The sound propagation in the sea is a key point in the study of the impact of underwater noise on marine fauna. In the case of shipping noise, the evaluation of the transmission losses is particularly important in the acoustical characterisation of the ship as a source of underwater noise. As a matter of 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 sound transmission at sea: frequency, water depth, sound celerity profile in the water column, bottom composition etc.. When performing measurements all these parameters should be in principle know to interpret correctly the data. The present work investigate the effects of uncertainties on the environmental parameters on the transmission losses that occur between the source (the ship)  and the receiver which can be represented by hydrophones in an experimental campaign or animals in a real case. The investigation has been carried out varying systematically the input parameters  in a numerical simulation of transmission losses performed by a ray tracing standard underwater noise propagation model.