Termination of heavy-duty polyester mooring ropes has long been an issue of concern in the marine renewable energy applications. In this study, experimental investigations were conducted on two different rope materials to investigate and compare the performance of filament, yarn, strand, sub-rope, 44 mm rope and 120 mm rope. The experiment setup consisted of 5 kN Instron Machine for testing filament, yarn and strand, 500 kN Denison Machine for sub-rope, 1500 kN and 30 MN tensile equipment for testing 44 mm and 120 mm ropes respectively. At constant test conditions, extensive experiments were carried out to examine the effects of various termination configuration on rope performance. The terminations used included Parafil socket (Viking 7 socket), splice and another novel termination called Stress Relief Socket. The results show that the use of stress relief socket has led to increased tensile performance of existing ropes by up to 13% for Akzo ropes. Considering the results of the tensile tests, the Stress Relief Socket has proved to have a significant advantage for replacement of existing methods of termination e.g. the splice. It should also be noted that the reproduction of the socket termination is more consistent than that of other methods of termination. The experimental outcomes can instruct future optimal mooring system design and marine renewable energy performances.