Alphatron ALPHASEAPILOT MFC - Loop Gain Calibration; Autotrim (Automatic Permanent Helm) Assessment

Operating manual ALPHASEAPILOT MFC Issue 1.1 Page 50 of 84
ALPHASEAPILOT MFC
2.22 Loop Gain Calibration
(i) Switch the Autopilot to STANDBY and enter the Set Up Menu per section 2.12 a).
(Vessel now under manual steering control).
(ii) Use the Autopilot Set Course knob to scroll through the Set Up parameters until
‘LOOP GAIN’ is displayed (4
th
parameter) and read the number of degrees (1.5
o
, 1.8
o
etc.) displayed in the centre column.
(iii) Rotate the illum. control (+/-) to increase or decrease the value shown (as required).
(iv) Exit the Set Up Menu (simultaneous 5 sec. operation of CANCEL and CONFIRM keys).
2.23 Autotrim (Automatic Permanent Helm) Assessment
Functional Description.
The Autopilot system is equipped with an Integrator, which enables the electronic control stages
to monitor the instantaneous position of the rudder in the STANDBY mode and to control the
mean position of the rudder in the ON mode.
In the STANDBY mode, the Autotrim (APH) integrator memorises and adopts any angle of
rudder offset (up to 20°) which exists at the instant that the Autopilot is switched from
STANDBY to ON.
This function is always operational when the Autopilot is switched from STANDBY to
ON and permits the Autopilot to copy the angle of offset rudder manually applied to
steer the vessel dead ahead on the desired heading (i.e. Trim compensated) at the
instant of Autopilot engagement.
In the ON mode, the Autotrim (APH) function continuously monitors any long term differences
between the Autopilot Heading Set and the mean course actually steered. Any apparent long-
term difference is compensated for by automatic trim reassessment over a period of time to
ensure the correct mean direction of the vessel through the water.
NB. The Autotrim function can be disabled if required by 5 second AUTOTRIM key operation
confirmed by illumination of the red corner keypad (OFF) LED.
The Autotrim timing period is factory set at 300 seconds for displacement vessels (5 minutes)
and 50 seconds for High Speed Craft for a maximum of 20° of rudder, but is re-programmable
via the Set Up Menu and is identified as Autotrim Secs (7
th
parameter).
APH timing periods of less than 200 seconds (3.3 minutes) are likely to degrade
Autopilot steering performance on vessels other than high-speed craft with
planing/semi planing hull forms. Timing periods greater than 300 seconds may
benefit larger ocean going displacement vessels subject to seagoing appraisal.
Autotrim Operating Modes.
(i) Autopilot switched from
STANDBY to ON - Autotrim function operational.
(ii) Autotrim key to OFF - Immediately cancels any
(5 second press) permanent helm rudder
offset angle and disables
the Autotrim function.