Figure 3. Corps dredge McFarland

ERDC TN-DOER-I2

July 2000

Dredge McFarland. The dredge McFarland (Figure 3) is a Corps dredge built in 1967 with a

rated capacity of 2,400 m3 (3,140 yd3) that is operated by the U.S. Army Engineer District,

Philadelphia. Instrumentation was installed 28 August 1999 on the McFarland to monitor and

collect hopper volume and vessel displacement data necessary to calculate TDS values.

Figure 3. Corps dredge McFarland

Dredge Columbus. The Columbus (Figure 4), owned and operated by B+B Dredging Company,

is a hopper dredge with a rated capacity of 3,361m3 (4,397 yd3). Since January 1998, this dredge

has worked for the Mobile District under rental contracts that specified not only ullage, draft, and

position measurement, but also the full suite of data parameters required for the SI hopper dredge

monitoring system. In addition to collecting TDS data, the SI (Rosati 1998) also incorporates

contract assurance requirements and is an analysis and reporting system to assist in the inspection

of contract dredging operations.

SENSORS

Hopper Level Sensors. Ultrasonic sensors were selected as the first type of measurement

technology to be investigated on the McFarland. Two ultrasonic ullage sensors (LUNDAHL

DCU-1104s) were installed over the hopper to measure the level of dredged material. The forward

sensor is pictured in Figure 5. Ullage (pronounced ` l-ij), as defined in Webster's (1983) dictionary,

is the amount that a container such as a cask or tank lacks being full. This ultrasonic sensor measures

the distance between sensor and dredged material by using a piezoelectric transducer to send out

cone-shaped sound waves in a series of pulses. These pulses reflect off the top of the hopper

material (slurry or water) and echo back to the transducer. The distance between the dredged

material surface and the transducer is calculated by the sensor from the time interval between the

pulse transmission and echo reception.