Yoshihisa Okada, Deputy General Manager, Propeller Design Dept., Nakashima Propeller Co Ltd presentation during the 2015 GREEN4SEA Forum
NAKASHIMA PROPELLER developed ECO-Cap as a new ESD with FRP. The strength of FRP is higher than that of Nickel Aluminium Bronze, therefore ECO-Cap was able to adopt thin fins on propeller caps for low resistance. As the results, the improvement of F.O.C. by ECO-Cap was confirmed abt. 2.8% in operating condition. On the other hand, NAKASHIMA PROPELLER developed “Ultimate Rudder” of new design concept by FRP. And we optimized the profile of “Ultimate Rudder” by CFD and confirmed the efficiency increase from 4.9 to 5.4% in self-propulsion test.
My presentation refers to our new product, GPX Propeller. This is the design concept of GPX propeller:
- Non Hub Vortex
- Small Blade Area
- Tip Rake
I am going to explain Non Hub Vortex and Small Blade Area.
Hub vortex technology
 |
 |
The conventional propeller has a strong hub vortex causing energy loss. On the contrary, the GPX propeller can absorb hub vortex cavitation saving energy.
Small blade area technology
 |
 |
GPX propeller adapts narrow legs, so expanded area decrease max. 20%. In that way it is reduced the frictional resistance of blade surface.
Model test and navigation results of GPX propeller are following. We measured chemical tanker, bulk carrier, cement carrier and car ferry. In navigation mode we confront a +4% efficiency increase in tankers.
Next is our new propeller cap with a fin. Eco cap is our trade name for new propeller cap with a fin. When we developed our new propeller cap fastly we investigated mechanism of hub vortex. You can see that hub vortex is consisting of several tangential flows from the trailing edge. So our new eco cap had to disturb this hub vortex. This is our solution. In our study we understand that number of the fins is several and that small size fins causes an important efficiency increase. So you can see that tangential flow was disturbed by eco cap.
And this is pressure distribution with and without eco cap. Left side is construction of propeller cap which has a negative pressure which is not good for efficiency. Right size is eco-cap calculation results which have a positive pressure increasing efficiency.
We carried out a model test for eco-cap using a propeller for large container vessel. This is the observation of hub vortex by air injection method.
Upper side is constraction type propeler cap. This is not hub vortex cavitation. This is only hub vortex. Lower side is eco-cap. There is no hub vortex condition
Blue line: propeller thrust (+0.3%) at design point.
Red line: propeller torque (-0.9%).
Green line: efficiency (+1.2%).
In model test we have to use 2 small size models in actual operation conditions. We installed Japanese car ferries our eco-cap and we measured fuel oil consumption and we resulted in an average 2.8% of fuel oil consumption decrease. It is difficult to produce the shin fins by NAB so we adapt FRP fins.
Next is ultimate rudder. Left side is normal rudder and in the right side is the conventional rudder bulb.
The leading edge of the conventional rudder bulb is far from propeller plane so it not effective I think so this is the weak point of conventional rudder bulb. Our solution is following. We adapt the rudder propeller cap by FRP so our leading edge of rudder bulb is closer to propeller plane compared with conventional rudder bulb. We also carried out CFD calculation and model test for 208BC.
Bellow is the CFD calculation and rotational flow line of normal rudder. You can see strong rotational flow.
And this is the rotational flow line of Ultimate Rudder. We see a reduction of rotational air flow and we think this solution is effective.
Model tests results are following. As you can see we have 5% to 6% of BHP reduction.
In conclusion, we are propeller makers but we are also dealing with energy saving devices and the optimization of these products.
Above article is an edited version of Yoshihisa Okada’s presentation during the 2015 GREEN4SEA Forum
You may view his presentation video by clicking here
| Click here to view all the presentations on this GREEN4SEA Forum |
———————————————————————————————
About Yoshihisa Okada
Deputy General Manager, Propeller Design Dept., Nakashima Propeller Co Ltd
Yoshihisa Okada has Bachelor at Hiroshima Institute of Technology. He joined Nakashima Propeller since 1982. Since then, he has been in charge of propeller design for various types of commercial vessels for 20 years. He is deputy general manager at propeller design department.
In the onset, I was open with you propecia before and after has changed my being. It has become much more fun, and now I have to run. Just as it is improbable to sit.
