NT888G MK2 AUTOPILOT OPERATING MANUAL
2.23 Evaluating/Altering the Autotrim (APH) Time Constant (Continued).
In most cases the factory set AUTOTRIM time constant of 600 seconds will be found
to be optimum for a wide range of displacement vessels. High Speed Craft will
normally use lower time constants (factory default 100 seconds). However,
adjustment to reduce or increase the time may sometimes be required.
To Evaluate Autotrim Time Constant: -
(i)
The Autopilot must be set to ON, the ship stable on course and the
heading noted.
(ii)
By altering the trim of the vessel (i.e. shooting a trawl, reducing engine
revs on one engine of twin prop. vessels etc.) The heading will initially
change and will remain incorrect (i.e. difference between course set and
course steered) until the requisite amount of Autotrim is applied.
Correction Period Too Long
Reduce time constant *
Correction Period Too Short
Increase time constant
* NB.
Unnecessary reduction of time constant can degrade overall steering
performance. If in doubt consult Navitron Systems Ltd.
To Alter the Autotrim Time Constant: -
The Autotrim time constant is accessed via the Setup Menu: -
(i)
Set the Autopilot to
STANDBY
and enter the Set Up Menu
(simultaneous 5 secs operation of
CANCEL & CONFIRM
keys)
(ii)
Use the Set Course knob to scroll through the Set Up parameters until
AUTOTRIM SECS
is displayed (9
th
parameter) and read the number of
seconds in the centre column.
(iii)
Rotate the illum. control (+/-) to to set the required time constant.
(iv)
Exit the Set Up Menu (simultaneous 5 sec operation of the
CANCEL &
CONFIRM
keys).
2.24 The Counter Rudder Control Setting.
Evaluating the Counter Rudder Setting.
The Autopilot Counter rudder function continuously monitors the rate of change of
heading (Rate of Turn) of the vessel and is principally responsible for the application
of ‘Counter’ or ‘Opposite’ rudder as follows: -
Counter
-
Counters or ‘checks’ any sudden departure from the steady
course steered by applying exaggerated short-term angles of
rudder measured against the rate of turn away from the
specified heading.
