Rudder with bulb fins saves more than 5 per cent energy

Mitsui O.S.K. Lines, Japan Hamworthy and Akishima Laboratories are conducting research and development on Propeller Boss Cap Fins and an energy-saving rudder with bulb fins. Their research shows an energy saving effect of more than 5 per cent with this type of rudder alone.

 

In the development of the energy-saving rudder with bulb fins, the companies have enhanced the energy-saving performance and improved horsepower by taking advantage of the steering effect of the rudder of JHC, a specialised manufacturer of high lift rudder such as schilling rudder. The features of the developed rudder are as follows:

  1. In order to recover the swirling flow of the propeller, the reaction shape is designed as a high thrust blade section and the rudder horn is also twisted and integrated so as to increase thrust due to the negative pressure on the rudder.
  2. By reducing the size of the end plate under the rudder, the resistance is reduced and the propeller swirl flow is also blocked.
  3. The large central bulb has a flat front surface to reduce the propeller inflow speed and improve propeller efficiency.

A Japan Bulk Carrier (JBC) hull was used, which is open to the public as a general large-sized hull and widely used in various research and development. Generally, it is difficult to improve the horsepower by 4 per cent or more with a normal reaction rudder. However, with the developed rudder, Computational Fluid Dynamics (CFD) showed a 5.7 per cent improvement in horsepower and a self-propulsion test in a large towing tank confirmed 5.2 per cent improvement.

The developed rudder has been applied to the slender ship types as well, and an energy-saving effect of 4.4 per cent has been confirmed by CFD. In the future, the companies plan to conduct a large towing tank test after performing optimisation work. They are also aiming for a synergistic effect with the torque reduction effect of Propeller Boss Cap Fins for future installation on actual ships. The developed rudder has been patented.

Author: Mariska Buitendijk

Mariska Buitendijk is one of SWZ|Maritime's journalists as well as the magazine's copy editor.