Dredging Greenly

DEME’s focus on safeguarding the environment led to its decision to pioneer the use of greener LNG dual-fuel engines in dredgers.

Text: Richard Orange Photo: Wärtsilä

Dredging is perhaps the most demanding task an engine can perform, so when the Belgian group DEME opted for Wärtsilä’s 34DF dual-fuel LNG engines for the latest addition to its dredging fleet, it was a sign the technology had come of age.

But according to Jan Gabriël, the company’s Head of Construction and Conversion, the main reason to fuel its new “Antigoon” class dredger “Scheldt River” with LNG was environmental rather than operational.

Compared to diesel, LNG has at least 20% lower carbon emissions, nitrogen (NOx) emissions are reduced by approximately 80%, sulphur (SOx) emissions are near eliminated. The engines produce virtually no soot.

“Emissions-wise this really is a game-changer,” Gabriël argues. “It’s part of the continuous quest of DEME to be environmentally friendly.”

All dredgers operate close to shore, often in cities, ports and harbours, making their emissions highly visible to the public, but DEME’s focus on LNG and dual-fuel engines differentiates it from its main competitors.

The company’s stated vision is “to create land for a sustainable future.” Safeguarding the environment is one of its five core values.

There is a commercial advantage to this environmental approach, too. Increasingly, DEME’s government and corporate customers reward contractors who demonstrate that they can fulfil a contract with lower harmful emissions.

“Some really advanced schemes are being put into place that incentivise contractors who can do the work with less fuel consumption and less carbon dioxide production,” Gabriël says. “If you are good at that, you can be slightly higher in price.”


Perhaps the most immediate trigger for DEME’s decision was a tightening of the International Maritime Organisation’s MARPOL Annex VI regulation for SOx and particulates emissions for Sulphur Emissions Control Areas (SECA) at the start of 2015, reducing the limit to 0.10%.

This meant that shipping companies could no longer operate diesel fuelled dredgers with standard fuel in the Baltic Sea, the North Sea, North America and Canada, and the US Caribbean.

A new SECA was announced in China’s Yangtze region in August, and SECAs are being considered for Singapore, and the Australian coast.

“We have analysed a number of other solutions, such as scrubbers, but we are not satisfied with the result,” Gabriël said. “You are taking the sulphur oxide emissions out of the air but then – in the basic but approved installations, – depositing them in the sea, which for us is not a satisfying solution.”

The other main solution, using low-sulphur marine fuel, would have meant higher fuel costs.

“When we made the decision at the end of 2014, there was still a serious gap between the price of LNG, in terms of net calorific value compared to the price of low-sulphur diesel oil. Now that economic case is a bit less pronounced, but we expect that to change.”

Other drivers were technological and regulatory. In September 2014, Wärtsilä informed Gabriël that the company’s dual-fuel engine was now capable of directly driving a centrifugal dredge pump.

Previously, LNG dual-fuel engines could not cope with the fast-load variations created by such pumps when, for example, a dredger’s suction tube moves from dredging soft sand to a patch of heavy rock.

“For us, this was a key element, and up until then, it was not possible. So when Wärtsilä mentioned this to me, it opened up a new possibility,” Gabriël says.

According to Giulio Tirelli, Director of Marine Engineering in Wärtsilä Marine Solutions, the change was a result of improvements in optimising the engine parameters, including the engine control.

“We had to tune the engine in a different way to enlarge the engine’s operational field. We improved the automation system, the fuel injection system and fine-tuned some key components,” he says.


The fine-tuned system involves monitoring the combustion in the engine more frequently and precisely, improving combustion control capabilities and allowing for more effective repetitiveness of combustion cycles.

Before committing itself, DEME put the new engine to the test in laboratory conditions that simulated the most demanding dredger operations. Then, after Wärtsilä carried out some final adjustments, they judged that the engine was sufficiently responsive.

“The engines are doing really well. So we are looking forward with a certain degree of confidence,” Gabriël says. “After a few months of operations, we will know for sure. It would be naive to say there will be no problems, but after the intensive testing, we will not have serious difficulties.”

The Scheldt River’s design was made possible by the new set of rules the IMO brought in for gas-fuelled ships in June 2015, which permitted the gas tank to be located closer to the hull, allowing Royal IHC to design an LNG dual-fuelled dredger which did not depart too much from a standard dredger design. DEME ordered the ship in the spring of 2015.

The big draw-back from DEME’s point of view is the shortage of places to refuel LNG vessels, with bunkering facilities at present existing in Sweden, Norway, Finland, Spain, and the US West Coast.

“Our decision was that we had to move forward and break through this chicken-and-egg issue,” Gabriël says. “What we see is that things are moving. It’s not developing rapidly enough in our view, but it is taking off.”

By the end of this year, LNG bunkering will be possible at Zeebrugge in Belgium, and next year in Rotterdam in The Netherlands. Dunkirk in France is also planning a facility, and we expect to see facilities in Hamburg, and downstream of London.

“We think we have made a good decision,” Gabriël concludes. “It was not easy because we are the pioneers, but we believe in this solution, and we are now looking forward to our first experience in operating LNG vessels.”

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