The future of dredging: sustainable vessels and equipment

By Erik van der Blom – R&D Manager at Royal IHC

The global dredging industry is facing a number of challenges linked to climate change and its consequences over the coming years. While a number of opportunities for dredging companies are expected, as rising sea levels will increase the requirement for dredging and maritime construction works worldwide, another repercussion will be strict emission regulations for exhaust gases.

This will have a significant impact on the design of dredging vessels and equipment, and the type of fuels to be used. As a result, there is a continuous search for more sustainable methods of dredging, and ways to power dredging vessels.

The number of emission-controlled areas (ECAs) around the world is rising and rules regarding shipping are becoming more rigorous. The IMO (International Maritime Organisation) is proposing new, stricter regulations for sulphur and nitrogen emissions. In the future, it is highly likely that the maritime industry can expect an increase in legislation regarding the reduction of CO₂, particulate matter and black carbon.

Strict emission limits are already in place in some emission-controlled areas, such as the North Sea and the coastal waters around North America. The effects of these are already being felt, because the majority of the world’s largest vessels use heavy fuel oil (HFO) for power. “Emission regulations will have an impact on the design and operation of dredging vessels,” says IHC’s Manager R&D, Erik van der Blom.

“As a vessel designer or owner, you have to think ahead. That means considering where the vessel will be operating, what type of projects it will be involved with, and what emission regulations will be in place a few years from now. At keel-laying stage, a vessel must comply with new legislation. If companies only start to consider this aspect when the regulations are in place, it may already be too late.

The rise of LNG

“Emission regulations are intrinsically tied to fuel. This, in turn, has an effect on the choice of engine, and the entire layout of the dredging vessel. However, it isn’t simply a case of switching engines, it’s a complex design process with numerous variations. The choice that a dredging company makes regarding the engine has an effect on the arrangement of the vessel, the propulsion system and even the controls system.”

As an experienced designer and builder of dredging vessels, IHC is proactively working to overcome these challenges. Sustainability has become one of the most important drivers for the company’s innovation programme. In this way, IHC is seeking to increase the performance – and reduce the environmental footprint – of dredging vessels and equipment.

Liquefied natural gas (LNG) is rapidly becoming one of the fuels of choice for new vessels. LNG-fuelled ships eliminate sulphur oxide emissions, and offer a significant reduction in the release of nitrogen emissions. Dual-fuel engines, which operate through both diesel and LNG, are also increasing in popularity because they provide dredging companies greater flexibility, as they are able to operate in areas where LNG is not yet available.

Integrating LNG in a hopper dredger is a challenge. It requires three times the volume for storage compared to diesel, for example, and this has a significant effect on a vessel’s design.

“We have had to overcome the challenge of LNG storage and integration of the LNG fuel system for the new vessels ordered by DEME,” says Erik. “An important design choice is where to situate the LNG storage tank. In one vessel, we positioned the tank in the aft ship just above the engines, and on another, we placed this in the fore ship underneath the accommodation. Besides positioning the LNG tank, safety zones around the LNG fuel system also have to be taken into account – it’s a complex process.”

An innovative fleet

Both of these vessels have now been launched: MINERVA in December 2016 and SCHELDT RIVER in January 2017. MINERVA was the world’s first LNG-powered trailing suction hopper dredger (TSHD), which was an important milestone for the dredging industry. The 3,500m³ dual-fuel vessel was issued a ‘Green Passport’ and a ‘Clean Design’ notation.

Alongside MINERVA, SCHELDT RIVER featured an IHC-patented two-speed propulsion drive. This ensures that fuel savings can be made when sailing at lower speeds. Both vessels also feature a newly developed wing-shaped bow thruster tunnel, which improves the vessels’ manoeuvrability.

“It sounds obvious, but it was essential to incorporate multiple functionalities during the design process,” continues Erik. “It wasn’t simply a case of selecting the best location for the LNG fuel tank. We also had to consider the operational requirements of the vessel, and the locations where crew members would be working during operations. Essentially, we’re trying to achieve a balance between safety restrictions and operational requirements.”

This attention to detail is also present in IHC’s design of SPARTACUS. This vessel for DEME will not only be the world’s largest cutter suction dredger (CSD), but also the first CSD to be powered by LNG. In addition, the environmentally-friendly SPARTACUS features other innovations, such as a waste heat recovery system that converts heat from the exhaust gases to electrical energy.

The 15,000m³ TSHD BONNY RIVER also highlights DEME’s commitment to sustainability. The vessel’s hydrodynamic hull and dual-fuel engines ensure optimal fuel consumption, while the closed process water circuit minimises the turbidity generated by overflow water. This enables BONNY RIVER to dredge in environmentally sensitive areas.

Continuous optimisation

“It’s important to mention that sustainable product development is not all about switching to LNG, it’s much broader than that,” explains Erik. “Take the hull, for example. We’ve been working on optimising hull shapes for decades. Every time we try to further enhance the design, it’s an incremental improvement that results in hull shapes that are optimised for the customer’s specific operations and sailing speeds.

“We have also developed a two-speed propulsion system, as utilised on MINERVA and SCHELDT RIVER. This was a result of analysing dredgers operating in practice, and measuring the fuel and power consumption during the dredging cycle. As a result, we found out that hopper dredgers are working in partial load conditions much more than we expected.

“This is why our propulsion drive system can operate at two gear settings. For example, once a dredger sails inside a harbour it usually cannot sail at full speed. At this point, the crew can switch the gear of the propulsion system, enabling the engine to work at a better efficiency point. In a way, it’s comparable to a gearbox on a vehicle.”

A changing world

As our world evolves, the maritime industry will continue to demand cleaner, more effective and environmentally-friendly solutions, such as LNG. “Thanks to our practical experience, we now understand the challenges of working with LNG,” concludes Erik. “It’s different for each type of vessel, and IHC’s focus is on ensuring that each ship delivers the highest performance for its specific operation.

“With regards to climate change, there are opportunities for the dredging industry. Rising sea levels will affect urban areas and the dredging industry can play a role in protecting them. At IHC we contribute to that by developing innovative vessels that deliver the highest possible performance and loading capacity, while constantly working on the reduction of fuel consumption and emissions.”

Erik blom is one of the speakers at the DredgingToday Conference. He will take part in the thematical session: “ Climate change and its impact on dredging”. For more information about the program, please click here. Tickets are available via registration.dredgingconference.com.