Currently, there are two highly controversial topics in ship industry, which are the reducing the cost of oil used and decreasing the emission of chemical gas through efficient energy consumption with technological innovation. This paradigm shift caused the ship industries to become involved in green shipping. This phenomenon is not only visible in domestic markets but also in international markets as well.
In order to reduce emission gases and operating expenses, increasing number of newly constructed ships are integrating the slow steaming system. Slow steaming system restricts the air flow of compressor and the turbine to increase the efficiency of turbocharger in the operating range of a main engine with two or more turbocharger. However, fuel saving engines equipped with slow steaming system are causing the harmful vibration on the exhaust gas manifold of the main engine.
Furthermore, if additional torsional stress and amplitude of the shafts exceed the limit value regulated by classes with in the operating range of the shaft’s torsional vibration exceeds the limitation within the normal operating range of the engine, it could result in fatigue of the shaft and accelerate the wear in the gear system it may be caused to broke the shafts. Since shaft vibration also causes vibrations such as local vibration of the engine room and hull vibration, it is essential to limit the revolution of the shaft or limit the additional torsional stress in the design stage.
There are several ways to control torsional vibration, which are controlling the exciting force, avoiding the critical revolution from operating area, and reducing the response level of the vibration. Changing the ignition sequence of the engine or changing the angle of the crank to unequal interval are mostly used method to control exciting force changing ignition sequence helps to control torsional vibration from critical revolution, and changing the angle of the crank to unequal interval helps to control torsional vibration of main critical revolution or particular sub-main revolution. This method should consider both the engine’s revolution and engine’s structural vibration. Next, increasing the mass moment of inertia of tuning/turning wheel allows to avoid the critical revolution from operating area. Also, changing the stiffness by changing the diameter of the counter shaft or propeller shaft helps to avoid the critical revolution. To reduce the response level of the vibration, mostly used method is to use a torsional vibration damper and increase the damping energy to control additional torsional stress.
In conclusion, onboard vibration was measured by analytical analysis of vibration from shafts torsional vibration response and vibration from engine’s major component exhaust manifold that changed exciting force in ship’s main engine due to Integration of Slow Steaming. As a result, the integration of slow steaming causes the increase of exciting force in the main engine and affects the shaft’s torsional vibration and hull vibration. Thus, pre-inspection is crucial and countermeasures in case of resonance is essential.