Sperry Marine NAVIKNOT 600 SD, Operation, Installation And Service Manual

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NAVIKNOT 600 SD 056353/J
Operating Principle 1-5
1.3 Operating Principle
To determine the longitudinal and transverse ground speeds, the sys-
tem makes use of a self-contained satellite sensing system, consisting of
the satellite PCB with two GPS receivers inside the electronics unit and
the antenna unit connected to it.
The satellite PCB combines the data from the GPS receivers with data
from built-in rate gyros to determine the vessel’s heading, velocity,
course, and attitude. While the heading is referenced to the vessel’s
fore-and-aft line, the velocity and course represent the vessel’s motion
vector, i.e. the magnitude and direction of its motion over ground.
The sensed data are sent to the processing PCB inside the electronics
unit, which resolves the velocity data into the vessel-referenced longitu-
dinal and transverse ground speeds.
The speed vectors combined with the sensed rate of turn data are used
to discern between translational and rotational movements of the ves-
sel. These are used to determine the bow and stern transverse speeds
shown on the “docking display” page.
To determine the longitudinal water speed, the system utilizes the prin-
ciple of Doppler-shifted sound waves.
The transducer contains two transmitter/receiver windows, which trans-
mit and receive signals in the forward and aft directions respectively.
The sensing signals are high frequency sound pulses, generated by the
preamplifier D, which also detects the return echo from the water in-
between transmissions. The preamplifier processes the return signals
and transmits the sensed speed in a digital format to the NAVIKNOT
electronics unit.
Figure 1-2:
Sensed and calculated
speeds and directions
The electronics unit transmits all speed data to receiving external equip-
ment and to the connected CDUs. From the longitudinal ground and
water speeds, the electronics unit also calculates the distances travelled
and maintains the total and daily mile counters for both the ground and
water distances.
vessel's motion vector
over ground (course and
velocity; sensed)
longitudinal ground speed
(calculated)
longitudinal water speed
(sensed)
heading (sensed)
transverse ground speed
(calculated)