NT888G MK2 AUTOPILOT OPERATING MANUAL
2.18 Autopilot Engagement (ON)…(Continued)
(The AUTOTRIM function defaults to ON whenever the Autopilot is switched from
STANDBY to ON – unless reprogrammed in Set Up. As a result, provided the rudder
is positioned to steer the vessel dead ahead immediately prior to Autopilot
engagement, any rudder offset angle (Trim or Permanent Helm) manually determined
for this purpose will be sampled and held by the Autopilot and the vessel will continue
to steer dead ahead).
2.19 Initial Course Keeping Performance.
Provided the Autopilot YAW value is set to No.1 (minimum Yaw) in the CONTROLS
Menu, corrective rudder will be demanded and applied by the Autopilot system for
any short term yaw angle in excess of 0.7 degree.*
* (The ultimate addition of Counter rudder and Autotrim significantly increases
heading resolution in practice – i.e. increases sensitivity to Yaw).
PORT Yaw will result in STBD rudder application confirmed by illumination of the
GREEN chevron situated immediately above the Set Course knob. Conversely
Starboard Yaw will initiate PORT rudder and the RED chevron.
The actual angle of corrective rudder applied to correct Yaw will be directly
proportional to the Yaw angle and to the Controls Menu setting of the RUDDER
value.
Too much applied rudder will promote OVERSTEER (Overcorrection).
Insufficient applied rudder will promote UNDERSTEER (Undercorrection).
Understeer Characteristics
Large deviations or protracted
periods off the Heading Set due to
insufficient rudder application in
response to Yaw: -
Typical stretched
‘S’ characteristic
of Understeer
Action required: -
Increase Rudder
Control Setting.
(Clockwise)
Oversteer Characteristics
Autopilot applying too much rudder
causing vessel ‘weave’ which may
increase to a tight ‘S’ pattern: -
Typical tight ‘S’
characteristic of
Oversteer
Action required: -
Reduce Rudder
Control Setting.
(Anticlockwise)