Trials verify Energopac reduces fuel costs

30 Sep 2010
Wärtsilä's Energopac is an integrated propeller and rudder design that delivers significant reductions in fuel costs

Wärtsilä's Energopac is an integrated propeller and rudder design that delivers significant reductions in fuel costs

In recent trials carried out in co-operation with the Spliethoff Group, a company that manages more than 55 multi-purpose cargo vessels, it was shown that the Wärtsilä Energopac solution delivers significant reductions in fuel costs.

The trials involved eight 17,700 dwt vessels, six of which were fitted with standard rudders and two with Energopac. The trials have shown that the Energopac solution saves close to 4% power in design condition. This represents annual fuel cost savings of more than $120,000 (at fuel prices in July 2010).

“After 6 months of operation, it has been shown that the reality confirms the theory,” says Frank Louwers, director at Spliethoff. “This facilitated our decision to install the Energopac propulsion solution on the next series of another 5 vessels.”

Launched in 2008, Wärtsilä's Energopac is an easy-to-install rudder/propeller combination that features a rudder bulb located behind the propeller hub. The bulb is mounted on a custom-designed full-spade flap rudder. As each Energopac installation is designed to fit a specific vessel, it can be fully optimised for energy efficiency without compromising manoeuvrability or comfort levels. Wärtsilä's in-house computational fluid dynamics (CFD) resources are used in developing an optimal design for the total system.

High performance propeller designs usually involve a compromise between increased efficiency and reduced vibration levels. Differences in rudder resistance are significant, especially when small corrective steering forces are used to keep a vessel on course. Energopac's sophisticated full-spade flap rudder delivers optimum rudder balance and manoeuvring performance, and also enables a smaller overall rudder blade area with lower consequent rudder drag. In transit conditions, where only relatively small steering angles are required to keep the vessel on course, the rudder bulb remains within the shadow of the fairing cap wake.

For ships with highly-loaded controllable-pitch propeller systems, such as RoRo vessels, ferries, container/multipurpose vessels and vessels with an ice class notation, the potential savings with Energopac are large. Bornholmstrafikken’s RoRo vessel Hammerodde, for example, reported that results are even better than the predictions obtained from model tests carried out prior to the installation of the Energopac solution. 

In addition to the Energopac systems already delivered, another 20 Energopac systems have been ordered and will be delivered in 2010 and 2011. Reductions in fuel consumption depend on the vessel type, its operational profile and also on the reference propeller and rudder. The performance improvements determined through CFD calculations and/or model tests indicate power reduction values ranging from a minimum of 2% to a maximum of 9%.

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