EEDI (Energy Efficiency Design Index) came into effect mandatory in Jan.
2013, and the ship owners definitely required a higher efficiency propulsion system than ever
before. Hence, the shipyards have been conducting an optimization of ESD (Energy Saving Device)
system in self-propulsion test for each project. As the results, the shipyards have
installed a rudder bulb as an effective ESD.
The rudder bulb is a popular ESD system from a long time ago. Mewis1) described that the rudder
bulb was developed by Costa in 1952 and the efficiency improve by the rudder bulb for a container
vessel was 1% on average. Fujii et al.2) developed “MIPB (Mitsui Integrated Propeller Boss)” as an
advanced rudder bulb. The feature of MIPB was a streamlined profile from propeller cap to rudder.
According to their paper, the efficiency improve by installing MIPB was 2-4%.
Recently, NAKASHIMA PROPELLER Co., Ltd. developed ECO-Cap (economical propeller
cap)3) as a new ESD with FRP (Fiber Reinforced Plastics). The strength of FRP is higher than that
of NAB (Nickel Aluminium Bronze), therefore ECO-Cap was able to adopt thin fins on propeller
caps for low resistance. Although the material used for the energy- saving propeller cap
was generally NAB, the research results on FRP showed that FRP could be used as ESD due to their
properties such as lightweight and flexibility.
As explained above, the authors thought that there was a possibility to evolve the rudder bulb
profile using the easily moldable FRP compared with NAB. This paper described about the development
of “Ultimate Rudder” of new design concept by FRP. The authors optimized the profile of “Ultimate
Rudder” by CFD and confirmed the efficiency increase from 4.9 to
5.4% in self-propulsion test
