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Finnish engine manufacturer Wärtsilä claims that shipowners can reduce fuel consumption by up to 9 percent and shave thousands off their bunker fuel bills by installing its new Energopac propulsion and manoeuvring solution for energy optimization.

Officially launched during the SMM 2008 exhibition in Hamburg, Germany, Wärtsilä says Energopac is an easy-to-install rudder/propeller combination that uses a rudder bulb behind the propeller hub mounted on a custom-designed full spade flap rudder.

Finnlines, the Helsinki-based shipping company linking Finland to ports throughout Europe, has ordered Energopac to be fitted on six sister vessels currently being built for delivery in 2009.

The energy saving capacity of Energopac is based on optimizing the interaction between the vessel's propeller and rudder. Wärtsilä says its in-house Computational Fluid Dynamics (CFD) capabilities have enabled an optimal design for the total system.

Speaking about the new rudder system, Teus van Beek, Director of R&D, Energy Efficiency, Wärtsilä Ship Power, said "Energopac will effectively reduce operational costs for any vessel with a considerable share of non-stop sailing in its operational profile, and will work very well for vessels with a relatively large propeller hub.

"For a vessel using a conventional rudder/ propeller arrangement, hub losses are significant, but these can now be avoided by applying the Energopac system."

Van Beek added "More and more ship owners are looking to invest in technology that improves energy efficiency, and with it fuel consumption and emissions, throughout their fleets, especially with fuel prices at an all-time high."

According to Wärtsilä, a 20,000 dwt cargo vessel with a main engine of 8000 kW and a controllable pitch propeller installation, could benefit from annual fuels savings of USD 45,000 for each percentage point in power reduction.

On a 22 knots twin-screw Ropax ferry with an installed power of 25,000 kW, Wärtsilä claims that Energopac will generate annual savings of over USD 125,000 per percent. For a 5000TEU-plus containership with 50,000 kW installed on one fixed pitch propeller, Energopac could realise an annual reduction in fuel costs of USD 300,000 per each percentage of improvement.

"Energopac can do this" said van Beek. "It will improve overall performance by 2-9 %. Energopac will be custom designed for each individual vessel to give maximum fuel savings. And this will be done without compromising on either manoeuvrability or comfort."

In order to produce better water inflow angles and improved cavitation behaviour, the leading edge of the rudder is twisted and subsequently more aligned with the propeller's slipstream, Wärtsilä says. A fairing hubcap guides the propeller slipstream around an individually designed rudder bulb, thereby substantially decreasing the drag. Vibrations are therefore reduced to a minimum.

This arrangement differs from earlier energy-efficient rudder systems. In the new design, the bulb is fixed to the rudder blade and turns together with the rudder. The Energopac rudder is also equipped with a flap, which Wärtsilä says ensures "superb manoeuvring characteristics with only relatively small steering angles needed to keep the vessel on course". This is said to considerably reduce steering losses whilst in transit.

The rudder part of the Energopac will be made by Becker Marine Systems and an intrinsic component of Energopac is Becker Marine Systems' patented KSR (King Support Rudder) bearing arrangement, which has been used to provide a slimmer rudder profile, resulting in low resistance. It also allows the Energopac system to be installed on any size of vessel, according to Wärtsilä.

Model tests were performed with both single and twin-screw ships. In both, Wärtsilä claims the Energopac application resulted in significant reductions in required power and fuel consumption. Where the system replaced another sophisticated propeller-rudder arrangement, a 2 percent power decrease was noted. When the system was used in place of a conventional propeller and semi-spade rudder configuration, Wärtsilä says an 8% efficiency gain was recorded.