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Hopper Dredges

A Hopper dredge is a propelled floating plant which is capable of dredging material, storing it onboard, transporting it to the disposal area, and dumping it. Hopper dredges perform the largest and most dangerous jobs - clearing channels and offshore sandbars from the mouths of major rivers. Hopper dredges move like a ship. When dredging, they move very slowly. Normally, you can tell when they are dredging by the signals on the main mast. During the day, a black ball over a black diamond over another black ball will be shown. At night, a red light over a white light over another red light means the dredge is working. These signals also indicate that the dredge is restricted in its ability to maneuver and you must stay clear of the vessel. When the dredge's hopper is loaded, the dredge maneuvers both in and out of the channel to reach the relocation site. During this time, the dredge may move much faster and may turn frequently. Direct pumpout is a common method of removing dredged material from hopper dredges. A hopper dredge fills its hoppers as it dredges the bottom. The dredge then moors to a structure, buoy, or multiple buoy berth. Hoses connected to a pipeline extending to shore are attached to the hopper dredge discharge manifold. The dredge mixes the dredged material with water to form a slurry and pumps the slurry from its discharge manifold through the hoses and pipeline to a designated discharge location.

The hopper dredge WHEELER is operated by the New Orleans District, US Army Corps of Engineers. It is the largest seagoing hopper dredge in the United States. The WHEELER keeps waterway channels clear from Key West, Florida, to Brownsville, Texas. Although the dredge is maintained in a state of readiness for worldwide operations, it spends the majority of its time operating in the Southwest Pass of the Mississippi River, dealing with shoaling problems that occur during high and low water. The WHEELER is staffed with 56 civil service mariners. The crew is divided into two operating tours, each of 28 men and women alternating two weeks on/ two weeks off. Their working schedule consists of 10 and 12 hour days, including weekends. The dredge operates 24 hours a day, 7 days a week. Every 14 days it docks for fuel, supplies, water, and engine maintenance.

The WHEELER is a "trailing suction" hopper dredge. That is, it operates much like a giant vacuum cleaner. The uniquely designed with three large drag arms and an impressive pumping capacity. To dredge a channel, the drag arms are lowered over the side to the channel bottom. While the WHEELER travels forward at a speed of approximately 2 knots, the drag arms suck a water and sand mixture, known as slurry, from the channel bottom. The slurry passes through the drag heads and pipelines into the hopper.

With all pumps and drag arms operating, the WHEELER fills its hopper with slurry in about 11 minutes; however, pumping continues to allow sediment to displace the water in the hopper and obtain a maximum load of as much as 7,872 cubic yards of sediment. On a good operating day, the WHEELER can remove 100,000 cubic yards of material, or about 7,000 dumptruck loads, from a project site. The dredged material is transported from the channel being maintained to an authorized Dredge Material Containment Area, where it is deposited by opening 14 hopper doors on the WHEELER's bottom and allowing the material to fall to the ocean floor.

Philadelphia is home to the McFarland, one of only four oceangoing hopper dredges in the Corps' Minimum Dredging Fleet and the only dredge in the world with triple capability for direct pumpout, bottom discharge and sidecasting. The vessel and its crew of 60 have two missions: (1) emergency and national defense dredging worldwide and (2) planned dredging in commercial waterways, mainly federal navigation projects along the Atlantic and Gulf Coasts. In a typical year the McFarland removes about seven million cubic yards of dredged material.

The Dredge McFarland, operated and maintained by Philadelphia District, is an essential part of the Corps' fleet of ships. The McFarland is one of only four oceangoing hopper dredges in the Corps' Minimum Dredging Fleet. The vessel and its crew of 60 have two missions - emergency and national defense dredging worldwide, and traditional dredging along the Atlantic and Gulf coasts. In a typical year the McFarland removes about seven million cubic yards of dredged material.

The McFarland, with close to 50 officers and crew, is uniquely equipped with triple capability for direct pumpout, bottom discharge and sidecasting. It has a twofold mission: Emergency and national defense dredging anywhere in the world; and Planned dredging in the Delaware River and Bay. Like a vacuum cleaner, the dredge scoops out navigation channels to make them deeper, then either discharges the material in deep water, sidecasts it aside the channel, pumps it to an upland disposal area where some of it can later be used for construction, or pumps it directly onto a beach or coastal wetland needing renourishment. The McFarland can dredge around the clock in any environment, and can handle a variety of materials including silt, sand, clay and shells.

The "McFarland"'s hull was built by the Bethlehem Steel Shipbuilding Corporation with all the design drawings and dredging machinery supplied by Ellicott International, of Baltimore, Maryland. She was built in 1967 for the Corps of Engineers hopper dredge fleet, which then consisted of 15 trailing suction hopper dredges. The vessel was delivered to the Galveston District Corps of Engineers, and primarily maintained the main ship channels in Texas and the Gulf of Mexico. The ship displaces 10,000 tons when loaded and draws about 23 feet. The "McFarland" is a twin screw vessel with 3,000 horsepower (2237kw) on each shaft, and twin rudders. Also included is a 500-horsepower (373kw) electric bow thruster, which helps turn the ship around easily in her own water.

The maintenance of navigation channel infrastructure along the Oregon coast and the Columbia River requires dredging that is is accomplished, in part, through the operation of two Corps-owned hopper dredges, Essayons and Yaquina, and a sand bypass dredge, Sandwick. These sea-going dredges, home-based in Portland, Ore., also work at other locations along the West Coast as well as Hawaii and Alaska.

The Yaquina was designed by the U.S. Army Corps of Engineers and constructed by the Norfolk Shipbuilding and Dry-dock Corporation of Norfolk, Virginia, in 1981. Delivered to Portland District in 1981, the Yaquina helps to maintain the entrance bars and harbors on the California, Oregon and Washington coasts. Because of its size, the Yaquina is particularly well suited for dredging the smaller, shallow coastal entrances.

The Yaquina is automated for operations with an unattended engine room and semiautomatic dragarm handling system. Sophisticated instrumentation allows constant production monitoring and enables the dredge crew to maintain maximum dredging efficiency 24 hours a day. The dredge normally works continuously, tying up eight hours or less per week for fuel, water, supplies and maintenance. There are two crews of 20 each, working an 8-day-on/6-day-off schedule, with both crew working the day shift on tie-up day.

The Dredge Essayons is the latest dredge to be built for the U.S. Army Corps of Engineers. Delivered to the Portland District in 1983, the Essayons helps to maintain the entrance bars and harbors on the coasts of California, Oregon, Hawaii and Alaska. Because of its size and dredging depth, the Essayons is automated for operation with an unattended engine room and semiautomatic dragarm handling system. Sophisticated instrumentation allows constant production monitoring and enables the dredge crew to maintain maximum dredging efficiency 24 hours a day. The Essayons is also equipped for direct pumpout. Two crews of 23 each are assigned to the vessel. They work alternately, one week on and one week off.



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