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Understanding Dredging

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Dredging for Gold

2021-07-02 Lauren Grieco
cutter suction dredger, rohr idreco, dredger, gold, alluvial, mining, colombia

Colombian gold mining company Mineros Aluvial is going to great depths to dig for gold as well. An electric-powered vessel doing the digging, making it an operation deserving of a gold medal.

Deep-sea mining practices are an alternative to land mining practices which require labour-intensive processes to extract valuable resources. Deep-sea mining is gradually becoming charted territory for the dredging industry. For example, DEME Group’s ongoing studies on collecting the nodules lying on the sea floor show they are richer in nickel, cobalt, manganese and copper than those extracted from land with labour-intensive and emission-generating processes. Since the resources are lying on the sea floor at depths of 4.5 kilometres, specialised vessels, such as the 25-tonne deep-water robot named Patania II, are required to pick them up.

While 4.5 kilometres makes 28 metres look like child’s play, it is still a long way’s away and a challenge for precise manoeuvring for most vessels. Therefore, Mineros Aluvial is employing a specialised CSD in their search for gold. Ordered in 2020 and commissioned in Q1 of 2021, this electric-powered, deep-digging dredger was constructed by ROHR-IDRECO Dredge Systems, a builder specialised in zero-emission equipment and based in Doetinchem, the Netherlands.

By the numbers, the vessel is impressive coming in at 53 metres long, with a beam of 8.6 metres and weighing 255 tonnes. It has an output capacity of 270 cubic metres per hour. To keep the ladder in the golden position with such high output, seven hydraulic winches are needed. Due to the enormous forces which are released, these winches require powerful drive systems.

Maritime supplier Marotechniek summoned Bosch Rexroth in Sweden to specially develop the vessel’s seven winches. Without the need for gearboxes, the electric-powered Hägglunds drives maximise space on deck by connecting directly to the winches. In addition to saving space, there is lower inertia which according to Michel Maat, an engineer at Marotechniek, ensures ‘one revolution of the motor really equals one revolution of the winch. This means the winches can be adjusted very precisely – perfect for controlling the cutter-suction dredger, to stop it hitting the bottom, for instance’. In addition, gearbox-free electric drives can go for as long as 15 to 20 years before requiring any maintenance, meaning this gold digger is changing the game in more ways than one.