Lake Services is currently using the system for dredging small channels in Baltimore County, near Baltimore, MD. "These channels sometimes go out in open water a mile or more away from any landmark or device that we could use as a positioning device," says Firth.
The operator simply plots the limits of the channel into the system. "If the channel is, say, 50 ft. wide, we plot both sides and each of the turns. Just like a surveyor, we plot all of this information into the device and it puts us on the map," Firth points out. "The channel may be several thousand feet long with several turns in it. And as we work down through there, we can see where we've been and clearly define where we are."
Swimming into place
Using the customized GPS as a guide, the excavator operator is able to accurately maneuver the barge from one position to the next. This is achieved via a specially adapted barge spud operating system linked with the excavator hydraulics.
"A hydraulic excavator normally uses six circuits, but they almost always have a seventh hydraulic circuit that is generally used for a hammer or other device," says Firth. He devised a way to use this circuit to power the large steel pipes, or spuds, that control barge movement.
"The excavator operator can shift the barge location by using a foot pedal to the seventh hydraulic circuit to operate a winch located behind the excavator. This hoists the spud pipes," Firth explains. "The excavator can then swim to the new location using the arm and bucket of the Volvo long-reach excavator, with the differential GPS to guide him."
Once the barge arrives at the desired location, the operator counter-rotates and aligns it as needed using the excavator swing circuit. "The dredge material barges have hardened corners and edges to allow them to be manipulated by the excavator bucket and assist the tug in the landing and sailing of the barges," says Firth.
The spud is then engaged via the excavator foot pedal to hold the new position. "This spud system allows a tremendous amount of flexibility," Firth states. "It's just like working on a tracked excavator and crawling to the [work area]."
In addition, the system reduces the number of workers needed on the barge. "It allows the operator to have complete control without having an extra person on board," says Firth. "Normally, for example, a standard crane spud barge would have a deck winch that has its own engine and its own operator."
And with the GPS system on board, there is no longer any guesswork when moving across open water. "The operator could be sitting out there in the middle of a fog," Firth comments, "and in a matter of seconds he could swim to [the next location], place the spuds down and position himself exactly where he wants to be."
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