Page 120 - Electronic Navigation Cyber Book

minutes. This period may be changed by altering the charging time of the
capacitor.

Rudder
Rudder limit control sets a finite limit on the rudder angle obtained
irrespective of the angle commanded by the automatic control circuitry.
Obviously if the rudder was permitted to exceed design parameters
severe damage may be caused.
The rudder potentiometer enables the ship's steering characteristics to
be modified in accordance with the changing requirements caused by
loading and speed factors. This control determines the absolute degree
of rudder command obtained for every degree of steady-rate heading
error. For example, if this control is set to '2', the rudder will move through
2° for every degree of heading error.
The counter rudder control determines the degree of opposite helm to be
applied if it is demanded by the control circuit. The control permits daily
adjustments to be made as dictated by loading conditions.

Weather
The effect of weather and sea conditions can be effectively counteracted
by the use of this control. The circuits controlled by this switch
progressively desensitize the control amplifier, which in turn causes an
increase in the dead band width. The control also imposes an increasing
time delay on the rudder command signal in order that the ship will
recover naturally when under the influence of repetitive yaw. This means
that the steering gear is not subjected to continual port/starboard
commands. Thus the higher the setting of the weather control, the wider
will be the dead band. This increases the amplitude of yaw that can be
tolerated before the steering gear is enabled.

Non-follow-up mode (NFU)
The rudder is manually controlled by means of two position port/starboard
lever switches. These switches energize the directional valves on the
hydraulic power unit directly, thus removing the rudder feedback control.
In this mode the normal autopilot control with repeat back is by-passed
and the rudder is said to be under 'open loop' control. There is no
feedback from the rudder to close the loop. The helmsman closes the
loop by observing the rudder angle indicator and operating the NFU
control as appropriate.

Follow-up mode (FU)
In this mode the FU tiller control voltage is applied to the error amplifier
(Figure 9.9) along with the rudder feedback voltage. Rudder action is now
under the influence of a single closed loop control.
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