Empirical Study of the Relationship Between Vessel Age and Machinery Failure Rates in Nigerian Coastal Tanker Operations

The relationship between vessel age and machinery reliability has important implications for maintenance planning, insurance risk assessment, and regulatory inspection prioritisation in coastal tanker fleets. This study empirically investigates the association between vessel age and machinery failure incident rates among coastal tankers engaged in petroleum product distribution between Nigerian refineries and coastal terminals. A quantitative research design was employed using machinery failure incident data extracted from maintenance management records and engine log abstracts of thirty coastal tankers, covering a combined operational period of one hundred and eighty vessel-years. Failure rates were computed for major machinery systems including main propulsion, auxiliary generators, steering gear, and cargo pumping systems, and regressed against vessel age, maintenance expenditure per engine running hour, and dry-docking interval as explanatory variables. Negative binomial regression analysis was applied to account for the overdispersed count nature of the failure data. Results confirm a statistically significant positive relationship between vessel age and machinery failure rate for main propulsion and auxiliary generator systems. Maintenance expenditure per running hour is found to significantly moderate the age-failure relationship, with adequately maintained older vessels achieving failure rates comparable to younger vessels. The study contributes an empirical failure rate model to the coastal tanker management literature. Keywords: vessel age, machinery failure, coastal tankers, maintenance expenditure, negative binomial regression