ComNav Commander P2 & P2VS Installation & Operation How Autopilots Work
Document PN 29010074 V4.1 - 19 -
An Autopilot System
This is a block diagram of the major components of an autopilot system:
COMPASS
READS THE VESSEL'S
ACTUAL HEADING AND
SENDS IT TO THE SPU
PROCESSOR (SPU)
CALCULATES THE RUDDER
POSITION NEEDED TO STEER
THE VESSEL ON THE DESIRED
HEADING, AND CONTROLS THE
STEERING SYSTEM
ACCORDINGLY
STEERING SYSTEM (ACTUATOR)
[HYDRAULIC RAM OR ELECTRIC MOTOR
WHICH IS MECHANICALLY CONNECTED
TO THE RUDDER]
MOVES THE RUDDER IN RESPONSE TO
CONTROL SIGNALS FROM THE SPU
RUDDER FOLLOWER UNIT (RFU)
[MECHANICALLY CONNECTED TO RUDDER]
MEASURES RUDDER POSITION AND SENDS
IT TO THE SPU
NAVIGATION DEVICES
[OPTIONAL]
SUPPLY NAVIGATION
INFOMRATION TO THE SPU
IN NMEA 0183 FORMAT
CONTROL HEAD
DISPLAYS STATUS AND HEADING
INFORMATION FROM THE SPU, AND
ALLOWS THE OPERATOR TO INPUT
STEERING COMMANDS & OPERATING
PARAMETERS
Figure 1 – Basic Autopilot System
The Compass indicates the direction in which the boat is pointed – often referred to as the
“actual Heading”. Depending on the type of boat & installed equipment, the Compass may
be a magnetic compass, an electronic fluxgate compass, a gyroscopic compass, or a GPS
Compass.
A reliable Compass is absolutely vital to an autopilot – because, without it,
the autopilot has no way of knowing which way the boat is headed.
The actual Heading is fed electronically from the Compass to the Processor (SPU) – which is
the “brains” of the autopilot. The SPU contains the microcontroller(s) & other electronic
hardware, and the sophisticated control software necessary to steer the boat on any desired
Heading.
The Control Head, normally located in the wheelhouse, is the interface between the boat’s
operator (that’s you …) and the autopilot. The Control Head displays information about what
the autopilot is doing, and it has various controls (buttons &/or knobs) that allow you to give
commands to the autopilot.
The final part of the picture is the Steering System. In order for the autopilot to steer the
boat, there must be a steering system capable of moving the rudder independently of the
ship’s helm. This might be a hydraulic ram that is connected to the rudder post or tiller
quadrant, or an electric motor connected to the steering cables.
But no matter what type of steering system the boat uses, electronic signals from the SPU tell
the system to move the rudder, when needed – how far and in which direction.
Your autopilot may also have a Rudder Follower Unit (also called a Rudder Feedback Unit, or
just “RFU”), a device that tells the SPU what position the rudder is in at any given time.
To Next Page
Loading...
