Katsumi Yonekura

COUNTER-ROTATING PROPELLERS

A double reverse revolution propeller apparatus having a front (6) and a rear (7) propeller is disclosed, in which the rear propeller is rotated at higher speeds than the front propeller. In another aspect, when seizure occurs, an inner shaft (8) is disconnected from an engine at an inner shaft connection unit (10) and connected to an outer shaft at an inner and outer shaft connection unit to be driven in the same direction as the outer shaft. In still another aspect, the ratio in absorption horsepower of the front propeller to the rear propeller is set to be substantially equal to the ratio in rotational speed of the front propeller to the rear propeller. In a further aspect, one or both of the front and rear propellers include a variable pitch propeller. In a still further aspect, the front propeller has more blades than the rear propeller.

Development of Contra-Rotating Propeller System for Large Ships

To meet the recent strong demands for energy saving, a contrarotating propeller (CRP) system was developed by Mitsubishi Heavy Industries Ltd (MHI) for application to large ships. The idea of a CRP is not new, having originated about 150 years ago. Technical problems that have stood in the way of the practical application of CRP systems for large merchant ships were: (1) the need to develop a reliable bearing and sealing system for contrarotating shafts, (2) a compact reversing gear system, and (3) an optimum design method and a performance evaluation method for a CRP system. Some solutions to these problems were developed by MHI recently, and put into practice by utilizing the oil-lubricated plain bearing system, lip seals, and a star type epicyclic gear system. One of the unique aspects is the introduction of the asynchronous CRP (ACRP) system, where the shaft speed of the forward propeller is lower than that of the aft propeller; by this means a large energy saving was achieved. This system, after one-years full-scale stand tests, was fitted to a car carrier. The carrier has since been put into commercial operation without any troubles and with an energy saving of more than 13 percent. The basic idea of the MHI CRP system, results of stand tests on bearing, seal and shaft alignment, and application of the MHI CRP system to the full-scale ship are reported, together with the results of full-scale measurements and service experience.