The research aimed at further improvement of the technology of measuring swimmers’ active drag by the small perturbation method (SPM) at the average maximal swimming velocity (v_0max). For better reliability and accuracy of measurements, a standard variant of SPM was developed to measure automatically active drag (F_r(ad)), dimensionless coefficient of hydrodynamic force (C_x) and total external mechanical power P_to in different competitive swimming techniques during a single 50 m trial. The study involved twelve elite swimmers who specialized in front crawl at the distances of 100 and 200 m (780–850 FINA Points). From our measurements, in front crawl the results are following:​ v_0max = 1.909 ± 0.017 m·s⁻¹, F_r(ad) = 106.892 ± 7.276 N, C_x = 0.311 ± 0.028 and P_to = 204.033 ± 13.221 W. For objective estimation of the results, a verification variant of SPM was applied:​ P_to = 1.911 ± 0.018 m·s⁻¹, F_r(ad) = 107.033 ± 7.232 N, C_x = 0.311 ± 0.030 and P_to = 204.467 ± 12.982 W. The correlation analysis of the results obtained by the standard and verification variants of SPM confirms high accuracy and reliability of the method used (r = 0.988 for v_0max;​ r = 0.979 for F_r(ad);​ r = 0.988 for C_x(ad);​ r = 0.979 for P_to). The measurement error, including the method error and the devices error, does not exceed 2.4 %. This method has also a systematic error that reduces the measured data in the same direction from the actual values (min = -2.1 %;​ max = -2.9 %). This error should be taken into account when analyzing and evaluating the measured hydrodynamic characteristics of swimmers.