Locating a target from range measurements using only one mobile transducer has been increased over the last years. This method allows us to reduce the high costs of deployment and maintenance of traditional fixed systems on the seafloor such as Long Baseline. The range-only single-beacon is one of the new architectures developed using the new capabilities of modern acoustic underwater modems, which can be time synchronization, time stamp, and range measurements. This document presents a method to estimate the sources of error in this type of architecture so as to obtain a mathematical model which allows us to develop simulations and study the best localization algorithms. Different simulations and real field tests have been carried out in order to verify a good performance of the model proposed.