The sound propagation in the sea is a key point in the study of the impact of underwater noise on the marine fauna. In the case of shipping noise, the evaluation of the transmission losses is particularly important for the acoustical characterization of the ship as a source of underwater noise. In fact, measurements of underwater noise emissions from commercial ships are carried out at sea typically during the sea trials. This means that measurements can be carried out all around the world in a continuously changing environment, therefore with very different boundary conditions that can lead to different results in terms of noise levels. Several parameters influence the sound transmission at sea: frequency, water depth, sound celerity profile in the water column, bottom composition. When performing measurements such parameters should be in principle known to correctly interpret the data. The present work investigates the effects of uncertainties on the environmental parameters on the transmission losses that occur between the source (the ship) and the receiver (the hydrophone). The numerical investigation of the transmission losses is carried out by means of a ray tracing and a wave number integration code systematically varying the input parameters.