Sitex SP38 Autopilot, Installation And Operation Manual

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How Autopilots Work
Sitex SP38 Installation and Operation
Document PN 29010101 V2r0
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Changing Heading
Heading changes are very simple with a Sitex autopilot as well. Imagine for example, that the
autopilot is steering your boat Southwest, and you now wish to change direction to
Southeast (see Figure 2 ).
To initiate the turn in AUTO mode, you would simply turn the knob on the Control Head
to set the desired Heading (as shown on the Control Head’s display screen) to 135°…
Southeast.
After that, the autopilot behaves much the same as when maintaining a Heading –
but with an initially large “Heading error” (90°to Starboard, in this example) that must
be dealt with:
•
When the SPU moves the Rudder to Port, it will probably be by
quite a bit, maybe even all the way to the stops – but not
immediately so the boat doesn’t turn too rapidly.
•
Eventually, the actual Heading will match the desired Heading
… and the boat will then be going Southeast.
•
The SPU will keep steering the boat on the new 135° Heading,
and maintaining that Heading until another Heading is selected.
Autopilot is steering vessel
on a heading of 225° (SW)
Autopilot responds to the
change in desired heading
Operator selects new
desired heading of 135° (SE)
by moving the rudder to
Port -- vessel begins to turn
As the actual heading
approaches the new desired
heading, the Autopilot starts
to move the rudder back
towards mid-ships position
then straighten out
the new heading slightly,
Autopilot to "over-shoot"
Typical response is for the
heading of 135° (SE)
the vessel on the new
Autopilot is now steering
N
Figure 2 – Heading Change in AUTO Mode