow around the hull, rudder action and variations in propeller speeds are incorporated based on empirical data derived from model tests or from analysis of full scale data. An increasingly important effect on vessel moving in ports is due to ship-ship interactions or ship-port structure interactions, the last being, for instance, bank suction effects where banks can also be submerged structures or local water depth changes. It is common practice to include such effects based on tabulated interaction data derived from model tests or off-line computations using more or less complicated hydrodynamic models ranging from strip-theory-based interaction models to double-body potential flow using panel models or even full-blown CFD computations.