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Magellan NAV 6500/NAV 651098
NM on the courseline in 1 hour, his SOA is 30 knots, whereas SOG
would be 34 knots.
SOG. (Speed Over Ground) This is the speed at which the vehicle/
vessel is moving in respect to the earth. SOG is measured in knots,
miles per hour, or kilometers per hour. (This is not the same as speed
through water, if you are travelling by boat.)
STR. Steering. The difference between COG and CTS. If COG is
25° and CTS is 30°, then STR is 5° Right.
TTG. Estimated time en route to reach the active waypoint.
TRN. Turning is the difference between COG and BRG. If COG is
80° and BRG is 75°, TRN is 5° left.
VMG. Velocity made good is the component of the velocity that is in
the direction of the destination. In the above example, the boat is
travelling directly towards the destination even though not on the
courseline originally set. In this case, all of this velocity is being ap-
plied towards arriving at the destination, (i.e., VMG = SOG). Should
the boat veer away from this course and travel in a line parallel to the
original courseline (A
1
;B
1
) it would be travelling on a course that would
not intercept the destination waypoint. As the boat moved along, less
and less of its velocity would be applied toward arriving at the destina-
tion. By the time point D is reached, none of the velocity is applied to
getting closer to the destination and the VMG would be 0. As it moves
to point E, it is moving away from the destination and its VMG is a
negative value.
XTE. XTE (cross track error) is the perpendicular distance from your
boat to the left or right of the courseline that you are traveling. As you
will see in the discussion of
other data items, XTE is im-
portant in computing them
accurately. Keeping XTE at
a minimum will help main-
tain the most direct route to
your destination. This illus-
tration shows a boat
courseline. The arrows be-
tween the boat and the
courseline is the distance of
XTE and this boat is to the
left of the courseline. This
boater would need to steer
right to close the XTE.
A
Courseline
B
C
D
E