Operation Manual

Autopilot Operation
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2.16 Glossary
ASF corrections, Loran - Additional secondary phase factor is the
amount in microseconds, by which the time difference of an actual
Loran signal that has traveled over varied terrain, differs from that of
an ideal signal over an all-seaweather path. (ie. Loran signals travel
slower over ground). The ASF correction is a value added (or
subtracted) to a measured Loran position, to attempt to restore the
position accuracy.
Chart Datum - A geographic reference system based on mathematical
models of the earth's shape is the basis for mapping and charting
positions in Latitude and Longitude. There are a number of local
reference datums, each with its own mathematical model of the earth.
Therefore, the position in one reference system does not coincide with
that determined from another reference system. Each chart lists the
Datum used.
COG - Course Over Ground - The actual direction of progress of a
vessel, between two points, with respect to the surface of the earth, The
vessels heading may differ from the course over ground due to the
effects of wind, tide, currents.
GPS - Global Positioning System - This system consists of 18 satellites
plus 3 spares in fixed orbits, circling the earth at an altitude of
approximately 20,200 km. The system will provide the user with 24
hour a day all weather position coverage, with an accuracy of 15 to 100
meters.
Loran C - A complex radio navigation network developed by the US
coast guard, to assist a navigator in determining his precise location.
The acronym, Loran C, stands for Long Range Navigation. It is an all
weather 24 hour a day electronic system of shore based radio
transmitters.
Magnetic variation - A magnetic compass points to the magnetic north
pole. The difference between this direction and true north is the
magnetic variation. The amount and direction of this variation is
dependent upon where on the earth you are located.
NMEA 0183 - A format (language) designed to permit communication
between various types of marine electronic equipment. In essence this
is a two-wire shielded, serial data link, permitting one device to talk
while other devices listen. Numerous different sentences are available,
permitting communication between various different devices.
Route - A stored sequence of waypoints. These waypoints will be
listed in the order in which you desire to follow them. The AP300DLX
permits the storage of up to 20 routes.
SOG - Speed over ground is the actual speed of the vessel relative to
the ocean floor.