That means the GLDD ATB dredge has to adjust the connection in varying sea states as the relative elevation between the tug and the barge changes.Īnother complication: This ATB will spend most of its time in shallow water, defined as no more than 1.5 times the vessels’ draft. By contrast, the GLDD unit takes on and discharges its loads at sea in a variety of conditions. Such ATBs are loaded and unloaded at the dock in static conditions, and the tug can disconnect from the barge as its draft changes. GLDD performed tank testing at MARIN (Marine Research Institute Netherlands) in Wageningen, Netherlands.Īs a dredge, the GLDD ATB has operating characteristics that set it apart from typical ATBs - many of which transport oil products. The two hulls of an ATB are not as efficient as the single hull of a conventional ship. GLDD went to great lengths to achieve optimal hull forms for the tug and barge. “To be competitive, you need to be able to sail long distances at a given speed,” Becker said. The dredge also will load and unload multiple times a day. On a land reclamation project, for example, the distance between the offshore source of the sand and land being reclaimed may be 50 miles. Time spent moving the hopper is also a major contributor to unit costs. Ellis Island has a capacity of 14,788 cubic yards - roughly 18 percent more than the next largest U.S. The amount of dredged material a vessel can carry in its hopper is a big factor in unit costs. In our research and development, that was our goal,” said Steve Becker, GLDD’s senior vice president, plant and equipment. “In dredging, to be competitive you want to be the low-unit-cost provider. Yet moving briskly between the dredging site and the dumping spot will be crucial to the ATB’s success. Speed might not seem like a major concern when deepening a navigation channel or pumping sand onto a low-lying coastal area threatened by rising sea levels. Together, the tug and barge represent the first ATB hopper dredge built in the U.S.Īnother feature sets them apart: They will be remarkably fast for vessels of this type, capable of 14 knots with the barge fully loaded. As they enter service this year, the barge will be the largest of its kind in the U.S.
Mackie and its hopper dredge barge Ellis Island are indeed unusual vessels. Great Lakes Dredge and Dock Company describes its new articulated tug-barge unit as “a game changer” and it’s easy to see why.
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