Experts from Svitzer, Rolls-Royce Solutions and Robert Allan Ltd explained why biofuels and methanol are important fuels for tugboats
Rolls-Royce Solutions is developing methanol-combustion engines for tugboats and other maritime applications following studies to determine the most cost-effective decarbonisation solution.
In a technical presentation at ITS 2022, Rolls-Royce Solutions director for applications in marine engineering Tobias Kohl explained how the company made this decision while working with Svitzer on future propulsion technologies.
He said Rolls-Royce’s mtu engine range will be approved in 2023 for combusting biofuels and sustainable renewable fuels, such as hydrogenated vegetable oils (HVO).
“In the short term, we are focused on emissions optimisation from diesel engines through engineering hybrid propulsion systems, and through the qualification and approvals to use sustainable fuels, such as HVO,” said Mr Kohl.
By 2026, Rolls-Royce expects to have developed a methanol-burning mtu engine for tugboats, which will reduce carbon emissions.
These engines could be developed from mtu 4000 Series diesel or gas-burning engines that Rolls-Royce already supplies for new tugs. “Our cylinder tests have been successful, and we are currently developing mtu 4000 Series methanol engines,” he said.
These engines will comply with the latest IMO Tier III and US Environmental Protection Agency Tier 4 emissions standards for minimal SOx, NOx and particulate matter. “With methanol, there is no need for selective catalytic reduction or particulate filters,” Mr Kohl said.
Rolls-Royce plans to further decarbonise tugs by developing hydrogen fuel cells for integrated propulsion systems and expects to have them validated by 2030.
“In the long term, we need to work towards overcoming the challenges associated with hydrogen and fuel-cell integration to improve the feasible usage of decarbonised fuels,” said Mr Kohl.
For the medium term, Rolls-Royce’s focus is on developing combustion engines and hybrid propulsion.
“As a result of the tug study, it is clear to see the benefits of combustion engines systems, both diesel and methanol, compared with fuel cell and battery systems today,” he explained, as engines “have low volume requirements, low system weight and low capital expenditure.”
Mr Kohl expects the costs for green diesel and green methanol to remain relatively high in the short to mid-term. Hence, “battery-powered tugs have the potential to gain market share, but only if operators are able to live with reduced operational requirements.”
For more flexibility, tug owners could consider biofuels now and methanol to fuel tugs in the future. Methanol can also provide the hydrogen source for fuel cells when they are available.
Fuels versus batteries
Svitzer group head of technical innovation Thomas Bangslund spoke about balancing propulsion selection, the tug operating profile, infrastructure and operational realities.
“The current flexibility of tugs in terms of operation and location might need to be sacrificed, especially when thinking about hydrogen and battery propulsion,” he said.
“Batteries would be efficient for propulsion, but there is not enough power in the grid and not enough infrastructure for fast and timely charging.”
In the future, tugs will need to be design-optimised for the intended operating location and operational profile.
“A redeployment will only be possible if the fuel infrastructure is available at the new location, and if the operational requirements are similar,” said Mr Bangslund.
For these reasons, Svitzer is not planning to invest in battery-powered tugs as it constantly redeploys harbour and escort tugs between ports and operating regions.
Mr Bangslund said Svitzer already uses HVO extensively in the UK and is starting to adopt this in the European fleet. Svitzer is also considering using methanol in combustion engines and is designing a new concept for its tugboats.
Innovative design
Svitzer worked with Robert Allan Ltd (RAL) to design the TRAnsverse tug with a unique towing arrangement, increased stability and enhanced manoeuvrability.
“The idea for the tug started with an innovative new type of towing staple that would allow for 180˚ free movement of the tow line while also generating a high righting moment,” said Mr Bangslund.
“This allows the tug to safely generate high steering forces without compromising the stability of the tug.”
This is then coupled with the concept of a double-ended tug to enhance the capabilities of the overhead guide staple with increased manoeuvrability. This design could be scaled for all types of harbour and terminal operations, especially ship escort.
Robert Allan Ltd director of project development James Hyslop explained how the initial design was analysed and redefined through model testing.
The Canadian naval architects developed 3D computerised and physical models for thorough assessment, using finite element modelling and computational fluid dynamics.
RAL then used HSVA’s ship modelling basin in Hamburg, Germany to “determine which hull appendages would give the best performance and also the optimal placement of the new staple,” said Mr Hyslop.
“Dual shallow side skegs were found to be the most efficient setup for this design, for directional control versus side-stepping performance,” he explained.
TRAnsverse tug was optimised for four basic operational modes in harbour towage and ship escort. These were push-pull on a ship’s side; centre-lead forward; centre-lead aft and indirect escort pull at speeds between 6 to 12 knots.
“TRAnsverse tug can push transversely on the moving assisted vessel at higher power levels than an equivalent azimuth stern drive tug,” said Mr Hyslop.
“Side pushing can be accomplished with the tug at any angle to the ship. TRAnsverse can easily escape from the suction force generated between tug and ship at speed. It can be quickly and easily positioned without imparting unwanted towline forces.”
TRAnsverse tug can be used for bow-to-bow operations, direct and indirect breaking and steering when escorting ships and direct pull steering.
“Its double-ended design allows for easier positioning and higher margins on manoeuvrability in the event of single drive failure,” said Mr Hyslop. “Omni-directional propulsion allows for safe, quick and easy transitions from one mode to another.”
Challenge ahead
Svitzer head of decarbonisation Gareth Prowse explained how the Maersk subsidiary plans to achieve its ambitious decarbonisation targets, with the TRAnsverse tug one of the strategy components.
He said the scale and challenge of the task of getting to zero carbon emissions is huge as there is a global fleet of around 20,250 tugs, almost all running on diesel.
“We need to find ways to change the fleet and use alternatives to reduce carbon emissions,” said Mr Prowse.
Svitzer alone operates 435 vessels in 32 countries and produces around 280,000 tonnes of CO2 annually.
He does not expect the tug industry as a whole, or Svitzer, to be able to decarbonise these fleets through newbuild investments. “The global fleet will need 715 new tugs per year to meet the 2050 target,” he said. Svitzer would need to order 24 new tugs each year, where it currently takes delivery of around 10 per year.
“We cannot build our way to be carbon neutral by 2040; we need to look at different fuels,” said Mr Prowse. “There will be increasing costs as low-emissions tugs come with higher price tags.”
Svitzer is pushing ahead with its decarbonisation strategy on three fronts. It is changing the behaviour of its crews to reduce emissions during transits and towage, and is investing in the TRAnverse tug, with the first under construction by Sanmar in Turkey.
Svitzer is also investing in new fuels, such as HVO now and methanol in the future.
“We are working with suppliers for sustainable tugs and are committed to a 50% reduction in carbon intensity of the fleet by 2030,” said Mr Prowse. “And then being fully carbon neutral by 2040: it is a big challenge.”
Being an early adopter brings advantages, such as being ahead of potential regulations such as the European Union’s Emissions Trading System, which could cover vessels over 300 gt in future years. But there are investment risks and the potential for making an incorrect decision.
“If owners wait, then there may not be enough time to adapt quick enough to meet regulations, so we need to act first,” said Mr Prowse.
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