When the cruise ship industry adopts hybrid-powered propulsion, it is a clear indication that the future lies in batteries married to hydrocarbon-fuelled engine systems

In 2018, Norwegian operator Hurtigruten signed Rolls-Royce to start a massive retrofit job of its fleet, that will see at least six cruise ships converted to LNG and electric power. Soon, Hurtigruten will launch the first of two expedition ships that can run for up to one and a half hours purely on batteries.

Commenting on the project, Hurtigruten chief executive Daniel Skjeldam said: “This is an investment for the future, and a historic day for us, for the environment and for the whole, 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.”

Mr. Skjeldam has run the numbers. According to Hurtigruten, fuel consumption and emissions on the expedition ships will fall by about 20%.

Rolls-Royce has supplied the power plants – four electrically adapted, medium-speed Bergen-class B33:45 engines – for the expedition vessels. “In the next few years batteries will drive larger vessels for longer distances,” says Rolls-Royce vice-president of power electric systems John Roger Nesje.

And Scandinavia could be the catalyst. The pressure from environmentally conscious authorities in the region is becoming so great that most ferries in these waters will likely be updated with cleaner propulsion in the near future.

Norway is a case in point. DNV GL senior consultant for environmental technology and compliance Martin Christian Wold predicted in a technical article released in May: “DNV GL expects no new LNG-fuelled vessels to be ordered for the Norwegian trade. In fact, some existing LNG ferries will be retrofitted for electrical or hybrid propulsion.”

Wold’s conclusion is based on a tender for new ferries launched recently by the county of Hordaland, famous for its many fjords and islands. The tender was framed in a way that put a high weighting of 30% on clean propulsion; thus it had the unexpected effect of only attracting bids for all-electric ferries.

“We expected some degree of electrification on most ferry connections but we were surprised about the high degree of electrification we ended up with,” says Karl Inge Nygard, leader of the legal department in Skyss, the agency that organises public transport in the county.

The result of the tender is that more than US$1Bn will be spent on fully electric vessels and other low-emission onboard technology, in the form of automatic mooring systems, and onshore where buffer batteries will be installed on ports.

The tender has also put pressure on the operators of existing ferries in Norway – and inevitably in other Scandinavian countries – to cut emissions as quickly as possible. In Hordaland, as classification society DNV GL reports, there are 20 ferries with an average age of 29 years that between them “emit as many noxious fumes as all the buses of the county combined”. Because current ferry contracts expire between 2018 and 2020, most of these operators will have to start putting aside a retrofit budget.

It is unlikely however that Norway’s ferry fleet will go all-electric overnight. In a technical paper released late last year titled Hybrid propulsion is part of the future for RoPax ferries, Wärtsilä noted that hybrid-powered ferries, especially ropax vessels that require more grunt, will figure prominently among the 30 predicted additions to the fleet over the next few years. As the company explained though, these will be plug-in hybrid ferries.

Driving four-stroke

The rapidly accelerating shift to four-stroke hybrid propulsion is a product of several forces that are spreading outwards from specifically regulated areas, such as Norway’s fjords. Quite apart from emissions, clattering diesels are becoming unpopular in a growing number of ports, natural reserves, special marinas and other low-noise areas.

But the shift to quieter and cleaner four-strokes could not happen without advances in battery technology. Switzerland-based battery maker Leclanché has, for instance, devised increasingly high-capacity and versatile diesel-electric systems for a variety of ships, including work boats such as tugs and cargo vessels, where the extra short-term grunt delivered by batteries is good for pulling and towage. It is also good for peak-shaving – load management that reduces running costs.

Leclanché chief executive Anil Srivastava enthuses about “the huge opportunity for marine vessels across the world to reduce their harmful emissions and cut their operating costs by leveraging battery storage technology.”

The group’s latest technology is a Marine Rack System – a ready-to-sail product that is scaleable in size and capacity, rated to 1,000 volts, liquid-cooled, and available with either water mist or foam-based fire-fighting systems.

Complete package

In Finland, Wärtsilä has come up with a complete hybrid package that the group believes is a world first. Named Wärtsilä HY, it integrates engines, energy storage and power electronics. All three are linked up with a new energy management system and when the system is operating in so-called “green mode”, there are no emissions whatsoever.

Already the recipient of a stamp of approval from Lloyds Register, Wärtsilä HY has been developed with an eye firmly on the future. “There is a notable trend in the marine sector towards hybrid propulsion solutions,” its engineers stated in the above-mentioned technical paper. “These are anticipated to represent a significant percentage of all contracted ships within the coming 10 years.”

Wärtsilä plans to roll out dedicated versions of the system for every category of vessel, but the group is starting with tugs and medium-sized ferries. The first customer for the Wärtsilä HY package is Italian tug owner and operator, Rimorchiatori Riuniti, which expects to launch its new hybrid-powered vessel in early 2019.

Getting in early

Planning for hybrid newbuilds must begin early, partly because the rate of development in electric power is so rapid that allowances for future technology need to be made. “As new energy sources and propulsion developments evolve, the future demands and possibilities should be taken into serious consideration during the planning of newbuild ferries,” said Wärtsilä.

As regards larger ferries, Wärtsilä does not expect traditional four-stroke engines to be rendered obsolete any time soon. “As a basic configuration, we see that in transit operations the most efficient [system] is with direct mechanical propulsion,” the paper’s authors conclude. “However when manoeuvring or operating at low loads, it is normally more efficient to run with electric power.”

As an example of an effective hybrid solution, Wärtsilä proposes two 12-cylinder Wärtsilä 31 dual-fuel engines, each with two-speed reduction gearboxes. (As an aside, the Guinness Book of Records judged the Wärtsilä 31 to be the world’s most efficient four-stroke engine at its release in 2015.)  To this combination is added a power take-in/power take-off (PTI/PTO) system.

Combined, this configuration gives available propulsion power of 10 MW on each propeller. The result is that the vessel runs at normal service speeds under main engines alone, while the PTI/PTO units supply power for the other onboard consumers, using the PTO as a generator. However, the PTI/PTO units serve as the connection to the vessel’s electrics, including the batteries.

The auxiliary engine set-up is built around one eight-cylinder Wärtsilä 31DF (for dual fuel) and one nine-cylinder 20DF. Between them, they act as generating sets for the ship’s hotel load, doubling up as extra propulsion power for low-load operations via the PTI, and for charging the batteries. Three tunnel thrusters – two in the bow and one aft – do the rest.

Charging up

While engine manufacturers have been hard at work on hybrid propulsion, there has also been rapid progress in port-side recharging systems, where the main challenge is to reboot the electrics as quickly and smoothly as possible. The technology has moved from complicated and time-consuming plug-and-charge all the way to a Bluetooth-like wireless system that delivers the juice without any physical contact between the vessel and the charging unit. The system works even if there is a half-metre gap between the charging unit and the vessel.

None of these technologies were even on the horizon a few years ago. The rapid progress made since then shows where hybrid power is heading and how quickly it is likely to get there.