THE MISSION RELIABILITY OF SHIP PROPULSION

Abstract

ABSTRACTTHE APPLICATION OF RELIABILITY theory to ship propulsion machinery is briefly reviewed, and then the weaknesses of the conventional approach to this application are pointed out. These weaknesses are principally the lack of distinction between complete failures and partial failures, and the inability to show the significance to the value of machinery reliability found. It is then pointed out that the significant information is the probability that the ship complete its assigned mission, not the probability that the machinery operate without failure, and that these two probabilities are not the same. The weather is used as an example of another uncertain factor that bears on the probability of a successful mission. A simulation technique is then outlined for finding the probability of mission success, this probability being called the mission reliability. For purposes of discussion, success is simplied to mean completion of a voyage within a specified time. The simulation technique examines all factors that influence voyage time, and calculates this time for enough cases to build up a statistical picture. The result can be presented as a distribution of voyage times; the mission reliability can be read from the distribution, and the effect of changes, such as relaxing the specified voyage time, can also be seen. Partial and complete failures in the machinery plant are examined component by component, and their influence on voyage time is included in the analysis, but no propulsion plant reliability, as such, is found. Results of examples worked for both commercial and military ships are included to further explain the method.