Life Cycle Cost analysis conducted on various classes of ships have proved that the cost of the operation and maintenance of a ship can be approximately 50% to 60% of its Life Cycle Cost. Considering the fact the cost of ships are normally several millions or billions of dollars, it can be seen that the cost of maintenance is quite a significant amount in the annual budgets of the ship owners. Therefore various options are considered by the ship owners to reduce the maintenance cost without any major impact on the performance of the equipment and the operational availability of the ships. In addition proper maintenance of the ships are also necessary to reduce the risk of environmental pollution and to ensure safety of men and material at sea.
Some of the most common maintenance concepts followed by ship owners are as follows:
Reactive or Corrective Maintenance: Reactive or Corrective maintenance, also known as Break Down Maintenance is based on the policy of ‘Run Until It Breaks’. This is the most avoided kind of maintenance onboard ships as it poses a serious safety risk. In this case, no actions are carried out to maintain the equipment and it is expected that the equipment will fulfill its design capability for the for the duration of its designed life. Reactive maintenance may at times prove to be cost effective type of maintenance through the life cycle of an equipment, provided the failure of the equipment does not lead to any major catastrophe. But considering the fact that most of the equipment onboard ships are critical, Reactive Maintenance is the least recommended mode of the maintenance of equipment onboard.
Preventive Maintenance: Preventive Maintenance or Scheduled Maintenance is the most common mode of maintenance followed onboard ships. This system reduces the malfunctioning of the equipments and thereby reducing the downtime. Preventive maintenance is a calendar based or running hour based maintenance concept which employs various scheduled offline testing methodologies to conduct periodic assessment of the system and thereafter carry out the maintenance activities as prescribed in the schedule. The detailed procedure and schedule for the preventive maintenance routines such as change of filters, insulation tests, lubrication etc. are normally advised by the manufacturer and, if followed correctly, it ensures efficient running of the equipment resulting in reduced life cycle cost.
Predictive Maintenance: The Predictive Maintenance method analyses the causes, symptoms and effect relationship of the equipment’s performance to predict the requirement of any corrective actions. In the case of a Predictive Maintenance program the key values of the equipment are measured or monitored and the values obtained are compared with the standard set of values for the respective equipment to identify the deviations if any. The causes of the deviations found are thereafter analyzed to identify the maintenance routines to carried out normalize the equipment’s performance parameters.
Condition Based Maintenance: Condition Based Maintenance is the maintenance activity carried out based on the knowledge of the condition of an equipment obtained from routine or continuous monitoring. Condition Based Maintenance is similar to the Predictive Maintenance but uses both online and offline test data to decide up on the requirement of maintenance to be carried out. In the case of Condition Based Maintenance, if the test results fall in the normal or acceptable range, the scheduled Preventive Maintenance may be skipped which shall reduce the maintenance effort and the associated costs. Application of a customized Condition Based Maintenance plans are now gaining wider acceptance in the shipping world with the classification societies such as DNV coming up with the standards which permit the inclusion of this maintenance methodology in the overall maintenance program of ships.
Several aspects of an equipment including its functionality and criticality are to be considered before deciding up on the maintenance program for each equipment. The choice of the maintenance strategy also varies based on the class and type of the ships. The criteria for deciding the maintenance program for a commercial ship is different from that of a military ship. Commercially available analysis tools such as the FMECA, RCM, RAMS may be used to support the selection of the maintenance strategy. The continuous quest of the ship owners for a safe and economical maintenance methodologies has led to the introduction of Reliability Centered Maintenance in which an optimized maintenance strategy is formulated through a combination of Preventive, Predictive and Condition Based Maintenance practices best suited for the particular equipment. The advancements in the engineering and technology have led to the development of more reliable and rugged marine equipments and the monitoring systems which have revolutionized the maintenance requirements and widened the scope for introduction of more efficient and frugal maintenance programs for ships in future.