Page 17: of Marine News Magazine (August 2005)

16 18

By Larry Pearson

A new, "environmentally friendly" dredge has joined the U.S. Army Corps of Engineers in the St. Paul, Minn.

District. The dredge Goetz was christened June 24, 2005, at the Mississippi River levee at Winona, Minn. The 20- in. cutter head dredge was named in honor of William L.

Goetz, longtime chief of the St. Paul District's Construc- tion-Operations Division. Goetz was a leader in adopting new dredging practices required by changes in environ- mental laws in the 1970's.

The new dredge incorporates modern technology that will support efficient and environmentally safe dredging operations consistent with Goetz's philosophy.

Key to the design philosophy behind this dredge is its diesel electric design. "With a diesel electric system, the use of hydraulics is at a bare minimum," said A. K. Suda, whose Metairie, La.-based firm designed the Goetz. "With no hydraulics, there is no hydraulic oil to leak into the river," Suda added.

All of the main systems that use power are driven by electric motors. "Electric motors run quieter and cleaner than hydraulic systems and diesel engines that run below or above the power curve produce polluting emissions,"

Suda said. The AC variable frequency electric winches, cutter and pump drives offer advantages in control, effi- ciency, noise abatement and environmental friendliness giving the Goetz a projected life of 50 years or more.

The Goetz is 225 ft. long by 40 ft. wide with an eight- foot depth and a five-foot draft. Air draft is 45 ft. and the dredging depth is 28 ft. at a 45-degree angle. The vessel uses a 22-in. diameter suction pipe and a 20-in. discharge pipe. LeTourneau Shipyard in Vicksburg, Miss. built the

Goetz. Prime contractor was Oilfield-Electric-Marine,

Inc. (OEM) of Houston, Texas. Both OEM and

LeTourneau are divisions of Rowan Companies, whose major business is building offshore oil drilling rigs.

The hull of the Goetz was constructed under ABS clas- sification Maltese-Cross A-1 Barge River Service. All equipment hard points were analyzed to transmit weight to hull members and reduce vibration to as low a level as reasonably possible.

As with any dredge, the key specification is its pump- ing capacity. The Goetz will produce an estimated 1066 cubic yards of a water-sand slurry (25 percent solids) at 5,000 ft. through a 20-in. discharge line.

The Goetz uses a GIW model 22 x 20 x 54 pump rated at 1812 hp passing a flow of 17,000 gpm rotating at 491 rpm. A Lufkin single reduction parallel shaft speed reducer (gearbox) transmits a minimum of 1800 hp from a motor speed of 690 rpm.

Two dredge pump electric motors are installed in series powering the gearbox producing 1811 hp at 690 rpm. The two motors use 480 VAC 3-phase, 40-76 hertz with 117 hertz maximum. The electric motors are TT 1150 AC

Vector Duty motors by OEM.

The pump motors are controlled and driven by an

OEM V31800 AC drive system. The drive is rated at 1700 kW continuous duty with 150% overload capacity. "The drive system takes AC current from the generators rectifies it to DC and inverts it back to AC at a designat- ed frequency and voltage," said Pat Williams, director of dredging and marine for OEM.

The Goetz can also deliver its 1,066 cubic yards of

August, 2005 • MarineNews 17

DREDGE REPORT

New Dredge Goes to Work on

Upper Mississippi

The U.S. Army Corps of Engineers dredge Goetz at LeTourneau Shipyard, Vicksburg, Miss. Inset is one of two styles of dredge heads carried by the Goetz.

AUGUSTMN2005 3(17-24).qxd 8/1/2005 4:10 PM Page 17