#Industry News
Staying stable in icy waters
With sea ice melting and vessels venturing deeper into polar regions, rapid advances in stabilising technologies are required
When National Geographic’s Endurance ventures deeper into Russia’s Arctic waters than any previous cruise ship on its maiden voyage in 2020, it will bristle with ice-class technology, including a full array of stabilisers that combine with Ulstein’s X-Bow to inhibit yaw and rolling.
The vessel will become just one of two high-end cruise ships to tackle the route – but more are certain to follow.
As more ice melts, the gradual opening of the Northern Sea Route (NSR) is stimulating demand for rugged technology that can withstand the extreme temperatures, inevitable encounters with ice and slow-steaming.
LNG carriers, container ships, general cargo ships and cruise ships are undertaking voyages into these and similar waters that were long considered out of bounds for anything but specially equipped naval vessels; most of them submarines ghosting below the pack ice.
Among other passages, Chinese shipping giant Cosco has completed five, largely exploratory, transits of the NSR, according to a mid-2019 study by Ecory on behalf of the OECD’s International Transport Forum. The first Cosco vessel to trial the route, Tian En, carried a cargo of wind turbines on a sometimes challenging voyage in late 2018. “After all the ice-zones and storms, we made it,” the ship’s master Chen Xiangwu told reporters. The Arctic route chopped about a third off the Suez route and saved 300 tonnes of fuel.
A few days later, container ship Venta Maersk, one of Maersk Line’s new Baltic feeders, called at the port of Saint Petersburg after completing a trial passage from Vladivostok to Bremerhaven. Icebreakers had to be called in to get the vessel, one of the biggest ice-class ships, through the East Siberian Sea.
The attraction of the NSR for cargo-carrying vessels is that it slashes travel times by about 40% compared with the southern route, which takes vessels through the Suez Canal. As the OECD study estimates, a voyage from Hamburg to Yokohama through the Suez Canal, travelling at an average speed of 15 knots for the 11,585 nautical miles, takes 32 days. That compares with 14 days for the 7,356 nautical miles of the NSR at an average speed of 14 knots.
The maths seems obvious. Yet the NSR comes with its own costs. In this highly sensitive environment where pollutants take much longer to be absorbed, specialised fuels are required, reducing the apparent saving in running expenses. Insurance rates and other costs can be three times higher than taking the longer way around. And, points out the study, “initial investment in ice-class vessels is 20-30% higher compared to a benchmark vessel.”
Nor can the route be used year-round. As the study explains: “Yearly variations of sea ice are relatively unpredictable. Ice massifs [effectively mountains] might block certain routes. And extreme weather conditions such as fog and extremely low temperatures [are probable].” Additionally, the draught varies considerably in certain areas such as Dmitry Laptev, where it can get as low as 6.7 m, making it unsuitable for bigger vessels.
Given the constraints, nobody is predicting that the NSR will compete with the Suez Canal at any time before the middle of the century, if at all. But unless the ice of the last few centuries returns, the passage will certainly get busier, boosting demand for stabilisers and other ice-class equipment. “We expect an increasing number of transits and local sea trips in the NSR area, with relatively small vessels aimed at niche markets,” the study says.
But ice-thick routes like the NSR will continue to excite interest for expeditionary voyages. When Ocean Victory, Sunstone Ships’ latest Infinity-class vessel, is delivered in March 2021 by builder China Merchant Heavy Industries, one of its most important technologies will be the latest version of Rolls-Royce’s zero-speed stabilisers. Designed to operate in ice-class 1A conditions, the stabilisers are proving themselves on a wide range of vessels operating in the Arctic and Antarctic, such as Poseidon Exhibition’s Sea Spirit, which was retrofitted with zero-speed versions in mid-2019 for cruises in the Greenland and Barents seas.
Stabilisers are mandatory for those times when a vessel is slowed, moored or anchored in the kind of scenic conditions for which guests are paying, as well as for environmental reasons. At slow or zero speeds, fuel consumption and emissions are dramatically reduced but the overriding reason is the purpose for which the technology was originally intended, namely stability.
Taking the plunge
That is why the Royal Australian Navy took the plunge in early 2019 on an innovative Quantum stabiliser for its new offshore patrol vessels under construction by Luerssen. Patrol vessels need to operate at slow and zero-speed, for instance when coming alongside.
Since its establishment in 1985, Fort Lauderdale-based Quantum has taken a left-field approach to the stabilising function. A few years ago, Quantum’s marine engineers, naval architects and its hydraulic technology were put to work on a motion control system that operated at low speeds: effectively, a stabiliser for loitering and dead stop. The result was MAGLift; not the traditional fin but a rotor stabiliser that swings and spins cylinders in the desired direction.
A hit with the military, commercial and private yacht market, MAGLift was also installed on the National Geographic’s 72 m Venture and several other similar-sized vessels. The general configuration was for a set of fins forward with the rotors mounted aft. “This provides superb stability for zero-, slow- and higher-speed requirements,” said business development manager Katie Ross.
For ice-class conditions, MAGLift can be retracted or pocketed. The rotors are also placed strategically below the ice belt.
Quantum’s latest development, Dyna-Foil, is a dual-purpose design based on a foil shape that is claimed to work equally well at zero speeds and underway. Fully retractable like MAGLift, Dyna-Foil was developed with extreme ice-class conditions in mind. As the company explains, these are conditions where “the stabiliser is required but needs to be completely stowed to avoid potential damage from contact with any ice.” Thus for ice-class vessels or those with a high block coefficient where externally mounted appendages would not be suitable, the system comes with a “fully pocketed” version.
Dyna-Foil creates its own forces through the swinging action of the unit. “This action creates water flow over the surface of the foil, thus generating lift,” the company explains. “The direction of swing determines the direction of lift force generated. Both the angle of attack and swing speed are controlled variables that are adjusted to provide the optimum stabilisation.”
A lot of research went into the profile of the foil itself. It was shaped to provide the maximum amount of lift at low angles of attack, which has the effect of reducing drag. The positioning of the foil to counter the vessel’s rolling motion is almost instantaneous. When the vessel is underway, the foil is angled at 90 degrees to the centre line of the hull.
Quantum maintains that the system is superior to the traditional fin technology (although that has been much refined in recent years): “The stabiliser moment generated by the Dyna-Foil is up to 150% greater than those [generated] by a standard fixed fin at zero speed of the same size.” The heart of the system is the 5000 Series algorithm-controlled unit that, says Quantum, will eventually be incorporated in all the designs. For its Dyna-Foil, Quantum developed a compact hydraulic unit built around stored energy accumulators and variable motor control; a system that imposes less demand on the vessel’s overall energy supply.
Attention on activators
Meanwhile, the activating system on stabilisers – effectively the engine – is receiving a lot of attention. For its Aquarius 100 retractable stabilisers, Rolls-Royce could be moving towards electric motors rather than hydraulic units. As head of sales for Rolls-Royce Dunfermline Paul Crawford told Marine Propulsion earlier this year: “There is less maintenance needed and less equipment. I see this used especially within ferries in the future as many are becoming electric.”
Although not a ferry, ice-class, 110gt Dutch tug Astra has been retro-fitted with an electrically powered MagnusMaster system based on rapidly rotating cylinders. (The name derives from the Magnus Effect first investigated by German physicist Heinrich Magnus.) Suitable for vessels up to 30-m long, MagnusMaster has been installed on a wide range of ships, including trawlers. Useful for workhorse vessels, when the engine is put in neutral, the rotors immediately retract.
According to MagnusMaster: “The biggest advantage of a rotor system in comparison to a fin-driven conventional system is the greater roll-dampening at lower speeds.”
In the near future, manufacturers of stabilisers may start booking orders from international navies because of increased military activity in polar regions, especially in the Arctic. After a long absence by NATO forces, there is pressure to resume patrols in response to the growing presence of the Russian navy.
And as the West responds to the Russian threat, with more navy operations likely to take place in the North Atlantic, the implications for ice-class technologies such as stabilisers look promising.
- The stabiliser that doesn’t get wet
Unlike most other systems, Perth, Australia-based Veem’s marine gyro stabiliser is bolted inside the hull, not outside it. Lacking any appendages, the gyro stabiliser does not come into contact with the water at all (except that it is cooled by seawater). Yet “roll motion can be virtually eliminated at all speeds including zero,” says to Veem’s product manager Paul Steinmann.
The gyro stabiliser is not designed for cruise ships, but for smaller and nimbler vessels between 65 and 3,000 or more tonnes such as tugs, sport fishing boats, patrol boats and offshore support vessels. The technology is considered particularly suitable for walk-to-work situations. And, adds Veem, the efficiency of the technology is such that it opens up a range of headings because it means the vessel can better handle quartering seas.
The operating principles are based on a spinning fly wheel. When the vessel rolls, it triggers the flywheel to rotate in the axis of the vessel’s movement. The result is known as ‘precession motion’ (not precision) that, combined with the spinning flywheel, creates what is known as ‘stabilising torque’. In short, the vessel stops jumping around.
And, further unlike standard hull-mounted stabilisers, gyro stabilisers can be installed just about anywhere – off the keel line, high or low, forward or aft, depending on the trim of the vessel. The system will also work in combination with other stabilisers, such as flume tanks and fins.
