When thinking about maintenance, a shipping channel is not likely the first thing to come to mind. However, maritime professionals know that these waterways require periodic attention. As tides, currents and river flow cause sand, gravel and silt to build up over time, the depth of a channel is reduced. The sediment must occasionally be removed from the bottom of the channel to maintain safe water depths for ship navigation and ensure that traffic flow to ports continues uninterrupted.
Additionally, as the amount of trade and cargo moving through ports has increased, the size of commercial vessels also has increased. These larger ships require deeper channels through which to navigate.
The U.S. Army Corps of Engineers constantly surveys the depth of waterways to determine when sediment buildup may become a navigation concern and requires dredging to clear the channels. In fact, more than 300 million cu. yds. (2.29 million cu m) of dredged materials are removed from U.S. navigation channels each year to accommodate the shipping industry’s larger vessels.
Donjon Marine Company has recognized maintenance dredging as an opportunity to increase its business. Founded in 1964, the company’s primary focuses include marine salvage, transportation and ocean engineering. However, Donjon Marine capitalized on the changing shipping industry to expand its services by entering the dredging arena.
Based in Hillside, NJ, a suburb of Newark, Donjon Marine takes advantage of its proximity to the Atlantic Ocean by working on dredging projects for nearby river channels and straits that feed into the ocean.
One such job was a Corps project to deepen the Arthur Kill River channel, the waterway that separates New Jersey from the New York City borough of Staten Island. Corps engineers determined the channel needed to be taken from a depth of 38 ft. (11.6 m) down to 43 ft. (13 m) to accommodate the new, larger ships that navigate the waterway.
The Corps’ survey of the project area showed that the dredging would be so deep that Donjon Marine’s crew would not only have to remove requisite silt, but also would need to remove 60,000 cu. yds. (45,873 cu m) of rock. This survey result is not uncommon; as channels become deeper, layers of sand and silt often give way to rock.
The Donjon Marine project crew knew it would load the company’s new Caterpillar 385C hydraulic excavator onto the dredge Newark Bay, but needed a tool that attached to the excavator to break up the rock. While excavator manufacturers make recommendations on the size of attachments that are appropriate for their machines, finding a recommended attachment that was right for the job was key.
A tool that was too small would slow down the project and a tool that was too heavy would place too much weight on the front of the dredging barge and cause it to tip. Donjon Marine turned to its long-time equipment supplier, Hoffman Equipment of Piscataway, NJ, for a suggestion on equipment that fit the excavator and was capable of handling the rock removal task.
After listening to the requirements of the job that Donjon Marine had ahead, Hoffman Salesperson Carmen Gibilisco determined that the Atlas Copco HB 7000, the largest and most powerful hydraulic breaker on the market, was suited not only to the excavator and the demanding job, but also to underwater breaking. Considering the challenging task ahead, the Donjon Marine crew was convinced this breaker had the right features for the job.
Weighing 15,400 lbs. (7 billion kg), this breaker fit the weight specifications for the excavator and dredging barge while offering an impact force that could effectively break up the rock. The HB 7000 is often found in mining and rock quarry applications, but the breaker also is available with an underwater kit that makes it suitable for underwater breaking applications.
Atlas Copco’s underwater system applies a compressed air source to the percussion chamber of the breaker to keep a positive displacement of air constantly coming out of the bottom of the breaker.
Without this compressed air, the piston would draw water into the percussion chamber on its upstroke when the breaker was submerged. If the piston comes down on water, it can pressurize the water enough to break internal components and catastrophically damage the breaker. Since the breaker would be working more than 40 ft. (12.2 m) under water, this kit was essential in ensuring the tool operated properly.
Donjon Marine Project Superintendent Jim Wright knew the right breaker would be paramount to removing the rock quickly and efficiently.
“We had a large amount of rock to get through, so we wanted the largest and very best breaker on the market,” said Wright. “Atlas Copco’s breaker definitely did the job.”
After the silt was cleared away, the HB 7000 started its work of breaking up the rock. Next, the large pieces of rock were gathered from the bottom of the channel with a dredging bucket and deposited onto a dump scow. The scow then carried the load of rock 22 mi. out to sea for disposal. The HB 7000 offered several features to help the dredging crew keep the entire project running smoothly.
The HB 7000’s StartSelect system was one of the breaker’s features that helped make the rock removal process efficient. With the StartSelect system set to Auto Stop, the HB 7000 will not function until the breaker comes up against a solid object, which helped an operator avoid hitting areas where rock was not present and eliminated the damaging effects of blank firing. This feature greatly reduces the possibility of internal damage and increases the life of the hammer.
The HB 7000 also worked in conjunction with a GPS unit and excavator cab-mounted screen to help operators “see” the dredging area. The GPS unit created a map of the area to be dredged and allowed operators to position the breaker with precision. These systems are examples of some of the technologies that equipment manufacturers have developed to help crews operate their tools safely while ensuring the job was done efficiently.
“These new systems help operators work more precisely in the dredging area, because extra passes that aren’t needed cost time and money,” said Wright. “The systems also help us from missing any materials that need to be dredged, which means we do a better and more thorough job.”
Even with modern technology and ideal working conditions, the harsh environment of working underwater can cause equipment to require service. When the breaker developed a hydraulic oil leak during the project, Atlas Copco took care of the issue immediately by flying service technicians to the site to fix the leak. This fast repair got Donjon Marine back to the project quickly and with little delay.
While extremely large ships that needed extra room to navigate or stormy weather that brought choppy seas sometimes caused the project to slow, the HB 7000 helped Wright and his crew keep the project on schedule by removing an average of 700 cu. yds. (535 cu m) of rock each day. When the water was calm and channel traffic was low, the HB 7000 enabled the crew to remove up to 1,000 cu. yds. (765 cu m) of rock in one day.
Two years after starting work on the channel, Donjon Marine completed the deepening project.
Because of the success in using the HB 7000 on the Arthur Kill River project, the company recently purchased a second HB 7000 to prepare for upcoming rock-breaking projects.
The Corps plans to bid future contracts for dredging the Arthur Kill River channel down to a depth of 50 ft. (15.2 m). The continued deepening of the channel reflects the Corps’ dedication to providing larger ships access to the river’s docks. Moreover, this trend toward deepening channels extends beyond the United States.
According to a September 2000 Corps report, container ports around the world are deepening navigation channels down to between 49 and 53 ft. (15 and 16 m) to accommodate the larger ships that will travel international waterways.
The shipping industry’s need for deeper channels means more dredging contract opportunities for companies like Donjon Marine.
With more than 40 years of experience and tools like the HB 7000 on projects, Donjon Marine anticipates more business while creating safer navigation channels to facilitate the flow of maritime traffic in and out of the nation’s ports.
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