DATA COLLECTION AND ANALYSIS

The ullage sensors were mounted over the hopper and as close to

the vessel center line as possible, with one located forward and one

aft. Specified accuracy of this sensor is 0.25 percent of range with

no temperature gradient. Because the speed of sound in air changes

with air temperature variation, the sensor compensates for tempera-

ture changes. Calibration of the ullage sensors is confirmed by

manually measuring the distance from the hopper ullage datum

down to the dredged material surface and comparing these values

with the sensor/computer-calculated ullage value (which incorpo-

rates the sensor offset elevation). The Columbus has ullage sensors

that work in a similar fashion but use pulsed radar waves instead.

Draft Sensors. The sensor that measures the McFarland's draft

is a strain gauge-type pressure transducer (draft transducer) that

was integrated into the existing pneumatic "bubbler" system used

to measure draft (Figure 6). The McFarland uses a single bubbler

line that runs from the keel (located near the center of the vessel

and hopper area) up to the bridge and operates by maintaining a constant low flow of air in the line

that purges or "bubbles" out the line at the keel. The dredge Columbus has fore and aft draft sensors

that measure pressure as well. The draft transducer calibration is confirmed by comparing

sensor/computer-generated draft output with visual sightings of the hull draft markings of the vessel.

DATA COLLECTION AND ANALYSIS

Columbus Data Collection and Analysis System. The SI for hopper dredges is a system

that monitors dredge position and dredge state, computes TDS, and reports and manages the data