Damen Converts Vessel to Trailing Suction Dredge While Afloat
Damen field service engineers work on the submersible dredge pump prior to installing it onto the trailing pipe.
Last June, just before spring breakup, Damen Dredging installed trailing suction equipment on the Dutch multi-function vessel Litsa while the vessel was afloat at Arkhangelsk, in Northern Russia. The installation converted the vessel to a trailing suction dredge, equipped to dig sand in the open ocean and deliver it to adjacent barges or directly to another location.
The multi-purpose vessel Litsa with dredging equipment installed on the starboard side. The vessel also has cable laying equipment consisting of a Kobelco 7250 crane and a Hella hydraulic deck crane, and a Bezemer 300 ton linear winch.
The Litsa has a length of 91.4 meters (300 feet), beam of 27.43 meters (90 feet) and depth of 6.1 meters (20 feet). It accommodates a crew of 35.
The dredging system was fabricated at Damen’s yard in Nijkerk, the Netherlands and delivered by ship to St. Petersburg, Russia, where all gear was hoisted onto inland barges heading northeast to Arkhangelsk in Northern Russia, where it was installed on the Litsa. The work had to be finished in time for the short dredging season, which extends from the beginning of July to the end of October.
The complete dredging system was designed to install as a unit, without requiring drydocking or serious modification to the barge. The gantries, winches and swell compensator all were pre-installed on a foundation, which was welded to the deck. After the drive systems and controls were installed and connected, the installation was complete and the dredge was ready to work.
The trailing pipe elbow slides in-board and does not need a slide flange construction. The discharge spreader has its own winch and foundation making it into a complete kit.
The 650 mm (25.6-inch) trailing pipe mines sand at a maximum 28 meter (92-foot) depth. The starboard-mounted trailing pipe is outfitted with a submersible dredge pump, directly driven by a 700 kW electric motor. The sand is pumped over deck to a discharge spreader on the port side. An uninterrupted carousel of five barges sails alongside to be filled continuously. The sand production is closely monitored using the density and flow meter on-board, and the low mixture overboard connection. The barges vary from 1,000 cubic meters (1,308 cubic yards) to 2,850 cubic meters (3,728 cubic yards).
The control system has separate screens displaying the trailing pipe position, the dredgepump performance and the draghead position using proprietary Damen software.
Other gear was delivered in containers, which were installed on the vessel. One 30-foot container houses the diesel-electric set with frequency drive for the submersed dredge pump motor. A 20-foot container houses the dieseldriven jet pump, which feeds pressurized water to the draghead. Another 20-foot container holds the diesel-hydraulic installation, which controls the gantry cylinders, winches, swell compensator and dredge valves. The swell compensator bottles are also installed in this container.
The hoisting system was welded directly to the starboard deck of the Litsa.
On the bridge, a control panel was mounted with all controls for the diesels and hydraulics, with separate screens displaying the trailing pipe position, the dredge pump performance and the dredge and draghead position, all using Damen software.
The discharge spreader on the port side loads barges sailing alongside.
The Litsa’s job in the summer of 2013 was offshore of Nova Zembla in Northern Russia for Russian energy company Gazprom Neft Shelf, and included filling barges that backfilled subsea pipeline, dredging sand to directly backfill trenches, and pumping rock imported from Norway to cover the pipeline.
The dragarm allows dredging to 28 meters (92 feet) depth.