How Autopilots Work
Sitex SP38 Installation and Operation
Document PN
29010101
V2r0
-
23
-
Following a Track: AUTO/ALC Mode
Some
Sitex
autopilots (including the
SP38
), provide another way to keep your boat on a
specific
Track
: Automatic Leeway Correction.
This feature can be turned on in
AUTO
mode.
ALC
is similar to
NAV
mode, in that it uses
NMEA0183 or NMEA2000 Latitude and Longitude data to sense if the boat is following the
desired Track.
Unlike
NAV
mode, however, a
Sitex
autopilot with the
ALC
feature only needs Latitude
and Longitude data in
AUTO/ALC
mode. It does not need Cross-Track Error data from the
external Navigation System, nor to have any waypoints set in the system. The
ALC
feature
calculates the Cross-Track Error on its own, using the desired Heading active at the point
in time when
AUTO/ALC
mode is first engaged.
Power Steer: “Drive by Wire”
Most
Sitex
autopilots have a
POWER STEER
mode, which provides a way for the user to
control the rudder directly. In effect, the autopilot acts as a sort of “electronic steering
wheel”, allowing the operator to steer the boat manually, in a similar way as when using a
standard manual steering wheel or tiller – but instead steering the boat with the autopilot’s
Control Head, or any remote controls it is equipped with.
Steering, when using the autopilot in this mode, is done with two buttons and/or a knob
on the Control Head. Button 1 and/or a clockwise turn of the knob, will move the rudder to
Starboard, causing the boat to turn that way; the other button, and/or a counter-clockwise
turn of the knob, will move the rudder to Port so that the boat turns that way.
Using the buttons/knob, the rudder can be placed in any desired position where it will
remain. This feature is useful when docking or manoeuvring, because the person steering
the boat can take their hands off the controls between rudder movements.
Additional Technical Information
Mathematically, the autopilot’s steering algorithms are based on a control method known
as a “PID Loop” … an acronym for a “Proportional, Integral, Derivative” error-correction
technique.
The amount of rudder movement to correct for any Heading error (or to make a turn), is
continuously re-computed, in a processing loop, as a value that is:
Proportional to the error (or how much more of the turn is still to be done).
An Integral of the error/turn … how big for how long.
A Derivative of the error/turn … how fast it is changing.
Many references can be found on PID Loops, on the internet and elsewhere, if you want
to know more.
Sitex
also occasionally holds training seminars – check with your dealer for
more information.
Summary of Contents for SP38 Autopilot
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Page 14: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 13 ...
Page 15: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 14 Introduction ...
Page 16: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 15 ...
Page 26: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 25 ...
Page 35: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 34 Installation ...
Page 36: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 35 ...
Page 74: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 73 ...
Page 108: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 107 ...
Page 109: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 108 Advanced Operations ...
Page 110: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 109 ...
Page 123: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 122 Care and Maintenance ...
Page 124: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 123 ...
Page 127: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 126 Appendices ...
Page 128: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 127 ...
Page 156: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 155 Warranty ...
Page 157: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 156 User Notes and Settings ...
Page 158: ...Sitex SP38 Installation and Operation Document PN 29010101 V2r0 157 ...