Full LNG ahead: The future of dredgers

IHC and Wärtsilä are betting that LNG-powered dredgers like the Scheldt River will service clients mindful of controlling emissions.


With its signature ball-topped air traffic control tower keeping everything on schedule, Changi International Airport is a feat of traveller-centricity. The buildings, gardens and runways also stand testament to another feat: the dredging of 36 million m3 of sand from the nearby seabed to build the airport in the first place. Other cities have similar tales to tell. 

“Dredging has been crucial for the development of these cities and ports,” says Richard Brakenhoff, an industry analyst at Rabobank. “Singapore ranks second globally in the transshipment of containers. Without dredging, this would never be the case. Rotterdam’s transshipment of containers rose by 6.4% per annum between 1975 and 2014. This could only happen thanks to dredging.” 

From 2000, the dredging market has grown around 8% a year. Peter Raimond, a ship systems engineer at Dutch shipbuilder Royal IHC, which is working with Wärtsilä on the world’s first dual-fuel LNG dredger, expects continued strong demand. 

“Sooner or later, Singapore is going to start up again, China will need more and more resources. So although the market has a very cyclic behaviour in the long term, the trend generally is up,” he says. “The market will be asking for more and more ships and not only new ships, also replacements.” 

The last decade has seen a rapid growth in the scale of dredging vessels – in 2000, the biggest trailing suction hopper carried less than 24,000 m3. A decade later, two vessels with almost double that capacity were launched. Installed power capacity has also increased. In early 2015 Belgium’s Jan de Nul ordered a cutter suction dredger with installed power capacity of 40,000 kW – the biggest yet.

IHC research engineer Benny Mestemaker links scale to scale; increased capacity to drive down costs in huge projects like The World, the set of artificial islands in Dubai that required the dredging and depositing of some 300 million m3 of material, as well as the construction of the largest breakwater in history. Another driving factor has been the increasingly large container ships, with dredgers put to use to deepen and enlarge harbours.

And now a new trend has grown in importance: the need to control emissions. 

“We saw a trend in the market that LNG would become important so we started already with this five years ago, and in this process we started talking with Wärtsilä about the engines and about what they could do,” Mestemaker says. 

The market has now responded. Belgian dredging company DEME this year ordered its first two LNG dual-fuel dredgers from Royal IHC, for delivery in the spring of 2017. 

The largest, a new generation “Antigoon” class dredger called Scheldt River, will be powered by two Wärtsilä 34DF engines, one 12-cylinder and one 9-cylinder. The dredger will have a capacity of 8,000 m3. IHC and Wärtsilä hope such dredgers will serve European markets, particular in Sulphur Emission Control Areas such as the Baltic and North Sea. 

“There are still people who are reluctant,” Raimond says of the engine. “But it’s just the way forward, it’s going to be there. It’s better technology, so just like the diesel engine replaced the steam engine, this is the next step.” 

Dredgers running on LNG produce 25% less carbon dioxide emissions than those running on diesel, with practically no sulphur and particle emissions. 

“In dredging we are used to operating quite near the coast, and we have a lot of problems with emissions, especially in Western Europe and the United States, but also in some Asian countries emissions are becoming more important,” Mestemaker explains. 

IHC development engineer Leonard den Boer, who has been working with Raimond and Mestemaker, sees other clear advantages, such as LNG being cheaper. 

“The price is lower than diesel, so you have higher investment in your ship because of the LNG installation, but the price of the fuel is lower.” 

And on top of reduced emissions and smaller fuel bills, there’s the question of load. 

“In general the frequent and very rapid changes in loads – from 20 to 10% or from 40 to 60 – is very demanding of the engine,” Dick Heidelberg, Wärtsilä Marine Solutions & Services Account Manager, explains about the dredger load profile.


 “You also want to have a constant load on the pump, especially when you’re discharging sand over longer distances, because you don’t want the pump to get stuck or slow down, which risks the slurry in the pipe sinking to the bottom, and then you can’t restart it again. So it’s crucial that the engine runs at constant power.”

DEME visited Wärtsilä’s test centre in Vaasa, Finland, at the start of September to oversee testing of the engine that will power its new ship. 

“The customer was here to look at load simulations in the laboratory, and they were very impressed that the load pickups were even better than they expected,” says Henrik Wilhelms, Director of Marine Solutions at Wärtsilä. “By tuning the engines and working on optimising them, today dual-fuel engines are at the same level as the diesel.” 

IHC believes that the performance of LNG dual-fuel dredgers remains slightly behind their diesel equivalents – with Mestemaker describing navigating the slim margin between the engine misfiring and knocking as “like going between Scylla and Charybdis” – in other words, navigating between two evils.

But Wilhelms argues that recent advances in turbo charging, variable valve timing designs, gas injection and other ways of controlling the burning process have closed the gap. 

“If you went back a year or two ago, we said the same thing, we said that the biggest challenge for dual fuel was the poor load pickup,” he said. “The learning curve has been quite steep but now we are pretty confident.”

Should DEME’s two new ships perform well once they are launched in 2017, Wärtsilä’s LNG engines will be proven for almost any application.

IHC believes that at least a partial move to LNG is inevitable in the dredger market.

“I think it’s like the first hybrid car for Toyota – that same thing,” Raimond says of the new ships. “We believe that dual-fuel engines will be as important for shipping and dredging as batteries will be for cars.”


How to build a harbour


Picking the location is a matter of math

If the port is tied to a specific project, say a coal mine, you need to assess potential sites close to that project. How expensive would a railroad, pipeline or road link be? If it is to address a regional shortage of export or import capacity, you need to assess how near the site is to major commercial, manufacturing or commodity producing areas. How close is it to major road and rail links? How close is it to existing or planned rival ports? 

Next you need to consider land availability, the suitability of soil, water depth, currents, and protection from the sea. Finally, you need to look at social and environmental concerns. Do you need to move human settlements? How will it impact coastal ecosystems? In developed countries, new ports are often built on brownfield sites. 

Get money, land and legal go-aheads 

The next step is to tie down funding, obtain land and secure government permissions. This will mean carrying out environmental impact assessments, detailed land and sea surveys, and financial modelling. In both the cases of London Gateway, the UK’s newest port, and Maasvlakte 2, Rotterdam’s new harbour, this process took five years. As Maasvlakte 2 was constructed in a nature reserve, the developers agreed to establish a new seabed nature reserve and a new dune in order to secure approvals. 

Clear the site 

For brownfield sites, preparations can be substantial. In the case of London Gateway, Royal Dutch Shell removed 80,000 tonnes of steel from its former gas terminal before handing over the site to Dubai Ports World (DPW). DPW then had to relocate 350,000 animals before it could begin work. 

Dredge away

You first need to dredge, both to deepen the harbour entrances and bays and to gain sand for land reclamation. To build the harbour wall of Maasvlakte 2, Boskalis and Van Oord used 23 trailing suction hopper dredgers to transport 210 million m³ of sand from 12 km away. It then used four cutter-suction dredgers to deepen the entrance to the new harbour and the port basins to 20m below the average water level. Even for London Gateway, built on the site of an existing harbour, DPW needed to dredge 30 million m3 of sand and mud. 

Build defences

If your port is exposed, you need to construct sea defences. For Maasvlakte 2, the defences required 20,000 concrete blocks – each weighing 40 tonnes – and 7 million tons of broken rock.

With sea levels expected to rise, you want to raise the level of the site to protect the port from flooding. The London Gateway site was raised by 2m and the site of Maasvlakte 2 by 5m.

Next you need to construct a quay wall, sinking foundations deep into the seabed. 

After that, you need to lay the roads and railroads, both of which will need firm concrete foundations to withstand heavy cargoes.

Finally, you need to construct port buildings and bring in and install heavy machinery, such as quay cranes and gantry-mounted cranes.


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