Abstract: Localisation of underwater sources is possible by means of measurements of the delay between signals, which are radiated by the source. There are many time delay estimation methods, one of them is the gradient type adaptive algorithm. One of estimation parameters is convergence coefficient, which influences on speed of the estimation process. Selection of the optimal value of this coefficient guarantees achievement of the estimated value of time delay in the shortest time. The value of this coefficient depends on received signals to noise ratio. In this paper has been shown time delay estimation with gradient type adaptive algorithm and factors, which influence on the value oj convergence coefficient. There also has been shown influence of SNR on working of the time delay estimation, which can be used in the underwater source localisation system. For research have been used real acoustics signals radiated by a moving ship.