Estimation of Maintainability Characteristics on Diesel Engine Plant
Hachiro KIDO* and Takeshi HASHIMOTO**
Man-hour is most important factor to evaluate the maintainability. Man-hour as in multiply repairing hours per case and number of repairers per case are depend on the difficulty and urgency of the recovering works. Thus, this paper tried to find the relationship between man-hour and effected factors to the maintainability by applies the MIL-HDBK472. The basic data used about 90000 cases statistical failure data from ships. According to the statistical data, man-hour approximated a Logarithmic Normal Distribution. And man-hour are effected on four primary factors. These factors are the difference of an installation systems, the difference of number of repairers, the difference a kind of ships and the difference of main engine outputs. Then, we made some equations to estimate man-hour using above four primary factors. Furthermore, we made some evaluation table to calculating the estimated MH based on human factors and circumstances factors. Finally, this estimated equations of maintainability characteristics are compared with the actual data from ships.
Key Words: Reliability. Maintainability, Dependability, Diesel Engine, Statistic Data-Base
The maintenance hour and the number of repairers are changed depend on the difficulty and the urgency of the works. However, it is not appear as effective factors that are different of circumstances condition like a crew's career, repairer's skillfulness or knowledge, number of crew, consists of crew, sea route, season, sea condition, weather, current and different of internal condition like a kind of ship, ship's shape, size, ship's age, dead weight, engine type, output of engine, engine complexity, speed, load and torque.
Also, man-hour which is multiply repairing hour per case and number of repairers per case when trouble occurred, is changed by the contents of maintenance. For example, maintenance work is more increase the man-hour compare with a investigation work like a watch keeping tour. It is requested more deeply experience and knowledge on technique. Furthermore, number of attendance persons are depend on operation mode like a Port Rest Stand-Bye Engine and Navigation Mode. Maintainability are different each groups which are port relief group: deck crews or yard workers. These factors effect man-hour when trouble is occurred. This paper tried to find the relationship between man-hour and effected factors that applies the MIL-HDBK 472 to the statistic data from a ship's plant. According to the statistical data, man-hour approximated a Logarithmic Normal Distribution. Furthermore, man-hour are effected on above some human factors and circumstances factors.
Then, we made some equations and evaluation table to estimate man-hour using above characteristics. And, this estimated equations for MH applies to 30 devices of engine plant. Finally, we carried out and investigated the coefficient of correlation between estimated values and statistitical data, also made a comparison graph with the actual ship's data..
* Marine Technical College
12-24 Nishikuracho Ashiya City Japan
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** Kobe University of Mercantile Marine