Because of the heat flow and temperature, marine diesel engines exhaust gas energy is by far the highest desirable among the waste heat sources of a ship. Waste heat recovery systems generate electrical power by using this exhaust gas energy. This study measures how much the power turbine generator improves the system's efficiency for three engine loads and three ambient conditions. This study presents a power turbine generator using a six-cylinder low-speed marine diesel engine. Thermodynamic analyses are performed by considering three ambient conditions and three diesel engine loads, and the exergy destruction of each component, exergy efficiency, exergy destruction rate, efficiency increases, and power output of the system are calculated. In addition, the payback period is calculated according to the installation cost of the power turbine generator and the cost of the fuel saved annually. Based on the analysis, the highest power output for the power turbine generator occurred under 100% engine load and winter ambient conditions, and the lowest power output occurred under 75% engine load and tropical ambient conditions. Alternatively, for the same ambient conditions, the highest efficiency increase occurred at 90% engine load, and the lowest efficiency increase occurred at 100% engine load. In the power turbine generator, it is observed that the shortest payback period is 100% engine load and winter ambient conditions.