It is interesting to note that there are occasional wide excursions
from the fluxgate reference course but the apparently heavily damped CMG output from the
GPS receiver, at about 7300 seconds to about 7600 seconds, remains fixed at about 050°
when the vessel had actually been at various courses between 050° and 115°. Hence,
derived outputs have to be handled with care until such time that measures to ensure
quality within defined specifications can be implemented.
Applications of Derived Outputs
There are several applications where the management of a vessel would
benefit from the availability of GPS derived outputs described earlier in this paper. The
role of such outputs in determining the predicted path of the vessel, in managing its
steering, consumption and stresses are obvious.
Figure 4: Container Ship Trials - Plots every 30 seconds
In November, 1995 the author was responsible for the conduct of trials
aboard a large container ship (LOA 292.15 m). These trials were principally for the
purpose of validating and fine tuning the mathematical model of the same vessel
implemented on our simulator. This was the first set of trials on which we utilised two
GPS sensors spatially separated by a distance of over 200 metres. Post processing of
observations allowed us to obtain doppler differentiated measures of velocity in 3
dimensions separately at each position. These were then used to calculate velocity
components along the heading as well as athwartships. Several trials were conducted and
the results of one of these trials, a starboard turn with 20 degrees
