Water test (hopper dredges)

ERDC TN-DOER-I6

March 2001

Water test (hopper dredges). The objective of the water test is to assure data consistency

for TDS calculation by comparing the SI system-measured specific gravity of water to an

average specific gravity of water determined from hopper water sample analyses. The clean

hopper is filled with water to check operation and data reporting of ullage and draft sensors,

and respective data collection hardware and software. The sensor-measured specific gravity

of the water is calculated and compared to the average specific gravity of water samples

taken from various locations in the hopper that are measured with a temperature-

compensated hand-held refractometer. Because of the absence of solid particles, the ideal

calculated value of TDS should equal zero with water (of a known density) in the hopper.

Water test (pipeline dredges). Water is pumped through the pipeline to check operation

and accuracy of slurry velocity and slurry density.

Trim-trim test (hopper dredges). The trim-trim test also checks operation and data

reporting of ullage and draft sensors. Two independent inclination (trim-trim) angles are

calculated from the ullage sensor measurements and difference in displacement by the draft

sensors. If the respective sensors are functioning correctly, then subtraction of these angles

should (ideally) equal zero.

Relative water level test (hopper dredges). The objective of the relative water level test is

to check the accuracy of ullage and draft sensor-measured values of the same water plane for

hopper dredges with bottom dump doors. The bottom dump doors are opened to allow the

water level surrounding the dredge to equalize with the water level in the hopper. When

compared, ullage and draft measurements should equal the fixed distance between the draft

and hopper level sensors.

Hopper ullage/level check (hopper dredges). The objective of the hopper ullage/level

check is to verify the accuracy of the ullage/level sensor measurements. Hopper level is

measured with a weighted tape measure at stations located by the ullage sensors.

Simultaneously, ullage sensor measurements are observed, recorded, and compared with the

tape measurements.

Draghead/cutterhead depth check (hopper/pipeline dredges). The objective of this check

is to verify the accuracy of draghead/cutterhead depths recorded from depth measurement

sensors. Draghead/cutterhead depths are measured manually and compared with sensor

values.

Draft/displacement check (hopper dredges). This test verifies the accuracy of forward and

aft displacement sensors. In relatively calm waters (to minimize wave-induced measurement

error), external forward and aft drafts (both starboard and port) are observed, recorded, and

then compared to draft sensor measurements.

Corps SI Software Installation. The Corps will install the SI system software on the dredge

and verify it to be operational on or about the time of the dredge inspection. The SI software can

be installed on the Shore System at any time during the contracting process.