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PROPULSION New Propeller Boss Cap Fins Provide Significant Improvement In Efficiency A result of concentrated research effort for the past two years, Propel- ler Boss Cap Fins (PBCF) are said to show significant economic fea- tures for all vessels. To date, research for improving propeller efficiency due to vortexes in the slipstream of the propeller has concentrated on the loss of effi- ciency due to the propeller tip vor- tex. There have been many designs and devices tested for reducing this effect. Until recently, very little research has concentrated on the efficiency loss due to the propeller hub or boss. Theoretical calculations for propel- ler performance which includes the influence of the hub have only re- cently become possible. The result of joint research ef- forts by Mitsui OSK Lines Ltd., West Japan Fluid Engineering Lab- oratory Co. Ltd., and Mikado Pro- peller Co. Ltd. since September 1986, PBCF is designed to decrease the induced resistance due to the vortexes generated by the boss cap. PBCF is a simple device, having the same number of fins attached to Photo showing the process of pouring visible chemical dyestuff. Advance coefficient(J) • Figure 1 the boss cap as that of the ship's propeller. The fins serve to control the flow over the propeller hub, thus diffusing the vortexes created by the hub. This effect is seen clearly in the two photographs of the model tests, included with this article. Pro- (continued) WE REACH FURTHER THAN YOU THINK With more than 130 years in the shipbuilding industry, the Ulstein Group today offers a wide range of marine equipment and services. Ship design, diesel engines, propulsion systems among other types of ships' equipment is our trade. All from one single supplier. Subsidiaries in 9 countries and representatives world-wide en- able you to reach one of Ulstein's 2100 employees wherever you are in the world. SINGAPORE - HONG KONG - CANADA - USA - WEST GERMANY - SPAIN - DENMARK - UNITED KINGDOM - NORWAY Good business relationship takes a long time to develop. Which is why we safeguard our reputation jealously. INTERNATIONAL A.S - SUPPLIERS TO THE MARINE INDUSTRY Telephone + 47 70 10 050. Telex + 0056 42 342. Telefax + 47 70 11 442. September, 1988 Circle 345 on Reader Service Card 61
