ERDC/CHL CHETN-IX-14
March 2004
5
Outside Jetties (OJ)
Inside Jetties (IJ)
Rebellion Reach (RR)
0
-5
-10
-15
-900
-600
-300
0
300
600
900
Distance from channel centerline, m
Figure 7. Cross sections as squat evaluation locations OJ, IJ, and RR
The average receiver elevations and the horizontal coordinates of the GPS receivers were used to
determine the equation of a plane. The equation of this plane was used to determine the elevation at
the center line of the ship at the forwardmost point on the bow and the aftmost point on the stern.
The difference in elevation between the at-rest (AR) plane and the underway (UW) plane along with
changes in WSE between the two plane locations were used to define the squat at the bow and stern.
The equation for observed bow and stern squat from the water level, GPS, and density data is given
by
Squat = (WSEUW - WSEAR ) + ( PlaneAR - PlaneUW ) + ( Density AR - DensityUW )
(9)
To filter out some of the variability in both the ship's speed and the antenna elevations, an average
for both were computed for 1 min prior to and 1 min after the point of evaluation. An "at rest" condi-
tion for each antenna was determined based on the minimum ship speed of the data. This "at rest"
condition was used as the base condition to compare the antenna elevations at higher ship speeds.
GPS receiver elevations and WSE are shown in Table 3 for the six ship and location combinations
that met the constant cross-section, constant speed, and antenna elevation requirements. Ship and
channel input data for the empirical squat equations are shown in Table 4. Observed and predicted
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