The opening of the Panama Canal was a disaster for midwestern US farmers. So, in 1930 the US government set about deepening the Mississippi River to improve its cargo traffic capabilities. 79 years later, one dredger is still on the job.
The Rivers and Harbors Act of 1930 authorised a 2.7m deep, 122m wide channel be removed from the bottom of the Upper Mississippi River to allow for reliable cargo traffic navigation. To that end, the US Army Corps of Engineers launched a fleet of Dredgers to undertake the task. Dredging is the process of removing and disposing of underwater sediments.
Dredges come in two main varieties: dustpan heads, which act like large underwater vacuums sucking up light sands and sediments; and cutter heads, which bore through the strata and are more fit for muddy, rocky lengths. With both styles, the loosened soil is then directed back towards a suction hose where it is pumped back to the ship and either stored on-board, pumped onto a smaller ship that ferries it away for disposal, or pumped back onshore for immediate disposal.
Video of the Cutter Head in Action:
Video of the Dustpan Head in Action:
The dustpan dredge Potter is the oldest active-service dredge on the Mississippi. It began its duties in 1932, just two years after the River and Habors Act and a year and a half before any other dredge. When it launched, the Potter was steam-powered and required its own dedicated fuel barge to help it maintain river miles 0 to 300. The Potter ran for 70 years before being “repowered” in 2001.
The process of “repowering” a dredge is, actually just what it sounds like. “Fuel oil consumption was so high with the steam plant that we had to refuel almost daily, so we needed two barges – one to refuel the dredge and another to refuel itself,” says First Mate Terry Bequette. So, a team from Halter Marine, the company contracted with the rennovation, tore out the steam plant and replaced it with three Caterpillar 3516B 1825-kilowatt diesel generators (two for operation and one standby) that run a 600-volt main bus.
That bus, powers two new 1200hp GE Electric Motors that drive the state-of-the-art dustpan head. The new head sweeps a 10m wide path along the river bottom, 20 nozzles lining the base of the dustpan stir up sediment as it passes. Sediment is sucked up through a 38-inch wide suction hose, powered by a new high-density dredge pump with nearly double the capacity of the old.
“What do I miss? The romance of steam, the memories of an era that is gone,” says Bequette. “What do I not miss? The smell, for one!”
[Wikipedia – Wikipedia – US Army, Corps of Eng. – Natl. Park Service – USACE Philadelphia District – Videos: US Army, Corps of Eng.]
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