In this paper, an LNG boil-off gas (BOG) reliquefaction plant operating in accordance with cascade vapor compression cycles, using propylene and ethylene as refrigerants, on board LNG carriers is investigated. As consequence of the analysis results, a new and original design is proposed to reduce power consumption and improve its exergy efficiency. Through energy and exergy analysis, a thermodynamic model is carried out to analyse and evaluate operating conditions as well as to obtain performance values such as the Coefficient of Performance (COP), exergy efficiency, irreversibilities and specific energy consumption. The thermodynamic analysis is performed using the Engineering Equation Solver (EES) software environment. The results of the improved design implemented on the reliquefaction plant for LNG tank conditions of -160.82 degrees C, a plant BOG input temperature of 125 degrees C and 25 degrees C seawater, give COP values of 0.22 and an exergetic efficiency of 37%, such values being 22.22% and 19.35% greater than the original design. The specific energy consumption decreases 14.66% to 0.64 kW h per kg/s of natural BOG. The proposal for improving efficiency is founded on BOG cold energy recovery and BOG compression heat rejection with cooling water in the intercoolers. (C) 2015 Elsevier Ltd. All rights reserved.