Stena Estrid has been hailed as the “most efficient ship in Stena’s history”.
Steno RoRo’s 215-m long, 3,100-lane m capacity Stena Estrid is the first in Stena Line’s new line of E-Flexers. Five of these vessels are for Stena Line and additional vessels will be on long-term charter for other ferry operators.
Nine E-Flexer vessels have been ordered and two have been delivered: Stena Estrid, delivered in November 2019 and Stena Edda, in January 2020.
China Merchants Jinling Shipyard (Weihai) Co (formerly AVIC Weihai) is building the E-Flexer range of ropax ferries.
Deltamarin is working on the project not only as a designer but also as a provider of comprehensive project management services to support the shipyard in the vessels’ construction. Deltamarin developed the concept of the vessel in close collaboration with Stena. Deltamarin says that in the design special attention has been paid to the vessels’ fuel efficiency as well as maximising the cargo space.
Stena RoRo project manager newbuilding Magnus Lander tells Passenger Ship Technology “The ship is designed for the Stena Line route network and to combine maximum cargo intake, quick turnarounds and high passenger comfort with low fuel consumption. The design is based on the legacy from many Stena projects in the past where optimal flexible performance has been sought for.”
Stena Estrid participated in sea trials to test the performance of the vessel including all the onboard systems such as the propulsion plants. The vessel is equipped with twin-screw Caterpillar marine propulsion drive trains with MPP 1410f propellers, shafts and packaged gearboxes.
The vessel has a maximum output of 12,600 kW and is equipped with a MaK 12 M 43 C engine. The main engines and propulsion packages for seven of the ropax series were supplied by Caterpillar Marine.
Stena Teknik project manager hydrodynamics Per Wimby says “After a long period of optimisation and testing with Weihai Shipyard, Deltamarin, MARIN and Caterpillar we now see the final product, which is the most efficient ship in Stena’s history.”
The propulsion solution was a collaborative effort involving Deltamarin, Stena, Caterpillar and Weihai Shipyard.
Speaking about the benefits of the propulsion system, Mr Lander says “Conventional ferries usually have four main engines for redundancy and to optimise the speed ranges with 85% MCR and shaft generator at constant speed. Stena Estrid is designed with two diesel-powered main engines, variable frequency shaft generators and with ability to feather the propeller blades on either side giving the vessel’s machinery a wider range to optimise the cost and fuel consumption. The ship is scrubber and gas-ready to meet any future route-specific requirements.”
Indeed, as Mr Lander points out, the vessel has a gas-ready design philosophy and description which includes drawings and calculations to convert the vessel to dual fuel. Space and calculations have been prepared to allow for a dual-fuel conversion at a later stage. He comments “It goes without saying that it is always good to do the homework before the exam and the vessel is ready to be converted should the price and availability for LNG be favourable for the operator.”
Hydrodynamic performance and innovation
Singling out other environmentally friendly and energy efficient features Mr Lander says “The ship’s hull has an excellent hydrodynamic performance. Two leading naval architect consultancy firms were competing to win the design by achieving the lowest resistance through the water. Stena Estrid’s Energy Efficiency Design Index (EEDI) is significantly better than similar older tonnage and regardless of which fuel will be consumed onboard, it will be much less than conventional tonnage.”
Mr Lander highlights other energy efficient and innovative solutions used:
Anti-fouling – Selektope (bio-repellent, organic, non-metal compound).
High lift streamlined flap rudders of twisted leading-edge type with rudder bulbs.
Trimmed thruster grids optimised for the design draft bulb wake, improving the hull performance even further.
Duck tail interceptor reducing the stern wake and optimising the hull performance.
Propellers with feathering mode which further optimises the speed ranges.
Fuel management system.
Stern tubes designed with anti-leaking system.
LED lightning for low energy consumption.
Variable frequency shaft generators.
Frequency-controlled pumps and fans.
WE Tech Solutions’ permanent magnet shaft generator and variable speed drive combination are used on the E-Flexer vessels. The Finnish technology company’s innovative configuration on the latest versions of the E-Flexer series make energy efficiency gains, contributing to a 25% reduction in CO2 emissions compared to current generation roro vessels. The solution in fact scooped the 2019 Marine Propulsion Efficiency Improvement Award.
The arrangement combines a variable frequency drive and permanent magnet shaft generator, along with a dedicated power management system. In power take-out mode, the system generates power for the ship’s electrical network. The shaft generator, driven by the main engine, can produce all the electricity required on board without using fuel to run auxiliary generators when sailing. The variable frequency drive allows the main engine to run at variable speed while producing electricity on board.
The concept drew plaudits for building on well-established energy saving principles, with a novel application of permanent magnet technology. One judge at the Marine Propulsion Awards praised the WE Tech system on Stena Estrid as a “good basic concept for a hybrid propulsion train” that could easily be extended with the addition of energy storage. Another highlighted it as “a real-life example of the extended use of permanent magnets” beyond their established uses in thruster and winch motors.
Stena Line fleet manager Bob Brouwer received the award with WE Tech sales manager Peter Lindström. "Stena Line has put the latest technology in its Chinese newbuilds and we will continue to add more such innovations in the future," Mr Brouwer said.
TURKISH MARITIME NEWS