Due stringent regulations for greenhouse gas emissions imposed by IMO, ship-owners / Managers are searching for cost effective solutions to equip vessels with energy saving devices (ESD) or highly efficient propellers and rudders.
To address adverse impacts on marine life, IMO is committed to reducing Underwater Radiated Noise (URN). The MEPC has approved revised guidelines (MEPC.1/Circ.906) which is in effect from 1 October 2023. Some of the approaches are around propeller design and wake flow improvement.
With today’s technology, lower underwater radiated noise is possible while also understanding improved propulsion efficiency. It is recommended to assess the effectiveness of propulsion improving component in design using full-scale ship computational fluid dynamics (CFD) simulations.
Cavitation in propeller is a major source of noise, vibration, loss of propulsion efficiency and propeller & rudder erosion.
Energy saving devices are pre swirl ducts & fins, wake equalizing ducts, propeller boss cap, contra-rotating propeller, grim vane wheel, rudder bulb, integrated costa propulsion or other modifications in order to improve efficiency. Potential savings are in range of 3–10% dependent on different measures.
One notable innovation is Propeller Boss Cap Fin (PBCF) developed by MOL-Tech Trade Ltd. The upgraded design PBCF reduces fuel consumption by approximately 5% by breaking up hub vortex generated behind rotating propeller. This enhances propeller thrust, reduces torque, vibration and noise through advancements in fin shape and height.
Nakashima Propellers Co have introduced Propeller Eco-Cap, which attaches very thin wings made from Fiber-glass Reinforced Plastic (FRP) to copper alloy cap body. This design reduces resistance and keeps weight difference to minimum compared to a regular cap.
Nakashima also introduced Ultimate Rudder having an Energy saving effect of about 6%. Rudder bulb is located near propeller with a rounded cap, allowing a configuration of bulb as close as possible to propeller.
KRISO has also developed propeller cap ‘K-cap and fin’. Additionally, KRISO has introduced vortex generator, a structure built in front of propeller, to control flow of fluid into propeller and improve propulsion efficiency.
Wake equalizing ducts (WED) are Grothues spoilers, Schneekluth duct, Sumitomo’s Integrated Lammeren Duct, Mitsui integrated ducted propeller & Becker Mewis Duct.
Becker Marine Systems offers energy saving devices including Becker Mewis Duct, giving power savings upto 8%. For ships with speeds above 18 knots, Becker Mewis Duct Twisted was introduced. Other devices as Becker Bulb rudder, Becker Flap rudder, Becker Twist and Becker Nozzle are available for energy efficiency.
Wartsila provides energy saving devices as Wartsila EnergoFin (propeller cap), EnergoFlow (Pre swirl stator), EnergoPac (Integrated propeller & rudder design) and Gate Rudder concept.