Mitsui O.S.K. Lines, Ltd. (MOL) announced that a group company MOL Techno-Trade Co., Ltd. (MOLTech), MOL, Japan Hamworthy Co., Ltd. (JHC) and Akishima Laboratories (Mitsui Zosen) Inc. (Akiken) are conducting research and development on the propeller-mounted energy-saving device called PBCF (Note 1) and the energy-saving rudder with bulb fins. We confirmed the energy-saving effect of more than 5% with only the energy-saving rudder with bulb fins.
In the development of energy-saving rudder with bulb fins (hereinafter the “developed rudder”), we have enhanced the energy-saving performance and improved horsepower by taking advantage of the steering effect of the rudder of JHC, a specialized manufacturer of high lift rudder such as schilling rudder. The features of the developed rudder are as follows.
- 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.
- By reducing the size of the end plate under the rudder, the resistance is reduced and the propeller swirl flow is also blocked.
- The large central bulb has a flat front surface to reduce the propeller inflow speed and improve propeller efficiency.
We used JBC (Japan Bulk Carrier) hull, 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% or more with a normal reaction rudder. However, with the developed rudder, CFD (Computational Fluid Dynamics) showed 5.7% improvement in horsepower and a self-propulsion test in a large towing tank confirmed 5.2% improvement.
The developed rudder has been applied to the slender ship types as well, and an energy-saving effect of 4.4% has been confirmed by CFD. In the future, we plan to conduct a large towing tank test after performing optimization work.
We will continue to improve the efficiency by aiming for a synergistic effect with the torque reduction effect of PBCF for the future installation on actual ships. The developed rudder has been patented.