Prewetting transitions are studied for Lennard-Jones (LJ) based dimer forming associating fluids, on a structureless surface represented by LJ 9-3 type potential, for various association strengths using grand-canonical transition matrix Monte Carlo (GC-TMMC) and histogram reweighting techniques. Occurrences of prewetting transition are observed for association strengths: epsilon(af)=2.0, 4.0, 6.0, 8.0, and 10.0. Structural properties, monomer fraction, and orientation order profile of thin-thick film of one-site associating fluids are presented. Wetting temperature, T(w), and prewetting critical temperature, T(pwc), increases with increasing association strength, which is in agreement with the results of the density functional theory (DFT). Length of prewetting line, on the other hand, is found to decrease first with increasing association energy until epsilon(af)=8.0 and subsequently found to increase substantially for epsilon(af)=10. This behavior is contrary to the prediction from the DFT. We observe that the boundary tension of thin-thick film via GC-TMMC and finite size scaling exhibits a maximum with respect to association strength.