ComNav 2001 Autopilot System
P/N 29010017 V1.0 - 27-
The standard baud rate for the 0183 data format is
4800 baud.
This data format was developed to allow a
number of pieces of electronic equipment on the
vessel to communicate with each other.
It consists of a large number of data 'sentences'
which can transmit anything from the vessel's
water speed to its present position from one
device to another.
A data sentence consists of a two letter
identification of the sending device, followed by
a three letter identification of the data sentence,
followed by the corresponding information.
The autopilot can understand a number of data
sentences which contain steering or speed
information. The autopilot ignores the two letter
device identifier, and only looks for
the three letter sentence identifier, so it will
receive information from any Nav. Device which
transmits the correct data sentences.
Some NMEA 0183 data sentences supply
heading from the beginning of track to the end of
the track, which remains constant until the Nav.
Device sequences to the next waypoint. This is
the best type of Heading To Steer information, as
it prevents the wandering which may occur when
the vessel is close to the destination waypoint as
described earlier.
Depending on the type of nav device and how it
is configured, the autopilot may sound its alarm
and display 'Arr' when the vessel is close to a
waypoint.
The variations of NMEA 0183, which are currently supported by the autopilot, along with the information the
autopilot uses from that sentence are listed below:
RMA - Loran C Navigation Information,
Receiver Status plus Vessel Speed plus Variation
RMC - GPS Navigation Information, Receiver
Status plus Vessel Speed plus Variation
The RMA or RMC data sentence is always
combined with the RMB data sentence.
RMB - Generic Navigation Information, Cross
Track Error plus Heading To Steer from vessels
present position to the end of the track (Degree's
True only).
APB - Autopilot Interface Format, (King
Version), Cross Track Error plus Heading To
Steer from the vessel's present position to end of
track.
APB - Autopilot Interface Format, (NMEA
Version), Cross Track Error plus Heading To
Steer from the vessel's present position to end of
track.
APA - Autopilot Interface Format, Cross Track
Error plus Heading To Steer from beginning to
end of track.
XTE - Cross Track Error, Cross Track Error
plus Receiver Status.
XTE is always combined with one on the
following:
BOD - Bearing Origin to Destination, Bearing
from the beginning of the track to end of the
track. This is the preferred heading format, or;
WBD - Waypoint Bearing Origin to
Destination, Proprietary output from Northstar
Lorans. Heading to Steer is from the vessel's
present position to the end of the track.
HSC - Heading Steering Command, Heading
To Steer from the vessel's present position to the
end of the track.
The vessel's speed is read from the RMA or
RMC data sentence or one of the following:
VBW - Vessel Speed relative to water from
Dual Doppler Speed Log.
VHW - Vessel Heading and Water Speed
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