Analytical Study of the Thermal Efficiency of Marine Power Plants Used in Nigerian Offshore Supply Vessels

Thermal efficiency of shipboard power plants determines fuel consumption, operating cost, and greenhouse gas emissions, and its analysis is of direct practical importance for offshore vessel fleet management. This study conducts an analytical investigation of the thermal efficiency of marine power plant configurations deployed aboard offshore supply vessels operating in Nigerian oil and gas field support roles. A thermodynamic analysis methodology was employed, using performance data collected from six offshore supply vessels with different power plant configurations: conventional single-engine direct drive, twin-engine gearbox arrangement, and diesel-electric propulsion. Data including fuel flow rates, engine load profiles, shaft power measurements, and waste heat recovery system outputs were collected through onboard instrumentation during standardised voyage segments. Second-law thermodynamic analysis and exergy analysis methods were applied to evaluate irreversibility losses in each configuration. Results indicate that diesel-electric configurations achieve higher overall system thermal efficiency at the partial load conditions characteristic of offshore support vessel operations, compared to mechanical drive configurations operating at off-design points. Waste heat recovery potential is found to be significant but largely untapped in the sampled vessels, with recovery systems absent or inoperative on four of the six vessels. The study contributes quantified thermal performance benchmarks specific to the Nigerian offshore support fleet. Keywords: thermal efficiency, marine power plants, offshore supply vessels, diesel-electric, exergy analysis