Recently, high supercharged diesel engines of four cycle medium speeds have become popular as the main engine of marine use. For the engine structure, the hanger bearing type has become widely used instead of the conventional bed plate type which has been the conventional for marine use. The authors have investigated into the point as to whether there lies any difference between the two types of engines by comparing their stiffness in both the horizontal and vertical directions with calculations based on actual tests. They concluded that there was no difference between the two types of frame structures in relation to the two rigidities, one, in the bearing region in the vertical direction and the other at the lower portion of the engine frame in the horizontal direction.
In engine rooms, the noise level is considerably high compared with other work places on shore. This has been accelerated by the employment of medium-speed geard diesel engines. Judging by the permissible criteria for noise exposure from the viewpoint of hearing conservation, it can be seen clearly that engine room crews are in danger of having their hearing impaired. The results of hearing tests of engine-room crews show clearly the occurrence of noise-induced permanent threshold shift centered at 4, 000 Hz. Moreover, it was recognized that the longer the noise exposure history becomes, the further hearing loss develops. However, in according to the hearing impairment evaluation through the speech average loss method, there were found very few crews suffering from “mild” hearing impairment who have frequent difficulty with normal speech. “Slight” hearing impairment among crews of pelagic fishing boats and trading ships belonging to the 6 major companies was approximately 17% and was smaller than expected. However, in the comparative studies of ferries with engine semi-control room and ferries without one, many crews of ships which do not have a semi-control room were observed to be suffering from hearing impairment. Further comparative studies must be conducted on the basis of differences in the conditions which affect hearing impairment.
With rapid progress in the technology of central-control systems for ships, a need for the reliability of main diesel engines and related equipment has been created. Towards this end, various methods, such as the reliability designing method, endurance testing method, system of monitoring abnormalities, system of maintenance and repairs, and so on, have been developed. But first of all, it is necessary to analyze the performance of the main diesel engine and its related equipment under service conditions, i.e. while the ship is running, before any such methods can be developed. This report deals with our experiments conducted aboard a 110, 000 DWt ore carrier in service on routes from Japan to South America or Australia. For the nearly two years since it was commissioned, we have kept continuous measurement and record of various aspects of its operation in relation to navigational conditions and engine performance in order to analyze the load and operating conditions of the engine and the aging of the ship and engine. As the results, it is understood that the load and operating conditions of the main diesel engine undergo complicated changes according to various conditions such as the ship's navigational conditions, aging, surrounding conditions, and etc. while the ship is running. We think some details of such changes have been clarified by our experiments. And through the various analyses, we have translated the complicated load conditions into a simplified pattern and estimated the influences of aging. The results, we believe, could be used as the basis for designing more reliable engines and making endurance test. On the basis of the data we have obtained, it is also possible to establish standards for producing systems for monitoring engine performance, for detecting abnormalities and for maintaining and repairing the engine. The data of our experiments and the results of their analysis will find many applications and will be useful in improving the reliability of marine diesel engines.
Piston crown of marine Diesel engine is subjected to the thermal and the mechanical stress which are superposed each other. The behavior of engineering metal under superposed stress should be evaluated, when the design and the fatigue life prediction are carried out. Two kinds of plain bending unnotched specimen of cast steel were tested under two kinds of superposed stress. One of them was the sequence with square wave variation of mean stress, and the other was the sequence with sinusoidal variation of mean stress. Two kinds of fatigue testing machine were used, one of them was Schenck type mechanical plain bending fatigue testing machine, and the other was an electro-hydraulic closed loop plain bending fatigue testing machine. Coefficients β and f have been proposed to explain the behavior of engineering metal under superposed stress. They were calculated from experimental results. A new method was proposed to predict the fatigue life of metal under superposed stress and on cumulative fatigue damage procedure. The predicted lives were in pretty well agreement with the service lives of piston crown and cylinder cover of marine Diesel engine.