Nakashima aims to improve propulsion, developing and producing energy-saving add-on products for the stern of the ship that increase energy efficiency.
Newly designed propeller cap for propeller hub vortex reduction
The hub vortex produced behind the propeller cap due to the circumferential direction of flow caused by the trailing edge of the propeller results in energy loss. By trial designing over 500 different types of propeller cap shapes, aiming to diffuse the hub vortex and recover the lost energy, we finally determined that the best result came from a cap shape with multiple blades attached, and this form became the basis for our ECO-Cap.
Verification by Pressure Distrubution
The pressure distribution behind a regular cap leads to increased resistance due to negative pressure, while with an ECO-Cap, positive pressure produces a propulsive force, increasing the propulsive force compared to a regular cap. In model tests, results were dependent on the propeller design (number of blades, pitch, boss diameter), but efficiency of about 1-1.3% was achieved.
Energy-Saving Effect of Approximately 3%
In order to reduce the resistance of ECO-Caps for use on actual vessels, very thin wings made from FRP (Fiber-glass Reinforced Plastic) were attached to a cap body made from a copper alloy. By using FRP materials, the difference in mass compared to a regular cap was also kept as low as possible, and when comparing results from attachment to a real vessel to before attachment of the ECO-Cap showed a 2.8% improvement in fuel consumption.
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