Selnekav,

You will need to take the difference in distance (156.6-154.8) mm = 1.8 mm and convert the 14" prop to mm or 14x25.4 = 355.6 mm. I think there is something wrong in your measurements from the rudder since 156.6 mm is just 6.16". Assuming that your measurements are correct, the formula to calculate the angle is arcsin of 1.8/355.6 or 0.25 degrees. It apperas that you need to increase the right thrust. Check your measurements again and let us know.

Vicente "Vince" Bortone