The increasing of fuel prices and global energy demand and enactment of new restrictive emissions regulations require more efficient and environmentally friendly engines to be designed. In this context, conversion of waste heat to useful energy is necessary to design more energy efficient vessel including using more efficient main engines and auxiliary engines. The aim of this study, thermodynamic characteristic of recovery of a ship's main engine waste heat is determined parametrically for waste heat recovery system (WHRS). Naturally, heat exchangers are used for waste heat recovery. Because of that reason, firstly shell–and–tube heat exchanger will be investigated parametrically. In order to make a more accurate calculation, it is important to reflect the pressure and enthalpy variations in the heat exchanger to the heat transfer calculations. After that the Transcritical Organic Rankine Cycle (TORC), which is recommended by many authors for the recovery of waste heat sources at low and medium temperatures, will be examined parametrically. The results show that increasing the number of pipes in the heat exchanger at a certain value may result in a decrease in system performance parameters that is The Net Power and Thermal Efficiency due to decreasing velocity of the mass flow in tubes. Moreover, The Net Power and Thermal Efficiency curves behaved differently with variable mass flow rate. Therefore, we will define performance parameter being important for WHRS.