The Ambitious ELLEN

ELLEN´s 4.3 MWh battery pack enables the ferry to sail back and forth between Søby and Fynshav in the Funen archipelago in southern Denmark. That is two times 10.7 nautical miles, with spare capacity in the battery pack, e.g. for a search and rescue or a man overboard situation.

This makes ELLEN the 100 percent electric-powered ferry with the longest reach in the world. This reach should also be seen in light of the 100 percent electric operation, as opposed to hybrid operation. This means that ELLEN has no combustion-based propulsion on board – nor a diesel emergency generator.

Prior to the commissioning of Ellen on 15 August last year, the record as a 100 percent electric-powered ferry was held by the Norwegian shipping company Norled, with their double-ended ferry AMPERE. This ferry has a 10-ton 1 MWh battery pack and two 450 kW propulsion engines for a range between charges of 3.2 nautical miles.

Achieving such a long reach, in parallel to introducing new technology such as pure electric operation of a larger ferry, was an ambitious goal. Therefore, the focus was not limited to all this new technology, but to a great extent also comprised good old-fashioned naval architecture craftsmanship.

Therefore, the idea of designing ELLEN as a double-ended ferry, meaning a design with an identic bow and stern and a wheelhouse to be used for sailing in both directions, was quickly abandoned. That design is an ideal solution for port calls since it saves time and energy on manoeuvres, but it is also a solution with many hydrodynamic compromises in relation to hull efficiency while sailing.

The majority of the ferry types to which ELLEN belongs are of the double-ended type. But ELLEN needs to have a service speed of 12 to 14 knots in order to maintain the desired schedule. That is 2-4 knots faster than what is usually considered the optimum speed with a double-ended hull.

ELLEN’s designer, the Danish Ærø-based naval architect Jens Kristensen, did not just design a typical modern single-ended hull, instead he chose to turn back the clock. This seems almost paradoxical, as ELLEN was also built as a world record in the rapid development race in the field of electric-powered ferries.

He was thus inspired by specific hull lines on former Ærø ferries all the way back in the 1950s and 1960s. As he put it, they were simply better at building small, slim ferries back then, which easily sailed 13-14 knots with limited machinery.

According to him, one reason for this is the important role played by the extremely slim hulls of the great ocean liners of the 1950s and 1960s in the minds of contemporary naval architects. This was later replaced by a focus on capacity.

In fact, when comparing the ferries of the ferry company Ærøfærgerne, which operates ELLEN, you can clearly see the outcome of drawing on the past for innovation – as in the case of ELLEN.

When Ellen sails 13 knots in fair weather, the output is 800 kW. But when one of the ferry company´s two sister ferries, ÆRØSKØBING and MARSTAL, sail under the same optimum weather conditions and at the same speed, they require 2,000 kW, which is the maximum output of the ferries. By comparison, ELLEN´s full output is only 1,500 kW, and if utilised, her speed would be 15 knots in good weather conditions.

To be fair, one should consider that the two sister ferries have space for 42 cars, compared to Ellen´s 31, but the score is still by far in favour of the new electric-powered ferry. Thus, for ELLEN, the ratio of kilowatts per passenger car is 25.8, while it is 47.6 for the 20-year-older fleet sisters.

They are therefore typical examples of ferries that were built at a time when energy efficiency was not yet highly prioritised in the design of new ferries. However, the wind shifted later with the shipping industry´s focus on reducing its carbon footprint – the same wind that is also driving the electrification of ferries.

ELLEN´s design was primarily due to a number of rational decisions. Subsequently, efforts were made to make the ferry look good. While the focus below the waterline was to have a very slim and efficient hull, the ferry design above the waterline was also characterised by a focus on energy efficiency, which contributes to ELLEN being a record-setting electric-powered ferry.

Here, the focal point was weight, and therefore, the ferry does not have an upper enclosed superstructure. The width of the passenger lounge on the main deck corresponds roughly to the total width of the two side casings on the two sister ferries, ÆRØSKØBING and MARSTAL. This means that the solution onboard ELLEN does not actually occupy more space on the car deck, which saves weight.

This solution also eliminates the need for an elevator, as the passenger lounge is at the same level as the car deck. It also greatly facilitates an easier evacuation and thus reduces the size of the crew. Finally, the open car deck eliminates the need for ventilation on the car deck and also for an inner ramp behind the bow visor – thus two more areas where weight can be saved.

Ellen´s lightweight was originally projected at 706.5 tonnes. However, the weight was exceeded by more than 40 tons during the construction of the ferry. Apart from a marginally greater steel weight, the excess weight was due to a number of newly developed systems for electric-powered ferries, such as foam extinguishing, cooling water and sprinkler systems for batteries and battery compartments.

These systems obtained type approvals very late in the construction process, and thus the weight and dimensions of the systems were only known late in the construction process. Additionally, the amount of cables and electrical components increased considerably compared to what was known at the beginning of the project.

When the E-ferry project started back in 2015, the plan was to use lightweight fibre-reinforced composites in the ferry superstructure to save additional weight. However, this proved difficult since ELLEN, to the greatest extent possible, had to be built in accordance with the SOLAS regulations in the EU-funded project. This would enable the concept of ELLEN to be exported to other ferry crossings in the EU.

Facts – ELLEN

• Call sign: OWJQ, Søby
• Type: Ro/ro passenger ferry
• Owner: The Municipality of Ærø
• Operator: Ærøfærgerne
• Shipyard: Søby Værft, Søby
• Yard number: 107
• Delivered: August 2019
• Design: Jens Kristensen Consulting Naval Architects
• Classification: DNV GL
• Notation: 1A1 Car ferry B Battery(Power) E0 Ice(C) PWDK R3
• Length o.a.: 59,5 m
• Length: b.p.: 57 m
• Beam mld: 12,8 m
• Gross Tonnage: 996
• Netto Tonnage: 299
• Deadweight: 192 tons
• Lightweight: 747 tons
• Trucks: 4 + 8 cars
• Cars: 31
• Passengers: 196 (summer) 147 (winter)
• Main machinery: 2 X Danfoss/Editron electric motors, each 750 kW
• Battery pack: Leclanché 4,3 MWh, approx. 56 tons
• Max speed: 15 knot
• Service speed: 13-14 knot
• Municipality payment: approx. 110,000,000 DKK
• Total building cost incl. port facilities and incl. EU funding: 224,000,000 DKK

About ELLEN and the project behind

• E-ferry is a project supported by the European initiative Horizon 2020 involving the design, building and demonstration of a fully electric powered ‘green’ ferry which can sail without polluting and CO2 emissions. It promotes energy efficient, zero GHG emission and air pollution, free waterborne transportation for island communities, coastal zones and inland waterways in Europe and beyond. 
• Τhe overall objective of E-ferry is to apply an extremely energy efficient design concept and demonstrate a 100 percent electric, emission free, medium sized ferry for passengers and cars, trucks and cargo in full-scale operation on longer distances than previously seen (> 5 nautical miles (Nm)) for electric drive train ferries, i.e. the medium range connections Søby-Fynshav (10.7 Nm) and Søby-Faaborg (9.6 Nm) in the Danish part of the Baltic Sea connecting the island of Ærø to the mainland. 
• E-ferry, goes beyond current limitations of similar efforts targeting medium range connections and is likely to be the ferry with the largest battery pack ever installed in a vessel.

Source: E-ferry