Figure 1.1 Basic components of a conventional marine
autopilot.
The four basic components are a compass, an electronic
control box, a rudder angle sensor (transducer) and the
steering drive.
A Junction Box, mounted below decks, contains most of the
system electronics and a Control Head, mounted at the
steering station provides the interface with the user.
Modern autopilots perform other functions as well and this
introduction explains how these fit in with the basic function
and how they provide a wider range of options for the user.
When the autopilot is first turned on, it rests in an idle
(STANDBY) state in which it displays the heading, but does
not steer the vessel. It is activated by switching it into the
PILOT state. At the moment this is done, the current heading
is put into memory as the reference course and the autopilot
starts steering to hold the heading on this reference course.
The user can change the reference course at any time and the
heading will swing round to match the new course.
There is another way of setting the reference course. If the
autopilot is connected to a GPS navigation receiver, the
heading is then controlled to place the vessel on a direct track
between the origin waypoint and the next waypoint.
