The most Reliable Energy Saving Device - Propeller Boss Cap Fins

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Creating a Clean Future for the World with Advanced
Energy-saving Devices

技術専任部長 小野 志郎

Shirou Ono
Associate General Manager-Technical PBCF Dept.


Q. How were you involved in the advanced PBCF development project?

I first became involved in developing our advanced PBCF in around 2009. At the time, our original PBCF patent was just expiring, and we took this as an opportunity to begin working on an improved version of the product. Since patent rights end 20 years from the date of application, we were primed and ready to launch a new and advanced PBCF. One aim of this project was to create a new, patentable replacement technology for PBCF. As the number of copycat products had increased at the time, we wanted to develop something more competitive that would contribute to increased sales. As such, we launched into R&D with the desire to build a more exceptional and effective PBCF based on our prestige as the founding brand of the product.

When finalizing the shape of the product, we drafted a design that accounted for a wide range of factors, such as the position and pitch angle of the fins relative the propellers, so that our PBCF would conform with an extensive variety of vessels. When PBCF was first developed, we created a formula for determining fin height, length and angle relative a variety of propeller types (4 to 6 blades). However, to formulate the optimal shape, we had to generate design charts that allowed for even more accurate designs by using towing tank tests and CFD (computational fluid dynamics) analysis. We later conducted inspections using actual ships.


Q. Please tell us about the improved features on the advanced PBCF and the biggest challenge you encountered during development.

One of the features added to our advanced PBCF is its larger fin height relative conventional models. A second feature is its streamlined configuration. While the action of the propellers tends to exert a stronger effect on the bow side of the fin, we found that significant resistance still remains in the stern and focused on streamlining the stern-side parts. The third feature we improved upon was the pitch angle. We added a twist to the fin shape by slightly changing the pitches in a radial direction.

Before our improved model took its final form, we discovered two important points thanks to CFD analyses and our many years of industry experience. The first was that to enhance performance and achieve greater energy efficiency, we would need to increase the fins' height. The second was that once the fins exceeded a certain height, resistance began to increase and no additional effects were achieved.

Increasing fin height also places more strain on the fin root, which requires this section to be made thicker. This, in turn, necessitates a body that is proportionately thicker as well, which presents the challenge of an increasingly heavy PBCF design.

Since PBCF is installed on the aft of the propeller shaft, its weight affects the ability of the entire shaft to bend and flex. When it is too heavy, it can dramatically reduce the operational lifetime of the stern shaft bearing. If the aft becomes excessively heavy, the entire propeller shaft system may need to be reconstructed. This necessitates an even more extensive design change. Our biggest challenge was to make sure this did not happen.


Q. Please tell us about how you plan to expand your PBCF operations in the future.

To get the same effects as a taller fin while controlling for height and avoiding any significant change in weight, the solution we constructed was to add a twist to the fin shape. We then conducted CFD analyses on the new twist design and determined the load that would be exerted on the PBCF. Using a FEM analysis, we evaluated PBCF strength and reduced fin thickness to the greatest extent possible within the allowable range. This helped us achieve a product that is slightly lighter than conventional types.

As a rule, when a ship is launched or modified, it must undergo safety inspections by a classification society such as Nippon Kaiji Kyokai (ClassNK). Nevertheless, PBCF accounts for only 3 to 4 percent of the weight of the propeller, placing it outside of regulatory concern, with almost no effect on maneuverability. This means it is not considered a vital product on the ship. As such, it is not subject to any approvals according to the class requirement. If the PBCF's weight was heavy enough to impact the shaft system, the entire shaft would have to be re-inspected. Compared to other energy-saving products that require welding, PBCF is installed and removed by bolts without the need for welding, providing clients with another added benefit. When a product requires welding, the hull of the ship is exposed to heat that can cause damage in some cases; as a result, classification societies may be required to carry out additional inspections. With PBCF, this step is unnecessary. The fact that this energy-saving device does not need to be inspected is just one more advantage our clients receive as well as why they select PBCF. In this way, we were able to employ our in-house technology to create an advanced PBCF that offers easy installation and reduces the burden placed on the ship and its owner.


Q. Please tell us about how you plan to expand your PBCF operations in the future.

PBCF helps reduce underwater noise, making it an ecologically-friendly product for marine life. In western nations, certain areas are monitored for underwater noise as part of conservation efforts to protect marine ecosystems. Thanks to the ability of PBCF to limit noise beneath the surface of the water, it is receiving extensive praise for its contributions to the environment. According to a paper we released, underwater noise can be reduced by around 5dB when installing the PBCF at a specified frequency range.

Indeed, PBCF already contributes to environmental conservation in a variety of ways, such as through reductions in CO₂ emissions and underwater noise. Moving forward, we will continue to improve the materials used for our PBCF. Our company also plans to develop more advanced energy-saving features by combining PBCF with other products and technologies. We promise to continue our research in order to help realize the IMO global CO₂ reduction targets (net zero GHG emissions project for international shipping).