Smooth, fast, quiet and almost vibration-free. That is, the latest trains running on hybrid diesel-electric power packs – and the maritime sector is taking note.
At first sight propulsion systems for trains do not appear particularly relevant for the maritime sector, but battery-powered drives are rapidly changing that view as shipowners opt for plants that reduce noise and vibration. And, increasingly, that is electric.
One manufacturer that, pinning its faith on batteries, spans the divide between rail and sea is MTU. “Electric motors and hybrid drives from MTU are set to be a core component of mobility in the future when it comes to marine propulsion and rail drives,” predicted the head of MTU’s marine and offshore application centre, Stefan Müller, more than two years ago.
It turned out to be a prescient observation. The Friedrichshafen-based group had just unveiled its Hybrid PowerPack for railcars, a quieter and more passenger-pleasing plant. Since then MTU has developed marine versions, sometimes for bespoke projects such as the high-speed 50-m yacht Nova Hybrid.
Propelled by twin MTU 12V 2000 M61 units that deliver 1,200 kW with the assistance of two electric motors, each pumping out 110 kW, this highly innovative, aluminium-hulled vessel has raised the bar in noise reduction. With the main plants turned off, the yacht can cruise at a highly respectable 9 knots in almost complete silence.
It is not quite like running on rails but close enough.
As the benefits and virtues of electric power become increasingly important, especially in the growing number of emission control areas (ECAs), MTU is booking more orders for its E-Drive propulsion systems. Its production hybrid propulsion units are of a modular and versatile design, covering electric power ranges of 100-600 kW per power train.
What works for rail does not necessarily work for ships, however. For instance, MTU’s Hybrid PowerPack is built on no less than 180 individual lithium-ion batteries weighing 360 kg. The marine application has two battery versions that are tuned to the vessel’s requirements.
Silent in the Antarctic
Although for reasons other than just silent sailing, Norwegian ferry company Hurtigruten is in the middle of a progressive conversion of its fleet from diesel-fuelled to hybrid gas-electric drive trains. Reduced noise and vibration are of course a benefit of installing Rolls-Royce’s B36:45 LPG power plants, but the overriding reason is to cut emissions in one of the original ECAs along the long Norwegian coastline.
“The combination of battery packs with the most environmentally friendly and effective gas engines in the market will provide a huge gain for the environment,” Hurtigruten chief executive Daniel Skjeldam said at the time.
For its new fleet of ice-class cruise ships Hurtigruten is going a step further. The first of the class, Roald Amundsen, was launched in July. Although relying on Rolls-Royce’s B36:45 gas-powered engines, which are calibrated to vibrate less, even under heavy loads, and emit less structural noise, the vessels will resort where possible to ‘soundless sailing’ under nothing but electric power. In fact, in its launch month Roald Amundsen became the first-ever cruise ship to sail purely on battery power.
The batteries are a sign of things to come. The two 627 kWh battery storage systems built by Corvus Energy are only the start. Mr Skjeldam predicts that within a couple of years Roald Amundsen’s engineroom will get a massive extra 7.1 MWh out of the batteries. The fuel savings are not insignificant either – Hurtigruten expects the hybrid system to save about 20%.
Given the storm of activity in batteries, notably in Asia and the USA, that is a reasonable assessment. According to research by McKinsey, the rate of advance in battery storage is off the scale. Just five years ago, they could store about 3 MW. Two years ago, storage had shot up to 40 MW, then in 2017 to nearly 70 MW. All this is happening while costs have plummeted – from US$1,000 per kilowatt hour in 2010 to US$230 in 2016 in the latest available figures.
As its power increases and cost decreases, it is inevitable that electric power will assume a bigger role in the engineroom of all kinds of vessels. Also presciently, it was none other than Roald Amundsen, the great Antarctic explorer, who foresaw 137 years ago that an electrically powered ship would sail to the frozen wastes.
As the technology of electric drives has improved, quiet, low-vibration sailing has become an important marketing tool – but it is not always down to the drive system. Baleària’s third LNG-fuelled high-speed catamaran ferry, Eleanor Roosevelt, is to be launched on the Mediterranean in 2020. The Spanish shipping company worked with Australia’s Incat Crowther to come up with a next-generation shape that makes light work of the waves and keeps passengers in comfort.
According to Baleària, the 123-m hull features “behaviourial enhancements”, primarily in the form of third central hull that houses a retractable T-foil. “The shape of the ship was specially designed to considerably reduce vertical acceleration for more comfortable journeys by lowering vibration and noise to unprecedentedly optimal levels,” the ferry company says.
Similarly, Ulstein’s X-Bow design is another example of how the shape of the hull can assist – or even exceed – the capacity of the driveline in cutting vibration and noise levels. The latest commission of an X-Bow ship, now running to more than 100, is for Lindblad Expeditions, working with National Geographic. The 124-m polar vessel will be launched in 2021.
As Ulstein says, the shape is the reverse of a conventional bow because it leans backwards instead of forwards. “An X-Bow vessel cleaves the waves, significantly reducing noise and vibration.” Also, not insignificantly in view of IMO regulations about providing a good working environment for crew, Ulstein says the design “is more comfortable for the crew,” mainly because there is much less slamming.
And sometimes it is not just the noise that passengers hear that driveline manufacturers must take into account. In Ontario, Canada, Blue Heron Cruise’s latest ferry has been proving the value of a high-speed engine mounted on the equivalent of shock absorbers – pre-engineered rubber mounts designed to cut vibration and noise in Unesco-designated Bruce Peninsular. Here environmental restrictions are also measured in the amount of decibels clocked by the local community living along the shore. The ferry can hit 40 knots.
And sometimes a ship has to run silently for machines – and fish. The latest vessel to qualify as a DNV GL-certificated Silent-R ship is the Ocean University of China’s 103-m Dong Fang Hong 3, a research vessel powered by Caterpillar’s MaK engines mounted on what the manufacturer describes as “double-resilient mountings, a two layer system [that] isolated our machinery from the engineroom floor at its best.”
As a result, the oceanographic survey vessel can run in almost total silence so that sensitive on-board machinery is not disturbed and the fish are not scared off. The technical term is “underwater-radiated noise.”
Incidentally, there are differing classifications of noise and vibration. According to DNV GL’s three standards, they run from ‘comfort class’ (high to acceptable related mainly to passenger comfort including noise, vibration and indoor climate), ‘vibration class’ (a more technical standard based on vibration levels in machinery, equipment and structures) and ‘silent class’ (also technical, it relates to ‘acoustically sensitive vessels with a low eco-footprint’ such as Dong Fang Hong 3).
So low-noise and low-vibration vessels keep passengers, crew and fish happy.