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Mechanism & Effect | Research and Development| PBCF | MOL Techno-Trade, Ltd.

The most Reliable Energy Saving Device - Propeller Boss Cap Fins

Mechanism & Effect

A Simple Construction, A Lifetime of Effects

Basic Mechanism

When a conventional boss cap is used, a strong vortex is generated which is called a "hub vortex" and results in a loss of propeller efficiency.
When a PBCF device is installed on the propeller boss, the hub vortex will be eliminated as downward flows after the blade are blocked by the fins of PBCF. As a result, the PBCF increases thrust and reduces shaft torque, improving propeller efficiency.

What is hub vortex?

The difference in flow velocity between the upper and lower surface of the propeller blade results in a strong downward flow from the trailing edge of the blade. The downward flow of each blade integrates into a strong hub vortex. As a result of the hub vortex, the propulsion energy of the propeller decreases.

The difference of the flow velocity hub vortex between upper and lower surface of the propeller blade results in a strong down flow from the trailing edge of the blade. The down flow of each blade combines and integrated into a strong hub vortex. Approximately 10% of the energy is scattered and is lost by this hub vortex and so on.


The strong down flow from the propeller blade trailing edge will be rectified by the PBCF fins to reduce the rotatable component, so that the fins will produce the force reducing the propeller shaft torque by 3% and more. In addition, thrust will be increased by over 1%.



The PBCF achieves an energy saving of about 5 percent at the same speed, or at the same horsepower, the vessel’s speed increases by about 2 percent by fitting the PBCF.

Other merits

  • Reduction of torque-rich conditions
  • Reduction of stern vibration and underwater noise
  • Elimination of rudder erosion

Past sales results of PBCF

We have analyzed more than 100 actual vessels, both small coastal ships and large ocean-going vessels, based on their sea trial results and actual voyage data. The PBCF will improve the propeller efficiency itself and its effect essentially will not depend on the type or size of the vessel, horsepower, RPM, vessel speed, etc.

  • Bulk carrier

    Bulk carrier

  • Wood chip ship

    Wood chip ship

  • Car carrier

    Car carrier