Picking the Teeth of a Dredge

When Great Lakes (Dredge #2) punched through the side bar at River Grove Park last week, I got a rare chance to take some close up pictures of men at work. Here’s what the “cutter basket” of a dredge looks like when it’s clean. Just looking at it, the teeth inspire fear. It looks like a nightmare out of a John Carpenter movie.

The rows of teeth stir up sand, and saw through roots and submerged deadwood. Pumps then suction the sand through the holes between the blades. Photo courtesy of Don Harbour.

Why Dredging Can Be So Slow

However, submerged plant material sometimes gets caught in the teeth and clogs the inlet. This slows the intake of sand. To restore the flow, the dredge operator calls for a service crew, lifts the cutter basket out of the water, and men remove the debris by hand. It was a real productivity show-stopper.

Before cleaning, roots and weeds clog the cutter basket.
During cleaning, men manually remove debris, such as the weeds you see in the background, that get caught on teeth.
Half hour later, after cleaning, the dredge finally lowers the cutter basket back into the water and resumes dredging. Note the pile of debris now in the boat.

For those who care to dig a little deeper into dredging, this web site explains how companies vary the shapes of cutter baskets to reduce the number of these time out situations. 

There’s a real science to the way they design these things. The objective is to reduce the number of unwanted objects that make it into the pipe. If the pipe clogs, it could take much longer to fix.

Posted by Bob Rehak on December 15, 2018

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