Abstract: This paper presents a numerical approach to simulate the performance of an acoustic modem operating in shallow water. The acoustic transmission in the shallow water channel is modelled as an impulse response function using a multilayered, range-independent ray tracing model. It is assumed that the performance is not only limited by signal-to-noise ratio (SNR), but also by the signal-to-corruptive multipath ratio (SMR). Numerical results are shown for both coherent (PSK) and incoherent (FKS) modulation schemes. The evaluation parameters that provide the estimated performance of the communication system are maximum range, datarate and available acoustic power. Optimum receiver depth is derived for shallow water channels such as the North Sea. The shallow water communication channel exhibits randomlike behaviour. This fact makes interpretations of numerical results very difficult. By introducing temporal variability in the model this problem is overcome to some extend.