In order to keep ship safety and to develop a high reliable marine engine, factors of marine engine troubles are analysed by the Principal Component Analysis Method.
Analysed data are concerned with marine engine troubles resulted in sea accidents, marine automatic control device troubles and marine diesel engine cylinder troubles. It is proved that the P.C.A. method is adequate for the analysis of trouble phenomena.
Main results are as follows;
1. Marine engine troubles are classified into five groups using principal factors interpreted as degrees of damage, mobility of machine and human factor.
2. Though it is hard to interpret principal components of automatic control device troubles because of low factor contribution, tree diagrams showing relation between many factors are obtained by proposed Quadrant Method.
3. Piston and cylinder cover troubles of diesel engine are expressed by two factors; one is the combination of engine size and cooling method and the other is designed pressure.

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The preventive maintenance is roughly divided into two categories by the nature of informations it uses for the system reliability predictions. The one is based on the statistical informations or data of reliability as a group of systems, and the other on the measured or monitored informations of the performance directly obtained from each individual system. Let us call the former SPM for short, and the latter MPM.
A reliability model is formulated for a case when MPM is applied to an elementary system, in which the detectable pre-failure defects are assumed to occur. Some conceptual features of MPM are thus analysed, and it is now possible to compare the merits of both types of PMs quantitatively under certain assumptions. Manpower ratio, reliability increment ratio, and maintenance cost ratio are defined and calculated for comparison, and the superiority of MPM is noticed.
In the Marine machinery field, there are increasing needs and the trend of developing MPM are recognized. However, the merits of MPM are not always self-evident, because the conditions of the maintenance on board are rather complicated. The present author believes that such a quantitative analysis as proposed herein will help to clarify the situations on board, and give a rational basis for promoting the developments of MPM.

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Advances in ship automation systems in recent years have resulted in lower manpower requirements on board, especially in engine rooms. Fewer crew members and shorter service time on board, however, have raised new problems i.e. less attention paid to engine performance and maintenance compared to more fully manned conventional ships. Furthermore, shipowners and engine builders have not been able to properly forecast possible engine troubles or schedule maintenance programs for individual ships based on data accumulated on a large number of ships in service.
In response to this problem, Yamashita-Shinnihon Steamship Co., Ltd. and Hitachi Zosen have jointly developed a new maintenance system for main diesel engines combining the expertise and experience of both a ship operator and engine builder, respectively.
The objective of the system is to maintain in-service engines in satisfactory working condition at all times to promote the safety and operational rates of ships. The system is designed to keep the latest information on the operational status and condition of each main engine, and to determine maintenance schedules, parts supplies and provide technical data from the standpoint of preventive maintenance.
The new system comprises two sub-systems. The first is a Data Processing system which centrally controls and processes all incoming information by a large computer. The second is an Operations System, which gives the final output using the data analyzed and processed in the Data Processing system to provide information on technical data, maintenance, repair work and parts supplies for each engine.

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From 1971 to 1972 several crude oil tankers equipped with a computer control system were completed in Japan. Among them was Tottori-maru, a 237, 000 dw steam turbine tanker, on which a centralized computer system for the control and calculation of cargo oil pumping, navigation and steam turbine plant was experimentally installed.
From her delivery of September 5, 1972 to date, the ship has accumulated about three years of actual operating result for the computer system. Despite having sometimes experienced troubles during this period, which were surmounted on all such occasions in co-operation with the shipbuilder's and computer maker's engineers, the system has now come to obtain the reliance of ship's personnel by its excellent performance and usefulness. Especially the pumping system is so depended on that no loading or unloading operation without the computer system is considered.
The author, who has engaged in the project through the planning, installation and also maintenance of the system as the team leader of the shipping company, describes that, although these experiences and data gained from the system are expected to be great help in design of practical computer control ships, 99.35% of overall system availability is not so good as expected. From the standpoint of ship owner he requires 100% of system availability with the exception of pre-scheduled system down for maintenance and proposes some opinions for the system design to improve reliability.

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