VESSEL REVIEW | Hydromer – Hydrogen-ready hopper dredger to serve France’s Occitanie region

The government of the Occitanie region in southern France recently placed a new trailing suction hopper dredger (TSHD) into service.

Built by local shipyard Piriou, the 70- by 16.7-metre (230- by 54.8-foot) Hydromer was designed by the French office of Norwegian naval architecture firm LMG Marin in cooperation with Piriou Ingenierie. It has since replaced an older, lower-capacity dredger in the same owner's fleet as part of an initiative that seeks to make the Occitanie region a "positive energy" region by 2050.

"It is the first dredger in the world designed to operate with a portion of its installed power being provided by a hydrogen fuel cell," Laurent Sorlin, Project Manager at LMG Marin France, told Baird Maritime. "The hydrogen system brick, which includes four high-pressure, compressed hydrogen storage units and a containerised fuel cell, is scheduled to be installed on board by the end of 2025."

Sorlin said that the 200kW hydrogen fuel cell will then allow a 20 per cent average reduction in fuel consumption and CO2 emissions, with emissions being reduced to zero during operations in port or in an anchorage. The fuel cell will be kept in a 15-foot container and will be supplied by Helion Hydrogen Power while the hydrogen will be locally produced from renewable sources by Hyd'Occ.

"Even without relying on hydrogen fuel, the dredger is capable of generating only minimal emissions well below the environmental protection measures currently in force," added Nikias Ioannidis of LMG Marin France's Business Development team. "Its environmental performance is due to its flexible diesel-electric propulsion system that also includes modern generators and exhaust aftertreatment systems."

The diesel-electric propulsion arrangement includes four Volvo Penta D16 559kWe IMO Tier III generators, a Volvo Penta D7 100kWe emergency generator, two Veth 700kW azimuthing thrusters, and a Veth 480kW electrically-driven bow thruster. The azimuthing thrusters can be easily removed through the top deck for maintenance or replacement, allowing work to be performed even with the dredger still afloat.

Fulfilling a need for greater capacity

Hydromer was built in fulfilment of a tender that called for a hopper capacity of greater than 1,250 cubic metres (44,100 cubic feet), a length of 80 metres (260 feet), a beam of 17.5 metres (57.4 feet), and equipment for extracting both sand and sludge, thus ensuring suitability for dredging at depths of between five and 20 metres (16 and 66 feet) and beach nourishment works in areas up to 30 metres (98 feet) deep and 16 kilometres (10 miles) off the coast.

"The owner also specified comfortable accommodation spaces with a minimum of 12 cabins including at least 10 single cabins laid out for up to eight days of continuous operation, which was not possible with the now retired dredger Cap Croisette," said Sorlin. "The wheelhouse also needed to have a highly ergonomic layout with a dredging console allowing direct vision on the dredging arm as well as excellent visibility both aft and forward of the navigation console."

The owner called for improved dredging performance courtesy of a larger suction pump size and greater total dredging arm length. The incorporation of two dredging arms would allow for optimised performance at various water depths. Suitability for coastal protection was another requirement since the owner's earlier dredger did not possess this capability, thus necessitating the delegation of works to external contractors.

As it will be used primarily in channels and port areas, the TSHD also needed to be capable of high manoeuvring performance and improved seakeeping and positioning regardless of wind and currents. The owner also requested that the vessel be capable of transit speeds of at least 10 knots at design draught and 11 knots empty even under Sea State two conditions.

The installation of the hydrogen system was also among the first of the owner's requirements to be specified. Onboard space needed to be available for four 20-foot compressed hydrogen storage containers from Mahytec, a hydrogen transfer system, and a fuel cell with a capacity of at least 200 kW.

"In light of the owner's concerns about minimising environmental footprint, and due to the vessel's intended use near urban and residential areas, compliance to rigorous requirements regarding emissions and discharges into the air and sea was specified along with limiting both airborne and underwater noise," Ioannidis told Baird Maritime.

The spaces on the external deck area forward of the 1,500-cubic-metre (53,000-cubic-foot) hopper, aft of the forward mooring deck, and starboard of the dredging system were deliberately kept free to permit installation of the compressed hydrogen containers. This is so there will also be ample space above and on the sides for safe handling during container swapping operations, which LMG Marin expects will be done on a weekly basis as the fuel cell supply has a maximum duration of one week.

Suitable for a range of extraction applications

The dredging setup supplied by Holland MT has the dredging arm on the deck with the draghead available in two configurations to allow work at various depths. The dredging arm is supported by two gantries and one service frame to allow it to slide down via a side rail. A swell compensator is also installed to compensate for vessel motions and to maintain the draghead at a constant position on the seabed.

Three doors located on the bottom of the hopper are coated in protective paint and are activated by independent cylinders on a platform located above the maximum hopper height. A dredging pump with a capacity of 6,000 cubic metres (212,000 cubic feet) per hour is installed on the hull bottom and is connected to the dredging pipes for hopper top filling and to the bow coupling for beach replenishment via the "rainbow jet" method. The dredging pump can fill the hopper to maximum capacity in as little as 20 minutes.

A suction pipe extension allows the TSHD to reach depths of 32 metres (105 feet) to collect sand to replenish beaches on the coast. This operation is achieved from the bow of the vessel by connecting the dredger to a floating discharge pipe of 500 metres (1,600 feet) or more in length.

The gantries and bow couplings are fitted with winches while an overflow device allows for the filling level to be adjusted depending on the density of any loaded sediment inside the hopper.

A jetwater system fitted with dedicated pumps helps separate the sediment on the seabed when passing through the draghead and for hopper washing during unloading operations.

The electronics setup includes X-band radars, an ECDIS, a sounder, an autopilot, compasses, VHF and UHF radios, and a GMDSS. A power management system is also fitted. The entire electronics suite complies with French flag category two navigation rules, which cover operation up to 200 nautical miles from the nearest port.

The crew accommodation includes ten air-conditioned individual cabins plus space for an additional four people. The accommodation is arranged on three levels and the elevated and forward wheelhouse provides a 360-degree view of the water and the dredging equipment.

New insights gained from design work

Integration of the hydrogen system posed a challenge for LMG Marin during the design work on the dredger.

"To identify, evaluate, and mitigate the potential impacts," said Sorlin, "a dedicated risk analysis was initiated and involved all parties including ourselves as designer, the shipyard, the vessel owner, the hydrogen system manufacturer, and designated experts together with Bureau Veritas and the French flag administration."

To ensure the vessel's suitability for its intended dredging operations, the hull side has been reinforced to help mitigate damage while the hopper is fitted with double plates for additional thickness to minimise the occurrence of corrosion due to the composition of the loaded dredged material within.

"The manoeuvring capabilities and seakeeping performance required by the owner necessitated further calculation to gauge the vessel's response in waves as well as its ability to withstand strong environmental conditions," Sorlin added. "Ship behaviour was enhanced by optimising the hull and appendages and by adjusting the bow thruster power and tunnel layout.

Sorlin explained that maintaining longitudinal equilibrium and stability also proved a challenging design constraint. Since ballasting operations cannot be conducted while dredging or while loading/unloading the hopper, a constant longitudinal equilibrium between empty and loaded conditions needed to be achieved. This requirement was satisfied through appropriate weight distribution so that only the forepeak ballast volume will be used to compensate for any tank level variation.

"In addition, fulfilling stability criteria with a low freeboard required us to maintain sufficient floatability volumes on the external decks. The vessel is thus allowed to navigate with a reduced freeboard below the international convention at maximum loaded draught and for only a part of its operations."

The designers also achieved the low acoustic footprint stipulated by the owner, thanks to the silent electrical propulsion and the specific structural features for noise and vibration dampening.

"From a project management point of view, each newbuilding allows us to enhance smooth communication and cooperation with shipyards, owners, and regulatory bodies," Ioannidis told Baird Maritime. "This was our first collaboration with Piriou, and we expect this will lead to future joint projects, thus extending the list of shipyards that LMG Marin France can work with to satisfy the requirements of various owners."

"Thanks to this project, we were also able to keep developing our capacity to integrate complex systems such as hydrogen systems into our designs, especially through dedicated risk analysis process," added Sorlin. "We have now become involved in numerous alternative design approaches and risk analysis methods, thus constantly improving our ability to anticipate and adequately address the technical challenges brought about by hydrogen and other alternative propulsion systems."

Hydromer is also notable for being LMG Marin France's first dredger newbuilding project, as an earlier dredger project was merely a retrofit to enable an existing vessel to operate on both diesel and LNG.

"The work on this newbuild TSHD also helped us increase our knowhow and skills in hydrogen system integration," Sorlin said. "This was due to the opportunity to work with hydrogen system manufacturers, hence allowing us to enhance our capacity to integrate such systems in future designs."

Construction of Hydromer's hull took place at Piriou-ATG Romania while final outfitting was undertaken at Piriou's Concarneau facilities. Sea trials were held in the Atlantic Ocean from the end of 2023 to the following January, when the vessel sailed on its delivery voyage to its new homeport of Sete.

Hydromer's area of operations will encompass the ports of Sète-Frontignan, Port-La-Nouvelle, and Le Grau du Roi, where it will perform maintenance dredging and coastal protection and stabilisation. Operations will be for ten months in one year, with the summer months dedicated to extensive maintenance to keep the vessel in service up to its maximum projected lifetime.