Recently, the slow speed 2-stroke diesel engine generator plant has become more attractive in the field of stationary application because it offers the advantages of low fuel consumption and low cost maintenance. These slow speed 2-stroke diesel engines which range from several thousand kW up to 50 MW are normally used at 100 to 200 rpm. These stationary units are operated at a constant speed, therefore it is impossible to avoid the speed range where annoying vibrations occur under operation, in the same manner as in marine use. Recently, environmental issues including vibration problems are considered more seriously by the customer. It is required that the effects of vibrations on the adjacent plant units in addition to the engine itself should be minimized. In order to comply with these customers' requirements, the change of firing order, the introduction of various kinds of balancers and dampers, etc. have been totally investigated at the design stage.
In the case of one of the stationary plants, a dynamic damper has been introduced successfully in order to reduce engine frame vibration. In this paper, the effectiveness of such dynamic dampers, which are arranged on both ends of the engine cylinder frame, is discussed.
These kinds of dynamic dampers have been widely used in engine shafting as well as in electric motors and recently they have been used for main towers and tall building as vibration reducing devices. The application of dynamic dampers can also be used effectively for reducing vibration levels on the hull superstructure.

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At present, there is no regulation on NOx emission from marine diesel engine. IMO MEPC 30 th session, however, has presented a target figure for the emission in 1990. Especially in the harbor and the straits, it is considered that NOx emission from ship damages the environment because of the concentration of the vessels in a limited area. In order to clarify the characteristics of NOx emission from CPP (controllable pitch propeller) ship and FPP (fixed pitch propeller) ship in the harbor, and to discuss the method of reducing the emission, ship speed [knot], NOx emission [ppm], engine output [kW], indicator diagram were examined by using a 1990GT/2795 kW ship equipped with CPP. In addition, cylinder gas temperature and heat release rate were calculated from indicator diagram to analyze the relationship between NOx emission and combustion. The results obtained from the examinations are as follows: (1) at the same engine load, driving CPP at higt revolution is effective in reducing the NOx emission; (2) maximum cylinder gas temperature correlates well with NOx emission [kg/h] ; (3) new criterion is proposed to estimate the reduction of NOx emission from sailing ship.

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Rubber is applied to highly-elastic couplings installed in geared diesel propulsion system. Taking advantage of its high elasticity and large damping effect, torque fluctuations transmitted to gear can be diminished. However, the dynamic behaviour of the shafting system including rubber is not comprehended exactly because of their complex characteristics and scant examples of detailed measurement under actual operation.
In order to make clear the dynamic characteristics, the authors did comprehensive full-scale measurement on two ships and have been analizing the results. The aim of this study is to show the actual torsional vibration of rubber damping system and to present a practical calculation method by modal analysis applicable to the system. This paper, which is the 1 st report of the study, is devoted to the illustration of the results of the full-scale measurement. At first, the framework of the measurement is explained. Then the dynamic response at each parts of rubber couplings is showed as well as general features of the rubber damping system.

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