Nonlinearity considerations in marine vehicle autopilot design

Some basic concepts in formulation of various types of ship manoeuvring mathematical models are discussed. Comparison of the two autopilots based on PID and PDF (pseudo-derivative feedback) algorithms showed the superiority of PDF autopilots over PID. Smooth rudder activity and heading responses with smaller overshoots were observed with the PDF autopilot. The results show that with PDF autopilots better performance can be achieved using linear or nonlinear ship models and the PDF autopilot has better transient behaviour and is robust to variation in the parameters and nonlinearities of the ship dynamics