Estimation of the probability of propulsion loss by a seagoing ship based on expert opinions

Abstract

serious categories of hazardous events 1 in shipping. In specific external conditions it may lead to a loss of ship together with people aboard. The loss of propulsive power may be an effect of the propulsion system (PS) failures or of errors committed by the crew in the system operation process. In the safety engineering language we say that the propulsion loss probability depends on the reliability of the PS and of its operators. Determination of that probability is in practice confronted with difficulties connected with shortage of data on that reliability. This pertains particularly to the cases of estimation in connection with decisions taken in the ship operation. In such cases we have to rely on subjective estimations made by persons with practical knowledge in the field of interest, i.e. experts. The experts, on the other hand, prefer to formulate their opinions in the linguistic categories, in other words in the language of fuzzy sets. The author’s experience tells also that in the expert investigations it is difficult to maintain proper correlation between the system data and the system component data. The paper presents a method of the subjective estimation of propulsion loss probability by a ship, based on the numericalfuzzy expert judgements. The method is supposed to ensure that proper correlation. It is adjusted to the knowledge of experts from ships’ machinery crews and to their capability of expressing that knowledge. The method presented has been developed with an intention of using it in the decision taking procedures in risk prediction during the seagoing ship operation, in the shortage of objective reliability data situations.