Reliability analysis on a ship system have developed as the increasing demand on the level of safety and reliability of the ship design. There are some significantly important of ship systems which support the ship operationalization. Failure on one system component can influence the functionality of the respective system and even can damage the whole ship function. If this is happen, the safety of the passengers and cargoes on the ship will be threatened. A comprehensive evaluation on the ship systems must be conducted so that the failure level of the system can be predicted. For the safety of the maintenance action on a system, model of the ship system maintenance must be designed. One common approach to be used on a maintenance modelling of a system is markov approach or markov modelling. The final result of the appoach is an availability index of a system as a consequences of the ship system maintenance. Output from this approach will become input for designing ship system maintenance strategy. This paper discusses the use of markov process approach in modelling maintenance of a ship system. In the final part of the paper, a maintenance modelling case for a ship fresh water cooling system is presented
