68 ST600R Autopilot Control UnitChecking the Rudder GainThe factory setting for rudder gain will provide stable control forinitial sea trials. However, vessels can vary widely in their responseto the helm, and further adjustment to the rudder gain may improvethe autopilot’s steering characteristics.It is important to ensure that rudder gain is set correctly on high-speed craft. Incorrect adjustment will lead to poor steeringperformance and is dangerous at high speeds.The following test will determine whether the rudder gain is set toohigh or too low.1. In clear water and with the autopilot in Auto, alter course tostarboard by 40° by pressing the + 10 key four times.• At cruising speeds, course changes of 40° should result in crisp turnsfollowed by an overshoot of no more than 5°. If this occurs therudder gain is adjusted correctly.• An excessively high rudder setting results in oversteer. This isrecognised by a distinct overshoot of more than 5° (A). Thiscondition can be corrected by reducing the rudder gain setting.• Similarly, an insufficient rudder control setting will result inundersteer which gives sluggish steering performance (B). If thevessel takes a long time to make the turn and there is no overshootthen the rudder setting is too low.
