Hi. I'm a computer science student developing a kalman filter for autonomous sailboat, but I severely lack knowledge of the physics behind sailboats. I have a wind sensor giving data about wind speed and wind velocity, problem is the data is unreliable. So i thought that i could estimate what the next value of wind direction would be based upon boat velocity, rudder angle, previous wind direction, previous coordinates (decimal degrees), and boat's compass course. Sounds easy.. but problem is I don't know what the compass course and wind direction would be after x time. Time intervals will be at most 5-10 seconds, to save some processing power. Would this be a circular motion? What I'm after is some equation that returns a estimate of current state of "rotation/circular motion" in degrees of boat caused by rudder angle, where time would be a factor. Also, is it possible to estimate water flow based upon wind & GPS data?