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 U.S. Army Corps of Engineers’ hopper dredge Essayons just finished vital maintenance dredging of the federal navigation channels in Honolulu, Barbers Point, Kahului, Hilo, and Nawiliwili commercial harbors.
The last time the federal navigation channels in these harbors were dredged was in 1999.
Hawaii is a maritime state over 2,400 miles from the mainland and far more dependent on its harbors than most of the United States. The Hawaii state DOT claims that over 80 percent of all consumer goods — food, clothing, autos, building supplies, machinery, paper, and allied products, medical supplies, and agricultural materials — are imported into the state. Of that 80 percent, approximately 98 percent enters Hawaii though commercial harbors on the major islands.
To ensure that these vital goods continue to arrive in Hawaii, the Essayons dredged approximately 300,000 cubic yards from the harbors and safely disposed of it at EPA-designated ocean disposal sites.
Home ported at the Corps’ Portland (Oregon) District, the Corps designed Essayons was built by the Bath Iron Works of Maine in 1982.
Operated by a merchant marine crew, the Essayons was delivered to the Portland District in 1983. The Essayons helps maintain entrance bars, rivers, and harbors on the coasts of California, Oregon, Hawaii, Alaska and, in emergencies, the Mississippi River. Because of its size and dredging depth, the Essayons is particularly well-suited for dredging the larger coastal entrances.
Posted on May 4, 2016 with tags Essayons, Hawaii, maintenance dredging, USACE.