ABSTRACT
During precise control of ship movements at small velocities and when dynamic positioning task is performed, disturbance has considerable impact at the control accuracy. Particular influence to the ship movements are during trials on isomorphic ship models which are used for captains training and also for control systems research in the Ship Handling Research and Training Centre at Silm Lake near Ilawa, Poland. Most of isomorphic ship models have been built in the 1:24 linear scale. According to the laws of mechanical similarity during trials on the lake time run
√ 24 ≈ 5
times faster than during operations on the real ship. The same scale 1:
√ 24 ≈ 1:5 must be used for compar-
ison of velocities in the real world and on isomorphic ship models. Therefore even small wind disturbance during tests affects ship model like quite strong wind and wave disturbance acts the real ship (Szalangiewicz 1996; Morawski 2007).
