Using retractable ‘wings’ to cut fuel consumption by 10%

Norway’s Liegruppen AS has ordered a new pelagic fishing trawler from Turkey’s Cemre Shipyard that could be the first such vessel fitted with retractable bow ‘wings’ to reduce fuel consumption.

Installed at the bow, the foils are anticipated to contribute to reducing vessel motions and energy consumption, according to the vessel’s designer, Norwegian naval architect Salt Ship Design. This will, in turn, reduce the fuel consumption and emissions considerably, while increasing the safety and comfort for the crew on board – less ship motions should translate into fewer incidents of sea sickness. The system will also enable the vessel to maintain higher speeds in rough sea conditions.

Installation of the retractable bow foils, manufactured by Trondheim-based Wavefoil, are subject to confirmation by Norway state-run Enova.

The first full-scale tests of the Wavefoils were conducted on the 45-m Faroese ferry Tesitin in September 2019. Unlike existing retractable roll stabiliser foils that are retracted horizontally, Wavefoils are retracted vertically into the ship’s hull. The captain can deploy or retract the Wavefoils with a push of a button on a touch screen on the bridge. Tests conducted on Tesitin during its first three months of operation with the Wavefoils indicated fuel savings of about 10%. Systems on two other vessels demonstrated fuel savings, motion dampening and system reliability.

Additionally, DNV conducted computational fluid dynamic (CFD) testing to assess the Wavefoil effect on ship resistance. One of the conclusions of the testing was the average fuel saving over time would depend on the vessel’s route and operational profile. “A complete assessment of the benefit of a Wavefoil installation for a given ship must therefore use wave statistics for the relevant routes combined with the hull lines of the ship in question,” concluded the study.

Wavefoil reported on social media it had been awarded a patent for the retractable foil mechanism in the US.

No LNG, but batteries

At 71.45-m long and 15-m wide, the new fishing trawler, Liafjord, will be smaller than the 86-m Libas – the world’s first LNG hybrid electric fishing vessel built for the Norwegian-family-run fishing business.

While not equipped with a MAN 6L51/60 DF four-stroke, dual-fuel engine for main propulsion like Libas, the new trawler will incorporate a battery pack and electric winches. Corvus was the supplier of the 508 kWh Corvus Orca Energy battery system for Libas, used for peak shaving operations.

Meanwhile, Liafjord will have propulsion and manoeuvring systems supplied by Brunvoll, covering the controllable-pitch propeller systems with shaft and stern tube, tunnel thrusters and control system. Brunvoll will deliver the equipment in Q4 2021 and Q1 and Q2 2022.

With a focus on energy efficiency, lower emissions and fuel savings, the newbuild fishing vessel’s propulsion system will be a two-speed system with power-takeoff /power take home (PTO )/(PTH) functions from a combined shaft generator/electric motor. This means that the ship can supply surplus energy to the main switchboard from the main engine in PTO mode, and in PTH mode the ship runs electrically in emergency mode.

The two-speed system is designed for high flexibility, with two different propeller speeds for efficient operation adapted to the ship’s operating profile. Optimisation of propeller speeds means that the 0-pitch loss is reduced to a minimum, and the ship achieves significant fuel savings, reduced emissions, and reduced costs.