Methods and locating systems are for determining an insulation fault location on an electric conductor of a subsea supply line. By applying electric voltage on the electric conductor, an electrochemical reaction takes place at an insulation fault location between the metallic conductor material and the seawater, the electrochemical reaction forming gas, which in turn is connected to developing noise. Sonic sensors capture the sonic waves produced inside and outside the subsea supply line and evaluate the measuring signals in order to determine the insulation fault location. Alternatively or additionally to capturing noise, the gas-bubble image patterns occurring at the insulation fault location are optically captured and consulted in order to determine the insulation fault location.