During the past ten years, the world’s shipping business has been affected greatly by the increasing price of fuel. Energy-saving research has been increased in order to find ways of reducing operating costs of ships. Wake equalizing ducts. Grim wheels, rudder--balls added thrust fins. reaction fins, and other devices have been developed. Among these devices, the energy-saving gain of the Grim wheel is high. but due to its complicated design and production, its production cost is high, and until n~ the technology of astern maneuvering with Grim wheels has not been fully mastered. Difficulties still have to be overcome.

Comparatively, the energy-saving gains of the added thrust fin is offset by its ease of running into fishing nets, and therefore its use is rather limited. Rudder-balls and wake equalizing ducts are simpler in structure. Low in manufacturing costs, lightweight easy to install, and good in energy-saving effect.

Therefore, the use of rudder-ball and wake equalizing ducts is highly recommended and is widely accepted by shippers. To explore the special features of rudder-halls and wake equalizing ducts, we have carried out model tank tests for the 65.650 DWT bulk carriers built by Jiang Nan shipyard and have obtained satisfactory results. According to the tank test results. at a draught of 12.50m and designed ship speed of 14.50 knots, an 8.38% reduction of DIIP has been obtained with the simultaneous use of rudder-hall and wake equalizing ducts. When the draught of 13.l()m and a ship speed of 14.5 knots the reduction of DHP is 8.76%. At ballast condition of 32.000t. it is only 4.0%. Therefore, the simultaneous use of rudder-hall and wake equalizing ducts is a practical solution for energy saving in fully laden vessels.

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