The energy saving capacity of Energopac is based on optimizing the interaction between the vessel's propeller and rudder. The leading edge of the rudder is twisted and subsequently more aligned with the propeller's slipstream, which in turn produces better water inflow angles and improved cavitation behaviour. A fairing hubcap guides the propeller slipstream around an individually designed rudder bulb, thereby substantially decreasing the drag. Vibrations are 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, ensuring superb manoeuvring characteristics with only relatively small steering angles needed to keep the vessel on course. This considerably reduces steering losses whilst in transit.
Model tests were performed with both single and twin-screw ships. In both, the Energopac application resulted in significant reductions in required power and fuel consumption. Where the system replaced another sophisticated propeller-rudder arrangement, a 2% power decrease was noted. When the system was used in place of a conventional propeller and semi-spade rudder configuration, an 8% efficiency gain was recorded, according to the company.
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, 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.