Naval architects have responded to owners’ calls for powerful tugs with a lower environmental footprint
Low-emissions tugs are being designed to handle larger ships and carry out more challenging towage projects. Architects are also producing tugs with reduced draughts to enable assistance in shallower waterways.
“There is a continued trend for smaller, but more powerful tugs,” says OSD-IMT technical manager Herm Jan de Vries, as he outlined key trends.
“Green technology to reduce emissions of CO2, NOx and SOx will continue lead the development of power generation and energy storage on board,” he explains.
“However, it still remains extremely difficult for owners to find a good business case to buy vessels that have incorporated this technology, because costs are high, and revenues are not increasing.”
Nonetheless, Mr de Vries thinks owners will eventually need to invest to reduce their environmental impact. “It looks like the wheels have been put in motion and there will be no way back,” he says.
Tug owners are facing uncertain future requirements for newbuildings. Key questions revolve around whether maritime trade will recover and grow following Covid-19, and what this will mean for the size of vessels and number of port calls in the future.
“Remember that investment in a vessel is done for the next 25 to 30 years,” says Mr de Vries.
“In an attempt to adapt to changing market conditions, owners are asking to future-proof vessels by designing them to accept technology such as selective catalytic reaction equipment, alternative fuels and other engines somewhere in the future, without too much cost and size impact today,” he explains.
For future requirements, OSD-IMT is designing a harbour tug with full-electric or hydrogen fuel cells and no engines. Its most recent design is for shallow-draught pusher tugs for river and coastal operations.
“The design and construction of such vessels must be lean and mean,” says Mr de Vries. “They need to be simple, to be constructed anywhere, but powerful and accommodate a relatively large number of crew, and of course, to be safe.”
PT Patria Maritim Perkasa is constructing the tugs in Batam, Indonesia for PT Patria Maritime Lines using an OSD-IMT7402 design. The first of this series, Patria 22, was delivered in August 2020.
These tugs are built for operations on the Barito River, South Kalimantan, Indonesia. They will be used to tow, push, berth and undock 91.4-m barges in water depths as low as 2.5-3 m. At least two more of these tugs will be built, with options for more if required.
Damen Shipyards has already produced its first all-electric harbour tug. It was launched from its Vietnam shipyard in December 2020 and is being outfitted for Port of Auckland.
This is a reverse stern drive (RSD) tug with batteries, a DC electric system and two electrically started Caterpillar C32 back-up generator sets.
These will drive a pair of thrusters with fixed-pitch propellers which can be controlled easily from zero up to maximum and are less complex than controllable-pitch propellers, says Damen Shipyards product manager for tugs Erik van Schaik*.
“The fully electric, zero-emissions Damen RSD-E 2513 tug is equipped with two 1.5-MWh battery packs, two 1-MW generator and FiFi [fire-fighting] sets and two 1.8-MW electrically driven rudder propellers,” he says.
“Batteries are charged with shore power and deliver all required energy during normal (un)berthing operations in the harbour with a maximum bollard pull of 70 tonnes.”
Damen uses Echandia’s air-cooled battery system consisting of Toshiba SCIB battery modules, based on lithium titanium oxide technology. “The battery systems are situated in an isolated, temperature-controlled room,” says Mr van Schaik.
He says these batteries can last 30,000 cycles, possibly throughout the life of the tug.
“Tugs can perform two to three average (un)berthing jobs in the harbour on a full battery,” he explains. “In a normal port, the vessel will be charged once a day and in an extremely busy port the vessel might be charged three times each day. This means 1,000 cycles a year and a battery lifetime of at least 30 years.”
Mr van Schaik says all-electric tugs have sufficient power to perform escort duties. “RSD-E Tug 2513 can deliver the maximum bollard pull of 70 tonnes for at least 30 minutes only on batteries, or for at least one hour on batteries plus generator sets,” he says.
“During escort tug operations and other operations where bigger autonomy is required, the IMO Tier III-compliant back-up generator sets run continuously to generate basic power supply up to 40 tonnes of bollard pull and batteries only deliver additional power to boost up to 70-tonnes bollard pull,” he explains.
Wärtsilä Marine Power director of business development Giulio Tirelli* says there should be no hurdles to applying hybrid technologies to escort tugs.
“The tug design principle for which a fully electric tug can be designed is the same as for a hybrid or conventional tug,” he explains. “The maximum bollard pull will be achieved independently from the maximum power the propulsion system can create and the thrusters can absorb.
“This is no different to any other tug,” says Mr Tirelli. “At the same time, having batteries producing an output power similar to an engine is rather difficult with current battery technologies.”
Navtek Naval Technologies developed the Zeetug30 design for an all-electric harbour tug after being approached by Turkish owner Gisas Shipbuilding Industry for smaller harbour tugs with lower emissions. After initial design development, Navtek turned to technology solutions partner BMA Technologies to get the development project underway,” says Navtek general manager Ferhat Acuner.
“One of our young design engineers suggested an all-electric battery-powered solution, a proposal that was greeted with some scepticism at first,” he says. “However, he convinced us to conduct a full study, and despite doubts about the technology’s ability to be applied to this type of vessel, final calculations proved otherwise.”
Gisas Power was built at TK Tuzla Shipyard to Zeetug30 design and delivered at the end of 2019. It has 18.7-m overall length and 6.7 m beam. “The main challenge was the sheer scale of the electrical power required to enable the tug to deliver the minimum 30 tonnes bollard pull,” says Mr Acuner. Another challenge was that using conventional variable speed drive technology would have taken up more space than was available on the tug.
To overcome this challenge, BMA Technologies approached ABB for technical support. ABB found a mobile drive from heavy-duty industrial applications was the solution, with liquid-cooled drives to fit within the tug’s limited footprint, providing the power needed for the 925-kW propulsion motors driving the thrusters.
Power for ship escort
Tugs employed for ship escort need to have sufficient power, stability and performance to manoeuvre large ships entering terminals.
Robert Allan principal and director of project development Jim Hyslop says terminal tug power ranges from 2,000 kW up to 4,000 kW per engine, according to the size of the ships they are handling. Some 28-m tugs have a bollard pull of 65 tonnes, while others in the global fleet range up to 42-m, with 120 tonnes of bollard pull.
Other features of escort tugs for safety, stability and performance are “good ergonomic design for visibility and access,” says Mr Hyslop, “plus suitable beam and vessel centre of gravity values, escort steering and braking performance.”
Naval architects need to evaluate and verify these features and parameters using 3D computer modelling and computational fluid dynamics (CFD). “Performance is evaluated in CFD to meet customer requirements,” he says.
If tugs are deployed to manoeuvre gas carriers into LNG terminals, they would have suitable deck machinery such as electrically driven escort winches. “Typically the requirement is for electrical equipment to be explosion proof for Class I – Division 2,” says Mr Hyslop.
Robert Allan’s designs for escort tugs is the RAstar series, as originally developed for the requirements of the Abu Dhabi Petroleum Ports Operating Co. “They were intended to set a new standard of performance and safety for escorting large ships carrying dangerous cargos,” says Mr Hyslop. “They have evolved over time into the de facto standard for escort tugs at petroleum terminals worldwide.” Its latest deliveries of these escort tugs were Thor of Scapa and Odin of Scapa, built by Sanmar to a RAstar 3200-SX design to handle tankers at the Flotta terminal in Orkney, Scotland.
*Erik van Schaik and Giulio Tirelli answered questions posted during Riviera’s Hybrid and electric tug viability: the future’s bright webinar, September 2020
Shallow draught tug variant unveiled
Robert Allan developed a shallow draught variant of its RAmparts 3200 design for Med Marine in response to a request for a harbour tug with a draught of less than 5 m to enter ports in Israel.
Med Marine went on to build 31.5-m tug Hadera at the Eregli Shipyard for National Coal Supply Corp (NCSC)’s fleet operating in the port of Hadera. Robert Allan provided a RAmparts 3200-SD design for a MED-A3280-SD-class tug that could also operate in shallow and difficult waters, such as rivers.
“Thanks to Robert Allan’s expertise, we were able to build this lower-draught MED-A3280-SD-series tug with full performance capabilities,” says Med Marine business development chief Eylül Turhan. “Besides limited draught requirements, NCSC’s request for noise levels even lower than IMO regulations enabled us to improve the tug further with tailored design revisions.”
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